Cat 793c Manual Servicio

Service Training Meeting Guide 682

SESV1682 March 1997

TECHNICAL PRESENTATION

793C OFF-HIGHWAY TRUCK

793C OFF-HIGHWAY TRUCK MEETING GUIDE 682

SLIDES AND SCRIPT AUDIENCE

Level II - Service personnel who understand the principles of machine systems operation, diagnostic equipment, and procedures for testing and adjusting.

CONTENT This presentation provides basic maintenance information and describes the systems operation of the engine, power train, steering, hoist and the air system and brakes for the 793C Off-highway Truck. The Automatic Retarder Control (ARC) and the Traction Control System (TCS) are also discussed.

OBJECTIVES After learning the information in this meeting guide, the serviceman will be able to: 1. locate and identify the major components in the engine, power train, steering, hoist and the air system and brakes; 2. explain the operation of the major components in the systems; and 3. trace the flow of oil or air through the systems.

REFERENCES 793C Off-highway Truck Service Manual 793C Off-highway Truck Parts Book Vital Information Management System (VIMS) Service Manual Fluid Power Graphic Symbols User's Guide

SENR1440 SEBP2503 SENR6059 SENR3981

PREREQUISITES Interactive Video Course "Fundamentals of Mobile Hydraulics" Interactive Video Course "Fundamentals of Electrical Systems" STMG 546 "Graphic Fluid Power Symbols"

© 1997 Caterpillar Inc.

TEVR9001 TEVR9002 SESV1546

Estimated Time: 8 Hours Visuals: 184 (2 X 2) Slides Serviceman Handouts: 4 Data Sheets Form: SESV1682 Date: 3/97

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SUPPLEMENTAL MATERIAL Specification Sheets 793B Off-highway Truck 793C Off-highway Truck

AEHQ5061 AEHQ5186

Salesgrams Vital Information Management System (VIMS) 793B Rear Axle Improvements 785B/789B/793B Introduction 789B/793B Feature Status

TELQ4478 TELQ3736 TELQ3725 TELQ4477

Video Tapes 793C Off-highway Truck--Service Introduction 793C Marketing Introduction 3500 EUI Service Introduction Intelligence of Powerful Connections Suspension Cylinder Charging TPMS Management/Technical Information TPMS Operating Tips Automatic Electronic Traction Aid (AETA) Introduction

SEVN4016 AEVN3742 SEVN2241 AEVN2974 TEVN2155 AEVN2211 AEVN2212 SEVN9187

Service Training Meeting Guides STMG 625 "793 Off-highway Truck" STMG 660 "785B/789B/793B Off-highway Trucks--Maintenance" STMG 681 "3500B Engine Controls--Electronic Unit Injection (EUI)"

SESV1625 SESV1660 SESV1681

Technical Instruction Modules Vital Information Management System--785B/789B/793B Off-highway Trucks Vital Information Management System--Introduction 3500 Electronic Engine Controls--Introduction 3500 Electronic Engine Controls--Off-highway Trucks Electronic Programmable Transmission Control (EPTC II) 769C - 793B Off-highway Trucks--Torque Converter and Transmission Hydraulic Systems 785B/789B/793B Off-highway Trucks--Steering System 769C - 793B Off-highway Trucks--Hoist System 769C - 793B Off-highway Trucks--Air System and Brakes Automatic Retarder Control System Automatic Electronic Traction Aid 769C - 793B Off-highway Trucks--Suspension System

SEGV2610 SEGV2597 SEGV2588 SEGV2589 SEGV2584 SEGV2591 SEGV2587 SEGV2594 SEGV2595 SEGV2593 SEGV2585 SEGV2599

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SUPPLEMENTAL MATERIAL (Continued) Booklets Know Your Cooling System Diesel Fuels and Your Engine Oil and Your Engine

SEBD0518 SEBD0717 SEBD0640

Special Instructions Using the ECAP NEXG4521 Machine Functions Service Program Module Using the 8T8697 Electronic Control Analyzer Programmer (ECAP) Using the 7X1700 Communication Adapter Group Use of 6V3000 Sure-Seal Repair Kit Use of CE Connector Tools Servicing DT Connectors Use of 8T5200 Signal Generator/Counter Group Repair of 4T8719 Bladder Accumulator Group Suspension Cylinder Servicing Using 1U5000 Auxiliary Power Unit (APU) Using the 1U5525 Attachment Group

SEHS9343 SEHS8742 SEHS9264 SMHS7531 SEHS9065 SEHS9615 SEHS8579 SEHS8757 SEHS9411 SEHS8715 SEHS8880

Brochures Caterpillar Vital Information Management System (VIMS) Caterpillar Electronic Technician Caterpillar DataView Diesel Engine Oil (CG4) Product Data Sheet How to Take a Good Oil Sample Air Filter Service Indicator Intelligence of Powerful Connections Caterpillar Fully Automatic Transmission Caterpillar Oil-cooled Multiple Disc Brakes Caterpillar Automatic Retarder Control

AEDK2946 NEHP5614 NEHP5622 PEHP5026 PEHP6001 PEHP9013 AEDK2966 AEDQ0066 AEDK2546 AEDK0075

Miscellaneous Electronic Diagnostic Code Pocket Card Pressure Conversion Chart 793B Transmission Assembly Wall Chart 793B Final Drive Assembly Wall Chart Improved Transmission/Drive Train Oil (IRM)

NEEG2500 SEES5677 SENR6834 SENR8602 PELE0179

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TABLE OF CONTENTS

INTRODUCTION ........................................................................................................................7 WALK AROUND INSPECTION...............................................................................................11 OPERATOR'S STATION............................................................................................................36 ENGINE......................................................................................................................................49 Cooling System.....................................................................................................................66 Lubrication System ...............................................................................................................77 Fuel System...........................................................................................................................80 Air Induction and Exhaust System .......................................................................................85 POWER TRAIN .........................................................................................................................90 Power Train Components......................................................................................................91 Power Train Hydraulic System ...........................................................................................103 Electronic Programmable Transmission Control (EPTC II)...............................................120 STEERING SYSTEM ..............................................................................................................128 HOIST SYSTEM ......................................................................................................................157 AIR SYSTEM AND BRAKES ................................................................................................177 Operator Controls................................................................................................................179 Air Charging System...........................................................................................................182 Parking and Secondary Brake System ................................................................................188 Service and Retarder Brake System....................................................................................195 AUTOMATIC RETARDER CONTROL (ARC) .....................................................................206 TRACTION CONTROL SYSTEM (TCS)...............................................................................211 CONCLUSION.........................................................................................................................221 SLIDE LIST..............................................................................................................................222 SERVICEMAN'S HANDOUTS...............................................................................................224

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INSTRUCTOR NOTES

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793C OFF-HIGHWAY TRUCK

C 1997 Caterpillar Inc.

1

INTRODUCTION This presentation provides an introduction to the Caterpillar 793C Off-highway Truck. Included in this package is a walk around inspection which provides information about daily service requirements and identifies the locations of the major components. The major systems of the truck will also be discussed. The major systems include the engine, power train, steering, hoist, and the air system and brakes. • 3516B DITA engine

The 793C is the largest rigid frame truck produced by Caterpillar. The 793C is equipped with a Caterpillar 3516B engine rated at 1716 kW (2300 gross hp) and 1616 kW (2166 flywheel hp). The load carrying capacity is 218 Metric tons (240 tons) at a Gross Machine Weight (GMW) of 376488 kg (830000 lbs.).

• Extended body canopy

This slide shows a view of the left side of the truck. Notice that the body canopy is extended over the cab to protect the front of the truck from falling objects.

• Fuel tank

The fuel tank is located on the left side of the truck.

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• Main system air tank: - Air starting - Service/retarder brakes • Main hydraulic tank:

Shown is the right side of the truck. The large air tank on the right platform supplies air for starting the truck and for the service and retarder brake system. The main hydraulic tank is also visible. The hydraulic tank supplies oil for the hoist system and the brake system.

- Hoist system - Brake system

• Torque converter case used as sump for converter and transmission

On the 793B truck, torque converter oil is also supplied from the main hydraulic tank. A transmission oil supply tank is located in front of the main hydraulic tank. The 793C now uses the torque converter case as the supply tank for the torque converter and the transmission.

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• 789B and 793C are similar • 793C has four air filters

The 793C is similar in appearance to the 789B and may be difficult to recognize from a distance. The 793C can be recognized by the four air filters and the diagonal access ladder. The 789B has only two air filters mounted in the same locations and is equipped with two vertical ladders.

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• Truck body

The truck body has a dual-slope main floor and a "vee" bottom to center the load and reduce spills. The steel used to construct the body has a yield strength of 6205 bar (90000 psi).

• Rear suspension cylinders

The rear suspension cylinders absorb bending and twisting stresses rather than transmitting them to the main frame.

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793C MAINTENANCE ice 793C Serv re Procedu

WALK AROUND INSPECTION 5 WALK AROUND INSPECTION • Read the Operation and Maintenance Manual

Before working on or operating the truck, read the Operation and Maintenance Manual (Form SEBU6995) thoroughly for information on safety, maintenance and operating techniques. Safety precautions and Warnings are provided in the manual and on the truck. Be sure to identify and understand all symbols before starting the truck. The first step to perform when approaching the truck is to make a thorough walk around inspection. Look around and under the truck for loose or missing bolts, trash build-up and for coolant, fuel or oil leaks. Look for indications of cracks. Pay close attention to high stress areas as shown in the Operation and Maintenance Manual.

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• Front wheel bearing inspection plug (arrow)

The front wheel bearing oil level is checked and filled by removing the plug (arrow) in the center of the wheel bearing cover. The oil should be level with the bottom of the plug hole.

• Tire inflation

Check the tire inflation pressure. Operating the truck with the wrong tire inflation pressure can cause heat build-up in the tire and accelerate tire wear.

NOTE: Care must be taken to ensure that fluids are contained while performing any inspection, maintenance, testing, adjusting and repair of the machine. Be prepared to collect the fluid in suitable containers before opening any compartment or disassembling any component containing fluids. Refer to the "Tools and Shop Products Guide" (Form NENG2500) for tools and supplies suitable to collect and contain fluids in Caterpillar machines. Dispose of fluids according to local regulations and mandates.

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1. Front wheel bearing axle housing breather

Inspect the condition of the front wheel bearing axle housing breather (1). The breather prevents pressure from building up in the axle housing. Pressure in the axle housing may cause brake cooling oil to leak through the Duo-Cone seals in the wheel brake assemblies.

2. Suspension cylinder grease outlet fittings

Two grease outlet fittings (2) are located on the front of each suspension cylinder. The grease supply line for the Auto Lubrication System is located at the rear of the suspension cylinder. No grease outlet fittings should be located on the same side of the suspension cylinder as the grease fill location. Having an outlet fitting on the same side of the suspension cylinder as the grease fill location will prevent proper lubrication of the cylinder.

• Make sure grease flows from outlet fittings

Make sure that grease is flowing from the outlet fittings to verify that the suspension cylinders are being lubricated and that the pressure in the cylinders is not excessive.

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1. Rear brake oil coolers 2. Parking brake release filter 3. Torque converter charging filter 4. Automatic lubrication injector bank

Located behind the right front tire are the rear brake oil coolers (1), the parking brake release filter (2), and the torque converter charging filter (3). One of the three injector banks (4) for the automatic lubrication system is also in this location. These injectors are adjustable and regulate the quantity of grease that is injected during each cycle (approximately once per hour). A solenoid air valve provides a controlled air supply for the automatic lubrication system. The solenoid air valve is controlled by the Vital Information Management System (VIMS), which energizes the solenoid ten minutes after the machine is started. The VIMS energizes the solenoid for 75 seconds before it is de-energized. Every 60 minutes thereafter, the VIMS energizes the solenoid for 75 seconds until the machine is stopped (shut down). These settings are adjustable through the VIMS keypad in the cab. INSTRUCTOR NOTE: For more detailed information on servicing the automatic lubrication system, refer to the Service Manual Module "Automatic Lubrication System" (Form SENR4724).

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• Hoist and brake hydraulic tank • Oil level sight gauges (arrows)

Shown is the hoist and brake hydraulic tank and the oil level sight gauges (arrows). The oil level is normally checked with the upper sight gauge. The oil level should first be checked with cold oil and the engine stopped. The level should again be checked with warm oil and the engine running. The lower sight gauge can be used to fill the hydraulic tank when the hoist cylinders are in the RAISED position. When the hoist cylinders are lowered, the hydraulic oil level will increase. After the hoist cylinders are lowered, check the hydraulic tank oil level with the upper sight gauge as explained above.

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• Final drives • Check magnetic plugs (arrow) for metal

• Flush all axle components after a failure

The rear axles are equipped with double reduction planetary final drives. The magnetic plug (arrow) should be removed from the final drives at regular intervals and checked for metal particles. For some conditions, checking the magnetic plug is the only way to identify a problem which may exist. The rear axle is a common sump for the differential and both final drives. If a final drive or the differential fails, the other final drive components must also be checked for contamination and then flushed. Failure to completely flush the rear axle after a failure can cause a repeat failure within a short time.

NOTICE The rear axle is a common sump for the differential and both final drives. If a final drive or the differential fails, the other final drive components must also be checked for contamination and then flushed. Failure to completely flush the rear axle after a failure can cause a repeat failure within a short time.

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1. Differential oil level sight glass

The differential oil level is checked by viewing the oil level sight glass (1). The oil should be level with the bottom of the inspection hole.

2. Rear axle oil level sensors

Two oil level sensors (2) provide input signals to the VIMS which informs the operator of the rear axle oil level.

3. Rear axle housing oil filter

A rear axle oil filter (3) is used to remove contaminants from the rear axle housing.

• Rear suspension cylinders

Check the charge condition of the rear suspension cylinders when the truck is empty and on level ground.

4. Automatic lubrication injector bank

The second of three injector banks (4) for the automatic lubrication system is mounted on the top rear of the differential housing.

5. Rear axle breather

Above the lubrication injectors is a breather (5) for the rear axle. Inspect the condition of the breather at regular intervals. The breather prevents pressure from building up in the axle housing. Excessive pressure in the axle housing can cause brake cooling oil to leak through the Duo-Cone seals in the wheel brake assemblies. INSTRUCTOR NOTE: For more detailed information on servicing the suspension system, refer to the Special Instruction "Suspension Cylinder Servicing" (Form SEHS9411).

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• Cable holds body up

The cable that holds the body up is stored below the rear of the body. Whenever work is to be performed while the body is raised, the safety cable must be connected between the body and the rear hitch to hold the body in the raised position.

WARNING The space between the body and the frame becomes a zero clearance area when the body is lowered. Failure to install the cable can result in injury or death to personnel working in this area.

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• Fuel tank • Fuel level sight gauge (arrow)

The fuel tank is located on the left side of the truck. The fuel level sight gauge (arrow) is used to check the fuel level during the walk around inspection.

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1. Primary fuel filter

The primary fuel filter (1) is located on the inner surface of the fuel tank.

2. Condensation drain valve

Open the drain valve (2) to remove condensation from the fuel tank.

3. Fuel level sensor

A fuel level sensor (3) is also located on the fuel tank. The fuel level sensor provides input signals to the VIMS which informs the operator of the fuel level.

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1. Torque converter and transmission oil level sight gauges

Supply oil for the torque converter and the transmission is contained in the torque converter case. Sight gauges (1) are used to check the oil level for the torque converter and the transmission.

2. Torque converter and transmission oil fill tube

Torque converter and transmission oil is added at the fill tube (2).

• Torque converter and transmission oil fill procedure

When filling the torque converter and transmission oil sump after an oil change, fill the sump with oil to the top of the upper sight gauge. Turn off the engine manual shutdown switch (see slide No. 23) so the engine will not start. Crank the engine for approximately 15 seconds. The oil level will decrease as oil fills the torque converter and transmission system. Add more oil to the sump to raise the oil level to the FULL COLD mark. Crank the engine for an additional 15 seconds. Repeat this step as required until the oil level stabilizes. Turn off the engine manual shutdown switch and start the engine. Warm the torque converter and transmission oil. Add more oil to the sump as required to raise the torque converter and transmission oil level to the FULL WARM mark.

NOTICE Failure to correctly fill the torque converter and transmission oil sump after an oil change may cause transmission clutch damage.

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1. Torque converter outlet screen

Shown is the location of the torque converter outlet screen (1). Oil flows from the torque converter outlet relief valve through the torque converter outlet screen to the torque converter and transmission oil cooler located on the right side of the engine. Oil from the torque converter and transmission oil cooler returns to the torque converter housing.

2. Transmission charging filter

Shown is the location of the transmission charging filter (2). Transmission charging oil flows through the transmission charging filter to the transmission control valves on top of the transmission and to the torque converter lockup clutch valve located on top of the torque converter.

3. TC/Transmission scavenge screen

The scavenge screen for torque converter and transmission oil is located behind the cover (3).

4. TC/Transmission S•O•S tap

Torque converter and transmission oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (4).

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• Brake cylinder breather (arrow)

Inspect the condition of the two breathers (arrow, one visible) for the brake cylinders. The second breather is located behind the cross tube. Oil should not leak from the breathers. Oil leaking from the breathers is an indication that the oil piston seals in the brake cylinder need replacement. Air flow from the breathers during a brake application is an indication that the brake cylinder air piston seals need replacement.

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• Front brake oil cooler filters (arrow)

Located in front of the fuel tank are the front brake oil cooler filters (arrow). Oil not used to raise or lower the hoist cylinders flows from the hoist valve through the front brake oil filters to the front brake oil cooler located above the torque converter.

• Automatic lubrication injector bank

The third injector bank for the automatic lubrication system is also located in this area.

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• Front suspension cylinder

Check the charge condition of the front suspension cylinders when the truck is empty and on level ground.

1. Air dryer

The air dryer (1) is located in front of the left front suspension cylinder.

2. Remote air supply connector

The air system can be charged from a remote air supply through a ground level connector (2) inside the left frame. INSTRUCTOR NOTE: For more detailed information on servicing the suspension system, refer to the Special Instruction "Suspension Cylinder Servicing" (Form SEHS9411).

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• Engine oil filters 1. Engine oil fill tube 2. Engine oil dipstick

The engine oil filters are located on the left side of the engine. Engine oil should be added at the fill tube (1) and checked with the dipstick (2).

3. Engine oil S•O•S tap

Engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (3).

4. Engine oil pressure sensor

The engine lubrication system is equipped with two oil pressure sensors (4). A sensor is located on each end of the oil filter base. One sensor measures engine oil pressure before the filters. The other sensor measures oil pressure after the filters. The sensors provide input signals to the second generation Advanced Diesel Engine Management (ADEM II) engine Electronic Control Module (ECM). The ECM provides input signals to the VIMS which informs the operator of the engine oil pressure. Together, these sensors inform the operator if the engine oil filters are restricted.

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1. High speed oil change connector

Engine oil can be added through the high speed oil change connector (1) located in the left front corner of the oil pan. Two engine oil level switches (2 and 3) provide input signals to the engine ECM. The engine ECM provides an input signal to the VIMS, which informs the operator of the engine oil level.

2. Add engine oil level switch

If the truck is equipped with the engine oil renewal system attachment, the upper oil level switch (2) tells the operator when engine oil must be added. The ADD ENG OIL message is a Category 1 Warning.

3. Engine oil level low switch

The lower oil level switch (3) tells the operator when the engine oil level is low and it is unsafe to operate the truck without causing damage to the engine. The ENG OIL LEVEL LOW message is a Category 2 or 3 Warning.

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• Secondary fuel filters • Fuel priming pump (arrow)

The secondary fuel filters and the fuel priming pump (arrow) are located above the engine oil filters on the left side of the engine.

NOTE: If the fuel system requires priming, it may be necessary to block the fuel return line during priming to force the fuel into the injectors.

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1. Manual engine shutdown switch

Before climbing the truck ladder, make sure that the manual engine shutdown switch (1) is OFF. The engine will not start if the manual shutdown switch is ON. If necessary, the switch can be used to stop the engine from the ground level.

2. Engine and access ladder light switches

The toggle switches (2) control the lights in the engine compartment and above the access ladder.

3. RS-232 connector for VIMS

The RS-232 service connector (3) is used to connect a laptop computer with VIMS PC software to upload new source and configuration files, view real time data or download logged information from the VIMS.

4. Battery disconnect switch

The battery disconnect switch (4) and VIMS service connector key switch (5) must be in the ON position before the laptop computer with VIMS software will communicate with the VIMS.

5. Key switch for VIMS service connector 6. VIMS service lamp

The blue service lamp (6) is part of the VIMS. The service lamp will turn on to notify service personnel that the VIMS has an active machine or system event. The service lamp flashes to indicate when an event is considered abusive to the machine.

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• Inspect radiator • Check air cleaner indicators (arrow)

While climbing the ladder, make a thorough inspection of the radiator. Be sure that no debris or dirt is trapped in the cores. Check the air cleaner indicators (arrow) located on both sides of the truck. If the yellow pistons are in the red zone (indicating that the filters are plugged), the air cleaners must be serviced.

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• Engine cooling systems: - Jacket water cooling system - Aftercooler cooling system 1. Engine coolant shunt tank 2. Coolant level gauges 3. Coolant level sensor

The cooling system on the 793C is divided into two systems. The two systems are the jacket water cooling system and the aftercooler cooling system. These two systems are not connected. When servicing the cooling systems, be sure to drain and fill both systems separately. The engine cooling system shunt tank (1) is located on the hood above the radiator. The coolant levels are checked at the shunt tank. Use the gauges (2) on top of the shunt tank to check the two coolant levels. A coolant level sensor (3) is located on each side of the shunt tank to monitor the coolant level of both cooling systems (guard removed for viewing sensor). The coolant level sensors provide input signals to the VIMS which informs the operator of the engine coolant levels.

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1. Automatic lubrication tank

Located on the right platform are the automatic lubrication system grease tank (1), the main air system tank (2) and the steering system tank (3).

2. Main air system tank 3. Steering system tank

Check the level of the grease in the automatic lubrication system tank with the grease level indicator located on top of the tank. A drain valve is located at the bottom right of the main air system tank. Drain the condensation from the air tank each morning.

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1. Upper sight gauge

The oil level for the steering system tank is checked at the upper sight gauge (1) when the oil is cold and the engine is stopped. After the engine is started, the oil level will decrease as the oil fills the steering accumulators.

2. Lower sight gauge

After the accumulators are filled, the oil level should be checked again at the lower sight gauge (2). When the engine is running and the accumulators are fully charged, the oil level should not be below the ENGINE RUNNING marking of the lower gauge. If the ENGINE RUNNING level is not correct, check the nitrogen charge in each accumulator. A low nitrogen charge will allow excess oil to be stored in the accumulators and will reduce the secondary steering capacity.

3. Steering tank pressure release button

Before removing the cap to add oil to the steering system, be sure that the engine was shut off with the key start switch, and the steering oil has returned to the tank from the accumulators. Then, depress the pressure release button (3) on the breather to release any remaining pressure from the tank.

4. Main steering oil filter

Also located on the tank are the main steering oil filter (4) and the steering pump case drain filter (5).

5. Steering pump case drain filter

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6. APU supplemental steering connector

If the steering pump fails or if the engine cannot be started, the connector (6) is used to attach an Auxiliary Power Unit (APU). The APU will provide supply oil from the steering tank at the connector (6) to charge the steering accumulators. Steering capability is then available to tow the truck.

7. Steering oil temperature sensor

The steering oil temperature sensor (7) provides an input signal to the VIMS which informs the operator of the steering system oil temperature.

INSTRUCTOR NOTE: For more detailed information on servicing the steering accumulators, refer to the Service Manual Module "793C Off-highway Truck Steering System" (Form SENR1452) and the Special Instruction "Repair of 4T8719 Bladder Accumulator Group" (Form SEHS8757). For more information on using the APU, refer to the Special Instructions "Using 1U5000 Auxiliary Power Unit (APU)" (Form SEHS8715) and "Using the 1U5525 Attachment Group" (Form SEHS8880).

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1. Parking/secondary brake air tank drain valve (arrow)

2. Windshield washer fluid reservoir

Another small air tank (not visible) is located behind the cab (see Slide No. 156). The air tank behind the cab supplies air to the parking and secondary brakes. Drain the moisture from the tank daily with the drain valve (1). Check the fluid level of the windshield washer reservoir (2).

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OPERATOR’S STATION • Transmission shift lever - Six speeds FORWARD

At the front of the center console is the transmission shift lever. The 793C transmission has six speeds FORWARD and one speed REVERSE. To the right of the shift lever is the back-up light switch (arrow).

- One speed REVERSE • Back-up light switch (arrow)

INSTRUCTOR NOTE: In this section of the presentation, component locations inside the operator’s station will be shown. Many of the components shown in this section will be further explained in the sections that follow.

