777F Off-Highway Truck Steering System Caterpillar

Relief Valve (Secondary Steering Backup) Test and Adjust

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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	g01257650
(1) Electric drive pump for the secondary steering and the brake release (2) Plug

Illustration 2	g02300173
Typical view of plug (2) on pump (1)

The main relief valve for the secondary steering is located behind plug (2) on electric drive pump (1) for the secondary steering and the brake release.

Illustration 3	g01525042
(3) Steering check and relief valve (4) Secondary system relief valve (5) Primary system relief valve

Illustration 4	g01522850
(3) Steering check and relief valve (4) Secondary system relief valve (5) Primary system relief valve (A) Pressure tap for steering system

The steering check and relief valve is located on the frame behind the right front suspension cylinder.

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 a temperature between 38 °C (100 °F) and 93 °C (200 °F).

2. Stop the engine.

Note: Backup relief valve (4) for the secondary steering has a higher pressure setting than the main relief valve for the secondary steering.

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.

3. Remove plug (2) from electric drive pump (1) for the secondary steering and the brake release. Use the setscrew that is located behind plug (2) in order to increase the pressure setting of the main relief valve for the secondary steering. Turn the setscrew clockwise. Approximately 3 turns of the setscrew will increase the pressure setting of the main relief valve for the secondary steering above the pressure setting of the backup relief valve for the secondary steering. Count the number of turns so that you can return the setscrew to the original setting.

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

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

Note: When the transmission gear selector is in P, friction from the wheel brakes will not allow the secondary steering system to turn the wheels all the way to the cylinder stops.

6. Place the transmission gear selector in N.

7. Check the pressure on the pressure gauge. The pressure setting of the backup relief valve for the secondary steering is 20700 ± 400 kPa (3002 ± 58 psi).

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Illustration 5	g01525114
(4) Back up relief valve for the secondary steering (6) Locknut (7) Setscrew

8. If the pressure needs to be adjusted, loosen locknut (6) . Use setscrew (7) to change the pressure setting.

9. With an allen wrench, rotate setscrew (7) clockwise by 1/4 turn in order to raise the pressure. Rotate setscrew (7) counterclockwise by a 1/4 turn in order to lower the pressure. Each 1/4 turn of setscrew (7) changes the pressure approximately 1183 kPa (172 psi).

10. Repeat Steps 7 through 9 until the pressure setting is correct.

11. When the pressure setting of backup relief valve (4) for the secondary steering is correct, adjust the pressure setting of the main relief valve for the secondary steering to the original pressure setting.

12. Install plug (2) . Remove the gauge from pressure tap (A) .

13. Put the transmission gear selector in P in order to apply the parking brakes.

Relief Valve (Secondary Steering Main) Test and Adjust

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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 6	g01257650
(1) Electric drive pump for the secondary steering and the brake release (2) Plug for the main relief valve for the secondary steering

Illustration 7	g02300174
Typical view of plug (2) on pump (1)

The electric drive pump for the secondary steering and the brake release is located on the frame behind the right front suspension cylinder.

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 a temperature between 38 °C (100 °F) and 93 °C (200 °F).

2. Stop the engine.

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

Note: With the transmission gear selector in the P position, friction from the wheel brakes will not allow the secondary steering system to turn the wheels all the way to the cylinder stops.

4. Place the transmission gear selector in theN position.

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Illustration 8	g01525142
(3) Steering check and relief valve (4) Secondary system relief valve (5) Primary system relief valve

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Illustration 9	g01522862
(3) Steering check and relief valve (4) Secondary system relief valve (5) Primary system relief valve (A) Pressure tap for steering system

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

6. Check the pressure on the pressure gauge. The pressure setting of the main relief valve for the secondary steering is 17225 ± 350 kPa (2498 ± 51 psi).

7. If the pressure needs to be adjusted, remove plug (2) for the main relief valve for the secondary steering. Use the setscrew that is located behind the plug to change the pressure setting.

8. With an allen wrench, rotate the setscrew clockwise by 1/4 turn in order to raise the pressure. Rotate the setscrew counterclockwise by a 1/4 turn in order to lower the pressure. Each 1/4 turn of the setscrew changes the pressure approximately 1288 kPa (185 psi).

9. Repeat Steps 7 through 8 until the pressure setting is correct.

10. Replace plug (2) for the main relief valve for the secondary steering and remove the test equipment.