Air is removed from the brake system by pumping it with the brake pedal: an assistant is required to perform this work.
Attention: This is a description of the work steps for vehicles without ABS. Operations for braking systems of vehicles with ABS (anti-lock device) are given at the end of the section.
If the air must be removed from the entire system, then this is done separately on each wheel brake. This occurs when air has entered each brake cylinder. In the case when only one caliper or wheel brake cylinder has been replaced or repaired, it is usually sufficient to bleed the air from this cylinder.
Caution: Open the bleed valves carefully so that they do not collapse. It is recommended to treat the valves with a rust remover approximately 2 hours before bleeding. If the valves are too tightly tightened, have the air vented in a workshop.
The sequence of operations for removing air:
- 1. Brake caliper or wheel brake cylinder rear right,
- 2. Brake caliper or wheel brake cylinder rear left,
- 3. Front right brake caliper,
- 4. Front left brake caliper.
Remove the dust cap from the brake cylinder bleed valve. Clean the bleed valve, put a clean hose on it, insert the other end into a bottle half-filled with brake fluid.
Have an assistant depress the brake pedal until the brake system is pressurized. This is felt by the increasing resistance as the pedal is depressed.
If sufficient pressure is reached, depress the pedal to the stop and hold it with your foot.
Open the bleeder valve on the brake caliper about half a turn with a wrench. Collect leaking brake fluid in a bottle. At the same time, pay attention to the fact that the end of the hose in the bottle is constantly below the level of the liquid poured into it.
As soon as the fluid pressure drops, close the bleed valve.
Repeat the process of pressurizing with the brake pedal until the pressure rises again. Press the brake pedal to the stop and hold it with your foot, open the bleed valve until the fluid pressure drops again, and close the valve again.
Repeat the process of removing air from the brake cylinder until air bubbles stop flowing together with the brake fluid that flows into the vessel.
After removing the air, remove the hose from the valve and put on the dust cap.
Similarly, remove air from the brake cylinders of other wheels, adhering to the order described above.
Caution: When venting, watch the fluid level in the expansion tank. The liquid level must not fall too low, otherwise air will be sucked through the expansion tank. Always top up with new brake fluid!
After removing the air, top up the liquid level in the compensation tank to the mark «MAX».
Vehicles with ABS
The removal of air from the hydraulic pipelines of the front and rear axles is carried out separately.
Vehicles with ABF/AAA/ABV engines from 7/95: If one or both chambers of the brake fluid reservoir are empty, the hydraulic system must be bled (workshop work).
Front axle
Turn off the ignition and depress the brake pedal about 20 times to build up high pressure.
Fill the brake fluid reservoir to the top.
Caution: The fluid level must not drop below the mark when bleeding air «MIN».
Put the free end of the hose down into the bottle onto the air bleed valve of the right caliper and open the valve.
Have an assistant depress the brake pedal repeatedly until the brake system is pressurized. This is felt by the increasing resistance as the pedal is depressed. After that, depress the pedal and open the bleed-on valve. Close the valve, as soon as the pedal rests on the bottom of the body, remove your foot from the pedal. This procedure must be carried out until no more air bubbles are released along with the brake fluid.
Close the bleeder valve, fill the expansion tank with new fluid.
Remove air from the second caliper in the same way.
Rear axle
Switch off the ignition and depress the brake pedal about 20 times to build up high pressure.
Depress the brake pedal and keep it depressed.
Turn on the ignition. Put the free end of the hose down in the bottle onto the bleeder valve from the right wheel brake cylinder or caliper, respectively, and open the valve. Keep the valve open until no more air bubbles come out with the brake fluid. The brake fluid flows out under the pressure generated by the built-in pump. At the same time, press the lever of the brake force regulator in the direction of the rear axle. Make sure that during the bleeding process, the liquid in the compensation tank never falls below the mark «MIN».
Caution: The ABS pump must not operate continuously for more than 120 seconds during this procedure. If this time is exceeded, it is imperative to maintain a pause of approximately 10 minutes for cooling.
Switch off the ignition.
Similarly, bleed the air from the second wheel brake cylinder.
Switch on the ignition and wait until the pump turns off by itself.
After removing the air, top up the liquid level in the compensation tank to the mark «MAX». Screw on the cover of the expansion tank and connect the plug.
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