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• Center console components: 1. Throttle back-up switch 2. Manual ether start aid switch 3. Key start switch 4. TCS switch 5. Parking brake switch 6. Windshield washer and wiper switch 7. Cigarette lighter 8. Brake retraction switch - Service hourmeter

Shown is the center console. In the center of the console are the throttle back-up switch (1), manual ether start aid switch (2), key start switch (3) and the Traction Control System (TCS) switch (4). The throttle back-up switch (1) increases the engine speed to 1300 rpm if the engine ECM detects that the throttle sensor signal is invalid. The manual ether start aid switch (2) allows the operator to manually inject ether when the coolant temperature is below 10°C (50°F) and engine speed is below 1200 rpm. The Traction Control System (TCS) switch (4) is used to test the operation of the TCS (formerly referred to as the "Automatic Electronic Traction Aid"). Shown below these components are the parking brake switch (5), the windshield washer and wiper switch (6), the cigarette lighter (7) and the brake retraction switch (8). The brake retraction switch (8) is used to release the parking brakes when towing the truck. The service hourmeter is located toward the rear of the center console.

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• Overhead light switches: 1. Headlights and parking/taillights 2. Panel lights 3. Interior cab light 4. Front flood/ladder lights 5. Fog lights

Located above the operator's head are several light switches: 1. 2. 3. 4. 5.

Headlights and parking/taillights Panel lights Interior cab light Front flood/ladder lights Fog lights

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1. Gauge cluster module: - Engine coolant temperature - Brake oil temperature - System air pressure - Fuel level 2. Speed/tach module: - Analog tachometer - Ground speed - Transmission actual gear 3. Dash backlit indicators: - Left and right turn signals - High beam indicator - Action light - Service/retarder brakes ENGAGED light

Located on the front dash are two of the VIMS output components. They are the gauge cluster module (1) and the speedometer/tachometer module (2). The four gauges in the gauge cluster module (from left to right and top to bottom) are: - Engine coolant temperature - Brake oil temperature - System air pressure - Fuel level The speedometer/tachometer module consists of an analog tachometer and a display window which shows the ground speed and the transmission actual gear. Several backlit indicators will appear in the upper area (3) of the display when they are active. The backlit indicators are: - Left and right turn signals - High beam indicator - Action light - Service/retarder brakes ENGAGED light

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1. Automatic Retarder Control (ARC) ON/OFF switch

To the right of the steering column is the Automatic Retarder Control (ARC) ON/OFF switch (1).

2. Message center module:

To the right of the ARC switch are two more components of the VIMS. They are the message center module (2) and the keypad module (3).

- Alert indicator - Universal gauge - Message display window

The message center module consists of an alert indicator, a universal gauge and a message display window. The alert indicator flashes when a Category 1 Warning is present. The universal gauge displays the status of the sensor selected for viewing by depressing the GAUGE key on the keypad. The message display window shows various types of text information to the operator.

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3. Keypad module

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The keypad module allows the operator or a service technician to interact with the VIMS. Some of the functions that can be performed by the keypad are: - Scroll parameters monitored by VIMS by depressing the GAUGE key. - Payload Monitor ON/OFF

PAYLOAD

7295623

- Calibrate Payload Monitor

PAYCAL

729225

- Payload Resettable Totals

TOT

868

- Reset Displayed Data

RESET

73738

- Display Self Test

TEST

8378

- Reset Service Light

SVCLIT

782548

- Set Lube Cycle Times

LUBSET

582738

- Manual Lube

LUBMAN

582626

- Show Acknowledged Events

EACK

3225

- Show Event Statistics

ESTAT

37828

- Show Event List

ELIST

35478

- Start Event Recorder

EREC

3732

- Start/Stop Data Logger

DLOG

3564

- Reset Data Logger

DLRES

35737

- Odometer Set/Reset (requires VIMS PC connection)

ODO

636

- Machine Status

MSTAT

67828

- Change Language

LA

52

- Change Units

UN

86

- Change Backlight

BLT

258

- Change Display Contrast (requires Updated Message Center)

CON

266

INSTRUCTOR NOTE: For more detailed information on the VIMS, refer to the Service Manual Module "Vital Information Management System (VIMS)" (Form SENR6059).

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GAUGE CLUSTER MODULE

SERVICE LAMP

SERVICE KEYSWITCH

VIMS RS-232 PORT

SPEEDOMETER/ TACHOMETER MODULE

12

MAIN MODULE

KEYPAD MODULE

3F

VIMS SERVICE TOOL AND SOFTWARE

ELECTRONIC TECHNICIAN/ECAP DISPLAY DATA LINK

VIMS

MPH km/h

MESSAGE CENTER MODULE

VIMS INTERFACE MODULE

VIMS INTERFACE MODULE

KEYPAD DATA LINK CAT DATA LINK

ADEM II CONTROL ACTION ALARM

ACTION LAMP CAT DATA LINK SENSORS

SENSORS SENSORS

VITAL INFORMATION MANAGEMENT SYSTEM (VIMS)

AUTO RETARDER CONTROL

TRANSMISSION CONTROL

34 • VIMS

As shown in some of the previous slides, the 793C is equipped with the VIMS which receives input signals from many sensors and also communicates with other electronic controls on the machine. The VIMS provides the operator and the service technician with a complete look at the current and past conditions of all the systems on the truck.

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35

• Behind the operator's seat are: - Fuse panel - ECAP/ET diagnostic connector (arrow)

Behind the operator’s seat are the fuse panel and the ECAP/ET diagnostic connector (arrow). The ECAP/ET diagnostic connector is used to connect the Electronic Control Analyzer Programmer (ECAP) or a laptop computer with the Electronic Technician (ET) software installed. While VIMS monitors all of the systems on the truck, the ECAP or ET is used for programming, running diagnostic tests and retrieving logged information from the engine, transmission and automatic retarder controls.

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36

• Electronic Technician (ET)

Shown is the communication adapter and a laptop computer with the Electronic Technician (ET) diagnostic software installed. The communication adapter is connected to the diagnostic connector shown in the previous slide.

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37

• VIMS connector (arrow)

Shown is a laptop computer with the VIMS PC diagnostic software installed. The laptop computer is connected to the VIMS diagnostic connector (arrow).

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38

• Hoist control lever (arrow)

The operator controls include the hoist lever (arrow) which is located to the left of the operator’s seat. The four positions are RAISE, HOLD, FLOAT and LOWER.

• Hoist lever in FLOAT for normal operation

The truck should normally be operated with the hoist lever in the FLOAT position. Operating with the hoist lever in the FLOAT position allows the hoist valve to provide some downward hydraulic pressure on the hoist cylinders and prevents an empty body from bouncing on rough haul roads.

• Electronically controlled hoist system

The 793C hoist system is different from previous trucks. The hoist system is electronically controlled.

INSTRUCTOR NOTE: The hoist system will be explained in more detail in the HOIST SYSTEM section of this presentation.

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39

• Operator controls: - Secondary brake lever (red) - Retarder lever (black) 1. Tilt steering lock 2. Turn signal and hazard switch

The operator controls on the steering column are the secondary brake lever (red), the retarder lever (black), the tilt steering lock (1) and the turn signal and hazard switch (2).

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1. Service brake pedal 2. Throttle pedal 3. Throttle position sensor

On the floor to the right of the steering column are the service brake pedal (1) and the throttle pedal (2). A throttle position sensor (3) is attached to the throttle pedal. The throttle position sensor provides the throttle position input signals to the engine ECM. The engine ECM provides an elevated engine idle speed of 1300 rpm when the coolant temperature is below 60°C (140°F). Above 60°C (140°F), the elevated idle rpm is gradually reduced until the coolant temperature reaches 71°C (160°F). Above 71°C (160°F), the engine will idle at 700 rpm.

• Elevated low idle reduced with throttle pedal

Increasing the low idle speed helps prevent incomplete combustion and overcooling. To temporarily reduce the elevated idle speed, the operator can depress the throttle momentarily, and the idle speed will decrease to 700 rpm for 10 minutes.

• Horn button and high beam switch (not shown)

On the floor to the left of the steering column are the horn button and the high beam switch (not shown).

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41

ENGINE • 793C uses 3516B engine

The 793C is equipped with the Caterpillar 3516B engine with a gross power rating of 1715 kW (2300 hp) and a net flywheel power rating of 1615 kW (2166 hp) at 1750 rpm.

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ADEM II CONTROL MODULE ELECTRONIC UNIT INJECTORS

3516B ELECTRONIC CONTROL SYSTEM COMPONENT DIAGRAM GROUND BOLT

DISCONNECT SWITCH

MAIN KEY START 15 AMP POWER RELAY SWITCH BREAKER

THROTTLE

24 V

TIMING PROBE CONNECTOR

ENGINE COOLANT TEMPERATURE

OIL LEVEL SWITCH (ADD)

REAR AFTERCOOLER TEMPERATURE

SPEED/TIMING SENSOR

ENGINE OIL PRESSURE (FILTERED)

ENGINE OIL PRESSURE (UNFILTERED)

OIL LEVEL SWITCH (LOW)

ETHER SOLENOID ATMOSPHERIC PRESSURE THROTTLE OVERRIDE SWITCH

MANUAL ETHER SWITCH

TURBO OUTLET PRESSURE (BOOST)

GROUND LEVEL SHUTDOWN SWITCH

RIGHT TURBO INLET PRESSURE FUEL FILTER SWITCH CAT DATA LINK

LEFT TURBO INLET PRESSURE CRANKCASE PRESSURE

RIGHT TURBO EXHAUST

A/C PRESSURE SWITCH

LEFT TURBO EXHAUST FAN CLUTCH SOLENOID FAN

FAN SPEED SENSOR

EXHAUST WASTEGATE SOLENOID

SERVICE TOOL EPTC II ARC VIMS

ENGINE OIL RENEWAL SOLENOID

SHUTTER SOLENOID PRE-LUBRICATION RELAY COOLANT FLOW SWITCH

42 • 3516B electronic control system component diagram

Shown is the electronic control system component diagram for the 3516B engine used in the 793C. Fuel injection is controlled by the second generation Advanced Diesel Engine Management (ADEM II) engine Electronic Control Module (ECM). Many electronic signals are sent to the ADEM II ECM by sensors, switches and senders. The engine ECM analyzes these signals and determines when and for how long to energize the injector solenoids. When the injector solenoids are energized determines the timing of the engine. How long the solenoids are energized determines the engine speed.

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43

• ECM (arrow)

Fuel injection is controlled by the ADEM II ECM (arrow) located on the right front of the engine.

• ECM has two 40-pin connectors

The previous ECM had one 70-pin connector. The ADEM II ECM has two 40-pin connectors.

• ECM cooled by fuel

The engine ECM is cooled by fuel. Fuel flows from the fuel transfer pump through the ECM to the secondary fuel filters.

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44

• Atmospheric pressure sensor (arrow)

The atmospheric pressure sensor (arrow) is located adjacent to the engine ECM. Formerly, this sensor was located in the compartment behind the cab. The engine ECM uses the atmospheric pressure sensor as a reference for calculating boost and air filter restriction and for derating the engine at high altitudes. The engine ECM also uses the atmospheric pressure sensor as a reference when calibrating all the pressure sensors.

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3516B IMPROVEMENTS INPUT SWITCHES AND SENSORS • COOLANT FLOW • REAR AFTERCOOLER TEMPERATURE • ENGINE OIL LEVEL • TURBOCHARGER TEMPERATURE • ENGINE OIL FILTER PRESSURE/RESTRICTION • ENGINE FAN SPEED • FUEL FILTER RESTRICTION • AIR CONDITIONER COMPRESSOR PRESSURE • CRANKCASE PRESSURE 45 • 3516B improvements

• Additional inputs

The 3516B engine has many improvements over the original 3516 engine. Some of the improvements are accomplished by adding additional switch and sensor inputs to the engine ECM. Adding additional inputs to the engine ECM allows the ECM to control the engine more precisely. Additional inputs to the 3516B ECM are: - Coolant flow is monitored. - Rear aftercooler temperature is measured. - Engine oil level is monitored. - Two turbocharger temperature sensors measure exhaust temperatures. - Two engine oil pressure sensors are located on the oil filter base to measure oil pressure and oil filter restriction. - Engine fan speed is measured (with variable fan speed attachment). INSTRUCTOR NOTE: The following slides will show some of the engine ECM input components. The remaining inputs to the engine ECM will be discussed when the systems they monitor are shown.

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46

1. Fuel filter bypass switch

Fuel filter restriction is monitored with a fuel filter bypass switch (1) located on the fuel filter base. The fuel filter bypass switch provides an input signal to the engine ECM. The ECM provides a signal to the VIMS which informs the operator if the secondary fuel filters are restricted.

• Fuel filter restriction event

If the fuel filter restriction exceeds 138 kPa (20 psi), a fuel filter restriction event is logged. No factory password is required to clear this event.

2. Air conditioner compressor switch

An air conditioner compressor switch (2) is located at the rear of the air conditioner compressor. If the truck is equipped with the variable fan speed attachment, the air conditioner compressor switch informs the engine ECM when the air conditioner system is ON. When the air conditioner system is ON, the ECM sets the variable speed fan at MAXIMUM rpm. Disconnecting the air conditioner compressor switch will also signal the ECM to set the fan speed at MAXIMUM rpm.

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47

• Crankcase pressure sensor (arrow)

The crankcase pressure sensor (arrow) is located on the right side of the engine above the engine oil cooler. The crankcase pressure sensor provides an input signal to the engine ECM. The ECM provides the signal to the VIMS which informs the operator of the crankcase pressure. High crankcase pressure may be caused by worn piston rings or cylinder liners.

• Crankcase pressure event

If crankcase pressure exceeds 3.6 kPa (.5 psi), a high crankcase pressure event will be logged. No factory password is required to clear this event.

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3516B IMPROVEMENTS PREVIOUS LOGGED EVENTS • AIR FILTER RESTRICTION • LOW OIL PRESSURE • HIGH COOLANT TEMPERATURE • ENGINE OVERSPEED 48 • Events logged by 3500 ECM and 3500B ECM

The 3500B ECM logs the four events of the previous 3500 engine plus some additional events. The four events logged by the 3500 ECM and the 3500B ECM are: Air filter restriction: Greater than 6.25 kPa (25 in. of water). Maximum derate of 20%. Low oil pressure: From less than 100 kPa (15 psi) at LOW IDLE to less than 300 kPa (44 psi) at HIGH IDLE. High coolant temperature: Greater than 107°C (226°F). Engine overspeed: Greater than 2200 rpm. NOTE: Factory passwords are required to clear all the events listed above.

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3516B IMPROVEMENTS ADDITIONAL LOGGED EVENTS

• OIL FILTER RESTRICTION

• HIGH CRANKCASE PRESSURE

• FUEL FILTER RESTRICTION

• LOW COOLANT FLOW

• HIGH EXHAUST TEMPERATURE

• USER DEFINED SHUTDOWN

• HIGH AFTERCOOLER TEMPERATURE

• LOW BOOST PRESSURE

• ENGINE OIL LEVEL LOW

• HIGH BOOST PRESSURE

49 • Additional logged events

Additional events logged by the 3500B ECM are: Oil filter restriction: Greater than 70 kPa (10 psi). No factory password required. Greater than 200 kPa (29 psi). Factory password required. Fuel filter restriction: Greater than 138 kPa (20 psi). No factory password required. Exhaust temperature high: Greater than 760°C (1400°F). Maximum derate of 20%. Factory password required. Aftercooler coolant temperature high: Greater than 107°C (226°F). Factory password required. Engine oil level low: No factory password required. Crankcase pressure high: Greater than 3.6 kPa (.5 psi). No factory password required. Coolant flow low: Factory password required. User defined shutdown: Parameters determined by the user. Boost pressure high: 20 kPa (3 psi) greater than desired. Maximum derate of 10%. No factory password required. Boost pressure low: 30 kPa (4 psi) lower than desired. Maximum derate of 10%. No factory password required.

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3516B IMPROVEMENTS SYSTEMS CONTROLLED BY ECM

• ETHER INJECTION • RADIATOR SHUTTER CONTROL • COLD CYLINDER CUTOUT • ENGINE START FUNCTION • ENGINE OIL PRE-LUBRICATION • VARIABLE SPEED FAN CONTROL • ENGINE OIL RENEWAL SYSTEM • EXHAUST BYPASS AT HIGH BOOST

50 • Engine ECM controls other systems

The engine ECM also regulates other systems by energizing solenoids or relays. Some of the other systems controlled by the ECM are:

• Ether injection

Ether Injection: Ether injection is controlled by the engine ECM or manually. The engine ECM will energize the ether injection relay only if: - The coolant temperature is below 10°C (50°F). - Engine speed is below 1200 rpm.

• Radiator shutter control

Radiator Shutter Control: On trucks that operate in cold weather, shutters can be added in front of the radiator. Installing shutters in front of the radiator allows the engine to warm up to operating temperature quicker. If a truck is equipped with the attachment radiator shutter control, the shutters are controlled by the engine ECM.

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Cold Cylinder Cut-out: The 3508B engine uses a cold cylinder cut-out function to reduce white exhaust smoke after start-up and during extended idling in cold weather. After the engine is started and the automatic ether injection system has stopped injecting ether, the engine ECM will cut out one cylinder at a time to determine which cylinders are firing. The ECM will disable some of the cylinders that are not firing. The ECM can identify a cylinder which is not firing by monitoring the fuel rate and engine speed during a cylinder cut-out. The ECM averages the fuel delivery and analyzes the fuel rate change during a cylinder cut-out to determine if the cylinder is firing.

• Engine runs rough during cold mode

Disabling some of the cylinders during Cold Mode operation will cause the engine to run rough until the temperature increases above the Cold Mode temperature. This condition is normal, but the operator should be aware it exists to prevent unnecessary complaints.

• Engine start function

Engine Start Function: The Engine Start function is controlled by ADEM II and the Electronic Programmable Transmission Control (EPTC II). The engine ECM provides signals to the EPTC II regarding the engine speed and the condition of the engine pre-lubrication system. The EPTC II will energize the starter relay only when: - The shift lever is in NEUTRAL. - The parking brake is ENGAGED. - The engine speed is 0 rpm. - The engine pre-lubrication cycle is complete or turned OFF. NOTE: To protect the starter, the starter is disengaged when the engine rpm is above 300 rpm.

INSTRUCTOR NOTE: The remaining improvements are described in the slides that follow.

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51

• Engine oil pre-lubrication 1. Pre-lubrication pump relay

2. Pre-lubrication pump

Engine Oil Pre-lubrication: Engine oil pre-lubrication is controlled by the ADEM II and EPTC II. The EPTC II signals the ADEM II when to energize the pre-lubrication pump relay (1). The ADEM II signals EPTC II to crank the engine when: - Engine oil pressure is 27 kPa (5 psi) or higher. - The pre-lubrication pump (2) has run for 15 seconds. (If the system times out after 15 seconds, a pre-lubrication fault is logged in the ADEM II.) - The engine has been running in the last 2 minutes. - Coolant temperature is above 50°C (122°F). NOTE: The ECAP and ET can enable or disable the pre-lubrication feature in the ADEM II. On some trucks, the pre-lubrication pump is located near the right front of the engine.

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2

3

52 • Variable speed fan control: 1. Fan control solenoid valve 2. Jacket water coolant temperature sensor

• Fan speed sensor (not shown)

Variable Speed Fan Control: If the engine is equipped with a variable speed fan, the engine ECM regulates the fan speed. Fan speed varies according to the temperature of the engine. The ECM sends a signal to the variable speed fan control solenoid valve (1) and engine oil pressure engages a clutch as needed to change the speed of the fan. The jacket water coolant temperature sensor (2) is located in the jacket water temperature regulator (thermostat) housing. The ECM uses the coolant temperature sensor information as the main parameter to control the fan speed. The aftercooler temperature sensors, air conditioner pressure sensor and brake cooling oil temperature sensors are also used as inputs to determine the required fan speed. A speed sensor (not shown) is located behind the fan pulley and informs the ECM of the current fan speed.

• Fan speed overrides

The variable speed fan feature can be turned off using the ECAP or ET service tool. Turning off the variable speed fan feature will set the fan speed at MAXIMUM rpm. Disconnecting the air conditioning compressor switch will also signal the ECM to set the fan speed at MAXIMUM rpm.

3. Turbo outlet pressure sensor

The turbocharger outlet pressure sensor (3) sends an input signal to the ECM. The ECM compares the value of the turbo outlet pressure sensor with the value of the atmospheric pressure sensor and calculates boost pressure. INSTRUCTOR NOTE: For more information on the variable speed fan, refer to the Service Manual "Variable Speed Fan Clutch" (Form SENR8603).

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• Engine oil renewal system components: 1. Oil filter 2. Oil renewal solenoid 3. Fuel pressure regulator • Oil mixes with fuel in fuel tank

Engine Oil Renewal System: Located on the right side of the engine are the components of the engine oil renewal system. Engine oil flows from the engine block through an oil filter (1) to the engine oil renewal solenoid (2). A small amount of oil flows from the engine oil renewal solenoid into the return side of the fuel pressure regulator (3). The engine oil returns to the fuel tank with the return fuel. The engine oil mixes with the fuel in the tank and flows with the fuel to the EUI injectors to be burned. When the engine oil renewal system is used, the operator must pay close attention to the ADD OIL message that the VIMS provides to the operator when makeup oil must be added (see Slide No. 54). The oil does not have to be changed when using the engine oil renewal system. When the engine oil renewal system is used, the engine oil filters, the engine oil renewal system filter, the primary fuel filter and the secondary fuel filters must all be changed at 500 hour intervals.

• Sample engine oil to check soot level

Engine oil samples must be taken regularly to ensure that the soot level of the engine oil is in a safe operating range.

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• Oil injection controlled by engine ECM • Engine oil renewal system parameters

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The ECM regulates the amount of oil that is injected by the engine oil renewal solenoid. Several parameters must be met before the ECM will allow the injection of oil through the engine oil renewal system. The parameters that must be met are: - Fuel position is greater than 10. - Engine rpm is between 1300 and 1850 rpm. - Jacket water temperature is between 63°C (145°F) and 107°C (225°F). - Oil filter differential pressure at high idle with warm oil is less than 70 kPa (10 psi). - Fuel filter differential pressure is less than 140 kPa (20 psi). - Engine oil level switches are sending a valid signal to the ADEM II control. - Engine has been running more than five minutes.

• Oil renewal adjusted with ECAP or ET

The engine oil renewal system can be turned ON or OFF with the ECAP or ET service tool. The amount of oil injected can also be adjusted by programming the ECM with the ECAP or ET service tool. The factory setting shown in the service tool is "0" and is equivalent to a 0.5% oil to fuel ratio. The ratio can be changed with the service tool from minus 50 (-50) to plus 50 (+50), which is equivalent to 0.25% to 0.75% oil to fuel ratios.

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54

The engine oil level switches (1 and 2) provide input signals to the engine ECM. The ECM provides an input signal to the VIMS which informs the operator of the engine oil level. 1. Add engine oil level switch

If the truck is equipped with the engine oil renewal system attachment, the upper oil level switch (1) will tell the operator when makeup oil must be added. The ADD ENG OIL message is a Category 1 Warning.

2. Engine oil level low switch

The lower oil level switch (2) will tell the operator when the engine oil level is low and it is unsafe to operate the truck without causing damage to the engine. The ENG OIL LEVEL LOW message is a Category 2 or 3 Warning.

• Low oil level event

If the engine ECM detects a low oil level condition (oil level below the lower switch), the ECM will log a low oil level event. No factory password is required to clear this event.

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55

1. Exhaust bypass valve

2. Wastegate solenoid valve - Controlled by engine ECM

Exhaust Bypass Control: An exhaust bypass (wastegate) valve (1) prevents excessive boost pressure by diverting exhaust gasses away from the turbochargers. The bypass valve is controlled by the engine ECM. Brake system air pressure is reduced to 380 kPa (55 psi) by a valve located outside the right rear of the cab and is supplied to the wastegate solenoid valve (2). If boost pressure exceeds a predetermined value, the ECM will open the wastegate solenoid and send air pressure to open the exhaust bypass valve. When the exhaust bypass valve is open, exhaust at the turbine side of the turbochargers is diverted through the muffler. Diverting the turbine exhaust pressure decreases the speed of the turbochargers which reduces the boost pressure to the cylinders.

• Engine wastegate solenoid checked with ECAP or ET

The wastegate solenoid valve can be controlled with the ECAP or ET service tool for diagnostic purposes. Connect a multimeter to the wastegate solenoid and set the meter to read DUTY CYCLE. Using the service tool, override the wastegate solenoid valve and use the multimeter to measure the corresponding duty cycle.

• Boost pressure events

If the actual boost pressure is 20 kPa (3 psi) higher than the desired boost pressure calculated by the ECM, a high boost pressure event will be logged. If the actual boost pressure is 30 kPa (4 psi) lower than the desired boost pressure calculated by the ECM, a low boost pressure event will be logged. If the ECM detects a high or low boost condition, the ECM will derate the fuel delivery (maximum derating of 10%) to prevent damage to the engine.

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2 1 4

3

56

Cooling System 1. Cooling system shunt tank • Engine cooling systems: - Jacket water cooling system - Aftercooler cooling system

The 793C is equipped with a shunt tank (1) to increase the cooling capacity. The shunt tank provides a positive pressure at the coolant pump inlets to prevent cavitation during high flow conditions. The cooling system is divided into two systems. The two systems are the jacket water cooling system and the aftercooler cooling system. The only connection between these two systems is a small hole in the separator plate in the shunt tank. The small hole in the shunt tank prevents a reduction of coolant from either of the two systems if leakage occurs in one of the separator plates in the radiator top or bottom tank. When servicing the cooling systems, be sure to drain and fill both systems separately.

