| 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. |
If the brake system has been disassembled or the oil has been drained the brake system should be refilled and purged of air. Use the applicable procedure in the following section to purge the brake system that is installed on your machine.
Purge Air from Brake Master Cylinder
The following steps explain the procedure and the parts that are required to purge the service brakes.
- Start the engine.
- Park the machine on level ground and lower the boom. Engage the parking brake.
- Place wheel blocks in front of the wheels and behind the wheels.
- Disengage the parking brake and stop the engine.
- Remove cover plate (1) and gasket (2) in order to gain access to the brake lines.
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| Illustration 1 | g00743542 |
Cover Plate for the Metering Pump (1) Cover plate (2) Gasket | |
- Disconnect the hydraulic return line (3) from the bulkhead fitting (4) and install a 6V-9508 Face Seal Plug in the open end of line (3) .
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| Illustration 2 | g00743546 |
Location of Brake Lines (3) Brake Return Line (4) Bulkhead Fitting (5) Hydraulic Line from the Joystick Control (6) Brake Line from the Master Cylinder to the Brake Cylinder (Boost) | |
- Connect a 6V-8934 Reducer (7) to bulkhead fitting (4). Connect a 7X-2444 Tee (8) to the reducer. Install a 6V-3965 Test Fitting (10) and a 6V-9828 Cap (9). Connect a 6V-7830 Pressure Gauge (11) to test fitting (10). This will leave two lines on the reservoir, line (5) from the joystick and line (6) from the master cylinder.
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| Illustration 3 | g00743548 |
Installation of the Pressure Gauge (4) Bulkhead Fitting (7) Reducer (8) Tee (9) Cap (10) Test Fitting (11) Pressure Gauge | |
- Attach 148-7109 Tube to the purge screw on the brake cylinder (boost). Place the free end of the tubing into a bucket.
Note: Before you attach the tube to the purge screw ensure that the purge screw is free of dirt.
- Loosen the purge screw on the brake cylinder (boost).
Note: You may observe some fluid leak from the purge screw. This is due to gravity. The leakage should be at low pressure.
- With the engine at low idle, move the joystick to the left and to the right. This will allow hydraulic fluid to move from the joystick to the reservoir. The reservoir will become pressurized. Check the pressure on the pressure gauge. Do not allow the pressure on the gauge to exceed 600 kPa (87 psi). The fluid flowing from the purge screw on the booster will appear pressurized and any air in the system may be observed leaving via the tube.
Note: The maximum allowed pressure in the reservoir will only be reached when the purge screw is closed off. While the brake system is purged, maintain a constant flow rate of oil. A reduced pressure will be observed on the pressure gauge.
- In conjunction to Step 10, depress the brake pedal several times. If the flow rate of oil from the purge screw drops, continue to move the joystick from left to right. This will repressurize the reservoir.
- Continue Steps 10 and 11 until the fluid from the purge screw on the booster has appeared clear for one minute. Approximately five minutes are needed to complete this procedure.
- Tighten the purge screw and remove the tubing from the booster. Remove the test equipment and connect the return line from the reservoir to the hydraulic tank.
Purge Air from the booster and Brake lines
- Attach 148-7109 Tube to one of the purge screws on the axle. Place the free end of the tube into a bucket.
- Loosen the purge screw on the axle.
- With the engine at low idle, begin to depress the brake pedal. This will cause the piston for the booster to stroke thus forcing oil from the booster and this will also force oil to the axle.
- Continue to depress the brake pedal for several minutes until the flow from the axle has appeared clear for one minute.
- Tighten the purge screw and remove the tubing.
- Repeat Steps 1, 2, 3, 4, and 5 on the second purge screw.
- Continue to depress the brake pedal for several minutes until the flow from the axle has appeared clear for one minute. This procedure should take less time.
- Move to the second axle and repeat Steps 1, 2, 3, 4, and 5 on the second purge screw.
After you have performed the above procedure and the brake pedal feels low, it may be necessary to allow the vehicle to sit for a short time. This allows any aerated oil to settle. Once the vehicle has sat for 30 minutes repeat the above procedures.
The Brake Pedal Degrades
The brake pedal is working correctly but the brake pedal degrades after one hour to 24 hours. This can be caused from a leak in the brake system. It is possible that a leak is present between two mating components. You should check that all connections are tight. An oil leak may not always be observed, unless the suspect connection is carefully examined under pressure. The oil may flow slowly and the oil may be observed at this point.