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 - wear a protective mask or respirator when servicing mechanisms. Never use gasoline or petroleum-based solvents to clean brake system components - use only branded cleaners or methyl alcohol!
Note. More detailed illustrative material on brake mechanisms is given in Chapter Brake system.
The condition of the components of the brake system, in addition to the regular checks specified in the vehicle’s routine maintenance schedule, should be assessed each time the wheels are removed or if signs of a malfunction of the brake system appear.
The following symptoms may indicate a malfunctioning brake component:
- 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).
1. Loosen the wheel nuts.
2. Jack up the car and put it on stands.
3. Remove wheels.
Disc brakes
1. Each brake caliper is equipped with two pads (internal and external). Pads are visible through a special viewing window in the caliper body (see accompanying illustration).
2. Evaluation of the residual thickness of the friction lining of the inner pad is made visually through the viewing window of the caliper. The outer block is easy to get to from the inside (see accompanying illustration). If the pads are worn beyond the allowable limit (see Specifications), it is necessary to replace the complex 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.
3. If it is difficult to visually assess the residual thickness of the pads, or if 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).
4. After the pads are removed from the caliper, clean them with a special tool and check the remaining thickness of the pads using a ruler or vernier caliper with a vernier scale.
5. Measure the thickness of the brake discs with a micrometer. Compare measurement results with regulatory requirements (see Specifications). If any of the discs is less than the minimum thickness, replace it (see chapter Brake system). If the thickness of the disc is normal, check its general condition. Pay attention to such defects as deep scratches, grooves, scuff marks, traces of overheating, etc. if necessary, remove the disk and give it to the groove (see chapter Brake system).
6. 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 - see accompanying illustration). 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).
Drum brakes
1. When checking the rear drum brakes, make sure the parking brake is released, then tap the outside of the drum with a soft-faced hammer to loosen the fit.
2. Remove brake drums.
3. Make a thorough cleaning of the brake mechanisms using a special cleaning compound.
Warning! Never blow off brake dust from the surface of components with compressed air or inhale it - the dust may contain asbestos that is harmful to your health!
4. Check the remaining thickness of the friction linings of the brake shoes (front and back). The thickness of the pad is measured from the outer surface to the metal substrate (glued overlays), or up to rivet heads (riveted lining). In the first case, the maximum allowable value is 3 mm (see accompanying illustration), in the second - 1.6 mm. If necessary, make a complex replacement of the shoes. The shoes must also be replaced if cracks are found, areas of the linings polished to a shine, or traces of brake fluid ingress.
5. Make sure that all brake assembly springs are properly connected and in good condition (see accompanying illustration).
6. Check assembly components for signs of brake fluid leaks. Using a finger or small screwdriver, carefully pry the rubber boots off the wheel cylinder at the top of the shoes (see accompanying illustration). Identification of any signs of leaks in these areas requires an immediate reconditioning of the cylinder assembly (see chapter Brake system). Also check all brake hoses and their fittings for signs of leaks.
7. Thoroughly wipe the inside of the drum with a clean cloth soaked in methanol. Avoid inhaling brake dust containing asbestos.
8. Inspect the drum surface for cracks, nicks, overheating, or other damage. If defects cannot be removed by surface treatment with fine-grained sandpaper, the drum should be given to a car service workshop for turning.
9. Repeat the procedure for the opposite brake components. Reinstall the drums, secure the wheels and lower the vehicle to the ground.
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 should 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, depress the pedal firmly 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 replaced (see chapter Brake system).
Parking brake
1. The parking brake is controlled by a lever installed between the front seats. After pulling the lever, cock it to the stop, while counting the number of clicks of the ratchet mechanism. If the number of clicks is out of range (see Specifications), the parking brake actuator must be adjusted.
2. Alternatively, the parking brake can be checked for proper operation by parking the vehicle on a downhill section of road and immobilizing the 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).