| NOTICE |
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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, "Caterpillar Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates. |
Purge screws are installed for bleeding purposes on the check and pressure reducing valve, on the front slack adjuster, on the center slack adjuster, and on each wheel of the front and center axles.
The brake lines will need bleeding whenever the brakes have been serviced or whenever a hydraulic line has been opened.
After major service work has been completed, it will be necessary to bleed the entire brake system. Bleed the entire brake system in the following sequence:
- Bleed the brake lines to the service brake control valve.
- Bleed the brake lines between the service brake control valve and the slack adjusters.
- Bleed the brake lines between the slack adjusters and the wheel brakes.
If the engine has not started and if work has been restricted to the lines between the check and pressure reducing valve and the service brake control valve, only bleed that part of the system.
If the engine has not started and if work has been restricted to the lines between the service brake control valve and the slack adjusters, only bleed that part of the system.
If the engine has not started and if work has been restricted to the lines between the slack adjusters and the wheel brakes, only bleed the lines that have been opened.
Bleed the brake lines to the service brake control valve.
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| Illustration 1 | g00671008 |
Location of the Purge Screws on the Check and Pressure Reducing Valve | |
The check and pressure reducing valve is located under the hinged cover at the rear of the cab.
- Ensure that the parking brake is engaged and that the transmission is in the NEUTRAL position.
- Attach two lengths of clear plastic tube to the two purge screws on the check and pressure reducing valve. Secure the free ends of the clear plastic tube into a suitable container for oil.
- Start the engine and operate at low idle for a period of ten seconds. Do not operate the service brake control.
- Stop the engine.
- Open the two purge screws. A mixture of oil and air will flow from the two purge screws, through the clear plastic tubes and into the container. When the oil flow stops, close the purge screws immediately.
- Repeat steps 3 to 5 until the oil flows free of air.
- Remove the clear plastic tubes from the purge screws. Clean up any spillage of oil.
Bleed the brake lines between the service brake control valve and the slack adjusters.
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| Illustration 2 | g00671009 |
Location of the Purge Screw on the Front Brake Slack Adjuster | |
The front brake slack adjuster is located on top of the front axle.
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| Illustration 3 | g00671010 |
Location of the Purge Screw on the Center Brake Slack Adjuster | |
The center brake slack adjuster is located on top of the center axle.
- Ensure that the parking brake is engaged and that the transmission is in the NEUTRAL position.
- Attach a length of clear plastic tube to each of the two purge screws on the front and center brake slack adjusters. Secure the free ends of the two clear plastic tubes into a suitable container for oil.
- Start the engine and operate at low idle. Do not operate the service brake control.
- Open the two purge screws.
- Ask an assistant to press lightly on the service brake control. Keep the light pressure on the service brake control. A mixture of oil and air will flow from the two purge screws, through the clear plastic tubes and into the container. When the oil flows free of air, close the purge screws immediately.
- Release the service brake control and stop the engine.
- Remove the clear plastic tubes from the purge screws. Clean up any spillage of oil.
Bleed the brake lines between the slack adjusters and the wheel brakes.
Note: The engine must be stopped and the parking brake must be engaged before bleeding the brake lines between the slack adjusters and the wheel brakes.
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| Illustration 4 | g00671011 |
Location of the Purge Screw on the Wheels of the Front and Center Axles | |
- Attach a length of clear plastic tube to the purge screw on the wheel that has been serviced. Secure the free end of the clear plastic tube into a suitable container for oil.
- Ensure that the parking brake is engaged and that the transmission is in the NEUTRAL position. Start the engine and operate at low idle. Do not operate the service brake control.
- Open the purge screw.
- Ask an assistant to press lightly on the service brake control. Keep the light pressure on the service brake control. A mixture of oil and air will flow from the purge screw, through the clear plastic tube and into the container. When the oil flows free of air, close the purge screw immediately.
- Release the service brake control and stop the engine.
- Remove the clear plastic tube from the purge screw. Clean up any spillage of oil.