1. Make sure that the brake mechanisms are not fully released or the brake pedal becomes «tough». This may require 20 or more brake applications during an extended test run.
2. Raise the car on a lift, and do not turn off the engine. Try turning the wheels of the car by hand.
Do you feel increased resistance to the rotation of any wheel?
- YES - go to step 3.
- NO - look for other causes of pad wear: front brake pad, rear brake pad, high pedal, or vehicle vibration.
Note. Check the following points when the car vibrates:
- front brake disc;
- rear brake disc;
- wheel beating.
3. Shut off the engine, press the brake pedal several times to allow atmospheric air to enter the vacuum cavities of the booster. After that, turn the wheels of the car again by hand to make sure that the wheels are completely released.
Do you feel increased resistance to the rotation of any wheel?
- YES - go to step 4.
- NO - Replace the brake booster.
4. Without disconnecting pipelines from the main brake cylinder, turn away nuts of fastening of the main brake cylinder and take away it from the vacuum amplifier. Recheck if there is any braking of any wheel.
Do you feel increased resistance to the rotation of any wheel?
- YES - go to step 5.
- NO - Check brake switch setting and pedal free play.
5. Loosen the brake pipe mounting bolts on the master cylinder, check the wheels for ease of rotation.
Is there any increased resistance to the rotation of any wheel?
- YES - go to step 6.
- NO - Replace master cylinder.
6. Loosen the bleeders on each caliper, then rotate the wheels to check for brake resistance.
Is there any increased resistance to the rotation of any wheel?
- YES - the brake mechanism of the wheel that does not fully release must be disassembled and the cause of the problem repaired.
- NO - Check and replace faulty brake lines. If any of the above faults cannot be found, replace the ABS or VSA modulator control unit. ABS, VSA.