Pilot Pressure to the Main Control Valve - Check

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Testing and Adjusting

966H Wheel Loader and 972H Wheel Loader Electrohydraulic System Media Number -RENR8858-10

Publication Date -01/10/2011

Date Updated -24/10/2011

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Pilot Pressure to the Main Control Valve - Check SMCS - 5051-535-PX ; 5059-535-PX Table 1

Required Tools Part Number

Description

Qty

1U-5481

Pressure Gauge Group

1U-5482

Pressure Adapter Group

1

(1)

1

8S-7630

(2)

Stand

2

8S-7641

(2)

Tube

2

8S-8048

(2)

Saddle

2

8S-7615

(2)

Pin

2

(1) (2)

The 198-4240 Digital Pressure Indicator is also available.

Optional Tooling

Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the attachments have been lowered, oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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Sudden movement or accidental starting of the machine can cause personal injury or death to persons on or near the machine. To prevent personal injury or death, perform the following: Park the machine on a smooth, level surface. Lower the work tool to the ground and engage the parking brake. Stop the engine and remove the key. Block the wheels and install the steering frame lock.

NOTICE Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Caterpillar Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates.

Machine Preparation for Troubleshooting 1. Park the machine on a smooth, level surface. Move the machine away from other operating machines and away from personnel. 2. Permit only one operator on the machine. Keep all other personnel away from the machine or in the operator's sight. 3. Position the work tool on the ground. 4. Engage the parking brake.

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Illustration 1

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5. Place the steering frame lock in the LOCKED position. ReferenceFor more information about preparing the machine for troubleshooting, refer to the Service Manual module Testing and Adjusting, "Machine Preparation for Troubleshooting" for the machine that is being serviced.

Pressure Test

Illustration 2

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1. Position the lift arms on the stands.

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Illustration 3

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Front guard

2. Ensure that the engine start switch is in the OFF position. Remove the front guard in order to access the main control valve.

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Illustration 4

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Main control valve (1) Pressure reducing valve (2) Pressure tap

3. Install a 8T-0850 Pressure Gauge from 1U-5481 Pressure Gauge Group or a 198-4240 Digital Pressure Indicator to pressure tap (2) on the main control valve. 4. Start the engine and warm the hydraulic oil to a normal operating temperature of approximately 49 to 65°C (120 to 150°F). 5. Run the engine at high idle. Raise the work tool until the lift cylinders are fully extended. 6. Observe the pressure gauge while the lift cylinders are fully extended. 7. The pressure reading should be at least 3515 ± 345 kPa (510 ± 50 psi). 8. When pressure is checked, position the lift arms on the lift arm supports. 9. If the pressure is correct, turn the engine start switch to the OFF position. a. Release the hydraulic pressure. Refer to the Service Manual module Testing and Adjusting, "System Pressure - Release". b. Remove the test equipment from the machine. Install the front guard.

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c. Start the engine and remove the lift arms from the stands. Position the work tool on the ground and turn the engine start switch to the OFF position. 10. If the pilot oil pressure is not correct, turn the engine start switch to the OFF position. If the pressure reading is not within specifications, there are several possible causes: • The pressure reduction valve for the pilot system needs to be adjusted. • Pressure reduction valves for the pilot system need to be replaced or a seal may be damaged. • The piston pump (implement)(pilot) is worn. The pump needs to be replaced. • Proportional solenoids require calibration. • The valve for the dead engine lower is leaking. • A damaged seal in one of the proportional valves in the pilot valve • The solenoid valve (hydraulic lockout) may be leaking. There may be a damaged seal. In order to adjust the pressure reducing valve, refer to the instructions below on adjusting the pressure reducing valve. ReferenceFor information about replacing the Piston Pump (Implement)(Pilot), refer to the Service Manual module Disassembly and Assembly, "Piston Pump (Implement)(Pilot) - Remove" and Disassembly and Assembly, "Piston Pump (Implement)(Pilot) - Install". ReferenceFor additional information on calibrations for the operator monitor, refer to the Service Manual module Testing and Adjusting, "Position Sensor for the Electrohydrualic Control Levers (Operator Monitor) - Calibrate, Position Sensor for the Lift Linkage (Operator Monitor) Calibrate, Position Sensor for the Tilt Linkage (Operator Monitor) - Calibrate, Position Sensor for the Joystick Control (Operator Monitor) - Calibrate, Main Control Valve (Operator Monitor) Calibrate". ReferenceFor additional information on calibrations for the Caterpillar Electronic Technician, refer to the Service Manual module Testing and Adjusting, "Position Sensor for the Electrohydraulic Control Levers and Joystick (Electronic Technician) - Calibrate, Position Sensor for the Lift and Tilt Linkage (Electronic Technician) - Calibrate, Main Control Valve (Electronic Technician) - Calibrate". ReferenceFor additional information on testing the valve for the dead engine lower, refer to Testing and Adjusting, "Pilot Oil Accumulator (Dead Engine Lower) - Test and Charge".

Adjusting the Pressure Reducing Valve

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Illustration 5

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Pressure reducing valve (1) (3) Adjustment screw (4) Locknut

1. 282-4349 Pressure Reducing Valve (1) reduces the pressure to the pilot system. 2. Before adjusting 282-4349 Pressure Reducing Valve (1) , release the hydraulic system pressure. Refer to Testing and Adjusting, "System Pressure - Release". 3. Ensure that the work tool is on the ground or that the lift arms are positioned on the lift arm supports. Turn the engine start switch to the OFF position. 4. Always, turn adjustment screw (3) clockwise in order to adjust the pressure. This will compensate for any internal friction inside the valve that would oppose the setting of the bias spring. For example, if the adjustment screw needs to be turned counterclockwise by 1/2 turn in order to decrease the pressure, turn the adjustment screw counterclockwise by one full turn. Then, turn the adjustment screw clockwise by 1/2 turn. 5. Loosen locknut (4) . Turn adjustment screw (3) clockwise in order to increase the pressure setting. One turn will increase the relief valve setting by 515 kPa (75 psi). Turn adjustment screw (3) counterclockwise in order to decrease the pressure setting of the relief valve. One turn will decrease the relief valve setting by 515 kPa (75 psi). 6. After adjustment screw (3) is turned for an adjustment, hold adjustment screw in place and tighten locknut (4) to a torque of 12 ± 2 N·m (106 ± 18 lb in). 7. Repeat Steps 5 through 9. 8. If pressure setting is not correct, repeat Steps 4 through 6. 9. If 282-4349 Pressure Reducing Valve (1) requires replacement, release the hydraulic system pressure. Refer to Testing and Adjusting, "System Pressure - Release". When a new

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reducing valve is installed, tighten the valve to a torque of 50 ± 5 N·m (37 ± 4 lb ft). Torque for the locking nut on the reducing valve is approximately 12 ± 2 N·m (106 ± 18 lb in). Copyright 1993 - 2013 Caterpillar Inc. All Rights Reserved.

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