770G and 772G Off-Highway Truck Systems Caterpillar

Main Relief Valve for the Secondary Steering

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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.

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. Continue turning the steering wheel against the cylinder 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) to 93 °C (200 °F).

2. Stop the engine.
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   Illustration 1	g03499576

3. Install a 198-4240 Digital Pressure Indicator with the 198-4238 Pressure Sensor at the pressure tap (1) for the steering system. Pressure tap (1) is located along the RH frame in the line between the steering manifold and the HMU.

4. With the operator in the cab, depress the towing pump switch on the console. Turn the steering wheel to the left to full lock. Check the secondary steering pressure. The pressure setting for the secondary steering is 17300 ± 400 kPa (2500 ± 60 psi).
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   Illustration 2	g02715023

5. If the pressure needs to be adjusted, stop the secondary steering pump to minimize oil loss during the adjustment process. Using a back-up wrench on the cartridge valve body, remove plug (3) on the secondary steering relief valve (4). The secondary steering relief valve is located on steering disable check valve (2). The steering disable check valve is located behind the front right tire.

   1. Use a wrench as a backup to hold the relief valve body from rotating during plug removal.

   2. Loosen the socket plug with an 8mm internal Allen socket or wrench.

   3. Adjust the set screw below the cap to proper setting. The adjuster screw of secondary relief valve (4) is located under the removed plug (3). With an allen wrench, rotate the setscrew clockwise by 1/4 turn in order to raise the pressure. Rotate the setscrew counterclockwise by 1/4 turn in order to lower the pressure.

   4. Using the backup wrench on the valve body, reinstall plug (3).

   5. With secondary steering pump on and steering wheel held to full steering lock, confirm the pressure setting is correct to 17300 ± 400 kPa (2500 ± 60 psi). Repeat Step 5.a to Step 5.e if further adjustment is required.

6. Remove the test equipment after the pressures are correct.