69D and 769D Off-Highway Truck and 771D Quarry Truck Hydraulic System Caterpillar

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Personal injury or death can result from sudden machine movement. Sudden movement of the machine or release of air pressure or oil pressure can cause injury to persons on or near the machine. To help prevent possible injury before testing and adjusting any air system or hydraulic system, perform the procedure in the Testing and Adjusting, "General Information" section.

1. Start the engine. Operate the engine at high idle.

2. Move the hoist control to the RAISE position. Hold the hoist control in the RAISE position for five seconds after the dump body is fully raised. Then, lower the dump body all the way to the truck frame.

3. Repeat Step 2 until the temperature of the hydraulic oil is between 65 °C (150 °F) and 121 °C (250 °F).

Cycle Times for Hoist Cylinders

1. Lower the dump body to the truck frame.

2. Operate the engine at high idle.

3. Raise the dump body to the fully raised position. Use a stopwatch to measure the required time.

The required time for full extension of the hoist cylinders is 9 ± 1 seconds.

The required time for full lowering of the hoist cylinders is 7 ± 1 seconds.

With the body down snub function and the body float function in the OFF position, the required time for full lowering of the hoist cylinders is 7 ± 1 seconds.

Cylinder Drift

Note: Perform this test with an empty dump body and hydraulic oil above 38°C (100°F).

1. Move the hoist control to the RAISE position.

2. When the first stage of the hoist cylinders is extended by 305 mm (12 inch), move the hoist control to the HOLD position.

3. The dump body will push the cylinder head of the first stage by 6.35 mm (0.250 inch) onto the second stage of the hoist cylinders. Use a stopwatch and record the required time.

The acceptable time for cylinder drift is relative to the temperature of the hydraulic oil in the hoist cylinders. See Table 1 for the acceptable time.

Excessive cylinder drift can be caused by the following conditions:

• Leaks in the lines between the hydraulic oil tank and the hoist cylinders

• Worn control valve spool

• Worn seals in the hoist cylinders