2. Coolant level gauges

The coolant levels are checked at the shunt tank. Use the gauges (2) on top of the shunt tank to check the coolant level.

3. Coolant level sensor

A coolant level sensor (3) is located on each side of the shunt tank to monitor the coolant level of both cooling systems (guard removed for viewing sensor). The coolant level sensors provide input signals to the VIMS which informs the operator of the engine coolant levels.

4. Pressure relief valves

Pressure relief valves (4) prevent the cooling systems from becoming over pressurized.

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57

• Jacket water cooling system

The jacket water cooling system uses 17 of the 30 cores on the right side of the radiator (approximately 60% of the total capacity). The jacket water cooling system temperature is controlled by temperature regulators (thermostats).

• Aftercooler cooling system

The aftercooler cooling system uses 13 of the 30 cores on the left side of the radiator (approximately 40% of the total capacity). The aftercooler cooling system does not have thermostats in the circuit. The coolant flows through the radiator at all times to keep the turbocharged inlet air cool for increased horsepower.

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58

1. Jacket water pump 2. Bypass tube 3. Jacket water thermostat housing

• High coolant temperature event

The jacket water pump (1) is located on the right side of the engine. The pump draws coolant from the bypass tube (2) until the temperature regulators (thermostats) open. The thermostats are located in the housing (3) at the top of the bypass tube. When the thermostats are open, coolant flows through the radiator to the water pump inlet. If the jacket water cooling system temperature increases above 107°C (226°F), the engine ECM will log an event that requires a factory password to clear.

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59

• Coolant flow warning switch (arrow)

Coolant flows from the jacket water pump, past the coolant flow warning switch (arrow), and through the various system oil coolers (engine, torque converter/transmission and rear brake). The coolant flow switch sends an input signal to the engine ECM. The ECM provides the input signal to the VIMS which informs the operator of the coolant flow status.

• Low coolant flow event

If the ECM detects a low coolant flow condition, a low coolant flow event will be logged. A factory password is required to clear this event.

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1. Engine oil cooler 2. Torque converter/ transmission oil cooler

Shown is the right side of the engine. The engine oil cooler (1) and the torque converter and transmission oil cooler (2) are visible in this view. The coolant flows through these coolers to the rear brake oil coolers located on the outside right frame.

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• Rear brake oil coolers (arrow)

Jacket water coolant flows from the rear brake oil coolers (arrow) to both sides of the engine cylinder block. Coolant flows through the engine block and through the cylinder heads. From the cylinder heads, the coolant returns to the temperature regulators and either goes directly to the water pump through the bypass tube or to the radiator (depending on the temperature of the coolant).

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THERMOSTAT HOUSING

JACKET WATER COOLANT FLOW

SHUNT TANK

ENGINE BLOCK

RADIATOR

ENGINE OIL COOLER

TORQUE CONVERTER/ TRANSMISSION OIL COOLER REAR BRAKE OIL COOLERS

JACKET WATER PUMP

62 • Jacket water cooling system circuit

Shown is the jacket water cooling system circuit. Coolant flows from the jacket water pump through the coolers to the engine block. Coolant flows through the engine block and the cylinder heads. From the cylinder heads, the coolant returns to the temperature regulators (thermostats) and either goes directly to the water pump through the bypass tube or to the radiator (depending on the temperature of the coolant). The shunt tank increases the cooling capacity and provides a positive pressure at the coolant pump inlet to prevent cavitation during high flow conditions. In this illustration and those that follow, the colors used to identify the various pressures in the systems are: Red Green Red and White Stripes Brown Orange Blue Yellow Purple

- Supply oil/water pressure - Drain or reservoir oil/water - Reduced supply oil pressure - Lubrication or cooling pressure - Pilot or load sensing signal pressure - Blocked oil - Moving components - Air pressure

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1. Aftercooler water pump 2. Shunt tank supply tube 3. Aftercooler circuit coolant tubes

The auxiliary (aftercooler) water pump (1) for the aftercooler cooling system is located on the left side of the engine. Coolant enters the aftercooler water pump from the radiator or the shunt tank supply tube (2). Coolant flows from the pump to the aftercooler cores through the large tubes (3)

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• Rear aftercooler temperature sensor (arrow)

Located in a tube at the rear of the aftercooler is the rear aftercooler temperature sensor (arrow). The rear aftercooler temperature sensor provides an input signal to the engine ECM. The engine ECM uses the rear aftercooler temperature sensor signal with the jacket water temperature sensor signal to control the variable speed fan attachment. The ECM also provides the input signal to the VIMS which informs the operator of the aftercooler coolant temperature.

• Rear aftercooler temperature event

If the rear aftercooler temperature increases above 107°C (226°F), the engine ECM will log an event that requires a factory password to clear.

• Front aftercooler temperature sensor

Another aftercooler temperature sensor is located in a tube at the front of the aftercooler. The front aftercooler temperature sensor does not send an input signal to the engine ECM. The front aftercooler temperature sensor provides an input signal directly to the VIMS.

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1. Front brake oil cooler

Coolant flows through the aftercooler cores to the front brake oil cooler (1) located at the rear of the engine.

• Aftercooler cooling circuit does not have thermostats

Coolant flows through the front brake oil cooler to the aftercooler section of the radiator. The aftercooler cooling system does not have temperature regulators (thermostats) in the circuit.

2. Front brake oil cooler diverter valve

When the service or retarder brakes are ENGAGED, the front brake oil cooler diverter valve (2) allows brake cooling oil to flow through the front brake oil cooler. Normally, front brake cooling oil is diverted around the cooler and goes directly to the front brakes. Diverting oil around the cooler provides lower temperature aftercooler air during high power demands (when climbing a grade with the brakes RELEASED, for example).

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AFTERCOOLER COOLANT FLOW SHUNT TANK AFTERCOOLER

FRONT BRAKE OIL COOLER

RADIATOR

AFTERCOOLER WATER PUMP

66 • Aftercooler cooling system circuit

Shown is the aftercooler cooling system circuit. Coolant flows from the aftercooler water pump through the aftercooler. Coolant flows through the aftercooler cores to the front brake oil cooler located at the rear of the engine. Coolant then flows through the front brake oil cooler to the aftercooler section of the radiator. The aftercooler cooling circuit does not have temperature regulators (thermostats) in the circuit. The shunt tank increases the cooling capacity and provides a positive pressure at the aftercooler water pump inlet to prevent cavitation during high flow conditions.

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Lubrication System 1. Engine oil pump 2. Engine oil pump relief valve

The engine oil pump (1) is located behind the jacket water pump on the right side of the engine. The pump draws oil from the oil pan through a screen. The relief valve (2) for the lubrication system is located on the pump. The engine also has a scavenge pump at the rear of the engine to transfer oil from the rear of the oil pan to the main sump.

3. Engine oil cooler bypass valve 4. Engine oil cooler

Oil flows from the pump through an engine oil cooler bypass valve (3) to the engine oil cooler (4). The bypass valve for the engine oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is plugged.

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68 • Engine oil filters

Oil flows from the engine oil cooler to the oil filters on the left side of the engine. The oil flows through the filters and enters the engine cylinder block to clean, cool and lubricate the internal components and the turbochargers.

1. Engine oil fill tube

Engine oil is added at the fill tube (1) and checked with the dipstick (2). A bypass valve for each filter is located in each oil filter base.

2. Engine oil dipstick

3. Engine oil S•O•S tap

Engine oil samples can be taken at the Scheduled Oil Sample (S•O•S) tap (3).

4. Engine oil pressure sensors

The engine has two oil pressure sensors. One sensor is located on each end of the oil filter base. The front sensor measures engine oil pressure before the filters. The rear sensor (4) measures oil pressure after the filters. The sensors send input signals to the engine ECM. The ECM provides the input signal to the VIMS which informs the operator of the engine oil pressure. Used together, the two engine oil pressure sensors inform the operator if the engine oil filters are restricted.

• Engine oil pressure event

If the engine oil pressure is less than 100 kPa (15 psi) at low idle to less than 300 kPa (44 psi) at high idle, the engine ECM will log an event that requires a factory password to clear.

• Engine oil filter restriction events

If the oil filter restriction exceeds 70 kPa (10 psi), a low oil filter restriction event will be logged. No factory password is required to clear this event. If the oil filter restriction exceeds 200 kPa (29 psi), a high oil filter restriction event will be logged. A factory password is required to clear this event.

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ENGINE OIL SYSTEM ENGINE BLOCK ENGINE OIL RENEWAL SYSTEM SOLENOID

TO FUEL SYSTEM

SCAVENGE PUMP

BYPASS VALVE ENGINE OIL FILTERS

ENGINE OIL COOLER ENGINE OIL PUMP

69 • Engine oil system

The engine oil pump draws oil from the oil pan through a screen. The engine also has a scavenge pump at the rear of the engine to transfer oil from the rear of the oil pan to the main sump. Oil flows from the pump through an engine oil cooler bypass valve to the engine oil cooler. The bypass valve for the engine oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is plugged. Oil flows from the engine oil cooler to the oil filters. The oil flows through the filters and enters the engine cylinder block to clean, cool and lubricate the internal components and the turbochargers.

• Engine oil renewal system

Some trucks are equipped with an engine oil renewal system. Engine oil flows from the engine block through an oil filter to an engine oil renewal system manifold. A small amount of oil flows from the engine oil renewal system manifold into the return side of the fuel pressure regulator. The engine oil returns to the fuel tank with the return fuel (see Slides No. 53 and 74).

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70

Fuel System • Fuel heater (not shown) • Primary fuel filter (arrow)

The fuel tank is located on the left side of the truck. Fuel is pulled from the tank through the fuel heater (not shown), if equipped, and through the primary fuel filter (arrow) by the fuel transfer pump located on the right side of the engine behind the engine oil pump.

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1. Fuel transfer pump 2. Fuel transfer pump bypass valve

The fuel transfer pump (1) contains a bypass valve (2) to protect the fuel system components from excessive pressure. The bypass valve setting is higher than the setting of the fuel pressure regulator which will be shown later. Fuel flows from the transfer pump through the engine ECM to the secondary fuel filters located on the left side of the engine.

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• Secondary fuel filters 1. Fuel priming pump

The secondary fuel filters and the fuel priming pump (1) are located above the engine oil filters on the left side of the engine. The fuel priming pump is used to fill the filters after they are changed.

2. Fuel filter bypass switch

A fuel filter bypass switch (2) is located on the fuel filter base. The fuel filter bypass switch sends an input signal to the engine ECM. The ECM provides the input signal to the VIMS which informs the operator if the secondary fuel filters are restricted.

• Fuel filter restriction event

If fuel filter restriction exceeds 138 kPa (20 psi), a fuel filter restriction event will be logged. No factory password is required to clear this event.

• Fuel flows to EUI injectors

Fuel flows from the fuel filter base through the Electronic Unit Injection (EUI) fuel injectors and the fuel pressure regulator and then returns to the fuel tank. The injectors receive 4 1/2 times the amount of fuel needed for injection. The extra fuel is used for cooling.

• Extra fuel used to cool injectors

NOTE: If the fuel system requires priming, it may be necessary to block the fuel return line during priming to force the fuel into the injectors.

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1. Fuel pressure tubes to injectors 2. Fuel pressure regulator

Fuel flows from the fuel filter base through the steel tubes (1) to the EUI fuel injectors. Return fuel from the injectors flows through the fuel pressure regulator (2) before returning to the fuel tank. Fuel pressure is controlled by the fuel pressure regulator.

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FUEL SYSTEM FUEL PRESSURE REGULATOR ENGINE OIL RENEWAL SYSTEM SOLENOID

CYLINDER HEAD

ENGINE BLOCK

SECONDARY FUEL FILTERS

FUEL TANK

PRIMARY FUEL FILTER

FUEL TRANSFER PUMP

ADEM II CONTROL

FUEL HEATER

74 • Fuel system circuit

Fuel is pulled from the tank through a fuel heater, if equipped, and through the primary fuel filter by the fuel transfer pump. Fuel flows from the transfer pump through the ADEM II control to the secondary fuel filters. Fuel flows from the fuel filter base through the fuel injectors in the cylinder heads. Return fuel from the injectors flows through the fuel pressure regulator before returning through the fuel heater to the fuel tank. Engine oil flows from the engine block through an oil filter to the engine oil renewal system manifold. A small amount of oil flows from the engine oil renewal system manifold into the return side of the fuel pressure regulator. The engine oil returns to the fuel tank with the return fuel. The engine oil mixes with the fuel in the tank and flows with the fuel to the injectors to be burned.

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75

Air Induction and Exhaust System

• Air filter restriction indicators (arrow)

The engine receives clean air through the four air filters located on the front of the truck. Any restriction caused by plugged filters can be checked at the filter restriction indicators (arrow). If the yellow piston is in the red zone, the filters must be cleaned or replaced.

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1. Turbocharger inlet pressure sensor

The turbocharger inlet pressure sensor (1) is located in a tube between the air cleaners and the turbochargers. The engine ECM uses the turbocharger inlet pressure sensor in combination with the atmospheric pressure sensor to determine air filter restriction. The ECM provides the input signal to the VIMS which informs the operator of the air filter restriction.

• Air filter restriction event

If air filter restriction exceeds 6.25 kPa (25 in. of water), an air filter restriction event will be logged, and the ECM will derate the fuel delivery (maximum derating of 20%) to prevent excessive exhaust temperatures. A factory password is required to clear this event.

2. Ether cylinders

If the truck is equipped with an ether start system, the ECM will automatically inject ether from the ether cylinders (2) during cranking. The operator can also inject ether manually with the ether switch in the cab on the center console (see Slide No. 30). Ether will be injected only if the engine coolant temperature is below 10°C (50°F) and engine speed is below 1200 rpm.

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• Series turbocharger system 1. Low pressure turbochargers 2. High pressure turbochargers

The 793C engine is equipped with a series turbocharger system. The clean air from the filters enters the larger low pressure turbochargers (1). The compressed air from the low pressure turbochargers flows to the inlet of the smaller high pressure turbochargers (2). After additional compression by the high pressure turbochargers, the air flows to the aftercoolers. After the air is cooled by the aftercoolers, the air flows to the cylinders and combines with the fuel for combustion. The turbochargers are driven by the exhaust gasses from the cylinders. The exhaust gasses first enter the smaller high pressure turbochargers. The exhaust from the high pressure turbochargers flows to the larger low pressure turbochargers. The exhaust gasses then flow through the low pressure turbochargers, the exhaust piping, and the mufflers.

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• Exhaust temperature sensor (arrow)

An exhaust temperature sensor (arrow) is located in each exhaust manifold before the turbochargers. The two exhaust temperature sensors provide input signals to the engine ECM. The ECM provides the input signal to the VIMS which informs the operator of the exhaust temperature.

• Causes of high exhaust temperature

Some causes of high exhaust temperature may be faulty injectors, plugged air filters, or a restriction in the turbochargers or the muffler.

• High exhaust temperature derates engine and logs event

If the exhaust temperature is above 760°C (1400°F), the engine ECM will derate the fuel delivery (maximum derate of 20%) to prevent excessive exhaust temperatures. The ECM will also log an event that requires a factory password to clear.

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EXHAUST SYSTEM WASTEGATE SOLENOID VALVE

EXHAUST BYPASS VALVE MUFFLER

FROM BRAKE AIR SYSTEM

PRESSURE REDUCING VALVE

HIGH PRESSURE TURBOCHARGER

AFTERCOOLER

FROM AIR FILTER LOW PRESSURE TURBOCHARGER

79 • Turbocharger speed reduced when exhaust bypass valve opens

This schematic shows the air flow through the air induction system. If boost pressure exceeds a predetermined value programmed in the engine ECM, the ECM will open the wastegate solenoid valve and send brake air pressure to open the exhaust bypass valve. The exhaust bypass valve will vent the exhaust gasses before they reach the turbochargers. Less exhaust gasses will flow through the turbochargers, and the turbocharger speed will decrease. The slower turbochargers reduce the boost pressure until the bypass valve closes and the exhaust gasses are again directed through the turbochargers.

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POWER TRAIN 793C

80 • Power train components: 1. Torque converter 2. Transfer gears 3. Transmission 4. Differential 5. Final drives

POWER TRAIN Power flows from the engine to the rear wheels through the power train. The components of the power train are: 1. 2. 3. 4. 5.

Torque converter Transfer gears Transmission Differential Final drives

INSTRUCTOR NOTE: In this section of the presentation, component locations and a brief description of the component functions are provided. For more detailed information on the Electronic Programmable Transmission Control (EPTC II), torque converter and ICM (Individual Clutch Modulation) transmission, refer to the Technical Instruction Modules "Electronic Programmable Transmission Control (EPTC II)" (Form SEGV2584-01) and "769C - 793B Off-highway Trucks--Torque Converter and Transmission Hydraulic System" (Form SEGV2591).

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Power Train Components • Torque converter: - Provides a fluid coupling - Multiplies torque - Provides direct drive operation

1. Inlet relief valve

The first component in the power train is the torque converter. The torque converter provides a fluid coupling that permits the engine to continue running with the truck stopped. In converter drive, the torque converter multiplies torque to the transmission. At higher ground speeds, a lockup clutch engages to provide direct drive. The NEUTRAL and REVERSE ranges are converter drive only. FIRST SPEED is converter drive at low ground speed and direct drive at high ground speed. SECOND through SIXTH SPEEDS are direct drive only. The torque converter goes to converter drive between each shift (during clutch engagement) to provide smooth shifts.

2. Outlet relief valve 3. Lockup clutch control valve 4. Outlet temperature sensor

Mounted on the torque converter are the inlet relief valve (1), the outlet relief valve (2) and the torque converter lockup clutch control valve (3). A torque converter outlet temperature sensor (4) provides an input signal to the VIMS which informs the operator of the torque converter outlet temperature.

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LOCKUP PISTON

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TURBINE

IMPELLER

TORQUE CONVERTER STATOR

CONVERTER DRIVE

TORQUE CONVERTER INLET OIL

FREEWHEEL ASSEMBLY

TORQUE CONVERTER LOCKUP OIL PASSAGE

82 • CONVERTER DRIVE - Output shaft rotates slower than engine rpm - Torque is increased • Torque converter components: - Lockup clutch - Impeller - Turbine - Stator

This sectional view shows a torque converter in CONVERTER DRIVE. The lockup clutch (yellow piston and blue discs) is not engaged. During operation, the rotating housing and impeller (red) can rotate faster than the turbine (blue). The stator (green) remains stationary and multiplies the torque transfer between the impeller and the turbine. The output shaft rotates slower than the engine crankshaft, but with increased torque.

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LOCKUP PISTON

TURBINE

IMPELLER

TORQUE CONVERTER DIRECT DRIVE STATOR TORQUE CONVERTER INLET OIL

STATOR

FREEWHEEL ASSEMBLY

TORQUE CONVERTER LOCKUP OIL PASSAGE

83 • DIRECT DRIVE - Lockup clutch engaged - Output shaft rotates at engine rpm - Stator freewheels

In DIRECT DRIVE, the lockup clutch is engaged by hydraulic pressure and locks the turbine to the impeller. The housing, impeller, turbine, and output shaft then rotate as a unit at engine rpm. The stator, which is mounted on a freewheel assembly, is driven by the force of the oil in the housing and will freewheel at approximately the same rpm.

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84

1. Transfer gears 2. Transmission 3. Differential

Power flows from the torque converter through a drive shaft to the transfer gears (1). The transfer gears are splined to the transmission. The transmission (2) is located between the transfer gears and the differential (3). The transmission is electronically controlled and hydraulically operated like all other ICM (Individual Clutch Modulation) transmissions in Caterpillar rigid frame trucks. The differential is located in the rear axle housing behind the transmission. Power from the transmission flows through the differential and is divided equally to the final drives in the rear wheels. The final drives are double reduction planetaries.

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POWER SHIFT PLANETARY TRANSMISSION

1

2

3 4 5

6

85 • Transmission is power shift planetary design

The transmission is a power shift planetary design which contains six hydraulically engaged clutches. The transmission provides six FORWARD speeds and one REVERSE speed.

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1. Rear axle oil pump

Shown is the differential removed from the rear axle housing. The rear axle cooling and filter system starts with a rear axle oil pump (1) that is driven by the differential. Since the pump rotates only when the machine is moving, no oil flow is produced when the machine is stationary. Cooling oil flow increases with ground speed to provide cooling when it is most needed.

2. Rear axle suction screen

The rear axle pump pulls oil from the bottom of the rear axle housing through a suction screen (2). Oil flows from the pump through a temperature and flow control valve located on top of the differential housing to a filter mounted on the rear of the axle housing. Oil then flows from the filter back to the valve located on top of the differential housing. Oil then flows from the valve to the rear wheel bearings and the differential bearings.

3. Differential bearing oil tubes

Oil flows through tubes (3) to the differential bearings.

4. Fiberglass shroud

The fiberglass shroud (4) reduces the temperature of the rear axle oil on long hauls by reducing the oil being splashed by the bevel gear.

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1. Differential oil temperature sensor 2. Rear axle temperature and flow control valve

3. Differential oil filter

4. Differential bearing oil supply hose

Oil flows from the pump past the differential oil temperature sensor (1) to the rear axle temperature and flow control valve (2). The differential oil temperature sensor provides an input signal to the VIMS. The temperature sensor input signal is used to warn the operator of a high rear axle oil temperature condition or to turn on the attachment rear axle cooling fan (if equipped). Oil flows from the temperature and flow control valve to the differential oil filter (3) mounted on the rear of the axle housing. Oil then flows from the filter back to the temperature and flow control valve. Some of the oil that flows from the temperature and flow control valve flows through the small supply hose (4) to the differential bearings.

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1. Differential oil filter restriction switch 2. Rear axle oil level switches

The differential oil filter restriction switch (1) and the two rear axle oil level switches (2) provide input signals to the VIMS. The differential oil filter restriction switch signal is used to warn the operator when the differential oil filter is plugged. The rear axle oil level switch input signals are used to warn the operator when the rear axle oil level is LOW.

• Differential oil filter service information

When the truck is initially put into operation, a 1R0719 (40 micron) filter is installed. This filter removes the rust inhibitor used during manufacturing. The 40 micron filter should be changed after the first 50 hours of operation and replaced with a 4T3131 (13 micron) filter. The 13 micron filter should be changed every 500 hours.

3. Differential carrier thrust pin cover

A differential carrier thrust pin is located behind the small cover (3). The thrust pin prevents movement of the differential carrier during high thrust load conditions.

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1. Differential oil pressure sensor

The differential oil pressure sensor (1) provides an input signal to the VIMS. The differential oil pressure sensor signal is used to warn the operator of a HIGH or LOW rear axle oil pressure condition. A LOW oil pressure warning is provided if the pressure is below 35 kPa (5 psi) when the differential oil temperature is above 52°C (125°F) and the ground speed is higher than 24 km/h (15 mph). A HIGH oil pressure warning is provided if the pressure is above 690 kPa (100 psi) when the differential oil temperature is above 52°C (125°F).

2. Temperature and pressure control valve

The temperature and pressure control valve (2) prevents high oil pressure when the rear axle oil is cold. When the oil temperature is below 43°C (110°F), the valve is OPEN and allows oil to flow to the rear axle housing. When the oil temperature is above 43°C (110°F), the valve is CLOSED and all the oil flows through the filter to a flow control valve located in the temperature and flow control valve. The temperature and pressure control valve is also the system main relief valve. If the pressure exceeds 690 kPa (100 psi), the temperature and pressure control valve will open to prevent high oil pressure to the rear axle oil filter. The flow control valve distributes the oil flow to the rear wheel bearings and the differential bearings.

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REAR AXLE OIL COOLING AND FILTER SYSTEM OIL COOLER

OIL FILTER

FLOW CONTROL VALVE TEMPERATURE/ PRESSURE CONTROL VALVE

DIFFERENTIAL OIL PUMP

REAR AXLE

SUCTION SCREEN

90 • Rear axle oil cooling and filter system

Shown is a schematic of the rear axle oil cooling and filter system. The differential oil pump pulls oil from the bottom of the rear axle housing through a suction screen. Oil flows from the pump through a temperature and flow control valve located on top of the differential housing.

• Temperature and pressure control valve

The temperature and pressure control valve, which is part of the temperature and flow control valve, prevents high oil pressure when the rear axle oil is cold. When the oil temperature is below 43°C (110°F), the valve is OPEN and allows oil to flow to the rear axle housing. When the oil temperature is above 43°C (110°F), the valve is CLOSED and all the oil flows through the differential oil filter and the oil cooler (if equipped) to a flow control valve, which is also part of the temperature and flow control valve.

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• Temperature and pressure control valve is main relief

The temperature and pressure control valve is also the system main relief valve. If the pressure exceeds 690 kPa (100 psi), the temperature and pressure control valve will open to prevent high oil pressure to the rear axle oil filter.

• Flow control valve prevents overfilling wheel bearing compartment

The flow control valve distributes the oil flow to the rear wheel bearings and the differential bearings. At high ground speeds, excess oil flow is diverted to the axle housing to prevent overfilling the wheel bearing and final drive compartments.

