773G and 775G Off-Highway Truck Power Train Caterpillar

Show/hide table

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.

Introduction

This test will show the following conditions if the conditions exist:

• The transmission charging pump section is good.

• The main relief valve is correctly set.

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.

Required Tooling

Illustration 1	g02689417
Digital Pressure Indicator Group (A)

Machine Preparation

1. Move the machine to a smooth horizontal location. Move away from any machines that are working and any personnel.

2. Move the transmission control to the NEUTRAL position. Fully raise the dump body of the truck.

3. Activate the parking brakes. Stop the engine.

4. Permit only one operator on the machine. Either keep other personnel away from the machine, or keep other personnel in the sight of the operator.

5. Place blocks in front of the wheels and behind the wheels.

6. Install the retaining pin for the dump body.

7. Make sure that the transmission is in the NEUTRAL position.

8. Make sure that all air pressure and oil pressure is released before any fittings, hoses, or components are worked on.

9. Push the brake pedal many times until there is no brake pressure.

Test Procedure

Illustration 2	g02677838
View of the rear of the torque converter (1) Gear pump

Illustration 3	g02677844
View of the right side of the transmission (2) Pressure tap for the main relief valve (3) Main relief valve

1. Connect tooling (A) to pressure tap (2).

2. Start the engine while the parking brakes are engaged. Run the engine at the low idle rpm while the transmission is in NEUTRAL. Check the pressure on the digital pressure indicator group. Record the pressure in Table 2.

3. Run the engine at the high idle rpm while the transmission is in NEUTRAL. Check the pressure on tooling (A). Record the pressure in Table 2.

4. When this test is complete, stop the engine and remove the test equipment.

5. If the pressure is not within the specifications in Table 2, refer to the "Adjustment Procedure".

Adjustment Procedure

Illustration 4	g02681258
(3) Main relief valve (4) Cover (5) Adjustment screw

Use adjustment screw (5) in order to achieve the correct pressure.

Problem: The oil pressure is too low.

Probable Cause

• Failure of the transmission charging pump section

• The setting of main relief valve (3) is too low. Adjust the relief valve to the low idle setting.

Problem: The oil pressure is too high.

Probable Cause

The setting of main relief valve (3) is too high. Adjust the relief valve to the low idle setting.

Worksheet