938H Wheel Loader and IT38H Integrated Toolcarrier Hydraulic System Caterpillar

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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.

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	g01409733

5. Place the steering frame lock in the LOCKED position.

Pressure Test

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Illustration 2	g01409734
Right side of articulation joint (1) Pump discharge pressure tap

1. Install an 8T-0850 Pressure Gauge from the 1U-5481 Pressure Gauge Group or a 198-4240 Digital Pressure Indicator to pressure tap (1) .

2. Start the engine. Warm the hydraulic oil to a normal operating temperature of approximately 49 to 65 °C (120 to 149 °F).

3. Run the engine at high idle. Raise the work tool off the ground. Fully extend the lift cylinders.

4. Observe the pressure gauge while the lift cylinders are fully extended.

5. The pressure reading should be 27580 ± 690 kPa (4000 ± 100 psi) on the 938H. The pressure reading should be 25500 ± 690 kPa (3700 ± 100 psi) on the IT38H.

6. After the pressure has been checked, retract the lift cylinders. Lower the work tool to the ground.

7. If the pressure is correct, turn the engine start switch to the OFF position.

   1. Release the pressure from the hydraulic system. Refer to Testing and Adjusting, "System Pressure - Release".

   2. Remove the test equipment from the machine.

8. If the pilot oil pressure is not correct, turn the engine start switch to the OFF position. Proceed to "Adjusting the Pressure Reducing Valve".

Adjusting the Signal Relief Valve

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Illustration 3	g00384713

1. Position the lift arms on the stands.

2. Turn the engine start switch to the OFF position.

3. Release the pressure from the hydraulic system. Refer to Testing and Adjusting, "System Pressure - Release".

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Illustration 4	g01409732

4. Remove front guard (2) in order to access the main control valve.

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Illustration 5	g01409731
(3) Signal relief valve

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Illustration 6	g01409735
Signal relief valve (4) Adjustment screw (5) Locknut

Note: Always turn adjustment screw (4) in a clockwise direction 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 a half of a turn in order to decrease the pressure, turn the adjustment screw counterclockwise by one full turn. Then, turn the adjustment screw clockwise by a half of a turn.

5. Loosen locknut (5). Turn adjustment screw (4) clockwise in order to increase the pressure setting of the valve. Turn the adjustment screw counterclockwise in order to decrease the pressure setting.

6. After adjustment screw (4) is turned for an adjustment, hold adjustment screw in place and tighten locknut (5) to a torque of 12 ± 2 N·m (105 ± 18 lb in).

7. Repeat the pressure test.

8. If the pressure is not correct, repeat Step 1 through Step 7.

9. If the pressure reducing valve requires replacement, release the pressure in the hydraulic system. Refer to Testing and Adjusting, "System Pressure - Release". When a new pressure reducing valve is installed, tighten the valve to a torque of 40 ± 5 N·m (30 ± 4 lb ft).

10. After the pressure is correctly set, reinstall front guard (2). Extend the lift cylinders. Remove the stands. Lower the work tool to the ground.