The secondary brake system utilizes the parking brake in order to apply braking force. When the parking brake is released by oil pressure from the diverter valve, the secondary brake system will not function.
If the truck needs to be towed with a dead engine, the diverter valve must be shifted manually. The diverter valve diverts oil flow from the electric secondary pump in order to release the parking brakes.
An auxiliary power unit must be used as a separate hydraulic source to the service brakes in order to provide any braking to the machine. Without an auxiliary power unit, the service brakes will only function until the service brake accumulators are exhausted.
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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. |
Reference: See Operation And Maintenance Manual, "Towing With Inoperable Engine" for more towing information.
| Required Tools | ||
|---|---|---|
| Part Number | Description | Required Amount |
| 6B-5072 | Terminal Bushing | 1 |
| 6V-3966 | Fitting As | 1 |
| 198-4240 | Digital Pressure Indicator | 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.
- Block the wheels.
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Illustration 1 g01221687 The wheel and the tire are removed for ease of viewing. - 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 plate (2) and the spool (3) to the left. After the spool is shifted, tighten the clamp bolts. This will allow supply oil to flow to the parking brake release valve.
Show/hide tableNOTICE 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 g01266313 View of the inside left frame rail behind the center tube
The truck body is removed for ease of viewing. - The return lines from the parking brake valve and the traction control valve must be capped in order to supply brake oil pressure.
Remove tank return line (4) from tee fitting (5). Install a cap on the tee fitting and install a plug in the tank return line.
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Illustration 3 g01265397 Top view of differential - Use a coupler and a hose to connect a 8T-0857 Pressure Gauge to pressure tap (4) 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 and tighten the tow line or tow bar. Refer to Operation and Maintenance Manual, "Towing the Machine" for guidelines.
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Illustration 4 g01253620 Show/hide table
Illustration 5 g01261568 (6) Quick Evac pump section
(7) Electric motor
(8) Parking brake release pump section
(9) Secondary steering pump section - An electric pump provides supply oil pressure in order to disengage the parking brakes. This pump also supplies oil to the secondary steering system and the pump is used for the Quick Evac system.
Press the brake release and secondary steering switch (5) in order to activate the pump. Hold the switch until the pressure on the pressure gauge that was installed in Step 5 stops rising.
- While you depress the brake release and secondary steering switch, rotate the steering wheel to each side in order to check the steering.
- Apply the service brake pedal on the disabled machine in order to check the braking. If the brakes are functioning, release the service brake pedal.
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Illustration 6 g01268870 - Connect the hydraulic output of a suitable auxiliary power unit to port (8) in order to charge the service brake accumulators with oil. Consult your Caterpillar dealer for more information.
Note: The service brake accumulators must remain charged in order to provide any braking for the machine.
- Apply the service brake pedal on the disabled machine in order to check the braking.
- Remove the blocks from the wheels.
- Move the transmission control to the NEUTRAL position.
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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.
- Whenever you steer the disabled machine, depress the brake release/secondary steering switch.
- During towing, continue to watch the pressure gauge that was installed in Step 5. Do not continue to tow the machine if the oil pressure is below
2760 kPa (400 psi) .
| NOTICE |
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Do not allow oil pressure to drop below Partial brake engagement could occur and can result in brake damage. Brakes must be fully released when towed machine is moving. |