Possible malfunctions of the brake system, their causes and methods of elimination (VAZ-21051)

Cause	Method of elimination
Insufficient braking efficiency
Brake fluid leaking from front or rear brake wheel cylinders	Replace defective wheel cylinder parts, wash and dry the pads and drums, bleed the hydraulic drive system
Air in the brake system	Remove air from the system
The rubber seals in the brake master cylinder are damaged	Replace the seals and bleed the system
The rubber hoses of the hydraulic drive system are damaged	Replace the hoses
Spontaneous braking with the engine running
Air leak in the vacuum booster between the valve body and the protective cap:
- destruction, distortion of the lid seal or poor fixation due to damage to the locking parts, wear of the seal	– replace the vacuum booster
– insufficient lubrication of the lid seal	– remove the protective cap and apply grease to the seal
Incomplete release of braking of all wheels
No free travel of the brake pedal due to incorrect position of the brake light switch	Adjust the position of the switch
The protrusion of the vacuum booster adjusting bolt relative to the mounting plane of the master cylinder is damaged	Adjust the protrusion (1.25 - 0.2 mm) of the adjusting bolt
The vacuum booster valve body is seized due to swelling of the diaphragm or pinching of the booster cover seal or protective cap	Replace the vacuum booster
Clogged compensation hole in the master cylinder	Clean the hole and bleed the hydraulic system
Swelling of the rubber seals of the master cylinder due to gasoline, mineral oils, etc. getting into the liquid.	Thoroughly flush and bleed the system with brake fluid, replace damaged rubber parts, bleed the hydraulic drive system
Brake master cylinder piston sticking	Check and replace the master cylinder if necessary, bleed the system
Braking of one of the wheels with the brake pedal released
The rear brake shoe tension spring is weak or broken	Replace the spring
Piston seizing in wheel cylinder due to corrosion	Disassemble the cylinder, clean and wash the parts, replace the damaged ones
Swelling of the wheel cylinder sealing rings due to ingress of fuels and lubricants into the liquid	Replace the rings, flush the hydraulic system with brake fluid
No clearance between the pads and the drum	Adjust the parking brake
Violation of the position of the caliper relative to the brake disc when loosening the mounting bolts to the bracket	Tighten the mounting bolts, replace damaged parts if necessary
Increased brake disc runout (more than 0.15 mm)	Grind the disc, if the thickness is less than 9 mm, replace the disc
Car starts or pulls to one side when braking
Brake fluid leak in one of the wheel cylinders	Replace the seals and bleed the system
Wheel brake cylinder piston sticking	Check and eliminate piston sticking in the cylinder, replace damaged parts if necessary
A blockage in any steel tube due to a dent or clog	Replace the tube or clean it and bleed the system
Different tire pressures	Adjust the pressure
Incorrect wheel alignment angles	Adjust the wheel alignment angles
Contamination or oiling of discs, drums and pads	Clean the brake components
Incorrect installation of the pressure regulator	Adjust its position
The pressure regulator is faulty	Repair it or replace it
Increased brake pedal force
The vacuum booster air filter is clogged	Replace the air filter
The vacuum booster valve body is seized due to swelling of the diaphragm or pinching of the booster cover seal or protective cap	Replace the vacuum booster
The hose connecting the engine vacuum pipe is damaged or its fastening on the fittings has become loose	Replace the hose or tighten the clamps that secure it
Swelling of cylinder seals due to gasoline, mineral oils, etc. getting into the liquid.	Thoroughly flush the entire system, replace damaged rubber parts; pump up the system
Squealing or screeching brakes
Weakening of the rear brake shoe tension spring	Check the tension spring and replace it with a new one if necessary
Ovality of rear brake drums	Boring the drums
Oiling of friction linings	Clean the pads with a wire brush, using warm water and detergents. Eliminate the cause of liquid or grease getting on the brake pads
Wear of linings or inclusion of foreign bodies in them	Replace the pads
Excessive brake disc runout or uneven wear	Grind the disc, if the thickness is less than 9 mm, replace the disc