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FIRST REDUCTION RING GEAR

SECOND REDUCTION RING GEAR

SECOND REDUCTI CARRIER SECOND REDUCT PLANETARY GE

FINAL DRIVE SECOND REDUC SUN GEAR

FIRST REDUCTION SUN GEAR

FIRST REDUCTION CARRIER

FIRST REDUCTION PLANETARY GEAR

91 • Double reduction planetary gear final drive

Shown is a sectional view of the double reduction planetary gear final drive. Power flows from the differential through axles to the sun gear of the first reduction planetary set. The ring gears of the first reduction planetary set and the second reduction planetary set cannot rotate. Since the ring gears cannot rotate, the first reduction sun gear causes rotation of the first reduction planetary gears and the first reduction carrier. The first reduction carrier is splined to the second reduction sun gear. The second reduction sun gear causes rotation of the second reduction planetary gears and the second reduction carrier. Since the second reduction carrier is connected to the wheel assembly, the wheel assembly also rotates. The wheel assembly rotates much slower than the axle shaft but with increased torque.

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92

Power Train Hydraulic System • Torque converter housing is oil sump

The torque converter housing is the oil sump for the torque converter and transmission oil supply.

• Four section pump: 1. Transmission scavenge 2. Torque converter charging 3. Transmission charging

A four section torque converter and transmission pump is located at the rear of the torque converter. The four sections (from front to rear) are: 1. 2. 3. 4.

Transmission scavenge Torque converter charging Transmission charging Transmission lube

4. Transmission lube 5. Transmission oil return screen

The transmission scavenge section pulls oil through the magnetic screens located at the bottom of the transmission. The scavenged oil from the transmission is transferred into the torque converter housing through the transmission oil return screen located behind the cover (5).

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93

• Transmission magnetic scavenge screens (arrow)

Shown is the location of the transmission magnetic scavenge screens (arrow). These screens should always be checked for debris if a problem with the transmission is suspected. Oil is scavenged from the transmission by the first section of the pump (shown in Slide No. 92).

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• Torque converter/ transmission suction screen cover (arrow)

The three rear sections of the torque converter and transmission pump pull oil from the torque converter housing sump. Most of the required oil supply is pulled directly from the torque converter and transmission oil cooler return oil. The remaining required oil supply is drawn through a suction screen located behind the cover (arrow).

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1. Torque converter charging filter 2. Torque converter inlet relief valve

Oil flows from the torque converter charging section of the torque converter and transmission pump to the torque converter charging filter (1) located on the front of the hydraulic tank. Oil flows from the torque converter charging filter to the torque converter inlet relief valve (2).

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96

• Torque converter inlet relief valve (arrow)

Oil flows from the torque converter charging filter to the inlet relief valve (arrow) mounted on the torque converter. The inlet relief valve controls the maximum pressure of the supply oil to the torque converter. The torque converter inlet relief pressure can be measured at this valve by removing a plug and installing a pressure tap. Oil flows through the inlet relief valve and enters the torque converter.

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1. Torque converter outlet relief valve 2. Outlet relief valve pressure tap

Torque converter charging oil either drops to the bottom of the housing or flows through the torque converter outlet relief valve (1). The outlet relief valve limits the pressure inside the torque converter. The outlet relief pressure can be measured at the tap (2) on the outlet relief valve.

3. Torque converter outlet screen

All the oil from the torque converter outlet relief valve flows through the torque converter outlet screen (3) to the torque converter and transmission oil cooler located on the right side of the engine (see Slide No. 60). Oil flows from the torque converter and transmission oil cooler back to the torque converter housing.

4. Torque converter outlet screen bypass switch

A torque converter outlet screen bypass switch (4) provides an input signal to the VIMS which informs the operator if the torque converter outlet screen is restricted.

5. Torque converter outlet temperature sensor

A torque converter outlet temperature sensor (5) provides an input signal to the VIMS which informs the operator of the torque converter outlet temperature.

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1. Transmission charging filter

Oil flows from the transmission charging section of the torque converter and transmission pump to the transmission charging filter (1).

2. Filter bypass switch

A transmission charging filter bypass switch (2) sends an input signal to the VIMS which informs the operator if the transmission charging filter is restricted.

• Transmission charging oil flows in two directions:

Transmission charging oil flows in two directions from the transmission charging filter:

- To torque converter lockup clutch valve - To transmission control valves

3. S•O•S tap

- Transmission charging oil flows to the torque converter lockup clutch valve located on top of the torque converter. - Transmission charging oil also flows to the transmission control valves located on top of the transmission. Torque converter and transmission oil samples can be taken at the Scheduled Oil Sample (S•O•S) tap (3).

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1. Torque converter lockup clutch valve supply port

The transmission charging pump supplies oil to the torque converter lockup clutch valve through the inlet port (1). When the lockup clutch solenoid (located on the transmission housing) is energized by the transmission control, the lockup clutch valve supplies oil to ENGAGE the lockup clutch in the torque converter.

2. Torque converter lockup clutch pressure tap

Torque converter lockup clutch pressure can be measured at the tap (2). Torque converter lockup clutch pressure should be 2205 ± 70 kPa (320 ± 10 psi) at 1300 rpm or higher. Do not check the torque converter lockup clutch pressure below 1300 rpm.

• Do not test converter lockup pressure below 1300 rpm

The transmission control uses a dual stage relief valve for clutch supply pressure. At high idle in torque converter drive, transmission charging pressure should be 3065 kPa (445 psi) maximum. At low idle in torque converter drive, transmission charging pressure should be 2480 kPa (360 psi) minimum. During torque converter lockup (DIRECT DRIVE), clutch supply pressure is reduced to extend the life of the transmission clutch seals. At high idle in direct drive, the clutch supply pressure should be 1620 + 240 - 100 kPa (235 + 35 - 15 psi). The corresponding transmission charge pressure is reduced to 2205 ± 70 kPa (320 ± 10 psi).

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3. Torque converter output speed (TCO) sensor

The torque converter output speed (TCO) sensor (3) sends an input signal to the Electronic Programmable Transmission Control (EPTC II). The EPTC II memory also contains the engine rpm and the Transmission Output Speed (TOS) for each gear of the transmission. The EPTC II provides all these input signals to the VIMS.

• Clutch slippage is recorded in VIMS

Using the information from the EPTC II, the VIMS calculates if any slippage exists in the torque converter lockup clutch or any of the transmission clutches and stores this information in the VIMS main module. This information can be downloaded from the VIMS with a laptop computer.

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TORQUE CONVERTER LOCKUP CLUTCH CONTROL DIRECT DRIVE LOCKUP CLUTCH PILOT OIL PRESSURE LOCKUP MODULATION VALVE

SELECTOR PISTON

LOCKUP SOLENOID

TO LOCKUP CLUTCH

TO TRANSMISSION LUBE PUMP

LOCKUP REDUCING VALVE

ON

FROM TRANSMISSION CHARGE PUMP

TO STATION "D"

SHUTTLE VALVE RELAY VALVE

FROM TRANSMISSION CHARGE PUMP

100 • Lockup clutch valve operation

Shown is a sectional view of the torque converter lockup clutch valve in DIRECT DRIVE. Supply oil from the transmission charging pump is used to provide lockup clutch oil and has two functions: 1. Supply pressure is reduced to provide pilot pressure. 2. When the solenoid is energized, supply pressure is reduced by the modulation reduction valve to provide lockup clutch pressure.

• Lockup solenoid energized starts clutch modulation

The lockup solenoid has been energized and directs pump supply pressure to the relay valve. Before moving the selector piston, pilot oil moves a shuttle valve to the right which closes the drain and opens the check valve. Oil then flows to the selector piston. Moving the selector piston blocks the drain passage and the load piston springs are compressed.

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Compressing the load piston springs moves the modulation reduction valve spool down against the force of the inner spring. This initial movement opens the supply passage (from the transmission charge pump) and permits pressure oil to flow to the clutch. As the clutch fills, pressure oil opens the ball check valve and fills the slug chamber at the top of the reduction valve spool. At the same time, oil flows through the load piston orifice and fills the chamber between the end of the load piston and the selector piston. The load piston orifice provides a pressure drop and time delay in the flow of oil to the load piston chamber. The load piston orifice helps control the rate of modulation. Filling the load piston chamber is made possible when the selector piston covers the drain passage at the decay orifice. • Lockup clutch at maximum pressure

The load piston has now moved completely down against the stop. The modulation cycle is completed and the clutch pressure is at its maximum setting. Because this is a modulation reduction valve, the maximum pressure setting of the clutch is lower than the transmission charge pressure. At the end of the modulation cycle, the pressure in the slug chamber moves the reduction valve a small distance up to restrict the flow of supply oil to the clutch. This is the "metering position" of the reduction valve spool. In this position, the valve maintains precise control of the clutch pressure. Primary pressure is adjusted with shims in the load piston. Final lockup clutch pressure is not adjustable. If the primary pressure is correct and final lockup clutch pressure is low, the load piston should be checked to make sure that it moves freely in the selector piston. If the load piston moves freely, the load piston springs should be replaced.

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3 5

4

2

1

101

1. Transmission control valve supply port 2. Transmission charging oil return port 3. Torque converter lockup clutch solenoid

The transmission charging pump supplies oil to the transmission hydraulic control valve and the shift solenoids through the inlet port (1). Excess transmission charging oil either drops to the bottom of the housing to be scavenged or flows back to the torque converter housing through the outlet hose (2).

4. Lockup clutch pilot oil hose

The torque converter lockup clutch solenoid (3) is energized by the EPTC II when DIRECT DRIVE (lockup clutch ENGAGED) is required. Transmission charge pump supply oil flows through the small hose (4) to the lockup clutch control valve. The lockup clutch control valve then engages the lockup clutch.

5. Transmission charging pressure tap

The transmission charging pressure relief valve is part of the transmission hydraulic control valve. The relief valve limits the maximum pressure in the transmission charging circuit. Transmission charging pressure can be measured at the tap (5).

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1

3

2

102

1. Transmission clutch pressure taps

Shown is the Individual Clutch Modulation (ICM) transmission hydraulic control valve. Transmission clutch pressures are measured at the pressure taps (1).

• Priority valve pressure increased

The transmission hydraulic control valve contains a priority valve. The priority valve controls the pressure that is directed to the selector pistons in each of the clutch stations. The transmission priority valve pressure has been increased from 1720 kPa (250 psi) to 2585 kPa (375 psi). Increasing the priority valve pressure also increases the charging pressure available to the lockup clutch valve.

2. "D" Station controls dual stage relief valve

The "D" Station (2) is used to control the dual stage relief valve setting for the clutch supply pressure (shown on next slide).

3. Transmission lube relief valve

The transmission lube pressure relief valve (3) limits the maximum pressure in the transmission lube circuit.

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TRANSMISSION ICM HYDRAULIC SYSTEM LOCKUP SOLENOID

UPSHIFT PRESSURE

DOWNSHIFT UPSHIFT SOLENOID SOLENOID

DOWNSHIFT PRESSURE

ROTARY ACTUATOR

A

ON 3

E N1

TO TORQUE CONVERTER RELAY VALVE

NEUTRALIZER VALVE PRIORITY REDUCTION VALVE

PILOT OIL PRESSURE

CHARGING PUMP

TRANSMISSION CHARGING FILTER

LUBE PUMP

B

ROTARY SELECTOR SPOOL

PUMP PRESSURE

F C

SCAVENGE PUMP

OIL COOLER

G D

COOLER BYPASS VALVE

H

LUBE PRESSURE

RELIEF VALVE

TORQUE CONVERTER HOUSING

TRANSMISSION CASE

SELECTOR VALVE GROUP

LOCKUP DUAL STAGE RELIEF VALVE

PRESSURE CONTROL GROUP

LUBRICATION RELIEF VALVE

103 • ICM transmission hydraulic control valve

The transmission control group uses a dual stage relief valve for clutch supply pressure. At high idle in torque converter drive, transmission charging pressure should be 3065 kPa (445 psi) maximum. At low idle in torque converter drive, transmission charging pressure should be 2480 kPa (360 psi) minimum.

• Dual stage relief valve

Shown is a sectional view of the ICM transmission hydraulic control valve group. The rotary selector spool is in a position that engages two clutches. Pump supply oil from the lockup solenoid flows to the selector piston in station "D." Station "D" reduces the pump supply pressure, and the reduced pressure flows to the lower end of the relief valve. Providing oil pressure to the lower end of the relief valve reduces the clutch supply pressure. During torque converter lockup (DIRECT DRIVE), clutch supply pressure is reduced to extend the life of the transmission clutch seals. At high idle in direct drive, clutch supply pressure should be 1620 + 240 - 100 kPa (235 + 35 - 15 psi). The corresponding transmission charge pressure is reduced to 2205 ± 70 kPa (320 ± 10 psi).

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2

1 3

104

1. Transmission lube supply hose

Oil flows from the transmission lube section of the torque converter and transmission pump to the transfer gears through a hose (1). Transmission lube oil flows through the transfer gears and the transmission to cool and lubricate the internal components.

2. Transmission lube oil temperature sensor

The transmission lube oil temperature sensor (2) provides an input signal to the VIMS which informs the operator of the temperature of the transmission lube oil.

3. Transmission lube oil pressure tap

The transmission lube pressure relief valve is in the transmission case near the transmission hydraulic control valve. The relief valve limits the maximum pressure in the transmission lube circuit. Transmission lube oil pressure can be measured at the tap (3). At HIGH IDLE, the transmission lube pressure should be 110 to 207 kPa (16 to 30 psi). At LOW IDLE, the transmission lube pressure should be 5 to 65 kPa (.5 to 10 psi).

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TC LOCKUP VALVE

TORQUE CONVERTER AND TRANSMISSION HYDRAULIC SYSTEM TORQUE CONVERTER/ TRANSMISSION COOLER

TC CHARGING FILTER TRANSMISSION CHARGING FILTER

TC OUTLET RELIEF VALVE

TC/TRANS PUMPS

TC LOCKUP VALVE

TC INLET RELIEF VALVE TC OUTLET SCREEN

RETURN SCREEN

RETURN SCREEN

TRANSMISSION MAGNETIC SCREENS

SUCTION SCREEN

105 • Torque converter/ transmission hydraulic system

Shown is the torque converter and transmission hydraulic system. A four section torque converter and transmission pump is located at the rear of the torque converter. The four sections (from front to rear) are:

• Four section pump: 1. Transmission scavenge 2. Torque converter charging 3. Transmission charging 4. Transmission lube

1. 2. 3. 4.

Transmission scavenge Torque converter charging Transmission charging Transmission lube

The transmission scavenge pump pulls oil through the magnetic screens located at the bottom of the transmission. The scavenged oil from the transmission is transferred into the torque converter housing through the transmission oil return screen. The three rear sections of the torque converter and transmission pump pull oil from the torque converter housing sump. Most of the required oil supply is pulled directly from the torque converter and transmission oil cooler return oil. The remaining required oil supply is drawn through a suction screen located in the bottom of the torque converter housing.

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• Torque converter charging section

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Oil from the torque converter charging section of the torque converter and transmission pump flows through the torque converter charging filter to the inlet relief valve mounted on the torque converter. The inlet relief valve limits the maximum pressure of the supply oil to the torque converter. Torque converter charging oil either drops to the bottom of the housing or flows through the torque converter outlet relief valve. The outlet relief valve limits the pressure inside the torque converter. Most of the oil from the torque converter outlet relief valve flows through the torque converter outlet screen to the torque converter and transmission oil cooler located on the right side of the engine. Oil from the torque converter and transmission oil cooler returns to the torque converter housing.

• Transmission charging section

Oil from the transmission charging section of the torque converter and transmission pump flows through the transmission charging filter. From the filter, transmission charging oil flows in two directions: - Transmission charging oil flows to the torque converter lockup clutch valve located on top of the torque converter. - Transmission charging oil also flows to the transmission control valves located on top of the transmission. Excess transmission charging oil to the transmission control valves either drops to the bottom of the housing to be scavenged or flows back to the torque converter housing. When the torque converter lockup clutch solenoid is energized, pump supply oil flows to the lockup clutch control valve. The lockup clutch control valve then engages the lockup clutch.

• Transmission lube section

Oil flows from the transmission lube section of the torque converter and transmission pump to the transfer gears. Transmission lube oil flows through the transfer gears and the transmission to cool and lubricate the internal components.

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A12 A13 A14 A15 A16

SERVICE/ RETARDER BRAKE

706 - BR

A6

SECONDARY BRAKE

720 - PU

A20

HOIST LEVER

707 - PU

A28

BODY UP

E750 - PU

A27

KEY START SWITCH

307 - OR

B5

ENGINE SPEED

450 - YL

A29

CONVERTER SPEED

452- PU

A30

D996 - PU

B6

D997 - YL

B7

SHIFT LEVER SWITCH

D1

D2

2

12

13

TOS

5

6

7

8

219 - BK

A36

280 - BK

A37

227 - BK

MACHINE ID CODE

TRANSMISSION GEAR SWITCH

726 - BU

725 - GN

724 - YL

723 - OR

A21 A22 A23 A24 A25 A26 721 - BR

A31

G714 - PU

RAISE SOLENOID

A32

G711 - BR

FLOAT SOLENOID

A33

G712- GN

LOWER SOLENOID

B1

306 - GN

STARTER SOLENOID

B2

321- BR

B9 B10

893 - GN 892 - BR

9

BACK-UP ALARM RELAY DATA LINK

A3 A4 A5 703 - BU

4

722 - WH

3

710 - GN

709 - OR

A19

D3

11

A9 A10

A - 37 PIN CONNECTOR B - 10 PIN SURE-SEAL CONNECTOR

217 - BK 218- BK

EPTC II 10

SERVICE "SET" AND "CLEAR" SWITCHES

A17 A18

704 - GY

A11

712 - WH 713 - OR 714 - YL 715 - GN 716 - BU

705 - PK

711 - BR

UP, DOWN, LOCKUP SOLENOIDS

TRANSMISSION

106 Electronically Programmable Transmission Control (EPTC II) • EPTC II shifts the transmission electronically

The purpose of the EPTC II is to determine the desired transmission gear and energize solenoids to shift the transmission up or down as required based on information from both the operator and machine.

• Shifts controlled by electrical signals

The EPTC II receives information from various input components such as the shift lever switch, Transmission Output Speed (TOS) sensor, transmission gear switch and the hoist lever switch. Based on the input information, the EPTC II determines whether the transmission should upshift, downshift, engage the lockup clutch or limit the transmission gear. These actions are accomplished by sending signals to various output components.

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Output components include the upshift, downshift and lockup solenoids, the back-up alarm and others. The EPTC II also provides the service technician with enhanced diagnostic capabilities through the use of onboard memory, which stores possible diagnostic codes for retrieval at the time of service. With the use of a set of service switches, the service technician can access the different modes to gather the stored diagnostic codes or set the adjustable transmission gear limit functions.

• EPTC II connectors and pin numbers

Input and output components on the block diagram are accompanied with a letter and number. The letter A corresponds with the 37 pin connector and the letter B corresponds with the 10 pin Sure-Seal connector that are attached to the transmission control. The numbers next to the letters correspond to the pin numbers in the connector. For example, the shift lever switch is connected to the transmission control through six wires in the 37 pin connector at pin locations 11 through 16.

• Benefits of electronic communication

The Advanced Diesel Engine Management (ADEM II) engine control, the Automatic Retarder Control (ARC), the Vital Information Management System (VIMS) and the EPTC II all communicate with each other through the CAT Data Link. Communication between the electronic controls allows the sensors of each system to be shared. Many additional benefits are provided, such as Controlled Throttle Shifting (CTS). CTS occurs when the EPTC II tells the engine ECM to reduce engine fuel during a shift to lower stress to the power train.

• EPTC II used to control hoist system

The EPTC II is also used to control the hoist system on the 793C. Several changes have been made to the input and output signals through the EPTC II 37 pin CE connector. The changes are: 1. The bed raise switch has been eliminated and an input signal is no longer transmitted through Pin 7. 2. A Pulse Width Modulation (PWM) type position sensor provides the hoist lever input signal to Pin 28. 3. A raise solenoid output signal has been added to Pin 31. The output is a ground signal to a relay which sends +24 Volts to the raise solenoid. 4. A float solenoid output signal has been added to Pin 32. The output is a ground signal to a relay which sends +24 Volts to the float solenoid. 5. A power down solenoid output signal has been added to Pin 33. The output is a ground signal to a relay which sends +24 Volts to the power down solenoid.

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107

• Transmission electronic control

Shown is the Electronic Programmable Transmission Control (EPTC II). The EPTC II is located to the right of the operator’s seat in the center console. The control contains a diagnostic window with 12 Light Emitting Diodes (LED’s) and a three digit numeric display.

• Service switches (arrow)

The service switches (arrow) are used to interrogate the EPTC II for stored diagnostic information, event information and to program the transmission top gear limit functions. The switches are labeled with an "S" for "SET" and a "C" for "CLEAR."

• Diagnostic modes changed with service switches

The DIAGNOSTIC MODE of the Electronic Control is changed by DEPRESSING and HOLDING both service switches (SET and CLEAR). When the desired mode is shown on the display, the switches can be released. By following the instructions in the Service Manual, the serviceman can determine if the transmission electronic control system is operating correctly.

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EPTC II DIAGNOSTIC WINDOW D1

D2

D3

10 11

2

12

13

3

4

5

6

7

8

9

108 • EPTC II diagnostic window:

The onboard diagnostic window houses 12 status LED's along with a three digit numeric display.

- 12 status LED's - Three digit display

The functions of the three digit display and the status LED's are: 1. Three digits (D1, D2, D3) display numbers and letters or indicate circuit conditions. 2. DIAG PRESENT--A RED LED which indicates that the Electronic Control has detected a fault for which a diagnostic code has been stored in memory. The LED is ON if the fault is still present. 3. BODY UP--An AMBER LED which is ON when the body up switch is in use as sensed by a ground from the body up switch.

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4. RETARDER--An AMBER LED which is ON when the service brake or retarder is in use as sensed by a ground from the service/retarder brake pressure switch. 5. BRAKE--An AMBER LED which is ON when the secondary or parking brake is in use as sensed by an open from the secondary/parking brake pressure switch. 6. BODY RAISE--An AMBER LED which is ON when the hoist lever sensor is providing a signal to the electronic control. 7. HOLD--An AMBER LED which is ON when the hold pedal or switch is in use as sensed by a ground from the hold pedal or switch. (Not used on Trucks.) 8. CONT FAILURE--A RED LED which is ON or FLASHING when the electronic control has FAILED and should be replaced. 9. POWER--A GREEN LED which is ON when a nominal 24 Volts is available between pins 1 and 2 of the electronic control 37 pin connector. 10. TOS--An AMBER LED which is ON when the Transmission Output Speed (TOS) sensor is providing a signal to the electronic control. 11. TCO--An AMBER LED which is ON when the Torque Converter Output (TCO) speed sensor is providing a signal to the electronic control. 12. EOS--An AMBER LED which is ON when the Engine Output Speed (EOS) sensor is providing a signal to the electronic control. 13. MODE 1--An AMBER LED which is ON when the electronic control is NOT in Mode 0.

NOTE: The small LED at the bottom right of the three digit display has no diagnostic function. The small LED will always be ON. Service personnel should always view the diagnostic window with the small LED at the bottom right of the three digit display. When the small LED is at the bottom right of the three digit display, service personnel know that the window is being viewed in the correct orientation.

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109

• ECAP and ET service tools

The Electronic Control Analyzer Programmer (ECAP) and the Electronic Technician (ET) Service Tools can be used in place of the EPTC II diagnostic window. The ECAP and ET perform the same functions as the EPTC II diagnostic window and are capable of several additional diagnostic functions that the EPTC II window does not display. Additional diagnostic functions that the service tools can perform are: - Display the EPTC II internal clock hour reading. - Display the hour reading of the first and last occurrence for each logged diagnostic code. - Display the definition for each logged diagnostic code. - Display logged events. - Display the lockup clutch engagement counter. - Display the transmission gear shift counter.

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4

2

3 1

110

Shown is an example of one input component to the EPTC II and three output components from the EPTC II. 1. Transmission gear switch

The transmission gear switch (1) provides input signals to the EPTC II. The transmission gear switch inputs (also referred to as the actual gear inputs) are comprised of six wires. Five of the six wires provide a code to the EPTC II. The code is unique for each position of the transmission gear switch. Each transmission gear switch position will result in two of the five wires sending a ground signal to the EPTC II. The other three wires will remain open (ungrounded). The pair of grounded wires is unique for each gear position. The sixth wire is known as the "Ground Verify" wire, which is normally grounded. The "Ground Verify" wire is used by the EPTC II to verify that the transmission gear switch is connected to the transmission control. The "Ground Verify" wire allows the EPTC II to distinguish between loss of the transmission gear switch signals and a condition in which the transmission gear switch is between gear detent positions. Earlier transmission gear switches use a wiper contact assembly that does not require a power supply to Pin 4 of the switch. Present transmission gear switches are Hall-Effect type switches. A power supply is required to power the switch. A small magnet passes over the Hall cells which then provide a non-contact position switching capability. The Hall-Effect type switches use the same 10-Volt power supply as the transmission output speed sensor.

