Warning! Remember that the dust generated during the operation of the brake mechanisms may contain asbestos, which is extremely harmful to human health. Never blow off dust with compressed air or inhale it; when servicing mechanisms, wear a protective mask or respirator. Never use gasoline or petroleum-based solvents to clean brake system components - use only branded cleaners or methyl alcohol! Try to use only asbestos-free components when replacing pads.
This Section is devoted to checking only disk (front and rear) brake mechanisms. More detailed illustrative material in the Chapter Brake system.
1. The condition of the components of the brake system, in addition to the regular checks specified in the routine maintenance schedule, should be assessed each time the wheels are removed or if signs of a malfunction of the brake system appear. Disc brake pads are usually equipped with special indicators that indicate excessive wear of the friction linings with a characteristic squeal when braking.
2. The following symptoms may indicate a malfunction of the brake components:
- a) When braking, the car loses directional stability (pulling to one side);
- b) During braking, the brake mechanisms emit a screech or creak;
- c) Excessive travel of the foot brake pedal;
- d) When depressing the brake pedal, pulsations are felt;
- e) There are signs of a brake fluid leak (usually on the inner surface of wheel rims and tires).
3. Loosen the wheel nuts.
4. Jack up the car and put it on stands.
5. Remove wheels.
6. The caliper of each of the brake mechanisms is equipped with two pads - internal and external.
7. The ends of the pads are clearly visible through a special viewing window in the caliper body, as well as from the ends of the latter after removing the wheel. The assessment of the residual thickness of the friction lining of the inner shoe is made visually through the viewing window mentioned above. If the pads are worn beyond the allowable limit (see specs), it is necessary to make a complex replacement of the brake pads.
Note. Remember that the friction linings are riveted or glued to a metal backing, the thickness of which should not be taken into account in the measurement.
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8. If it is difficult to visually assess the residual thickness of the pads, or there is a need for a more detailed inspection of the pads, remove the caliper (s) and remove the pads for a more detailed study (see chapter Brake system).
9. After the pads are removed from the caliper, clean them with a special tool and measure the residual thickness of the pads using a ruler or vernier caliper with a vernier scale.
10. Measure the thickness of the brake discs with a micrometer. Compare measurement results with regulatory requirements (see specs). If the thickness of any of the discs is out of range, replace it (see chapter Brake system). If the thickness of the disc is normal, check its general condition. Pay attention to defects such as deep scratches, grooves, scuff marks, overheating marks, etc., if necessary, remove the disc and give it to the groove (see chapter Brake system).
11. Before replacing the wheels, inspect all brake lines for signs of damage, wear, deterioration due to aging of the material, signs of leakage, bends, twists and other deformations (in particular near the points of connection of flexible brake hoses to brake calipers). Check up reliability of fastening of hoses collars. Make sure that none of the brake hoses come into contact with sharp corners of adjacent body components, exhaust system and suspension (at any position of the steering wheel). If necessary, make appropriate repairs or correct the route of laying the lines. Replace defective components (see chapter Brake system).
Vacuum booster
1. Checking the proper functioning of the vacuum brake booster is carried out from the driver's seat.
2. With the foot brake pedal fully depressed, start the engine - the pedal should fall a little more.
3. With the engine running, depress the foot brake pedal several times. The amount of pedal travel must remain constant.
4. Depress the pedal, turn off the engine and continue to hold the pedal down for about 30 seconds more, during which it should not fall down or rise.
5. Start the engine again, let it run for a minute, then shut it off again. Again, firmly depress the pedal several times - the amount of travel should decrease with each stroke.
6. In the event of a negative result of the described test, the servo drive of the vacuum brake booster must be repaired or replaced (see chapter Brake system).
Parking brake
The assessment of the serviceability of the parking brake can be made by parking the car on a downhill section of the road and fixing it with a stationary parking brake with the transmission in neutral. If the brake does not hold the vehicle when cocking its lever to the required number of clicks, it is necessary to make an adjustment (see chapter Brake system).