793F AC Off-Highway Truck Hydraulic Fan and Steering System Caterpillar

Specifications

Introduction

The following test covers the instructions to test and adjust the pressure of the steering piston pump.

Required Tools

Illustration 1	g02571852

Machine Preparation

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Sudden movement of the machine or release of air or oil under pressure can cause possible injury or death to persons on or near the machine. To prevent possible injury or death, do the procedure that follows before testing and adjusting the Hydraulic System.

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

2. Move the shift control lever to the P position. Fully raise the dump body of the truck.

3. Install the retaining cables for the dump body.

4. Move the hoist control to the FLOAT position and lower the truck body until the cables are tight.

5. Move the hoist control to the HOLD position.

6. Stop the engine. Move the engine start switch to the OFF position.

   Note: The pressure will not be released from the steering accumulators when you use the battery disconnect switch or the engine shutdown switch.

7. While the engine is not running, turn the steering wheel completely in both directions. Continue to turn the steering wheel in both directions until the front wheels will not move.

8. Turn the engine start switch key to the ON position. Do not start the engine. Turn the engine start switch key to the OFF position.

   Note: This process releases any pressure that is in the solenoid valve which is used to purge the accumulator. Refer to Operation and Maintenance Manual, "Steering Accumulator Pressure - Release" for more information.

9. Ensure that all of the oil pressure is released before any fittings, hoses, or components are worked on.

10. 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.

11. Place wheel chocks in front of the wheels and behind the wheels.

12. Prior to the test, ensure that the following conditions are met:
    • All air is purged from the steering system

    • The steering system accumulators are precharged with nitrogen to 6890 kPa (1000 psi) at 21° C (70° F).

    • With engine off, the steering tank oil level should be filled to the full mark on the top sight glass.

    • After starting the engine, the steering tank oil level should drop to the full mark of the bottom sight glass within 1 minute.

Test Procedure

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Illustration 2	g03222577
(1) Pressure tap for the steering pump pressure

1. Installing Tooling (A) to pressure tap (1) .

2. Start the engine. Run the engine at low idle.

3. Check the pressure on tooling (A). Record the pressure in Table 1.

   If the pressure is not correct, refer to the "Adjustment Procedure".

4. Stop the engine and remove all test equipment.

Adjustment Procedure

Illustration 3	g02731340
Piston pump (steering) (1) Pump control valve (2) Adjustment screw

Steering piston pump pressure adjustments can be made at pump control valve (1) on the steering piston pump.

1. Perform the steps in the "Machine Preparation".

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Illustration 4	g02174554
(1) Pump control valve (2) Adjustment screw (4) Locknut

2. Remove the cap from adjusting screw (2) .

3. Loosen the locknut. Turn adjusting screw (2) clockwise in order to increase the discharge pressure of the steering piston pump. Adjust pump discharge pressure to target pressure. Tighten the locknut.

   Note: Always make pressure adjustments on the pressure rise.

4. Perform the "Test Procedure".