777F Off-Highway Truck Steering System Caterpillar

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Personal injury or death can occur if personnel are trapped between the wheel and the frame. The steering system is hydraulically controlled and wheels can crush personnel during movement. Use caution when working between the wheels and the frame. If the wheels must be turned, ensure that all personnel are clear of the machine before any movement.

Illustration 1	g02300153
(1) Steering check and relief valve (2) Back up relief valve for the primary steering (SS) Pressure tap for the steering system

Steering check and relief valve (1) is located behind the right front suspension cylinder.

Illustration 2	g01254347
(3) Steering piston pump (4) Pressure compensator valve (5) High-pressure cutoff valve

Steering piston pump (3) is located behind the engine on the front side of the pump drive.

1. Operate the engine at HI IDLE. Turn the steering wheel to the right or turn the steering wheel to the left until the steering cylinder stop is reached. Then, continue turning the steering wheel against the stop. Hold the steering wheel in this position for 3 seconds and then release the steering wheel. Continue this step until the oil in the steering system reaches at least 38 °C (100 °F).

2. Stop the engine.

3. Install the 198-4240 Digital Pressure Indicator with the 198-4238 Pressure Sensor at pressure tap (SS) for the steering system. Pressure tap (SS) is located on steering check and relief valve (1) behind the right front suspension cylinder.

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Illustration 3	g01254353
(4) Pressure compensator valve (5) High-pressure cutoff valve (6) Cap (7) Locknut (8) Setscrew

Note: Backup relief valve (2) for the primary steering has a higher pressure setting than high-pressure cutoff valve (5) .

4. Remove cap (6) from setscrew (8) on high-pressure cutoff valve (5) .

5. Loosen locknut (7) of high-pressure cutoff valve (5) .

Note: Do not increase the pressure setting of the relief valve too much. If the pressure setting of the relief valve is set too high, damage to the components of the system could occur.

6. Increase the pressure setting of high-pressure cutoff valve (5) by turning setscrew (8) clockwise. Approximately 1.5 turns of setscrew (8) will increase the pressure setting of the high-pressure cutoff valve above the pressure setting of the backup relief valve for the primary steering. Count the number of turns so that you can return setscrew (8) to the original setting.

7. Start the engine.

8. Operate the engine at LOW IDLE. Check the pressure on the pressure gauge. The pressure setting of backup relief valve (2) for the primary steering is 26000 ± 400 kPa (3771 ± 58 psi).

9. If the pressure needs to be adjusted, stop the engine.

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Illustration 4	g00526792
(2) Back up relief valve for the primary steering (9) Locknut (10) Setscrew

10. Loosen locknut (9) of backup relief valve (2) for the primary steering.

11. With an allen wrench, rotate setscrew (10) clockwise by 1/4 turn in order to raise the pressure. Rotate setscrew (10) counterclockwise by a 1/4 turn in order to lower the pressure. Each 1/4 turn of setscrew (10) changes the pressure approximately 1183 kPa (172 psi).

12. Repeat Steps 7 through 11 until the pressure setting is correct.

13. When the pressure setting of backup relief valve (2) for the primary steering is correct, adjust the pressure setting of high-pressure cutoff valve (5) to the original setting.

    1. Turn setscrew (8) to the original setting.

    2. Tighten locknut (7) .

    3. Install cap (6) .