773D Off-Highway Truck and 775D Quarry Truck Caterpillar

Towing With Inoperable Engine

Usage:

773D 7CS

This machine is equipped with spring applied brakes. These brakes are released with hydraulic pressure. If the engine is inoperable or if the power train is inoperable, the parking brakes are engaged and the machine cannot be moved.

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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.

When possible, engage the parking brake.
Block the wheels.
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Illustration 1 g00520259
A diverter valve is located on the rear of the hydraulic tank. The diverter valve must be shifted in order to provide supply oil to the parking brake release valve.
Loosen two clamp bolts (1) on the diverter valve and slide the plate and the spool (2) to the left. After the spool is shifted, tighten clamp bolts (1). This will allow supply oil to flow to the parking brake release valve.
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Illustration 2 g00630038
Use a coupler and a hose to connect a 8T-0857 Pressure Gauge to one of pressure taps (3) at the rear of the machine.

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NOTICE

When towing the machine, attach tow line to the front tow hooks or rear tow pin only.
Hook up the towing machine. Refer to Operation and Maintenance Manual, "Towing the Machine" for guidelines.

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In order to prevent possible personal injury, release the air pressure from the air tank before disconnecting any components of the air system.

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NOTICE

Do not exceed the air pressure of 830 ± 35 kPa (120 ± 5 psi) or damage can occur to the air system components.

Note: The air pressure in the air system must be at 550 kPa (80 psi) in order to allow the supply oil to disengage the parking brakes.
If there is not sufficient air pressure in the air system, the air system can be charged with air from another source.
1. Before you attempt to charge the system, remove the air pressure from the brake system.
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  Illustration 3 g00629768
2. Remove the plug from the front side of air dryer housing (4). Install a quick connect fitting.
3. Connect a hose from an outside air supply to the fitting on the air dryer. Charge the reservoirs to at least 550 kPa (80 psi). Do not exceed 830 ± 35 kPa (120 ± 5 psi).
4. Remove the supply hose.
Disengage the parking brake.
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Illustration 4 g00629769
An electric drive pump provides supply oil pressure in order to disengage the parking brakes. This pump also supplies oil to the secondary steering system. Press brake release and secondary steering control switch (5) in order to activate the pump. Hold switch (5) until the pressure on the pressure gauge that was installed in Step 4 stops rising.
Apply the service brake on the disabled machine in order to check the braking. If the brakes are functioning, release the brakes.
While you depress brake release and secondary steering control switch (5), rotate the steering wheel to each side in order to check the steering.

Remove the blocks from the wheels.

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NOTICE

Do not allow oil pressure to drop below 2760 kPa (400 psi) while towing. Partial brake engagement could occur and can result in brake damage. Brakes must be fully released when towed machine is moving.

Pull the disabled machine with the towing machine. During towing, continue to watch the pressure gauge that was installed in Step 4. Do not continue to tow the machine if the oil pressure is below 2760 kPa (400 psi).