777E and 777F Off-Highway Truck Power Train Caterpillar

Illustration 1	g01263621
Basic diagram for the power train system

The troubleshooting for the torque converter hydraulic system is divided into two sections:

• Torque converter

• Lockup clutch

This division is used to save time. The division makes finding the correct troubleshooting information easier.

Make reference to the following warning and pressure tap locations for all checks and tests.

If the problem area is not known, perform the checks and tests. Perform these checks and tests in order. For all of the tests, the oil must be at normal temperature of operation.

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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. Move the machine to a smooth horizontal location. Move the machine away from other machines and personnel.

2. Be certain that the transmission control is in the NEUTRAL position. Engage the parking brake. Stop the engine.

3. Permit only one operator on the machine. Keep all other personnel away from the machine or in the view of the operator.
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   Illustration 2	g00977541

4. Raise the body of the truck and install two retaining pins at the rear of the truck.

5. Make sure that all the hydraulic pressure is released before you attempt to loosen any fitting, hose or any component.

Transmission Speed and Torque Converter

Torque Converter Lines, Filter and Valves

Illustration 3	g01367943
Component locations (1) Transmission solenoids 1 through 7 (2) Transmission hydraulic control relief valve (3) Transmission lubrication relief valve (4) Transmission input speed sensor (5) Transmission section of hydraulic and transmission tank (6) Magnetic screen (7) Hydraulic section of hydraulic and transmission tank (8) Oil filter for the torque converter lockup clutch (9) Torque converter outlet relief valve (10) Torque converter inlet relief valve (11) Relief valve for the pilot control pressure (12) Torque converter (13) Pressure test port for the clutch modulating valve (14) Transmission output speed sensor 1 (15) Transmission output speed sensor 2 (16) Charge oil filter for the transmission (17) Charge oil filter for the transmission (18) Bypass check valve for the transmission cooler (19) Torque converter and transmission gear pump (20) Modulating valve for the torque converter lockup clutch (21) Charge oil filter for the torque converter (22) Brake and torque converter oil coolers (23) Transmission cooler

Illustration 4	g01367965
(11) Relief valve for the pilot control pressure

Illustration 5	g01367944
(9) Torque converter outlet relief valve (10) Torque converter inlet relief valve (20) Modulating valve for the torque converter lockup clutch (24) Pressure test port for the torque converter inlet pressure (25) Pressure test port for the torque converter outlet pressure (26) Pressure test port for the pilot pressure for the torque converter lockup clutch

Illustration 6	g01367945
(8) Oil filter for the torque converter lockup clutch (27) Outlet (28) Inlet (29) Oil sampling valve (30) Pressure test port (31) Bypass switch

Illustration 7	g01367949
(21) Oil filter for torque converter charging (32) Pressure test port (33) Inlet line (34) Outlet line