STMG 682 3/97 2. Upshift solenoid 3. Downshift solenoid

4. Lockup clutch solenoid

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The solenoid outputs provide + Battery voltage to the upshift solenoid (2) or the downshift solenoid (3) based on the input information from the operator and the machine. The solenoids are energized until the transmission actual gear switch signals the EPTC II that a new gear position has been reached. The length of time that the solenoid is energized is usually about 0.1 seconds when a single gear upshift is desired. The lockup solenoid output provides + Battery voltage to the lockup clutch solenoid (4). The lockup solenoid is energized by the EPTC II when in a DIRECT DRIVE gear. In FIRST gear, the solenoid will be energized when the Transmission Output Speed (TOS) reaches a predetermined value. When the machine is in CONVERTER DRIVE, the solenoid is de-energized by the EPTC II.

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STEERING 793C

111 STEERING SYSTEM This section of the presentation explains the operation of the steering system. As on other Caterpillar Off-highway Trucks, the steering system uses hydraulic force to change the direction of the front wheels. The system has no mechanical connection between the steering wheel and the steering cylinders.

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3 5

1

4

2 7

6

112

2. Lower sight gauge

The steering tank is located on the right platform. Two sight gauges are on the side of the tank. When the engine is shut off and the oil is cold, the oil should be visible between the FULL and ADD OIL markings of the upper sight gauge (l). When the engine is running and the accumulators are fully charged, the oil level should not be below the ENGINE RUNNING marking of the lower sight gauge (2). If the ENGINE RUNNING level is not correct, check the nitrogen charge in each accumulator. A low nitrogen charge will allow excess oil to be stored in the accumulators and will reduce the secondary steering capacity.

3. Combination vacuum breaker/ relief valve and pressure release button

A combination vacuum breaker/pressure relief valve is used to limit the tank pressure. Before removing the fill cap, be sure that the engine was shut off with the key start switch and the oil has returned to the tank from the accumulators. Depress the pressure release button (3) on the breather to vent any remaining pressure from the tank.

4. Case drain oil filter

Supply oil for the steering system is provided by a piston-type pump. Case drain oil from the pump returns to the tank through the filter (4). The remaining steering system oil returns to the tank through the main steering filter (5). Both filters are equipped with bypass valves to protect the system if the filters are plugged or during cold oil start-up.

• Steering tank

1. Upper sight gauge

5. Main steering filter

STMG 682 3/97

6. APU supplemental steering connector

7. Steering oil temperature sensor

- 130 -

If the steering pump fails or if the engine cannot be started, the connector (6) is used to attach an Auxiliary Power Unit (APU). The APU will provide supply oil from the steering tank at the connector (6) to charge the steering accumulators. Steering capability is then available to tow the truck. The steering oil temperature sensor (7) provides an input signal to the VIMS which informs the operator of the steering system oil temperature.

INSTRUCTOR NOTE: For more detailed information on servicing the steering accumulators, refer to the Service Manual Module "793C Off-highway Truck Steering System" (Form SENR1452) and the Special Instruction "Repair of 4T8719 Bladder Accumulator Group" (Form SEHS8757). For more information on using the APU, refer to the Special Instructions "Using 1U5000 Auxiliary Power Unit (APU)" (Form SEHS8715) and "Using the 1U5525 Attachment Group" (Form SEHS8880).

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4 3

1 2

113 1. Steering pump

The 793C is equipped with a load sensing, pressure compensated, piston-type pump (1). The steering pump is mounted to the pump drive. The pump drive is located on the inside of the right frame rail near the torque converter.

2. Load sensing controller

The steering pump operates only when the engine is running and provides the necessary flow of oil to the accumulators for steering system operation. The steering pump contains a load sensing controller (2) that works with an accumulator charging valve to monitor and control steering pump output.

• CUT-OUT pressure

The steering pump will produce flow at high pressure until the steering accumulators are charged with oil and the pressure increases to 21400 ± 345 kPa (3100 ± 50 psi) at LOW IDLE. This pressure is referred to as the CUT-OUT pressure. When the CUT-OUT pressure is reached, the accumulator charging valve reduces the load sensing signal pressure to the pump load sensing controller, and the pump will destroke to the LOW PRESSURE STANDBY position. During LOW PRESSURE STANDBY, the pressure should be between 2410 and 3445 kPa (350 and 500 psi).

• LOW PRESSURE STANDBY

• CUT-IN pressure

The pump operates at minimum swashplate angle to supply oil for lubrication, leakage and Hand Metering Unit (HMU) "thermal bleed." Because of the normal leakage in the steering system, the pressure in the accumulators will gradually decrease to 19200 ± 315 kPa (2785 ± 45 psi). This pressure is referred to as the CUT-IN pressure.

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When the pressure in the accumulators decreases to the CUT-IN pressure, the accumulator charging valve blocks the load sensing signal line to the load sensing controller from returning to the tank, and the pump will upstroke to maximum displacement (full flow). 3. LOW PRESSURE STANDBY pressure tap

A pressure tap (3) is located on the pump pressure switch manifold. If steering pump pressure is measured at this tap during LOW PRESSURE STANDBY, a gauge acceptable for testing maximum steering system pressure must be used to avoid damaging the gauge when the steering pump upstrokes to provide maximum oil flow.

4. Low steering pressure switch

Two pressure switches monitor the condition of the steering system on the 793C. One switch (4) monitors the output of the steering pump. The purpose of this switch is to monitor pump supply pressure during LOW PRESSURE STANDBY. The VIMS refers to this switch as the "low steering pressure" switch.

4. High steering pressure switch

The other steering pressure switch is mounted on the solenoid and relief valve manifold, which is located on the front frame rail below the engine. This switch monitors the steering system accumulator pressure. The VIMS refers to this switch as the "high steering pressure" switch.

• Steering pressure warnings only above 8 km/h (5 mph)

Both steering pressure switches provide input signals to the VIMS which informs the operator of the condition of the steering system. A steering system warning is only displayed if the ground speed is above 8 km/h (5 mph).

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1

3

4

2 5

6

114

1. Check valve 2. Solenoid and relief valve manifold 3. Accumulator charging valve 4. Steering directional valve 5. Steering system pressure tap 6. Steering system S•O•S tap

Steering pump supply oil flows through a check valve (1) to the solenoid and relief valve manifold (2). The solenoid and relief valve manifold connects the steering pump to the accumulator charging valve (3), the accumulators and the steering directional valve (4). The solenoid and relief valve manifold also provides a path to drain for the steering oil. When checking the steering system CUT-OUT and CUT-IN pressures, a gauge can be connected at the pressure tap (5). Steering system oil samples can be taken at the steering system Scheduled Oil Sampling (S•O•S) tap (6).

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2

1

3

115

1. Accumulator charging valve 2. CUT-OUT pressure valve 3. CUT-IN pressure valve

Shown is a closer view of the accumulator charging valve (1). Steering system CUT-OUT pressure is adjusted at the upper valve (2). Steering system CUT-IN pressure is adjusted at the lower valve (3). Steering pump supply pressure increases until the accumulator pressure acting on the accumulator charging valve shifts the cut-out and cut-in pressure valves. Together, the cut-out and cut-in pressure valves reduce the Load Sensing (LS) signal pressure (feedback pressure) to slightly above tank pressure. The pump is destroked to LOW PRESSURE STANDBY (CUT-OUT). When the pressure in the accumulators decreases, the cut-in and cut-out pressure valves shift again and block the load sensing signal pressure from the tank. The pump load sensing signal pressure becomes equal to pump pressure, and the steering pump returns to the FULL FLOW position (CUT-IN).

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STEERING PUMP DURING CHARGING (CUT-IN) CUT-OUT VALVE

FROM ACCUMULATORS

CUT-IN VALVE ACCUMULATOR CHARGING VALVE

TO ACCUMULATORS PUMP OUTPUT

HIGH PRESSURE CUTOFF VALVE ACTUATOR PISTON LOAD SENSING PRESSURE

FLOW COMPENSATOR LOAD SENSING CONTROLLER SWASHPLATE PISTON

116 • Steering pump operation • Actuator piston drained during maximum flow

After the engine is started, pressure increases in the steering accumulators. The pump load sensing controller is spring biased to vent the actuator piston pressure to drain. Venting pressure from the load sensing controller and the actuator piston positions the spring biased swashplate to maximum displacement (full flow). As pressure increases in the accumulators, pump supply pressure is sensed in the accumulator charging valve and on both ends of the flow compensator. When pressure is present on both ends of the flow compensator, the swashplate is kept at maximum angle by the force of the spring in the pump housing and pump discharge pressure on the swashplate piston. The pistons travel in and out of the barrel and maximum flow is provided through the outlet port. Since the pump is driven by the engine, engine rpm also affects pump output. NOTE: Because the signal lines are sensing pump supply pressure and not a "load" pressure, the steering system does not operate the same as other load sensing systems with a margin pressure.

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STEERING PUMP LOW PRESSURE STANDBY (CUT-OUT) CUT-OUT VALVE

FROM ACCUMULATORS

CUT-IN VALVE ACCUMULATOR CHARGING VALVE

TO ACCUMULATORS PUMP OUTPUT

HIGH PRESSURE CUTOFF VALVE

ACTUATOR PISTON

LOAD SENSING PRESSURE

FLOW COMPENSATOR LOAD SENSING CONTROLLER SWASHPLATE PISTON

117 • Accumulator charging valve shifts • Signal pressure decreases

• Pump at LOW PRESSURE STANDBY

Pump supply pressure will increase until the accumulator pressure acting on the accumulator charging valve shifts the cut-out and cut-in valves, and the load sensing signal pressure is reduced to slightly above tank pressure. The cut-out and cut-in valves shift when the pump outlet pressure is approximately 21400 ± 345 kPa (3100 ± 50 psi) at LOW IDLE. Pump oil (at LOW PRESSURE STANDBY) flows past the lower end of the displaced flow compensator spool to the actuator piston. The actuator piston has a larger surface area than the swashplate piston. The oil pressure at the actuator piston overcomes the spring force of the swashplate piston and moves the swashplate to destroke the pump. The pump is then at LOW PRESSURE STANDBY (cut-out). Pump output pressure is equal to the setting of the flow compensator. The LOW PRESSURE STANDBY setting is between 2410 and 3445 kPa (350 and 500 psi).

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In the NEUTRAL or NO STEER position, demand for oil from the accumulators is low. The pump operates at minimum swashplate angle to supply oil for lubrication, leakage and HMU "thermal bleed." Because of the normal leakage in the steering system, the pressure in the accumulators will gradually decrease to 19200 ± 315 kPa (2785 ± 45 psi). • Accumulator pressure decreases • Cut-in and cut-out valves shift • Pump returns to full flow

• Cycle time between CUT-OUT and CUT-IN: - With thermal bleed orifice, 30 seconds or more - Without thermal bleed orifice, between 6 and 7 minutes

When the pressure in the accumulators decreases to 19200 ± 315 kPa (2785 ± 45 psi), the accumulator charging valve cut-in and cut-out valves shift and block the load sensing signal line pressure from the tank. Pump oil pressurizes the load sensing signal line. The load sensing signal shifts the flow compensator spool and drains the actuator piston. Draining the actuator piston positions the spring biased swashplate to maximum displacement and full flow (CUT-IN). At LOW lDLE in the NEUTRAL or NO STEER position, the pump will cycle between the cut-out and cut-in conditions in intervals of 30 seconds or more. Connecting a pressure gauge to the pressure tap below the steering directional valve will indicate these steering system pressures. If the pump pressure cycles in less than 30 seconds, leakage exists in the system and must be corrected. Typical sources of leakage can be the accumulator bleed down solenoid or the back-up relief valve located on the solenoid and relief valve manifold. If a machine has an HMU with the thermal bleed orifice removed, the cycle time between cut-out and cut-in will be between 6 and 7 minutes. If the accumulator charging pressure cannot be adjusted within specifications, an adjustment of the high pressure cutoff valve is required. The high pressure cutoff valve is part of the load sensing controller mounted on the steering pump. The high pressure cutoff setting is 23100 ± 345 kPa (3350 ± 50 psi) at HIGH IDLE. The high pressure cutoff setting must be a minimum of 350 kPa (50 psi) higher than the accumulator charging (cut-out) valve setting at HIGH IDLE.

• High pressure cutoff valve adjustment

To adjust the high pressure cutoff valve on the load sensing controller, turn the cut-out valve adjustment screw completely in and count the number of turns so it can be returned to its original position later. With the engine at HIGH IDLE, adjust the high pressure cutoff valve to 23100 ± 345 kPa (3350 ± 50 psi). Return the cut-out valve adjustment screw to its original position and re-test the cut-out and cut-in valve pressures. NOTE: When testing or adjusting any steering system pressure settings, always allow the accumulator charge cycle to occur at least ten times before measuring the pressure. Failure to allow the charging cycle to occur ten times will result in inaccurate readings.

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ACCUMULATOR CHARGE VALVE DURING CHARGING (CUT-IN) FROM PUMP

TO PUMP CONTROL SIGNAL PORT

TO TANK FEEDBACK ORIFICE

CUT-OUT VALVE

FROM ACCUMULATOR

CUT-IN VALVE

118 • Accumulator charging valve

Shown is a sectional view of the accumulator charging valve during CHARGING (CUT-IN). During CHARGING, the cut-out spool is held to the right by the spring. The cut-out spool blocks the pump and load sensing signal passages from the feedback orifice. Signal pressure is equal to pump pressure and the high signal pressure causes the pump to upstroke to maximum displacement (full flow). As accumulator pressure increases, the cut-out spool will move to the left against the spring force. When accumulator pressure reaches the cut-out setting, the cut-out spool will open the pump and load sensing signal passages to the feedback orifice. The feedback orifice reduces the load sensing signal pressure to slightly more than tank pressure.

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ACCUMULATOR CHARGE VALVE LOW PRESSURE STANDBY (CUT-OUT) FROM PUMP TO TANK

TO PUMP CONTROL SIGNAL PORT FEEDBACK ORIFICE

CUT-OUT VALVE

FROM ACCUMULATOR

CUT-IN VALVE

119 • Accumulator charging valve

Shown is a sectional view of the accumulator charging valve in the LOW PRESSURE STANDBY (CUT-OUT) position. In the CUT-OUT position, accumulator pressure has increased to the cutout setting and both the cut-in and cut-out stems are fully shifted against the springs. The pump and load sensing signal passages are open to the feedback orifice. The feedback orifice reduces the signal pressure to slightly more than tank pressure. The feedback orifice is only required to initiate and maintain CUT-OUT. As the accumulator pressure decreases, the feedback pressure holds the cut-out spool to the left until the cut-in valve opens and vents the feedback pressure to the tank. The feedback pressure during CUT-OUT assists shifting against the spring. At the beginning of CUT-IN, the feedback pressure assists the spring force.

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ACCUMULATOR CHARGE VALVE BEGINNING STAGE OF CUT-IN TO PUMP CONTROL SIGNAL PORT

FROM PUMP TO TANK

FEEDBACK ORIFICE

CUT-OUT VALVE

FROM ACCUMULATOR

CUT-IN VALVE

120 • Accumulator charging valve

Shown is a sectional view of the accumulator charging valve in the beginning stage of CUT-IN. When accumulator pressure decreases to the cut-in pressure, the cut-in spool will move to the right and allow feedback pressure into the cut-in valve and cut-out valve spring chambers. The feedback pressure assists the cut-out and cut-in valve springs with shifting the cut-out and cut-in spools to the right. The cut-in spool continues to move to the right and blocks the center passage to the cut-out spool. When the center passage to the cut-out spool is blocked, signal pressure becomes equal to pump pressure. CUT-IN will occur when the cut-out spool shifts to a position in which the pump load sensing signal is no longer vented to feedback pressure. Signal pressure becomes equal to pump pressure, the pump upstrokes and the charging cycle begins.

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2 1

3

6 4

1 5

121

1. Check valve

Steering pump supply oil flows through a check valve (1) to the solenoid and relief valve manifold. The solenoid and relief valve manifold connects the steering pump to the accumulator charging valve, the accumulators and the steering directional valve. The solenoid and relief valve manifold also provides a path to drain for the steering oil.

2. Steering accumulator pressure switch

A steering accumulator pressure switch (2), an accumulator bleed down solenoid (3), a back-up relief valve (4), a steering system Scheduled Oil Sampling (S•O•S) tap (5) and a supplemental steering connector (6) are located on the solenoid and relief valve manifold.

3. Accumulator bleed down solenoid 4. Back-up relief valve 5. Steering system S•O•S tap

The check valve (1) prevents accumulator oil from flowing back to the steering pump when the pump destrokes to LOW PRESSURE STANDBY.

6. Supplemental steering connector

The steering accumulator pressure switch (2) monitors the steering accumulator pressure. The VIMS refers to this switch as the "High Steering Pressure" switch.

• Steering pressure warnings only above 8 km/h (5 mph)

The steering accumulator pressure switch provides an input signal to the VIMS which informs the operator of the steering system condition. A steering system warning is displayed only if the ground speed is above 8 km/h (5 mph).

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The accumulator bleed down solenoid (3) is used to drain pressure oil from the accumulators when the truck is not in operation. The back-up relief valve (4) is used to drain pressure oil if the steering pump high pressure cutoff valve does not open. Steering system oil samples can be taken at the steering system Scheduled Oil Sampling (S•O•S) tap (5) To operate the steering circuit on a disabled truck, an Auxiliary Power Unit (APU) connects to the supplemental steering connector (6) on the solenoid and relief valve manifold and to a suction port on the hydraulic tank (see Slide No. 112). The APU will provide supply oil to charge the accumulators. Steering capability is then available to tow the truck.

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SOLENOID AND RELIEF VALVE MANIFOLD SUPPLY FROM PUMP AND ACCUMULATORS

TO TANK

BLEED DOWN SOLENOID BACK-UP RELIEF VALVE

122 • Solenoid and relief valve manifold

Shown is a sectional view of the solenoid and relief valve manifold. The accumulator bleed down solenoid is activated by the bleed down solenoid shutdown control when the key start switch is moved to the OFF position. The bleed down solenoid shutdown control holds the solenoid open for 70 seconds.

• Bleed down solenoid drains accumulators

Pressure oil from the accumulators is sensed by the bleed down solenoid. When the solenoid is energized, the plunger moves and connects the pressure oil to the drain passage. Pressure oil flows through an orifice, past the plunger, to the tank. The orifice limits the return oil flow from the accumulators to a rate which is LOWER than the flow limit (restriction) of the steering oil filter in the hydraulic tank. When the solenoid is de-energized, spring force moves the plunger and pressure oil cannot go to drain.

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• Back-up relief valve protects system if pump does not destroke

The back-up relief valve protects the steering system if the steering pump malfunctions (fails to destroke). Pressure oil from the steering pump works against the end of the back-up relief valve and the spring. The relief valve unseats (opens) if oil pressure reaches approximately 26000 ± 400 kPa (3775 ± 60 psi) at a flow of 8 ± 2 L/min. (2 ± .5 gpm). Oil then flows past the relief valve and drains to the tank.

• Adjust back-up relief valve on test bench only

The back-up relief valve must only be adjusted on a test bench. The pressure setting of the back-up relief valve can be changed by adjusting the spring force that keeps the relief valve seated (closed). To change the relief valve setting, remove the protective cap and turn the adjustment screw clockwise to increase or counterclockwise to decrease the pressure setting. One revolution of the setscrew will change the pressure setting 3800 kPa (550 psi).

• Functional test of back-up relief valve (on machine)

A functional test of the back-up relief valve can be performed on the machine by installing a manual hydraulic pump at the location of the Auxiliary Power Unit (APU) connector and installing blocker plates to prevent oil from flowing to the accumulators. See the service manual for more detailed information.

NOTE: Using the functional test procedure to adjust the back-up relief valve will provide only an approximate setting. Accurate setting of the back-up relief valve can only be performed on a hydraulic test bench.

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1

2

123

1. Steering directional valve

The steering directional valve (1) is pilot operated from the HMU in the operator’s station. Five pilot lines connect these two components. The pilot lines send pilot oil from the HMU to shift the spools in the steering directional valve. The spools control the amount and direction of pressure oil sent to the steering cylinders. Four pilot lines are used for pump supply, tank return, left turn and right turn. The fifth pilot line is for the load sensing signal.

2. Steering system pressure tap

When checking the steering system cut-out and cut-in pressures, a gauge can be connected at the pressure tap (2).

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STEERING DIRECTIONAL VALVE NO TURN LEFT TURN CYLINDER

RELIEF/MAKEUP VALVE

TO TANK

RIGHT TURN CYLINDER

BACK PRESSURE VALVE RELIEF/MAKEUP VALVE

RIGHT TURN PILOT OIL

LEFT TURN PILOT OIL

COMBINER/CHECK SPOOL AMPLIFIER SPOOL

PRIORITY SPOOL LOAD SENSING PORT FROM ACCUMULATOR

HAND METERING UNIT SUPPLY AND THERMAL BLEED

124 • Steering directional valve components: - Priority spool - Amplifier spool with combiner/check spool - Directional spool - Relief/makeup valves - Back pressure valve

Shown is a sectional view of the steering directional valve. The main components of the steering directional valve are: the priority spool, the amplifier spool with internal combiner/check spool, the directional spool, the relief/makeup valves and the back pressure valve. Pressure oil from the accumulators flows past the spring biased priority spool and is blocked by the amplifier spool. The same pressure oil flows through an orifice to the right end of the priority spool. The orifice stabilizes the flow to the priority spool and must be present to open and close the priority spool as the flow demand changes. The same pressure oil flows to the HMU. After all the passages fill with pressure oil, the priority spool shifts to the left, but remains partially open. In this position, the priority spool allows a small amount of oil flow (thermal bleed) to the HMU and decreases the pressure to the HMU supply port. The lower pressure prevents the HMU from sticking.

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With the truck in the NEUTRAL or NO TURN position, all four working ports (supply, tank, right turn and left turn) are vented to the tank through the HMU. The directional spool is held in the center position by the centering springs.

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STEERING DIRECTIONAL VALVE RIGHT TURN LEFT TURN CYLINDER

TO TANK

RIGHT TURN CYLINDER

BACK PRESSURE VALVE

RELIEF/MAKEUP VALVE RELIEF/MAKEUP VALVE

RIGHT TURN PILOT OIL

LEFT TURN PILOT OIL

COMBINER/CHECK SPOOL

AMPLIFIER SPOOL

PRIORITY SPOOL LOAD SENSING PORT FROM ACCUMULATOR

HAND METERING UNIT SUPPLY AND THERMAL BLEED

125 • Steering directional valve during a RIGHT TURN

• Load sensing pilot pressure moves priority spool

• Pilot oil moves directional spool

When the steering wheel is turned to the RIGHT, the "thermal bleed" and venting of the four work ports to the tank is stopped. The increased supply pressure flows to the HMU and the load sensing pilot line. The load sensing pilot line directs cylinder pressure to the priority spool in the directional valve. Cylinder pressure is present in the HMU because pilot oil combines with accumulator oil in the combiner/check valve spool in the directional valve. The increased pressure in the load sensing line causes the priority spool to move to the right and allows more oil to flow to the HMU through the supply line. The load sensing pump supply pressure varies with the steering load. The priority spool moves proportionally, allowing sufficient oil flow to meet the steering requirements. Pilot oil flows through a stabilizing orifice to the right turn pilot port of the directional valve and moves the directional spool. Movement of the directional spool allows pilot oil to flow to the amplifier and combiner/check spools.

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• Pilot oil moves amplifier spool

- 149 -

The pilot oil divides at the amplifier spool. Pilot oil flows through a narrow groove around the combiner/check spool. The pilot oil is momentarily blocked until the amplifier spool moves far enough to the right to allow partial oil flow through one of eight orifices. Pilot oil also flows through a connecting pin hole and a stabilizing orifice to the left end of the amplifier spool and causes the amplifier spool to move to the right. Accumulator oil at the spring end (right end) of the amplifier spool flows through a mid-connecting pin to the left end of the amplifier spool and also causes the amplifier spool to move to the right.

• Pilot and accumulator oil combine in combiner/check spool

When the amplifier spool moves to the right, accumulator oil flows to the inner chamber, forcing the combiner/check spool to the left. Accumulator oil then flows through seven of the eight orifices. Pilot and accumulator oil combine. Oil flows across the directional spool (which has already shifted) for a RIGHT TURN.

• Turning steering wheel faster provides more flow to cylinders

The faster the steering wheel is turned, the farther the directional spool and the amplifier spool are shifted. A higher flow rate is available, which causes the truck to turn faster. The ratio of pilot and pump supply oil that combine is always the same because one orifice is dedicated to pilot flow and seven orifices are dedicated to accumulator supply flow. Return oil from the cylinders flows across the directional spool, around the relief/makeup valve, forces the back pressure valve open and returns to the tank.

• Pressure spike moves combiner/check spool and blocks flow to HMU

During a turn, if a front wheel strikes a large obstruction that cannot move, oil pressure in that steering cylinder and oil line increases. Oil flow to the cylinder is reversed. This pressure spike is felt in the amplifier spool. The combiner/check spool moves to the right and blocks the seven pump supply oil orifices to the steering cylinders. The amplifier spool moves to the left and blocks the pilot oil orifice. Pilot oil flow to the steering cylinders stops. The pressure spike is not felt at the HMU. If the pressure spike is large enough, the relief/makeup valve drains the pressure oil to the tank as previously described.

