784C and 785C Off-Highway Truck/Tractors Power Train 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.

Illustration 1	g00365394
Torque converter outlet relief valve (1) Torque converter outlet relief valve (AA) Pressure tap for torque converter outlet pressure

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

• The torque converter operates correctly.

• Torque converter outlet relief valve (1) is correctly set.

Procedure

1. Install 9U-7400 Multitach Tool Group on the engine. The tool can measure the engine rpm with the following methods:

   • Photo pickup and reflective tape

   • Magnetic pickup

   • Tachometer generator

   Note: The Electronic Control Analyzer Programmer (ECAP) or the Electronic Technician (ET) can be used instead of the multitach.

2. At pressure tap (AA), connect 177-7862 Hose Assembly to the nipple. Connect 8T-0854 Pressure Gauge to the hose.

3. Start the engine. Run the engine at the low idle rpm in NEUTRAL-1.

4. The drive wheels must not turn during a stall test. Be certain that the air pressure is at the normal pressure for operation. Engage the parking brakes and the service brakes.

   Note: If the brakes do not keep the machine from moving, put the machine against a solid object that will not move.

5. Be certain that the oil is at the normal operating temperature 80° to 140°C (180° to 250°F).

6. Move the transmission control to the REVERSE position.

7. Slowly increase the engine rpm to the maximum governor setting. The machine will try to move.

8. The engine rpm must be 1640 ± 65 rpm with the torque converter in a stall condition.

9. The pressure on the gauge must be 345 to 550 MPa (50 to 80 psi).
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   NOTICE
   Do not keep the torque converter in a stall condition for long periods of time. Damage could occur in the torque converter, the engine, and the brakes.

10. When this test is complete, put the transmission control in NEUTRAL. Stop the engine. Remove the test equipment.

Problem: The engine speeds are out of specification

Probable Cause

Illustration 2	g00336118
Engine information plate

• The specifications may have changed. Refer to the engine information plate in order to see the performance specification for the engine. Refer to the Technical Marketing Information for the Engine. This can be found on the Caterpillar Service Information System (SIS).

• Refer to the engine system Troubleshooting, SENR1128, "P-312 Can Not Reach Top Engine RPM" for problems that involve the engine.

• The torque converter failed.

Problem: The high idle rpm and the torque converter outlet pressure is correct, but the stall speed is too high

Probable Cause

• The torque converter is bad.

• The engine has too much power.

Problem: The torque converter outlet pressure is too low and the oil gets too hot during normal operation

Probable Cause

Perform the test in the power train Testing and Adjusting, "Relief Valve (Torque Converter Inlet) Pressure - Test and Adjust".

Problem: The torque converter outlet pressure is too low

Probable Cause

Perform the test in the power train Testing and Adjusting, "Relief Valve (Torque Converter Inlet) Pressure - Test and Adjust".

Illustration 3	g00287213
Torque converter outlet relief valve (1) Torque converter outlet relief valve (2) Spacers

Problem: The torque converter outlet pressure is too high and the oil temperature is not too hot

Probable Cause

The setting of the torque converter outlet relief valve is too high. Remove spacers (2). Refer to Table 2.

Problem: The torque converter outlet pressure is correct and the oil gets too hot during normal operation

Probable Cause

Refer to the power train Testing and Adjusting, "Brake Oil Overheating Troubleshooting".