824H Wheel Dozer, 825H Soil Compactor and 826H Landfill Compactor Electrohydraulic 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.

2. Lower the blade to the ground.

3. Install the steering frame lock.

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Illustration 1	g00865989
Front Frame

4. The cover for the pilot valve is located on top of the front frame. Remove four bolts (2) that are holding the cover to the front frame. Remove cover (1) from the front frame.

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Illustration 2	g00866053
Typical Example of a Pilot Valve (Oil Manifold)

Note: The pilot valve in Illustration 2 is for the 824H Wheel Dozer. The valves for the 825H Soil Compactor and the 826H Landfill Compactor are similar. The pressure tap will be located in the "P3" port on all the pilot valves.

5. Attach a 8T-0856 Pressure Gauge with a 6V-4144 Coupler to pressure tap (5) .

Test With A Running Engine

1. Start the engine and run the engine at high idle until the hydraulic oil is at normal operating temperature. After the oil is at normal operating temperature, set the engine speed to low idle. Normal operating temperature for this test is approximately 49 ± 3°C (120 ± 5°F).

2. Observe the pressure gauge. The pressure reading should be approximately 3450 ± 200 kPa (500 ± 30 psi) at 21 ± 2 L/min (5.5 ± 0.5 US gpm).

3. If the pressure is correct, proceed to "Test with a Nonrunning Engine". If the pressure is incorrect, proceed to 4.

4. Release the pressure in the hydraulic system.

   Reference: Refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.

5. Adjust pressure reducing valve (3) or replace the pressure reducing valve. Refer to Illustration 2 for the location of the reducing valve.

6. When you replace the pressure reducing valve, tighten the valve to the following torque 60 ± 7 N·m (45 ± 5 lb ft).

7. When you make an adjustment to the pressure reducing valve, tighten the locking nut to the following torque 13 ± 1.5 N·m (115 ± 13 lb in).

8. Repeat Step 1 and Step 2 in order to verify that the pressure is correct.

Test With A Nonrunning Engine

1. Start the engine and run the engine until the hydraulic oil is at normal operating temperature. Normal operating temperature is approximately 49 ± 3°C (120 ± 5°F).

2. Lift the blade to the full RAISE position.

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

4. Observe the pressure gauge. The pressure reading should be approximately 2070 ± 200 kPa (300 ± 30 psi) at 21 ± 2 L/min (5.5 ± 0.5 US gpm).

5. If the pressure is correct, start the engine and lower the blade to the ground. Remove the test equipment and install the cover over the main control valve. If the pressure is incorrect, proceed to Step 6.

6. Start the engine and lower the blade to the ground.

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

8. Release the pressure in the hydraulic system.

   Reference: Refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.

9. Adjust pressure reducing valve (4) or replace the pressure reducing valve. When you replace the pressure reducing valve, tighten the valve to the following torque 60 ± 7 N·m (45 ± 5 lb ft). Refer to Illustration 2 for the location of the reducing valve.

10. When you replace the pressure reducing valve, tighten the valve to the following torque 60 ± 7 N·m (45 ± 5 lb ft).

11. When you make an adjustment to the pressure reducing valve, tighten the locking nut to the following torque 13 ± 1.5 N·m (115 ± 13 lb in).

12. Repeat Step 1 through Step 4 in order to verify that the pressure is correct.