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126

• HMU (arrow)

The Hand Metering Unit (HMU) (arrow) is located at the base of the steering column behind a cover at the front of the cab. The HMU is connected to the steering wheel and controlled by the operator.

• Meters oil to directional valve

The HMU meters the amount of oil sent to the steering directional valve by the speed at which the steering wheel is turned. The faster the HMU is turned, the higher the flow sent to the steering cylinders, and the faster the wheels will change direction.

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HAND METERING UNIT NEUTRAL POSITION

T

L

R

P STATOR

METERING SECTION

CONTROL SECTION CENTERING SPRINGS

ROTOR SPOOL

PIN

DRIVE

SLEEVE

THERMAL BLEED PASSAGES

127 • HMU in NEUTRAL

Shown is a sectional view of the HMU in the NEUTRAL (NO TURN) position. The metering section is a small hydraulic pump which produces a specific (metered) amount of oil flow. This metered oil is then directed by the control section to the left or right turn port. As the steering wheel is turned faster, the flow of oil increases. More oil is sent to the steering cylinders, which allows the cylinders to move faster. When the steering wheel is in the NEUTRAL position (steering wheel stationary), the holes in the sleeve and the passages in the spool are not aligned. However, a small amount of pump oil from the inlet is allowed to flow through the center of the HMU. This small amount of oil flow (thermal bleed) keeps the HMU full and ready for a quick response to steering demands. The thermal bleed oil also helps keep the HMU warm during cold weather operation.

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When the steering wheel is turned, the spool, pin and drive start to turn. The sleeve does not turn at the same time because the diameter of the holes for the pin in the sleeve is slightly larger than the diameter of the pin. The slight delay in sleeve movement allows the spool to turn far enough inside the sleeve to align the holes in the sleeve with the grooves in the spool. The oil path for thermal bleed is then blocked by the rotation of the spool and the sleeve.

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HAND METERING UNIT RIGHT TURN

T

L

R

P STATOR

METERING SECTION

CONTROL SECTION CENTERING SPRINGS

ROTOR SPOOL

PIN

DRIVE

SLEEVE

128 • HMU during RIGHT TURN

When the steering wheel is turned to the RIGHT and the holes in the sleeve are aligned with the grooves in the spool, pump oil (P) at the inlet flows through the holes in the sleeve and the grooves in the spool. The oil in the grooves goes through other holes in the sleeve and into the lower passage. Oil flows through the lower passage to the metering section and is then directed into a space between the stator and the rotor. The rotor is splined to the drive. As the drive turns, the rotor turns and directs oil through the upper passage. The metered oil flows through the holes in the sleeve, the grooves in the spool and out of the sleeve through the right turn port (R). Metered oil from the port goes to the steering directional valve. Return oil from the steering cylinders flows through the tank port (T) in the HMU to the steering tank.

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When the steering wheel rotation is stopped, the spool, pin, drive and rotor stop turning. The centering springs that were compressed when the spool was moving now bring the spool and sleeve back to a NEUTRAL position. The holes in the sleeve no longer align with the grooves in the spool. Oil flow from the pump stops. Pilot oil to the steering directional valve stops, causing the wheels to remain stationary.

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129

• Steering accumulators (arrow)

Two steering accumulators (arrow) provide the supply oil during normal operation and temporary secondary steering if a loss of pump oil flow occurs. Inside the accumulators is a rubber bladder that is charged with nitrogen. The nitrogen charge provides energy for normal steering and secondary steering capability if steering pump flow stops. To check the secondary steering system, the engine must be shut off with the manual shutdown switch while leaving the key start switch in the ON position. When the manual shutdown switch is used, the bleed down solenoid is not energized and the accumulators do not bleed down. The truck can then be steered with the engine stopped. INSTRUCTOR NOTE: More detailed information on servicing the steering accumulators is in the Special Instruction "Repair of 4T8719 Bladder Accumulator Group" (Form SEHS8757). WARNING High pressure oil remains in the accumulators if the manual shutdown switch is used. To release the oil pressure in the accumulators, turn the key start switch to the OFF position and turn the steering wheel left and right until the oil is drained from the accumulators (steering wheel can no longer be turned).

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130

• Shutdown control (arrow)

Shown is the shutdown control (arrow) for the steering accumulator bleed down solenoid. The control is located in the cab below the center console. The steering accumulator bleed down solenoid is activated by the control when the key start switch is moved to the OFF position. The bleed down solenoid shutdown control holds the solenoid open for 70 seconds.

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HOIST SYSTEM 793C

131 HOIST SYSTEM • Hoist system controlled by EPTC II

The hoist system on the 793C Off-highway Truck is electronically controlled by the Electronic Programmable Transmission Control (EPTC II). The hoist control system operates similarly to the previous trucks. The four operating positions are: RAISE, HOLD, FLOAT and LOWER.

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132

• Hoist lever (arrow)

The operator controls the hoist lever (arrow). The four positions of the hoist lever are RAISE, HOLD, FLOAT and LOWER.

• Hoist lever normally in FLOAT position

The truck should normally be operated with the hoist lever in the FLOAT position. Operating with the hoist lever in the FLOAT position allows the hoist valve to provide some downward hydraulic pressure on the hoist cylinders and prevents an empty body from bouncing on rough haul roads.

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133

• Hoist control position sensor (arrow) • Sensor energizes three solenoids on hoist valve

• Sensor performs three functions: - Raises and lowers body - Neutralizes transmission in REVERSE - Starts cycle for TPMS

The hoist lever controls a Pulse Width Modulated (PWM) position sensor. The PWM sensor sends duty cycle input signals to the EPTC II. Depending on the position of the sensor and the corresponding duty cycle, one or two relays located behind the cab are energized. The relays then send +24 Volts to one or two of the three solenoids located on the hoist valve. The hoist valve is mounted on the frame near the right hoist cylinder. The hoist lever sensor also replaces the body raise switch (transmission neutralizer switch) that was located behind the operator’s seat. The hoist lever sensor performs three functions: - Raises and lowers the body. - Neutralizes the transmission in REVERSE. - Starts a cycle for the Truck Production Management System (TPMS). HOIST LEVER POSITION RAISE HOLD FLOAT LOWER

DUTY CYCLE RANGE 15% TO 29% 33% TO 51% 55% TO 70% 76% TO 90%

INSTRUCTOR NOTE: To see the hoist system input and output connections to the EPTC II, refer to Slide No. 106.

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134

• Hoist and brake oil hydraulic tank • Oil level sight gauges (arrows)

• Lower sight gauge used for filling tank with hoist cylinders RAISED

Shown is the hoist and brake oil hydraulic tank and the oil level sight gauges (arrows). The oil level is normally checked with the upper sight gauge. The oil level should first be checked with cold oil and the engine stopped. The level should again be checked with warm oil and the engine running. The lower sight gauge is used when filling the hydraulic tank with the hoist cylinders in the RAISED position. When the hoist cylinders are lowered, the hydraulic oil level will increase. After the hoist cylinders are lowered, check the hydraulic tank oil level with the upper sight gauge as stated above.

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2

1

135

• Rear of hoist and brake oil tank: 1. Suction screens 2. Rear brake oil cooler relief valve location

Shown is the rear of the hoist and brake oil hydraulic tank. The hoist system pumps pull oil from the hydraulic tank through the suction screens (1) located in the rear of the tank. Two rear brake oil cooler relief valves are located in the hydraulic tank at the left center connection (2). The setting of the oil cooler relief valves is 790 kPa (115 psi).

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1

2

136

1. Two section hoist pump

The hoist system oil is supplied by a two section pump (1) located at the top rear of the pump drive. Oil flows from the hoist pump to the hoist valve through two screens located above the hoist valve.

• Relief pressures different for RAISE and LOWER

The hoist system relief pressures are different in the RAISE and LOWER positions. The hoist system relief pressure during RAISE is 20370 + 700 - 0 kPa (2955 + 100 - 0 psi). The hoist system relief pressure during LOWER is 3450 + 350 - 0 kPa (500 + 50 - 0 psi).

2. Hoist system pressure taps

The hoist system pressure can be measured at the two pressure taps (2).

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1 2

3

5

4

137

2. Hoist screen bypass switches

Oil flows from the hoist pump through the hoist screens (1) to the hoist control valve. Two hoist screen bypass switches (2) provide input signals to the VIMS which informs the operator if the hoist screens are restricted.

3. RAISE position solenoid valve

The hoist valve uses parking brake release pressure as the pilot oil to shift the directional spool inside the hoist valve. The parking brake release oil pressure is 4700 ± 200 kPa (680 ± 30 psi). Three solenoid valves are used to direct the pilot oil to the ends of the directional spool. The solenoid valve (3) is energized by the hoist lever sensor in the cab when the sensor is in the RAISE position.

1. Hoist screens

4. Counterbalance valve

A counterbalance valve (4) is mounted on the left side of the hoist valve. The counterbalance valve prevents cavitation of the cylinders when the body raises faster than the pumps can supply oil to the cylinders (caused by a sudden shift of the load).

5. Hose to front brake oil cooler filters

When the hoist valve is in the HOLD or FLOAT position, all the hoist pump oil flows through the large hose (5) to the front brake oil cooler filters located outside the left frame. Excess oil from the parking brake release valve joins the hoist pump oil at the fitting connected to the large hose (5).

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2 3

4 1

5

138

1. Front brake oil cooler relief valve plug

An oil cooler relief valve is located in the hoist valve behind the large plug (1). The relief valve limits the front brake oil cooling pressure when the hoist valve is in the HOLD or FLOAT position. The setting of the oil cooler relief valve is 790 kPa (115 psi).

2. Pilot oil supply tubes

The hoist valve uses parking brake release pressure as the pilot oil to shift the directional spool inside the hoist valve. The parking brake release oil is supplied to the solenoid valves through the small tubes (2). Three solenoid valves are used to direct the pilot oil to the ends of the directional spool. The solenoid valves (3) on the front of the hoist control valve are energized by the hoist lever sensor in the cab when the sensor is in the LOWER or FLOAT position. No solenoids are energized when the hoist lever sensor is in the HOLD position.

3. LOWER and FLOAT solenoid valves

4. Hoist cylinder RAISE port

Supply oil flows to the raise port of the hoist cylinders from the upper right port (4) when the hoist lever sensor is in the RAISE position.

5. Hoist cylinder LOWER and FLOAT port

Supply oil flows to the lower port of the hoist cylinders from the lower left port (5) when the hoist lever sensor is in the LOWER or FLOAT position.

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PARKING BRAKE RELEASE PRESSURE RAISE SOLENOID

793C HOIST CONTROL VALVE FRONT BRAKE OIL COOLER RELIEF VALVE

HOLD TO TANK

TO HOIST CYLINDER HEAD END

LOAD CHECK VALVE

TO HOIST CYLINDER ROD END LOW PRESSURE RELIEF VALVE

COUNTERBALANCE VALVE

HIGH PRESSURE RELIEF VALVE DUAL STAGE RELIEF VALVE SIGNAL STEM

ROD END VENT SLOT TO FRONT BRAKE OIL COOLERS PUMP SUPPLY PORT LOWER SOLENOID

PARKING BRAKE RELEASE PRESSURE FLOAT SOLENOID

139 • Hoist valve in HOLD

Shown is a sectional view of the hoist valve in the HOLD position. The pilot oil at both ends of the directional spool is vented to the tank. The spool is held in the centered position by two centering springs. Passages in the directional spool vent the dual stage relief valve signal stem to the tank. All the hoist pump oil flows through the front brake oil filters to the front brake oil cooler. The position of the directional spool blocks the oil in the head end of the hoist cylinders. Oil in the rod end of the hoist cylinders is connected to the front brake cooling oil by a small vent slot cut in the directional spool. A gauge connected to the hoist system pressure taps while the hoist valve is in the HOLD position would show the restriction pressure of the front brake oil cooling circuit. The maximum pressure in the circuit should correspond to the setting of the front brake oil cooler relief valve. The setting of the oil cooler relief valve is 790 kPa (115 psi).

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PARKING BRAKE RELEASE PRESSURE RAISE SOLENOID

ON

793C HOIST CONTROL VALVE FRONT BRAKE OIL COOLER RELIEF VALVE

RAISE TO TANK

TO HOIST CYLINDER HEAD END

LOAD CHECK VALVE

FROM HOIST CYLINDER ROD END LOW PRESSURE RELIEF VALVE

COUNTERBALANCE VALVE

HIGH PRESSURE RELIEF VALVE DUAL STAGE RELIEF VALVE SIGNAL STEM

ROD END VENT SLOT TO FRONT BRAKE OIL COOLERS PUMP SUPPLY PORT LOWER SOLENOID

PARKING BRAKE RELEASE PRESSURE FLOAT SOLENOID

140 • Hoist valve in RAISE

Shown is a sectional view of the hoist valve in the RAISE position. The LOWER and FLOAT solenoids are de-energized and pilot oil is vented to the tank. The RAISE solenoid is energized and directs pilot oil pressure to the upper end of the directional spool. Pump oil flows past the directional spool to the head end of the hoist cylinders. When the directional spool is initially shifted, the two load check valves (one shown) remain closed until the pump supply pressure is higher than the pressure in the hoist cylinders. The load check valves prevent the body from dropping before the RAISE pressure increases. The directional spool also sends hoist cylinder raise pressure to the dual stage relief valve signal stem and the counterbalance valve. The dual stage relief valve signal stem moves down and blocks the supply pressure from opening the low pressure relief valve. The counterbalance valve is held open by the hoist cylinder raise pressure. Oil flowing from the rod end of the hoist cylinders flows freely to the front brake oil cooler.

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• High pressure relief setting checked during RAISE at HIGH IDLE

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If the pressure in the head end of the hoist cylinders exceeds 20370 + 700 - 0 kPa (2955 + 100 - 0 psi), the high pressure relief valve will open. When the high pressure relief valve opens, the dump spool moves to the left and pump oil flows to the front brake oil cooler. The high pressure hoist relief valve setting is checked at the two pressure taps located on the hoist pump. Check the relief pressures with the hoist lever in the RAISE position and the engine at HIGH IDLE.

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HOIST COUNTERBALANCE VALVE

HEAD END SIGNAL PRESSURE

TO FRONT BRAKE OIL COOLER

FROM HOIST CYLINDER ROD END

FROM PUMP

TO HOIST CYLINDER ROD END

RAISE POSITION

LOWER AND FLOAT POSITIONS

141 • Counterbalance valve

During RAISE, the counterbalance valve prevents the dump body from running ahead of the hoist pumps if the load shifts rapidly to the rear and attempts to pull the hoist cylinders. Signal pressure from the head end of the hoist cylinders holds the counterbalance valve open. Oil from the rod end of the hoist cylinders flows unrestricted through the counterbalance valve to the front brake oil cooler. If the head end pressure decreases below 6900 ± 690 kPa (1000 ± 100 psi), the counterbalance valve moves down and restricts the flow of oil from the rod end of the cylinders to the front brake oil cooler. During LOWER and FLOAT, the counterbalance valve allows unrestricted flow from the pump to the rod end of the hoist cylinders.

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PARKING BRAKE RELEASE PRESSURE RAISE SOLENOID

793C HOIST CONTROL VALVE

FRONT BRAKE OIL COOLER RELIEF VALVE

LOWER (POWER DOWN) TO TANK

FROM HOIST CYLINDER HEAD END

LOAD CHECK VALVE

TO HOIST CYLINDER ROD END LOW PRESSURE RELIEF VALVE

COUNTERBALANCE VALVE

HIGH PRESSURE RELIEF VALVE DUAL STAGE RELIEF VALVE SIGNAL STEM

ROD END VENT SLOT TO FRONT BRAKE OIL COOLERS PUMP SUPPLY PORT LOWER SOLENOID

ON

PARKING BRAKE RELEASE PRESSURE FLOAT SOLENOID

ON

142 • Hoist valve in LOWER (power down)

Shown is a sectional view of the hoist valve in the LOWER (power down) position. The RAISE solenoid is de-energized and pilot oil is vented to the tank. The LOWER and FLOAT solenoids are both energized and direct pilot oil pressure to the lower end of the directional spool. Supply oil from the pump flows past the directional spool, through the counterbalance valve, to the rod end of the hoist cylinders. Oil in the head end of the hoist cylinders flows to the tank. The directional spool also vents the passage to the dual stage relief valve signal stem. The dual stage relief valve signal stem allows supply pressure to be limited by the low pressure relief valve.

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If the pressure in the rod end of the hoist cylinders exceeds 3450 + 350 - 0 kPa (500 + 50 - 0 psi), the low pressure relief valve will open. When the low pressure relief valve opens, the dump spool moves to the left and pump oil flows to the front brake oil cooler. The low pressure hoist relief valve setting is checked at the two pressure taps located on the hoist pump. Check the relief pressures with the hoist lever in the LOWER position and the engine at HIGH IDLE.

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PARKING BRAKE RELEASE PRESSURE RAISE SOLENOID

793C HOIST CONTROL VALVE FRONT BRAKE OIL COOLER RELIEF VALVE

FLOAT TO TANK

FROM HOIST CYLINDER HEAD END

LOAD CHECK VALVE

TO HOIST CYLINDER ROD END LOW PRESSURE RELIEF VALVE

COUNTERBALANCE VALVE

HIGH PRESSURE RELIEF VALVE DUAL STAGE RELIEF VALVE SIGNAL STEM

ROD END VENT SLOT TO FRONT BRAKE OIL COOLERS PUMP SUPPLY PORT LOWER SOLENOID

PARKING BRAKE RELEASE PRESSURE FLOAT SOLENOID

ON

143 • Hoist valve in FLOAT

Shown is a sectional view of the hoist valve in the FLOAT position. The RAISE and LOWER solenoids are de-energized and pilot oil is vented to the tank. The FLOAT solenoid is energized and directs pilot oil pressure to the lower end of the small diameter spool located below the directional spool. The small diameter spool pushes against the directional spool and moves the directional spool up. Because the pilot pressure is acting on a smaller surface area, the directional spool does not move up as far as during LOWER. Pump supply oil flows past the directional spool, through the counterbalance valve, to the rod end of the hoist cylinders. Oil in the head end of the hoist cylinders flows to the tank. The directional valve is in a position that permits the pressure of the oil flowing to the front brake oil cooler to be felt at the rod end of the hoist cylinders.

• Operate truck with hoist lever in FLOAT

The rod end pressure helps to hold the body against the frame when traveling. The hoist lever should always be in the FLOAT position while traveling.

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144

• Front brake oil cooler filters (arrow)

When the hoist valve is in the HOLD or FLOAT position, all the hoist pump oil flows through the front brake oil cooler filters (arrow) located outside the left frame. Excess oil from the parking brake release valve also flows through these filters. Oil flows from the front brake oil cooler filters to the front brake oil cooler located above the torque converter.

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2 1

145

1. Front brake oil cooler diverter valve 2. Front brake oil cooler

The hoist and parking brake release pump oil flows from the front brake oil cooler filters, through the front brake oil cooler diverter valve (1), to the front brake oil cooler (2). When the service or retarder brakes are applied, air pressure is sent to the front brake oil cooler diverter valve. Normally, front brake cooling oil is diverted around the cooler and goes directly to the front brakes. When air is sent to the diverter valve piston, front brake cooling oil is allowed to flow through the front brake oil cooler. Since the coolers use the coolant from the aftercooler circuit, diverting oil around the coolers provides cooler aftercooler air during high power demands (when climbing a grade with the brakes RELEASED, for example).

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146

• Two-stage hoist cylinders

Shown are the twin two-stage hoist cylinders used to raise the body.

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HOIST SYSTEM

HOIST SCREENS

HOIST PUMP

FROM PARKING BRAKE RELEASE VALVE

HOLD POSITION SUCTION SCREENS

FRONT BRAKES

FRONT BRAKE OIL COOLER

TO HOIST CYLINDER ROD END DIVERTER VALVE

TO HOIST CYLINDER HEAD END

FRONT BRAKE OIL COOLER FILTERS FROM PARKING BRAKE RELEASE VALVE

147 • Hoist system circuit

The hoist system pumps pull oil from the hydraulic tank through suction screens. Oil flows from the hoist pump through the hoist screens to the hoist control valve. The hoist valve uses parking brake release pressure as the pilot oil to shift the directional spool inside the hoist valve. Three solenoid valves are used to direct the pilot oil to the ends of the directional spool. The solenoid valve on the right is energized in the RAISE position. The two solenoid valves on the left are energized in the LOWER or FLOAT position. When the hoist valve is in the HOLD or FLOAT position, all the hoist pump oil flows through the front brake oil cooler filters. Excess oil from the parking brake release valve joins with the hoist pump oil and also flows through the front brake oil cooler filters.

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An oil cooler relief valve is located in the hoist valve. The relief valve limits the front brake oil cooling pressure when the hoist valve is in the HOLD or FLOAT position. Hoist and parking brake release pump oil flows from the front brake oil cooler filters, through the front brake oil cooler diverter valve, to the front brake oil cooler. Service or retarder brake air pressure is sent to the front brake oil cooler diverter valve. Normally, front brake cooling oil is diverted around the cooler and goes directly to the front brakes. When air is sent to the diverter valve pistons, front brake cooling oil is allowed to flow through the front brake oil cooler. Since the coolers use the coolant from the aftercooler circuit, diverting oil around the coolers provides cooler aftercooler air during high power demands. Two hydraulic cylinders are used to raise the body away from the frame of the truck. When the hoist lever is held in the RAISE position, supply oil flows to the head end of the hoist cylinders and moves the two stage cylinders to their extended lengths. The oil from the rod end of the cylinders flows through the hoist valve into the front brake oil cooling circuit. When the hoist lever is moved to the LOWER or FLOAT position and the cylinders are extended, supply oil enters the rod end of the hoist cylinders and lowers the second stage of the cylinders. The oil from the head end of the cylinders flows through the hoist valve to the hydraulic tank.

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AIR SYSTEM AND BRAKES 793C

148 AIR SYSTEM AND BRAKES • Two brake systems: - Parking/secondary brake system - Service/retarder brake system

Two separate brake systems are used on the 793C Off-highway Truck. The two brake systems are: the parking/secondary brake system and the service/retarder brake system. The parking/secondary brakes are spring engaged and hydraulically released. The service/retarder brakes are engaged hydraulically by an air-over-oil brake system. The 793C Truck is also equipped with an air system. An engine driven air compressor supplies the air and fills two reservoirs. Air from the reservoirs provides energy to perform several functions:

• Air system functions

1. 2. 3. 4. 5. 6. 7.

Engine start-up Service and retarder brake control Secondary and parking brake control Windshield washer and wiper Automatic lubrication injection Horn Exhaust bypass (wastegate) control

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149

• Oil cooled brake assembly • Duo-Cone seals prevent oil from leaking or transferring

Shown is a cutaway illustration of an oil cooled brake assembly. The brakes are environmentally sealed and adjustment free. Oil continually flows through the brake discs for cooling. Duo-Cone seals prevent the cooling oil from leaking to the ground or transferring into the axle housing. The wheel bearing adjustment must be maintained to keep the Duo-Cone seals from leaking.

• Small piston ENGAGES secondary and parking brakes

The smaller piston (yellow) is used to ENGAGE the secondary and parking brakes. The parking brakes are spring ENGAGED and hydraulically RELEASED.

• Large piston ENGAGES retarder/service brakes

The larger piston (purple) is used to ENGAGE the retarder/service brakes. The retarder/service brakes are engaged hydraulically by an air-over-oil brake system.

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4

1

2

3

150

Operator Controls Several brake system control components are located on the center console at the right of the operator's seat. 1. Parking brake air switch

The parking brake air switch (1) controls the flow of air to the parking brake release valve.

2. Windshield wiper/washer switch

The windshield wiper/washer switch (2) controls the flow of air to the pump in the windshield washer reservoir and to the wiper motor in front of the cab.

3. Brake retraction switch

The brake retraction switch (3) is an electrical switch used to activate the electric pump that supplies oil for towing.

4. TCS switch

The Traction Control System (TCS) switch (4) is used to test the TCS (formerly referred to as the "Automatic Electronic Traction Aid").

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151

• Secondary brake lever (red)

Operator controls on the steering column are the secondary brake lever (red) and the retarder lever (black).

• Retarder lever (black)

The secondary brake lever allows the operator to modulate the engagement of the parking brakes. The secondary brake lever engages the same brake system as the parking brake air switch. The retarder brake lever allows the operator to modulate the engagement of the service brakes. The retarder brake lever engages the same brake system as the service brake pedal (shown in the next slide).

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152

• Service brake pedal (arrow)

On the floor is the service brake pedal (arrow).

• Horn control button (not shown)

Located on the floor to the left of the steering column is the horn control button (not shown).

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153

Air Charging System • Air compressor

The air system is charged by an air compressor mounted on the left front of the engine.

• Air compressor governor (arrow)

System pressure is controlled by the governor (arrow). The governor maintains the system pressure between 660 and 830 kPa (95 and 120 psi).

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1

3 2

4

154

1. Air dryer

Air flows from the air compressor to the air dryer (1) located in front of the left front tire. The air dryer removes contaminants and moisture from the air system. The condition of the desiccant in the air dryer should be checked every 250 hours and changed periodically (determined by the humidity of the local climate).

