777F Off-Highway Truck Hydraulic System Caterpillar

Note: Make sure that the filters and the screens are clean before you test any pressures. Make sure that the oil is at operating temperature before you perform this test.

Illustration 1	g01260245
(1) Pressure tap on the pump

Illustration 2	g01260375
(2) Tube assembly (3) Brake oil cooler relief valve

Illustration 3	g00532762
Section view of brake oil cooler relief valve (3) ( 3) Brake oil cooler relief valve (4) Shims

1. Connect 198-4240 Digital Pressure Indicator to pressure tap (1).

2. Remove tube assembly (2) from the hoist control valve.

3. Install a 2J-5608 Cover and install a 4J-0527 O-Ring Seal between tube assembly (2) and the hoist control valve.

4. Install tube assembly (2) with longer bolts.

5. Move the control lever for the hoist control to the HOLD position and start the engine.

   Note: Perform this test at low idle.

6. Look at the pressure gauge. The pressure reading should be 586 ± 14 kPa (85 ± 2 psi).

   Note: The pressure reading was the result of bench testing the relief valve at a flow rate of 38 L/min (10 US gpm). The flow rate of the pump at low idle is 167 L/min (44 US gpm). The resulting pressure may be higher than the value that is provided.

7. Stop the engine.

8. Remove the test equipment and install the original bolts in the hoist control valve.

Problem: The pressure is less than 586 ± 14 kPa (85 ± 2 psi).

Probable Cause

• Brake oil cooler relief valve (3) is stuck open.

• Brake oil cooler relief valve (3) is set too low. Add shims (4). Refer to Table 2.

Problem: The pressure is greater than 586 ± 14 kPa (85 ± 2 psi).

Probable Cause

• Brake oil cooler relief valve (3) is set too high. Remove shims (4). Refer to Table 2.