777F OEM Off-Highway Truck Caterpillar

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Personal injury or death could result when towing a disabled machine incorrectly. Block the machine to prevent movement before releasing the brakes. The machine can roll free if it is not blocked.

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Extended operation of the secondary steering motor could damage the motor and result in loss of emergency steering capability, which could cause injury or death. The Secondary Steering System should not be used for towing the machine or for other service procedures lasting longer than 5 minutes. The motor should be allowed to cool to ambient temperatures before reuse.

The parking brakes are spring-applied. The parking brakes are released by brake oil pressure.

Under normal conditions, the parking brakes are released by brake oil pressure that is stored in the secondary brake accumulator. The brake oil pressure in both brake accumulators is developed when the engine is running. Without adequate brake oil pressure in the secondary brake accumulator, the parking brakes are engaged and the machine cannot be moved.

When the engine is inoperable and the brake oil pressure from the service brake accumulator is depleted, the service brakes will not function and the secondary brake pedal will only apply braking force to the rear wheels.

Note: When the engine start switch is moved to the OFF position, solenoid valves will fully deplete the brake oil pressure from both brake accumulators.

Note: If the engine start switch remains in the ON position, and the transmission control is in the PARK position, a solenoid valve will only deplete the brake oil pressure from the secondary brake accumulator.

When the engine is inoperable and the brake oil pressure from the secondary brake accumulator is depleted, the parking brakes can be released by brake oil pressure that is developed by the brake release/secondary steering pump and then routed through the diverter valve.

When the parking brake is released by brake oil pressure through the diverter valve, only the secondary brake pedal can be used to stop the machine.

For more information on the braking system, refer to Operation and Maintenance Manual, "Braking".

In order to tow the machine with an inoperable engine, perform the following steps:

1. Place the transmission control in the PARK position and place the engine start switch in the ON position. Refer to Operation and Maintenance Manual, "Operator Controls" for more information.

2. Chock the wheels.
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   Illustration 1	g01280540

3. The diverter valve must be shifted in order to supply brake oil to the parking brake release valve.

   Loosen clamp bolts (3) on the diverter valve. Slide plate (2) and spool (1) to the left. After the spool is shifted, tighten the clamp bolts.

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   NOTICE
   Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat products. Dispose of all fluids according to local regulations and mandates.

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   Illustration 2	g01389500
   View of the inside left frame rail at the rear of the machine The truck body or the water tank is removed for ease of viewing.

4. If the machine is equipped with the Traction Control System (TCS), the pilot supply line from the traction control valve must be capped. This will minimize the bleeding down of the parking brake release oil pressure.

   Remove pilot supply line (4) from fitting (5). Install 6V-9829 Cap As on the fitting and install 6V-9508 Plug in the pilot supply line.

5. Use a coupler and a hose to connect a 8T-0857 Pressure Gauge to one of the following pressure taps:
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   Illustration 3	g01280712
   Top view of differential

   1. If the machine is not equipped with the Traction Control System (TCS), use pressure tap (6A).
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      Illustration 4	g01280616
      Two pressure taps are located on the TCS valve that is mounted to the left inside rear frame rail.

      Note: Either one of the pressure taps is suitable for a pressure gauge connection.

   2. If the machine is equipped with TCS, use pressure tap (6B).

6. Hook up the towing machine and tighten the tow line or tow bar. Refer to Operation and Maintenance Manual, "Towing the Machine" for guidelines.

7. Move the transmission control to the NEUTRAL position.
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   Illustration 5	g01637474

8. Press the brake release/secondary steering switch (7) in order to activate the pump. Hold the switch until the pressure stops rising on the pressure gauge that was installed in Step 5.

   Note: An electric pump supplies brake oil pressure in order to disengage the parking brakes. This pump also supplies oil to the secondary steering system.

9. While you depress the brake release/secondary steering switch, rotate the steering wheel to each side in order to check the steering.

10. Apply the secondary brake pedal on the disabled machine in order to check the braking.

11. Remove the wheel chocks.

12. Pull the disabled machine with the towing machine.

    1. Whenever you steer the disabled machine, depress the brake release/secondary steering switch.

    2. During towing, continue to watch the pressure gauge that was installed in Step 5. As the parking brake release oil pressure decreases, depress the brake release/secondary steering switch. Momentarily hold the brake release/secondary steering switch in order to provide adequate brake oil pressure and prevent the engagement of the parking brake. The pressure will decrease after approximately 30 to 45 seconds.