2. Purge valve signal hose

When the air compressor governor senses that system air pressure is at the cut-out pressure of 830 kPa (120 psi), the governor sends an air pressure signal to the purge valve through the hose (2). The purge valve opens and air pressure that is trapped in the air dryer is exhausted through the desiccant, an oil filter and the purge valve.

3. Air system relief valve

An air system relief valve (3) is located on the air dryer. A heating element (4) prevents moisture in the dryer from freezing in cold weather.

4. Heating element

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1

2

3

155

1. Service/retarder brake reservoir

Air flows through the air dryer and fills two reservoirs. The service/retarder brake reservoir (1) is located on the right platform. This reservoir also supplies air for the air start system. The second reservoir is located behind the cab and supplies air for the parking/secondary brake system.

2. Relief valve

A relief valve (2) is installed in the service/retarder brake reservoir. This relief valve serves as a back-up for the relief valve on the air dryer.

3. Condensation drain valve

Condensation should be drained from the tank daily through the drain valve (3).

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156

• Parking/secondary brake reservoir

Located behind the operator’s station is the parking/secondary brake air reservoir. A drain valve is located on the right side of the cab. Moisture should be drained from the reservoir daily through the drain valve (see Slide No. 28).

• Check valve (arrow)

A check valve (arrow) prevents a loss of air if an air line breaks upstream of the air reservoir.

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1

2

3

157

1. Pressure protection valve

Located behind the operator’s station is a pressure protection valve (1). If one of the accessory circuits fails, the pressure protection valve maintains a minimum of 482 kPa (70 psi) in the service brake circuit.

2. Air system pressure sensor

Also located behind the operator’s station is the air system pressure sensor (2). The air system pressure sensor provides an input signal to the VIMS which informs the operator if a problem exists in the air system.

3. Automatic lubrication solenoid air valve

The solenoid air valve (3) provides controlled supply air for the automatic lubrication system. The solenoid air valve is controlled by the VIMS. The VIMS ENERGIZES the solenoid ten minutes after the machine is started. The VIMS keeps the solenoid ENERGIZED for 75 seconds and then DE-ENERGIZES it. Every 60 minutes thereafter, the VIMS ENERGIZES the solenoid for 75 seconds until the machine is stopped (turned off). These settings are adjustable through the VIMS keypad in the cab.

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AIR CHARGING SYSTEM AIR COMPRESSOR AND GOVERNOR

AIR DRYER SERVICE/RETARDER BRAKE RESERVOIR REMOTE AIR SUPPLY CONNECTOR

PRESSURE PROTECTION VALVE

LOW AIR SWITCH

PARKING/SECONDARY BRAKE RESERVOIR

158 • Air charging system schematic

This schematic shows the flow of air through the air charging system. Air flows from the air compressor, through the air dryer, to the service/retarder brake reservoir. Air from the service/retarder brake reservoir enters the pressure protection valve. When the pressure in the service/retarder reservoir reaches 550 kPa (80 psi), the pressure protection valve allows air to flow to the parking/secondary brake reservoir, the air start system, the automatic lubrication system and the accessory circuits (wiper and horn). All reservoirs have a check valve at the air supply port to prevent a loss of air if a leak upstream of the reservoirs occurs.

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159

Parking and Secondary Brake System • Secondary brake valve (arrow) • Modulates parking brake engagement

The secondary brake valve (arrow) is controlled by the secondary brake lever in the cab. Normally, air flows through the secondary brake valve to the parking brake release valve. When the secondary brake lever is pulled down, the valve blocks the flow of air to the parking brake release valve. Blocking the air from the parking brake release valve positions the spool in the valve to drain the oil from the parking brakes, which allows the springs in the parking brake to ENGAGE the brakes. The secondary brake valve can be used to modulate parking brake engagement by metering the amount of air flow to the parking brake release valve. The parking brake air switch on the center console in the cab also controls the flow of air to the parking brake release valve.

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2 4

3 1

160

1. Parking brake release valve

Supply air from the parking brake air switch in the cab or the secondary brake valve flows to an air chamber in the parking brake release valve (1). The parking brake release valve contains an air piston that moves a spool. The spool either directs oil to RELEASE the parking brakes or drains oil to ENGAGE the parking brakes. A relief valve inside the parking brake release valve limits the system pressure for releasing the brakes.

2. TCS valve

The same oil that supplies the parking brake release valve also supplies oil to the Traction Control System (TCS) valve (2). The TCS valve automatically ENGAGES and RELEASES the rear parking brake of a wheel that is spinning at least 60% faster than the other rear wheel. The TCS test switch in the cab can be used to test the TCS.

3. Rear parking/secondary brake taps

The left and right rear parking/secondary brake pressures can be measured at the pressure taps (3).

4. Towing motor

If the parking brakes need to be released for service work or towing, the electric motor (4) can be energized by the brake retraction switch located in the cab. The motor drives a pump which sends oil through the parking brake release valve to RELEASE the parking brakes. Towing pump pressure is controlled by a relief valve in the towing pump.

• Pump provides flow to release parking brakes for towing

• Air pressure needed to release brakes for towing

Air pressure is also needed to release the brakes for towing. The piston chamber in the parking brake release valve must be pressurized to move the spool in the valve. The oil from the electrically driven brake release pump can then flow to the rear brakes.

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1 2

161

1. Parking brake release pump 2. Rear brake oil cooling pumps

Shown is the parking brake release pump (1) and the three rear brake oil cooling pumps (2). Parking brake release supply oil flows from the parking brake release pump, through the parking brake release oil filter, to the parking brake release valve.

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2 1

162

1. Parking brake release filter 2. Parking brake release pressure tap

Oil flows from the parking brake release pump, through the parking brake release filter (1), to the parking brake release valve. Parking brake release pressure can be measured at the filter by removing a plug and installing a pressure tap (2).

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TOWING SYSTEM

RELIEF VALVE

PARKING BRAKE RELEASE PUMP

PARKING BRAKE RELEASE VALVE

TO HOIST PILOT SYSTEM

CHECK VALVE TOWING PUMP RELIEF VALVE

TOWING PUMP

163

• Parking brake relief valve limits hoist pilot pressure

Normally, supply oil flows from the parking brake release pump, through the parking brake release filter, to the parking brake release valve. If air pressure is present from the parking brake air switch or secondary brake valve, supply oil flows past the relief valve, the check valve and the spool to RELEASE the parking brakes. The relief valve controls system pressure for releasing the brakes and for the pilot oil that is supplied to the three solenoids on the hoist valve. The setting of the relief valve in the parking brake valve is 4700 ± 200 kPa (680 ± 30 psi).

• Parking brake release system during towing

This schematic shows the flow of oil through the parking brake release system when the towing system is energized.

• Normal parking and secondary brake operation

Oil flow from the parking brake release pump has stopped. The towing motor is energized, and air pressure is present above the parking brake release valve piston. The air pressure moves the spool in the parking brake release valve down to block the drain port.

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Oil flows from the towing pump to the parking brake release valve and the parking brakes. The check valve in the parking brake release valve blocks the oil from the towing pump from flowing to the parking brake release pump. • Relief valve in towing pump controls brake release pressure

During towing, the parking brake release pressure is controlled by a relief valve in the towing pump. When the relief valve opens, oil transfers from the pressure side to the suction side of the towing pump. The setting of the relief valve is approximately 3790 kPa (550 psi).

• Towing pump check valve

A check valve in the outlet port of the towing pump prevents oil from flowing to the towing pump during normal operation.

• Procedure to check parking brake release system for towing

To check the brake release system used for towing, install a gauge on the parking brake release pressure tap on the rear axle. Use a long gauge hose so the gauge can be held in the cab. With the parking brake air switch in the RELEASE position and the key start switch in the ON position, energize the parking brake release switch on the dash used for towing. The parking brake release pressure should increase to 3790 kPa (550 psi). Turn off the switch when the pressure stops increasing. The parking brake release pressure must increase to a minimum of 3790 kPa (550 psi). During towing, the brake retraction switch on the dash must be energized whenever the parking brake release pressure decreases below this pressure or the brakes will drag.

NOTE: At least 550 kPa (80 psi) air pressure must be available at the parking brake release valve to ensure full release of the brakes for towing.

NOTICE Energize the brake retraction switch only when additional pressure is required to release the brakes. Leaving the brake retraction (towing) motor energized continuously will cause damage to the motor.

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PARKING/SECONDARY BRAKES SECONDARY BRAKES RELEASED PARKING BRAKES ENGAGED

PARKING BRAKE SWITCH

EPTC II SWITCH

PARKING BRAKE RELEASE PUMP

PARKING BRAKE RELEASE VALVE

SECONDARY BRAKE VALVE PARKING/SECONDARY BRAKE RESERVOIR

TO HOIST PILOT SYSTEM

164 • Parking/secondary brake system

Shown is the parking/secondary brake hydraulic and air system with the secondary brakes RELEASED and the parking brakes ENGAGED. Supply air from the parking/secondary brake air reservoir flows through the secondary brake valve and is blocked by the parking brake air switch. No air pressure is present to move the spool in the parking brake release valve. Supply oil from the parking brake release pump is blocked by the spool. Oil from the parking brake is open to drain through the parking brake release valve, which allows the springs in the parking brake to ENGAGE the brakes.

• Parking/secondary brake switch for EPTC II input

A parking/secondary brake switch that provides an input signal to the EPTC II is located in the air line between the parking brake switch and the parking brake release valve. When the parking or secondary brakes are ENGAGED, the switch signals the EPTC II to allow rapid downshifts.

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5

2

6

3

4

1

165

Service and Retarder Brake System 1. Service brake valve 2. Manual retarder valve 3. Automatic Retarder Control (ARC) valve 4. Left double check valve 5. Right double check valve 6. Brake ON switch

• Service brakes and manual retarder engage same relay valve

The service brake valve (1) is controlled by the brake pedal in the cab. Supply air for the service brake valve, the manual retarder valve (2) and the Automatic Retarder Control (ARC) valve (3) is supplied from the bottom port of the service brake valve. When the manual retarder is engaged, air flows from the manual retarder valve through the top of the left double check valve (4) and the right double check valve (5) to a relay valve near the brake master cylinders and a diverter valve on the front brake oil cooler. When the service brakes are engaged, air flows from the service brake valve through the bottom of the left double check valve (4). If the manual retarder and the service brakes are engaged at the same time, air from the system with the highest pressure will flow through the left double check valve (4) and the right double check valve (5) to a relay valve near the brake master cylinders and a diverter valve on the front brake oil cooler.

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The Automatic Retarder Control (ARC) system function is to modulate truck braking (retarding) when descending a long grade to maintain a constant engine speed. Previously, the ARC was installed in parallel with the manual retarder and the service brakes. On current machines, the ARC system is separate from the manual retarder and the service brakes. • ARC brake system engages separate relay valve

When the ARC is engaged, air flows from the ARC valve (3) to a separate relay valve located near the brake master cylinders. Air also flows from the ARC valve through the right double check valve (5) to the diverter valve on the front brake oil cooler. The switch (6) turns on the amber BRAKE ON light on the dash in the operator’s station when any of the brakes are engaged (manual retarder, service brake or automatic retarder).

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5 2 1

3 4

166

1. Service brake and manual retarder relay valve 2. ARC relay valve 3. Double check valves 4. Front brake cylinders 5. Rear brake cylinders

The front brake relay valve (1) receives metered air from only the service brake valve or the manual retarder valve. The rear brake relay valve (2) receives metered air from only the Automatic Retarder Control (ARC) valve. When the service brakes or manual retarder brakes are ENGAGED, the front relay valve opens and metered air flows from the service brake reservoir, through the double check valves (3), to the brake cylinders (4 and 5). The brake relay valve reduces the time required to engage and release the brakes.

• Brake relay valves reduce time to engage and release brakes

When the ARC brake system is ENGAGED, the rear relay valve opens and metered air flows from the service brake reservoir, through the double check valves (3), to the brake cylinders (4 and 5). The brake relay valve reduces the time required to engage and release the brakes.

• Double check valves separate brake systems

The double check valves (3) are used to separate the service brakes and manual retarder brakes from the ARC brake system. The brake cylinders operate by air-over-oil. When the metered air enters the brake cylinders, a piston moves down and pressurizes the oil in the bottom of the cylinders. Two cylinders (4) supply oil to the front brakes, and two cylinders (5) supply oil to the rear brakes. The pressure oil from the brake cylinders flows to a slack adjuster.

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1

2 3 4

167

1. Brake oil makeup tank

As the brake discs in the brake assemblies wear, more oil is needed from the brake cylinders to compensate for the wear. The makeup oil tank (1) supplies makeup oil for the brake cylinders. Oil from the brake cooling circuit provides a continuous supply of oil to the makeup oil tank. Low brake cooling flow can cause the makeup oil reserve to decrease and cause the brake cylinders to overstroke.

• Check brake makeup oil flow

To check for makeup oil flow, remove the cover from the makeup oil tank. With the engine at HIGH IDLE, a stream of oil filling the tank should be visible. If a stream of oil is not visible, the hydraulic system may have a restriction, pump flow may be low, or the brake oil cooling relief valve may be stuck open or set too low.

2. Brake overstroke switch

If air is in the system or a loss of oil downstream from the cylinders occurs, the piston in the cylinder will overstroke and cause an indicator rod to extend and open the brake overstroke switch (2). The switch provides an input signal to the VIMS which informs the operator of the condition of the service/retarder brake oil circuit. If an overstroke condition occurs, the problem must be repaired and the indicator rod pushed in to end the warning.

3. Brake cylinder bleed screw

Air can be removed from the brake cylinders through the bleed screws (3).

4. Brake oil temperature sensor

Shown is one of the four brake oil temperature sensors (4) located in the brake cooling oil return tube.

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168

• Front brake oil cooler diverter valve (arrow)

The air that flows to the two relay valves also flows to the front brake oil cooler diverter valve (arrow). Normally, front brake cooling oil is diverted around the cooler and goes directly to the front brakes. When air is sent to the diverter valve piston, brake oil is allowed to flow through the front brake oil cooler. Since the cooler uses the coolant from the engine aftercooler circuit, diverting oil around the cooler provides lower temperature aftercooler air during high power demands (when climbing a grade with the brakes RELEASED, for example).

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BRAKE CYLINDER BRAKES ENGAGED AIR PISTON

INDICATOR ROD

FROM MAKEUP TANK OIL PISTON

AIR INLET

TO SLACK ADJUSTER VALVE SPRING

ROD

169 • Brake cylinder ENGAGED

This slide shows a sectional view of the brake cylinder when the brakes are ENGAGED. Air pressure from the brake relay valve enters at the air inlet. The air pressure moves the air piston and the attached rod closes the valve in the oil piston. When the valve in the oil piston is closed, the oil piston pressurizes the oil in the cylinder. The pressure oil flows to a slack adjuster.

• Brake overstroke switch indicates loss of brake oil

If air is in the system or a loss of oil downstream from the cylinders occurs, the piston in the cylinder will overstroke and cause the indicator rod to extend and open the brake overstroke switch. The switch provides an input signal to the VIMS which informs the operator of the condition of the service/retarder brake oil circuit. If an overstroke condition occurs, the problem must be repaired and the indicator rod pushed in to end the warning. When the air pressure is removed from behind the air piston, the spring moves the air piston and the attached rod opens the valve in the oil piston. Any makeup oil that is needed flows into the passage at the top of the oil chamber, through the valve, and into the oil chamber at the right of the oil piston.

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3

2

3

4

4

1

170

1. Slack adjuster

The truck is equipped with two slack adjusters--one for the front brakes and one for the rear brakes. The slack adjuster (1) shown is for the rear brakes. The slack adjusters compensate for brake disc wear by allowing a small volume of oil to flow through the slack adjuster and remain between the slack adjuster and the brake piston under low pressure. The slack adjusters maintain a slight pressure on the brake piston at all times.

• Cooling oil pressure maintains clearance between discs

Brake cooling oil pressure maintains a small clearance between the brake discs.

2. Service brake pressure taps

The service brake oil pressure can be measured at the two taps (2) located on top of the slack adjusters.

3. Service brake bleed valves

Air can be removed from the service brakes through the two remote bleed valves (3).

4. Parking brake release pressure taps

The parking brake release pressure can be measured at the two taps (4) on the axle housing.

NOTE: Air can be removed from the front service brakes through bleed valves located on each wheel.

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BRAKE SLACK ADJUSTER

OIL FLOW TO BRAKE CYLINDER

SMALL PISTON LARGE PISTON

OIL FLOW FROM BRAKE CYLINDER

FROM WHEEL BRAKES

FROM WHEEL BRAKES

TO WHEEL BRAKES

TO WHEEL BRAKES

BRAKES ENGAGED

BRAKES RELEASED

171 • Slack adjuster RELEASED and ENGAGED

This slide shows sectional views of the slack adjuster when the brakes are RELEASED and ENGAGED.

• Large piston moves to ENGAGE brakes

When the brakes are ENGAGED, oil from the brake cylinders enters the slack adjusters and the two large pistons move outward. Each large piston supplies oil to one wheel brake. The large pistons pressurize the oil to the service brake pistons and ENGAGE the brakes.

• Small piston allows makeup oil to brakes

Normally, the service brakes are FULLY ENGAGED before the large pistons in the slack adjusters reach the end of their stroke. As the brake discs wear, the service brake piston will travel farther to FULLY ENGAGE the brakes. When the service brake piston travels farther, the large piston in the slack adjuster moves farther out and contacts the end cover. The pressure in the slack adjuster increases until the small piston moves and allows makeup oil from the brake cylinders to flow to the service brake piston.

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• Service brake springs move large pistons to center of slack adjuster

When the brakes are RELEASED, the springs in the service brakes push the service brake pistons away from the brake discs. The oil from the service brake pistons pushes the large pistons in the slack adjuster to the center of the slack adjuster. Makeup oil that was used to ENGAGE the brakes is replenished at the brake cylinders from the makeup tank.

• Large piston spring keeps pressure on service brake piston

The spring behind the large piston causes some oil pressure to be felt on the service brake piston when the brakes are RELEASED. Keeping some pressure on the brake piston provides rapid brake engagement with a minimum amount of brake cylinder piston travel.

• Check slack adjuster for correct operation

The slack adjusters can be checked for correct operation by opening the service brake bleed screw with the brakes RELEASED. A small amount of oil should flow from the bleed screw when the screw is opened. The small flow of oil verifies that the spring behind the large piston in the slack adjuster is maintaining some pressure on the service brake piston. Another check to verify correct slack adjuster operation is to connect a gauge to the pressure tap on top of the slack adjuster and another gauge at the service brake bleed screw location on the brake anchor plate casting. With system air pressure at maximum and the service brake pedal depressed, the pressure reading on both gauges should be approximately the same.

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SERVICE/RETARDER BRAKE AIR SYSTEM SERVICE BRAKE ENGAGED

FRONT BRAKE OIL COOLER DIVERTER VALVE

ARC RELAY VALVE

SERVICE RELAY VALVE

SERVICE BRAKE VALVE

RETARDER VALVE

BRAKE ENGAGED SWITCH

ARC VALVE

BRAKE CYLINDERS

172 • Service/retarder brake air system

This schematic shows the flow of air through the service/retarder brake air system when the retarder (manual and automatic) is RELEASED and the service brakes are ENGAGED. Supply air pressure flows from the large service brake air reservoir to the relay valves and the service brake valve. Supply air pressure flows from the service brake valve to the manual retarder valve and the ARC valve. The manual retarder valve blocks the flow of air to a double check valve. The ARC solenoids also block the flow of air to a double check valve and the ARC relay valve. The service brake valve allows air to flow to a double check valve that blocks the passage to the manual retarder valve. Air pressure from the service brake valve flows through the double check valve to the service brake relay valve and a second double check valve to the front brake oil cooler diverter valve. The service brake relay valve opens and metered air flows from the large service brake air reservoir to the brake cylinders. A pair of double check valves above the brake cylinders prevent the flow of service brake air to the ARC relay valve.

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TO FRONT BRAKES

REAR BRAKE COOLING CIRCUIT

TRACTION CONTROL SYSTEM (TCS) VALVE

PARKING BRAKE RELEASE VALVE

PARKING BRAKE RELEASE FILTER

TO REAR BRAKES

HOIST VALVE

REAR BRAKE OIL COOLERS

PARKING BRAKE RELEASE PUMP

BRAKE COOLING PUMPS

REAR BRAKES

PUMP DRIVE SUCTION SCREENS

OIL COOLER RELIEF VALVES

173 • Rear brake oil cooling circuit

Shown is the rear brake oil cooling circuit. The rear brake cooling pumps (see Slide No. 161) pull oil from the hydraulic tank through suction screens. Rear brake cooling oil pressure is controlled by two oil cooler relief valves located inside the hydraulic tank (see Slide No. 135). Oil flows from the rear brake cooling pumps through two rear brake oil coolers located behind the right front tire (see Slide No. 8). Oil flows from the rear brake oil coolers, through the rear brakes, and returns to the hydraulic tank.

• Parking brake release oil used to cool front brakes

Most of the oil that flows into the parking brake release valve flows through the valve and joins with the hoist system oil. The parking brake release and hoist system oil is used to cool the front brakes (see Slide No. 147).

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ENGINE SPEED SENSOR ENGINE SPEED

HARNESS CODE INPUTS A10

SERVICE INPUTS B6

SET

B7

CLEAR

HARNESS CODE PLUG

A17-19 36,37

DATA LINK

AUTOMATIC RETARDER CONTROL (ARC)

BRAKE ENGAGED LAMP

B9 B10 A5 A21

ARC ON/OFF SWITCH

BRAKE ENGAGED LAMP OUTPUT BRAKE ENGAGED PRESSURE INPUT AUTO RETARDER PRESSURE INPUT

A16

ON INPUT A11

OFF INPUT A26

A3

Diagnostic Display

A4

CONTROL OUTPUT SUPPLY OUTPUT

SUPPLY SOLENOID VENT

AIR FROM SERVICE BRAKE RESERVOIR

VENT CONTROL SOLENOID

BRAKE PEDAL AND VALVE

RETARDER LEVER AND VALVE

AUTOMATIC RETARDER VALVE AUTO RETARDER PRESSURE SWITCH BRAKE ENGAGED SWITCH

TO SERVICE BRAKE RELAY VALVE A - 37 PIN CONNECTOR B - 10 PIN SURE-SEAL CONNECTOR

TO FRONT BRAKE OIL COOLER DIVERTER VALVE

TO ARC RELAY VALVE

174 AUTOMATIC RETARDER CONTROL (ARC) • Automatic Retarder Control (ARC)

The Automatic Retarder Control (ARC) system function is to modulate truck braking (retarding) when descending a long grade to maintain a constant engine speed. The ARC system uses the service/retarder brake system to engage the brakes. If the ON/OFF switch is moved to the ON position, the ARC will be activated if the throttle pedal is not depressed and the parking/secondary brakes are RELEASED. The ARC system is disabled when the throttle is depressed or when the parking/secondary brakes are ENGAGED. The ARC is not connected to the service brakes and the manual retarder. When the ARC is engaged, air flows from the ARC valve to a separate relay valve located near the brake master cylinders. Air also flows from the ARC valve, through a double check valve, to the diverter valve on the front brake oil cooler.

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• ARC set to maintain 1900 engine rpm

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The ARC is set at the factory to maintain a constant engine speed of 1900 ± 50 rpm (engine speed setting is programmable). When the ARC initially takes control of retarding, the engine speed may oscillate out of the ± 50 rpm target, but the engine speed should stabilize within a few seconds. For proper operation of the ARC, the operator needs only to activate the control with the ARC ON/OFF switch and select the correct gear for the grade, load, and ground conditions. The ARC is designed to allow the transmission to upshift to the gear selected by the shift lever. After the transmission shifts to the gear selected by the operator and the engine speed exceeds 1900 rpm, the ARC will apply the retarder as needed to maintain a constant engine speed.

• ARC provides engine overspeed protection

The ARC system also provides Engine Overspeed protection. If an unsafe engine speed is reached, the ARC will engage the brakes, even if the ARC ON/OFF switch is in the OFF position and the throttle is depressed. Trucks approaching an overspeed condition will sound a horn and activate a light at 2100 rpm. If the operator ignores the light and horn, the ARC will engage the retarder at 2180 rpm. If the engine speed continues to increase, the EPTC II transmission control will either upshift (one gear only above shift lever position) or unlock the torque converter (if the shift lever is in the top gear position) at 2300 rpm.

• ARC provides programming and diagnostic capability

The ARC also provides service personnel with enhanced diagnostic capabilities through the use of onboard memory, which stores possible faults, solenoid cycle counts and other service information for retrieval at the time of service. By using of a set of service switches, service personnel can access different modes to gather the stored diagnostic information or set the adjustable engine speed control setting. The Auto Retarder Control receives signals from several switches and sensors. The control analyzes the various input signals and sends signals to the output components. The output components are two solenoids and a lamp.

INSTRUCTOR NOTE: For more detailed information about the Automatic Retarder Control (ARC) system, refer to the Service Manual Module "Automatic Retarder Control System" (Form SENR5683) and the Technical Instruction Module "Automatic Retarder Control System" (Form SEGV2593).

