Many malfunctions are eliminated by the methods indicated in subsection «Brake maintenance». They, with certain skills, are performed by the owner of the car. But in case of failure of the vacuum booster, pressure regulator and wheel cylinder of the rear wheel brake mechanism, it is necessary to contact a service station.
Increased brake pedal travel
Causes of the malfunction and how to fix it:
- leakage of brake fluid from the wheel cylinders of the brake mechanisms of the front wheel. Raise the front of the car and remove the wheel. Unscrew the fitting of the pipeline and disconnect the flexible hose from the line. Plug hose and tube openings to prevent leakage of brake fluid. Remove the hose from the suspension strut guide bracket. Unscrew the two bolts securing the shoe guide to the steering knuckle and remove the shoe guide assembly with the caliper and wheel cylinder. Disconnect hose 13 (see fig. 84) from the wheel cylinder, unlock and unscrew the bolts 12 securing the wheel cylinder to the guide pins. In order not to damage the protective cap, it is necessary to support the guide fingers beyond the edges with the key. Remove the guide 8 of the pads assembled with the fingers and remove the brake pads 9. Do not unscrew the bolts 14 connecting the caliper and the cylinder. Remove retaining ring 6 and protective cap 5 from cylinder and piston. Gently blow compressed air through the fluid inlet to push piston 4 out of cylinder 1. Wash all parts with warm water and detergent or isopropyl alcohol. Gasoline, diesel fuel or kerosene and other mineral solvents must not be used for flushing, as they cause damage to the sealing ring and protective cap. Carefully check the condition of the cylinder, piston and O-ring 3. If they are worn, damaged or severely corroded, replace the cylinder and piston or O-ring;
- leakage of brake fluid from the wheel cylinders of the brake mechanisms of the rear wheels (oil stains or streaks on the brake drums). Replace the wheel cylinders, having previously carried out the operations indicated in subsection «Checking the condition and replacing the brake pads of the rear wheel». If spare cylinders are not available, have O-rings or wheel cylinder assemblies replaced at a workshop. Rinse and dry the removed brake pads and drums. After installing all the parts in place, bleed the brake system;
- air in the brake system - see subsection «Removal of air from a hydraulic drive of brakes»;
- damage to the rubber seals in the main brake cylinder. In this case, the pressure in the circuits drops and the effectiveness of the brakes deteriorates. To restore the performance of the master cylinder, it is necessary to replace the seals. Disconnect the pipes from the master cylinder and the block with wires from the emergency brake fluid level sensor. Close the openings of the pipelines and at the master cylinder to prevent leakage of fluid and the ingress of foreign matter into them. Remove the cylinder assembly with the tank by unscrewing the nuts securing it to the vacuum booster. Remove the emergency brake fluid level sensor and drain the brake fluid from the reservoir and cylinder. It is not recommended to remove the reservoir from the master cylinder unless it is necessary. If it has arisen, it is necessary to pull the tank with force until the connecting sleeves come out of the sockets of the master cylinder. Loosen the locking screws and take out all the parts one by one. After making sure that all parts are in good condition, replace the seals with new ones and assemble the master cylinder in reverse order. When assembling, lubricate the cylinder bore, piston and O-ring with brake fluid. After installing the main cylinder in place and connecting pipelines to it, bleed the system.
Insufficient braking performance
Causes of the malfunction and how to fix it:
- oiled brake pads. Rinse and dry pads;
- piston jamming in the wheel cylinder. Remove and disassemble the wheel cylinder, eliminate the causes of jamming, replace damaged parts or the cylinder assembly (see subsection «The main malfunctions of the brake system and how to eliminate them»); pump the system;
- complete wear of pads. Replace brake pads (see subsection «Brake maintenance»);
- overheating of the brakes. With frequent and prolonged use of the brakes, the braking efficiency decreases sharply due to heating of the parts of the brake mechanisms. In this case, you must immediately stop the car and cool the brakes.
Incomplete release of all wheels
Causes of the malfunction and how to fix it:
- no free play on the brake pedal (see subsection «Brake pedal free travel adjustment»);
- jamming of the valve body of the vacuum booster. Replace the vacuum booster;
- swelling of the rubber seals of the master cylinder. Replace seals and bleed the system;
- jamming of the master cylinder piston. Replace master cylinder and bleed system.
Braking one of the wheels when the pedal is released
Causes of the malfunction and how to fix it:
- breakage or weakening of the return spring of the brake pads of the rear wheel. Replace spring (see subsection «Checking the condition and replacing the brake pads of the rear wheel»);
- seizure of the piston in the wheel cylinder due to corrosion or swelling of the sealing rings. Replace wheel cylinder or damaged parts;
- violation of the position of the caliper relative to the brake disc due to the loosening of the bolts securing the guide pads to the steering knuckle. Tighten the mounting bolts, if necessary, replace damaged parts.
Skidding or withdrawal of the car when braking
Causes of the malfunction and how to fix it:
- jamming of the wheel cylinder piston. Replace damaged parts or wheel cylinder assembly;
- blockage of any steel pipe due to a dent or blockage. Replace the tube or clean it and bleed the system;
- contamination or oiling of discs, drums and linings. Clean the parts of the brake mechanisms;
- incorrect adjustment of the pressure regulator actuator. Adjust the pressure regulator actuator at a service station;
- pressure regulator failure. Check the condition of the pressure regulator (see subsection «Brake maintenance») and if necessary, replace it at a service station;
- violation of the angles of the front wheels. Adjust wheel alignment (see section «pendants», subsection «Front suspension»);
- uneven tire pressure. Set normal pressure.
Increased pedal force when braking
Causes of the malfunction and how to fix it:
- vacuum booster failure. Replace the vacuum booster;
- damage to the hose connecting the vacuum booster and the engine intake pipe or loosening of its attachment to the fittings;
- swelling of cylinder seals due to gasoline, mineral oils, etc. entering the brake fluid. Thoroughly flush the entire system with isopropyl alcohol or brake fluid, replace seals and fluid, and bleed the system.
Squeak or vibration of wheel brakes
Causes of the malfunction and how to fix it:
- weakening of the return spring of the brake pads of the rear wheel. Replace spring (see subsection «Checking the condition and replacing the brake pads of the rear wheels»);
- ovality of the brake drums. To bore and grind the drums, not allowing its diameter to increase over 201 mm;
- oiling of friction linings. Clean the lining with a wire brush using warm water and detergent. Eliminate the causes of fluid or grease getting on the brake pads;
- lining wear. Replace brake pads (see subsection «Brake maintenance»);
- Excessive brake disc runout or uneven wear. Turn and grind the disc, and if the thickness is less than 10.8 mm, replace it.