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1 2

3

175

1. Automatic Retarder Control (ARC) 2. ARC diagnostic window 3. Service switches

Shown is the Automatic Retarder Control (1). The ARC is located in the compartment behind the cab. The control contains a diagnostic window (2) with 12 Light Emitting Diodes (LED’s) and a three digit numeric display. The service switches (3) are used to interrogate the ARC for stored diagnostic information, event information and to program the engine control speed. The switches are labeled with an "S" for "SET" and a "C" for "CLEAR." The DIAGNOSTIC MODE of the electronic control is changed by DEPRESSING and HOLDING both service switches (SET and CLEAR). When the desired mode is shown on the display, the switches can be released. By following the instructions in the Service Manual, the serviceman can determine if the ARC system is operating correctly.

• ECAP and ET service tools

The Electronic Control Analyzer Programmer (ECAP) and the Electronic Technician (ET) Service Tools can be used in place of the ARC diagnostic window. The ECAP and ET perform the same functions as the ARC diagnostic window and are capable of a few additional diagnostics that the ARC window does not display (see Slide No. 109).

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ARC DIAGNOSTIC WINDOW

1

2

3

4

5

6

7

10

11

8

12 13 D1

D2

D3

176 • ARC diagnostic window:

The onboard diagnostic window houses 12 status LED's along with a three digit numeric display.

- 12 status LED's - Three digit display

The function of the three digit display and the status LED's are: 1. POWER--A GREEN LED which is ON when a nominal 24 Volts is available between pins 1 and 2 of the electronic control 37 pin connector. 2. CONTROL EVENT--A RED LED which is ON or FLASHING when the electronic control has FAILED and should be replaced. 3. ARC PRESSURE--An AMBER LED which is ON when the ARC pressure switch is OPEN, which indicates the presence of brake air pressure at the ARC valve.

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4. RETARDER PRESSURE--An AMBER LED which is ON when the service brakes, manual retarder or auto retarder is in use as sensed by the CLOSED brake engaged pressure switch. 5. SECONDARY BRAKE--An AMBER LED which is ON when the secondary or parking brake is in use as sensed by the OPEN secondary brake pressure switch. 6. THROTTLE PEDAL--An AMBER LED which is ON when the throttle pedal is depressed as sensed by a signal from the throttle sensor. 7. ENG SPEED--An AMBER LED which is ON when the engine speed sensor is providing a signal to the control. 8. DIAGNOSTIC PRESENT--A RED LED which indicates that the electronic control has detected a fault for which a diagnostic code has been stored in memory. The LED is ON if the fault is still present. 9. Three digits (D1, D2, D3) display numbers and letters or indicate circuit conditions. 10. SERVICE MODE--An AMBER LED which is ON when the electronic control is NOT in Mode 0. 11. Not used at this time. 12. Not used at this time. 13. Not used at this time.

NOTE: The small LED at the bottom right of the three digit display has no diagnostic function. The small LED will always be ON. Service personnel should always view the diagnostic window with the small LED at the bottom right of the three digit display. When the small LED is at the bottom right of the three digit display, service personnel know that the window is being viewed in the correct orientation.

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177

TRACTION CONTROL SYSTEM (TCS) • TCS uses parking/ secondary brake system

The Traction Control System (TCS) uses the rear parking/secondary brakes (spring engaged and hydraulically released) to decrease the revolutions of a spinning wheel. The TCS allows the tire with better underfoot conditions to receive an increased amount of torque. The controls for the system are contained in the TCS electronic control. The TCS electronic control monitors the drive wheels through three input signals: one at each drive axle, and one at the transmission output shaft. When a spinning drive wheel is detected, the electronic control sends a signal to the selector and proportional valves which in turn engage the brake of the affected wheel. When the condition has improved and the ratio between the right and left axles returns to 1:1, the electronic control sends a signal to release the brake.

• TCS formerly called AETA

The TCS was formerly referred to as the "Automatic Electronic Traction Aid." The operation of the system has not changed. The main difference is the appearance of the electronic control. The TCS electronic control now looks like the EPTC II and ARC electronic controls. The Light Emitting Diodes (LED's) function the same as on the previous AETA electronic control, but they are arranged in a rectangular pattern instead of a straight line. The three digit numeric displays do not provide any function at this time. Also, the TCS is not on the CAT Data Link at this time and cannot communicate with the other electronic controls or the ECAP and ET service tools.

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1

2

178

1. TCS electronic control

2. Service/retarder brake switch - Stops TCS function - Performs diagnostic test

The TCS electronic control (1) is located in the compartment behind the cab. The electronic control contains a diagnostic window with 12 Light Emitting Diodes (LED’s) and a three digit numeric display. The diagnostic window is used to interrogate the TCS for diagnostic information. No Service Switches or Diagnostic Modes other than Mode 0 are available at this time. A service/retarder brake switch (2) provides an input signal to the TCS and performs two functions: 1. When the service brakes or retarder are ENGAGED, the TCS function is stopped. 2. The service/retarder brake switch provides the input signal needed to perform a diagnostic test. When the TCS test switch and the retarder lever are ENGAGED simultaneously, the TCS will engage each rear brake independently. Install two pressure gauges on the TCS valve and observe the pressure readings during the test cycle. The left brake pressure will decrease and increase. After a short pause, the right brake pressure will decrease and increase. The test will repeat as long as the TCS test switch and the retarder lever are ENGAGED.

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BATTERY + BATTERY -

132- PK 255 - BK

A1 A2

TRANSMISSION SPEED

768 - OR

A10

LEFT WHEEL SPEED

769 - BU

A29

RIGHT WHEEL SPEED

770 - GN

A3

774 - YL

SELECTOR SOLENOID - LEFT

A4

775 - BR

SELECTOR SOLENOID - RIGHT

A5

773 - GY

PROPORTIONAL SOLENOID

A9

767 - WH

+V TO BRAKE SWITCH AND WHEEL SENSORS

B9

893 - GN 892 - BR

DATA LINK (NOT USED)

TCS

A30 D1

D2

D3

2

214 - BK

A17

3

13

213- BK 212 - BK

A18 A19

4

12

216 - BK

A36

215 - BK

A37

SERVICE/RETARDER BRAKE SWITCH

772 - BR

B1

TEST SWITCH

700 - PK

MACHINE HARNESS CODES

5

6

7

8

9

10

11

B10 B2

A - 37 PIN CE CONNECTOR B - 10 PIN SURE-SEAL CONNECTOR

179 • TCS controls braking with electrical inputs and outputs

The TCS electronic control receives information from various input components such as the left and right wheel speed sensors, the transmission speed sensor and the service/retarder brake switch. Based on the input information, the TCS electronic control determines whether the left or right rear brake should be ENGAGED. These actions are accomplished by sending signals to various output components. Output components include the selector solenoid and the proportional solenoid. Input and output components on the block diagram are accompanied with a letter and number. The letter "A" corresponds with the 37 pin CE (Caterpillar Environmental) connector and the letter "B" corresponds with the 10 pin Sure-Seal connector that are attached to the TCS electronic control. The numbers next to the letters correspond to the pin numbers in the connector. For example, the TCS test switch is connected to the TCS electronic control through a wire in the 10 pin Sure-Seal connector at pin location 2.

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TCS DIAGNOSTIC WINDOW D1

D2

D3

2 3

13

4

12

5

6

7

8

9

10

11

180 • TCS diagnostic window:

The TCS onboard diagnostic window houses 12 status LED's along with a three digit numeric display.

- 12 status LED's - Three digit display

The functions of the three digit display and the status LED's are: 1. Three digits (D1, D2, D3) display numbers and letters or indicate circuit conditions (not used at this time). 2. LEFT AXLE PICKUP--An AMBER LED which is ON or FLASHING when the machine is moving. 3. RIGHT AXLE PICKUP--An AMBER LED which is ON or FLASHING when the machine is moving. 4. TRANSMISSION PICKUP--An AMBER LED which is ON or FLASHING when the machine is moving.

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5. SPEED PICKUP--An AMBER LED which is ON or FLASHING to indicate a fault (see NOTE below). 6. VEHICLE IDENTIFICATION--An AMBER LED which is ON when the harness code is incorrect. 7. LEFT BRAKE SOLENOID OR HARNESS--An AMBER LED which is ON when an OPEN or SHORT is present in the left brake solenoid or harness circuit. 8. PROPORTIONAL VALVE OR HARNESS--An AMBER LED which is ON when an OPEN or SHORT is present in the proportional solenoid valve or harness circuit. 9. RIGHT BRAKE SOLENOID OR HARNESS--An AMBER LED which is ON when an OPEN or SHORT is present in the right brake solenoid or harness circuit. 10. CONTROL BOX--A RED LED which is ON or FLASHING when the electronic control has FAILED and should be replaced. 11. POWER--A GREEN LED which is ON when a nominal 24 Volts is available between pins 1 and 2 of the electronic control 37 pin connector. 12. SERVICE BRAKE OR RETARDER--An AMBER LED which is ON when the service brake or retarder is in use as sensed by a GROUND from the service/retarder brake pressure switch. 13. TEST MODE--A RED LED which indicates that the test switch is in the ON position.

NOTE: To determine which pickup is at fault, actuate the test switch while driving in a straight line without wheel slippage. Count the number of flashes in each five second series of flashes: one flash indicates the left axle pickup, two flashes indicate the right axle pickup, three flashes indicate the transmission pickup, four flashes indicate to check the LED's. The small LED at the bottom right of the three digit display has no diagnostic function. The small LED will always be ON. Service personnel should always view the diagnostic window with the small LED at the bottom right of the three digit display.

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3 3 1

2

181

• TCS valve

The Traction Control System (TCS) valve is mounted inside the rear of the right frame rail. Two solenoids are mounted on the valve.

1. Selector solenoid

Electrical signals from the TCS electronic control cause the selector solenoid valve (1) to shift and select either the left or right parking brake. If the selector valve shifts to the left parking brake hydraulic circuit, the control oil is drained. The left reducing spool of the control valve can then shift and engage the parking brake.

2. Proportional solenoid

The proportional solenoid valve (2) controls the volume of oil being drained from the selected parking brake control circuit. The rate of flow is controlled by a signal from the TCS electronic control.

3. Left and right parking/secondary brake pressure taps

The pressure taps (3) can be used to measure the left and right parking/secondary brake pressure when performing diagnostic tests on the TCS.

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TRACTION CONTROL SYSTEM (TCS) ENGINE RUNNING/BRAKES RELEASED

BRAKE SWITCH

TEST SWITCH

SPEED DISTRIBUTOR

LEFT DRIVE AXLE

INPUT SIGNALS

BALL CHECK

TRANSMISSION SPEED SENSOR

ORIFICE

OUTPUT SIGNALS

SCREEN SELECTOR SOLENOID PARKING BRAKE VALVE RIGHT DRIVE AXLE PROPORTIONAL SOLENOID

182 • TCS operation with brakes RELEASED

Shown is the TCS with the engine running and the brakes RELEASED. When the machine is started: • Oil flows from parking brake release section of the pump through the oil filter where the flow is divided. One line from the filter directs oil to the parking and secondary brake valve. The other line sends oil to the pump signal port (right end of signal piston) of the TCS control valve. • Oil flow to the TCS control valve causes the ball check piston to move to the left and unseat the drain ball check valve. Opening the drain ball check valve opens a drain passage to the hydraulic tank.

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When the operator releases the parking brakes: • Air pressure is increased at the parking brake valve forcing the valve spool down. • Parking brake release oil can now flow through the parking and secondary brake valve to the TCS control valve. • In the control valve, oil closes the parking/secondary ball check valve and flows through the screen. • Oil flows through the right and left brake control circuit orifices. • Oil flows to the ends of the left and right brake reducing valve spools. • When the control circuit pressure is high enough, the reducing spools shift toward the center of the TCS control valve and parking brake release oil flows to release the brakes.

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TRACTION CONTROL SYSTEM (TCS) ENGINE RUNNING/LEFT BRAKE ENGAGED

BRAKE SWITCH

TEST SWITCH

SPEED DISTRIBUTOR

LEFT DRIVE AXLE

INPUT SIGNALS

BALL CHECK

TRANSMISSION SPEED SENSOR

ORIFICE

OUTPUT SIGNALS

SCREEN SELECTOR SOLENOID PARKING BRAKE VALVE RIGHT DRIVE AXLE PROPORTIONAL SOLENOID

183 • TCS operation with left brake ENGAGED

Shown is the TCS with the engine running and the left brake ENGAGED. When signals from the sensors indicate that the left wheel is spinning 60% faster than the right wheel, the following sequence of events occurs: 1. The TCS sends a signal to the selector solenoid valve and the proportional solenoid valve. 2. The selector solenoid valve opens a passage between the outer end of the left brake pressure reducing valve and the proportional solenoid valve. 3. The proportional solenoid valve opens a passage from the selector solenoid valve to drain. The proportional solenoid valve also controls the rate at which the oil is allowed to flow to drain. 4. Control circuit oil drains through the selector valve and enters the proportional valve.

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5. The reducing valve spool for the left parking brake shifts and blocks the flow of oil to the parking brake. 6. Oil in the left parking brake control circuit begins to drain. 7. The left parking brake begins to ENGAGE. 8. The left brake orifice restricts the flow of oil from the parking brake valve.

When the signals from the sensors indicate that the left wheel is no longer spinning, the following occurs: • The TCS stops sending signals to the selector solenoid and the proportional solenoid. • The selector solenoid valve and proportional solenoid valve block the passage to drain and allow the control circuit pressure to increase. • The left brake reducing valve spool shifts to the center position and blocks the passage to drain. • Parking brake release oil is directed to the left parking brake and the brake is RELEASED.

INSTRUCTOR NOTE: More detailed information about the Traction Control System (TCS) can be found in the Service Manual Module "Automatic Electronic Traction Aid" (Form SENR2986) and the Technical Instruction Module "Automatic Electronic Traction Aid" (Form SEGV2585).

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184

CONCLUSION This presentation has provided a basic introduction to the Caterpillar 793C Off-highway Truck. All the major component locations were identified and the major systems were discussed. When used in conjunction with the service manual, the information in this package should permit the serviceman to analyze problems in any of the major systems on these trucks.

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SLIDE LIST 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41.

Model view (left side) Model view (right side) Model view (front) Model view (rear) Subtitle slide--Walk Around Inspection Front wheel Wheel breather and suspension breathers Rear brake coolers and other filters Hydraulic tank Final drive Rear axle housing Body up retaining cable Fuel tank Primary fuel filter and drain Torque converter and transmission sight gauges Torque converter outlet screen Brake cylinder breather Front brake oil cooler filters Front suspension cylinder and air dryer Engine oil filters Engine oil change connector Secondary fuel filters Manual shutdown switch Air filters Shunt tank Air tank, grease tank and steering tank Steering tank Secondary brake reservoir drain Operator's station/shift console Operator's station/center console Operator's station/light switches Operator's station/instrument panel Operator's station/VIMS VIMS component diagram Operator's station/fuse panel Operator's station/ET laptop Operator's station/VIMS laptop Operator's station/hoist lever control Operator's station/steering column Operator's station/pedals Engine/right side

42. Electronic engine control system diagram 43. ADEM II electronic control 44. Atmospheric pressure sensor 45. 3516B improvements 46. Fuel filter restriction switch 47. Crankcase pressure sensor 48. 3516B improvements 49. 3516B improvements 50. 3516B improvements 51. Engine oil pre-lubrication 52. Variable speed fan control 53. Engine oil renewal system 54. Engine oil level sensors 55. Exhaust bypass control 56. Shunt tank 57. Radiator 58. Engine (front) 59. Coolant flow switch 60. Oil coolers 61. Rear brake oil coolers 62. Jacket water coolant flow circuit 63. Engine (left side) 64. Rear aftercooler sensor 65. Front brake oil cooler 66. Aftercooler coolant flow circuit 67. Engine oil pump 68. Engine oil filters 69. Engine oil system flow circuit 70. Primary fuel filter 71. Fuel transfer pump 72. Secondary fuel filters 73. Fuel pressure regulator 74. Fuel system flow circuit 75. Air filters 76. Turbo inlet sensor 77. Turbochargers 78. Exhaust temperature sensors 79. Exhaust system flow circuit 80. Subtitle slide--Power Train 81. Torque converter 82. Torque converter (converter drive) 83. Torque converter (direct drive)

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SLIDE LIST 84. Transmission, transfer gears and differential 85. Transmission (section) 86. Differential 87. Rear axle flow control valve 88. Rear axle 89. Rear axle flow control valve 90. Rear axle cooling system schematic 91. Double reduction planetary (section) 92. Torque converter/transmission pumps 93. Transmission scavenge screen 94. Torque converter suction screen 95. Torque converter charging filter 96. Torque converter inlet relief valve 97. Torque converter outlet relief valve 98. Transmission charging filter 99. Torque converter lockup valve 100. Torque converter lockup circuit 101. Transmission control and solenoids 102. Transmission ICM control 103. Transmission ICM hydraulic circuit 104. Transfer gears 105. Torque converter/transmission hydraulic circuit 106. EPTC II input/output diagram 107. EPTC II 108. EPTC II diagnostic window 109. ET laptop computer 110. Shift solenoids and actual gear switch 111. Subtitle slide--Steering System 112. Steering tank and filter 113. Steering pump 114. Steering valves 115. Steering accumulator charging valve 116. Steering pump (during charging) 117. Steering pump (low pressure standby) 118. Accumulator charging valve (during charging) 119. Accumulator charging valve (low pressure standby) 120. Accumulator charging valve (beginning of cut-in) 121. Steering solenoid and relief valve

122. Steering solenoid and relief valve (section) 123. Steering directional valve 124. Steering directional valve (hold) 125. Steering directional valve (right turn) 126. Hand metering unit 127. Hand metering unit (neutral) 128. Hand metering unit (right turn) 129. Steering accumulators 130. Steering bleed down control 131. Subtitle slide--Hoist System 132. Hoist lever switch 133. Hoist lever sensor 134. Hydraulic tank 135. Hydraulic tank screens 136. Hoist pumps 137. Hoist control valve (rear) 138. Hoist control valve (left side) 139. Hoist control valve (hold) 140. Hoist control valve (raise) 141. Hoist counterbalance valve 142. Hoist control valve (lower) 143. Hoist control valve (float) 144. Front brake oil cooler filters 145. Front brake oil cooler 146. Hoist cylinders 147. Hoist system circuit 148. Subtitle slide--Air System and Brakes 149. Oil cooled brake (section) 150. Operator's station/center console 151. Operator's station/steering column 152. Operator's station/pedals 153. Air compressor and governor 154. Air dryer 155. Service air reservoir (right platform) 156. Secondary air reservoir (behind cab) 157. Pressure protection valve 158. Air charging system 159. Secondary brake valve 160. Parking brake release valve 161. Brake pumps 162. Parking brake release filter 163. Towing system

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SLIDE LIST 164. Parking and secondary brake air system 165. Front of cab/service and retarder brake valves 166. Relay valves, brake cylinders and makeup tank 167. Brake cylinders and makeup tank 168. Front brake oil cooler diverter valve 169. Brake cylinder (engaged) 170. Slack adjuster 171. Slack adjuster (section) 172. Service brake and retarder air system 173. Brake cooling circuit 174. ARC system diagram 175. ARC control box 176. ARC diagnostic window 177. TCS control box (old and new) 178. TCS control box 179. TCS system diagram 180. TCS diagnostic window 181. TCS valve 182. TCS system (brakes released) 183. TCS system (brakes engaged) 184. Model view

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Serviceman's Handout No. 1

793C SERVICE TOOLS MAINTENANCE 2P8250 4C5084 4C9301 4C4911 1U9921 5P0957 5P3514 9U5617 5P8610 7S5437 7S9394 7F8240 1P0545 6V4040 1U5551 5P1720

Filter Strap Wrench Filter Cutting Tool Coolant Conditioner Test Kit Battery Load Tester Battery Post Cleaner Coolant and Battery Tester (°F) Coolant and Battery Tester (°C) Suspension oil fill unit Nitrogen Charging Adapter (for charging two suspension cylinders) Nitrogen Charging Group Tire Fill Air Hose (6 ft. long) Tire Valve Repair Tool Tire Gauge Nitrogen Tire Inflation Kit Valve Extension (for charging steering accumulators) Seal Pick

ENGINE 9S9082 4C8241* 1U5440 1U5470 9U5132

Engine Turning Tool Valve Lash Setting Gauge Fuel Flow Monitor Group Engine Pressure Gauge Group Injector Height Tool Group

*3500B engines require the 125-2744 Base instead of the 125-2742 Base used with 3500 engines.

ELECTRONIC CONTROL DIAGNOSTICS Laptop Computer for VIMS/Electronic Technician IBM Compatible Computer with DB-9 or DB-25 Pin RS-232 Serial Port Vital Information Management System (VIMS) JERD2093 Caterpillar Common Services Software JERD2137 VIMS Software License JERD2138 VIMS Software Subscription JERD2139 VIMS Software Subscription (additional copies) 127-9797 VIMS Computer to Truck Adapter Cable

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Serviceman's Handout No. 2

ELECTRONIC CONTROL DIAGNOSTICS Electronic Control Analyzer Programmer (ECAP) 8T8697 ECAP NEXG4521 Machine Functions Service Program Module (SPM) for ECAP 7X1700* Communication Adapter NEXG4523* Service Program Module (SPM) for Communication Adapter 139-4166* ECAP/ET Cable (connects Communication Adapter to machine; can also be used for Flash programming) 7X1420 ECAP Cable (earlier ECAP plastic port 1) 7X1851 ECAP Cable (current ECAP metal port 1) 7X1703 Holder for Communication Adapter 7X1180 ECAP Internal Expansion Board 7X1695* Timing Probe Cable 6V2197* Timing Probe Magnetic Pickup 6V3093* Timing Probe Adapter Sleeve *Also required to run ET. Electronic Technician (ET) JERD2124 Electronic Technician (ET) Software License (alternate to ECAP) JERD2129 ET Software Subscription (Engines and Machines) JERD2142 ET Software Subscription (Machines Only) 7X1425 ET Adapter Cable (connects ET to Communication Adapter) LERQ3133 HyperACCESS/5--Flash File Download Software ELECTRICAL 4C3406 9U7246 1U5804 6V3000 1P2305 8T0900 6V7070 9U7330 8T3224 7X1710 4C9024 9U7560 5P4205

Deutsch Connector Kit (HD10 with crimp tool) Deutsch Connector Kit (DT no crimp tool) Deutsch Connector Crimp Tool (part of 4C3406) Sure Seal Repair Kit Terminal and Connector Repair Kit AC/DC Clamp-on Ammeter Digital Multimeter (Beckman) Fluke 87 Digital Multimeter (reads Pulse Width Modulation PWM on EUI/ARC/VIMS) Multimeter Probes (for checking CE connectors) Signal Reading Probe Group (spade slides in connectors) Service Tool and Soldering Iron Battery Field Soldering Iron Group (used with 4C9024) 5/32 T-handle Allen wrench for DRC connectors

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Serviceman's Handout No. 3

POWER TRAIN 8T5200 6V4157 6V6064

Signal Generator (substitutes transmission/engine speed signals) Transmission/Hydraulic System Pressure Gauge Group Test Cover (top of ICM transmission)

TEMPERATURE MEASUREMENTS 4C6500 8T2844 4C6090 6V9130 8T5334 123-6700

Digital Thermometer Group Temperature Recorder Stickers Multichannel Temperature Selector Group Temperature Adapter Group (for Digital Multimeter) Surface Temperature Probe Infrared Thermometer with Laser Sight

MISCELLANEOUS 1U5481 1U5482 4C4892 8T5320 5P1404 1U5000 1U5525 1U8869 6V6042 8T5096 8T1000 FT1975

Pressure Gauge Group Pressure Adapter Group for 1U5481 ORFS Fitting and Gauge Group Hydraulic Test Group (contains blocker plates) Adapter (7/8-14 x 9/16-18 for brake bleed port) Auxiliary Power Unit (gas engine pump for towing) Auxiliary Power Unit Attachment Group Digital Dial Indicator Dial Indicator Contact Group Magnetic Dial Indicator Group Digital Positioner Group Suspension Gauge Block Stop Watch

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Serviceman's Handout No. 4

VIMS KEYPAD OPERATIONS - Scroll parameters monitored by VIMS by depressing the GAUGE key. - Payload Monitor ON/OFF

PAYLOAD

7295623

- Calibrate Payload Monitor

PAYCAL

729225

- Payload Resettable Totals

TOT

868

- Reset Displayed Data

RESET

73738

- Display Self Test

TEST

8378

- Reset Service Light

SVCLIT

782548

- Set Lube Cycle Times

LUBSET

582738

- Manual Lube

LUBMAN

582626

- Show Acknowledged Events

EACK

3225

- Show Event Statistics

ESTAT

37828

- Show Event List

ELIST

35478

- Start Event Recorder

EREC

3732

- Start/Stop Data Logger

DLOG

3564

- Reset Data Logger

DLRES

35737

- Odometer Set/Reset (requires VIMS PC connection)

ODO

636

- Machine Status

MSTAT

67828

- Change Language

LA

52

- Change Units

UN

86

- Change Backlight

BLT

258

- Change Display Contrast CON (requires Updated Message Center)

266

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INSTRUCTOR NOTES

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INSTRUCTOR NOTES

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INSTRUCTOR NOTES

SESV1682 3/97

Printed in U.S.A.