1. The reason for the loss of braking efficiency may be the unsatisfactory operation of the vacuum booster. For its express check, press the brake pedal several times with the engine off to remove the vacuum in the amplifier, and then, while holding the pedal, start the engine. If after starting the engine the pedal drops a little, the vacuum booster is working.
2. If the pedal remains motionless, check the integrity and reliability of the connection of the vacuum booster hose to the fitting on the engine intake pipe...
3....and with an amplifier. Replace or repair defective hose. If the hose is good, the vacuum booster needs to be replaced (see «Replacing the vacuum booster»).
Note. The vacuum booster hose is made in one piece with the check valve. Check if it works (see «Checking the operation of the vacuum brake booster»). If the non-return valve is defective, replace the vacuum booster hose assembly.
If braking is accompanied by a beating and pulsation of the brake pedal, you should first check the condition of the front disc brakes.
Note. The pulsation of the brake pedal of a car equipped with an anti-lock brake system is not a sign of a malfunction, as it is inherent in the design.
4. Having installed the car on a jack, one by one remove the front wheels and inspect the brake discs. The thickness of the brake disc must be at least 10.6 mm, the surface of the disc must be even and smooth on both sides. If the surface of the disc is covered with rust in places, which usually happens after a long parking of the car with wet brakes, try cleaning the working surface with a fine emery cloth. If this procedure does not help, you will have to give the discs for grinding or replace them with new ones.
5. Check up mobility of the piston of the brake mechanism. To do this, use a screwdriver to try to move the brake caliper. If the caliper cannot be moved, then the piston is stuck in the brake cylinder.
Attention! Jamming of the piston of the brake cylinder leads to the constant braking of the corresponding wheel when the pedal is released and the car skids when braking.
If braking is accompanied by car jerks and a creak in the area of the rear wheels, and also if the rear of the car skids during heavy braking, check the condition of the rear wheel drum brakes.
6. After placing the car on a jack, remove the rear wheels one by one, remove the brake drums (see «Removal and installation of a brake drum») and measure the diameters of their working surfaces. The inner diameter of the drum should be no more than 204.45 mm, the working surface of the drum should be even and smooth, without ring marks and clearly visible ovality (ovality can be determined by the unevenly worn working surface of the drum). If the inner diameter of the drum is larger than the permissible one, the annular risks are very deep or the uneven wear of the working surface is clearly visible, the drum will have to be replaced with a new one.
Note. The parking brake actuates the rear brakes by a cable connecting the parking brake lever and the brake shoe control mechanism. Many drivers try to use the parking brake as little as possible in order to prolong it «life», and achieve the opposite result. If you do not use the parking brake, dirt and moisture stagnate in the sheaths of the cable, the cable becomes rusty, stops moving and breaks. Therefore, use the parking brake when necessary, but do not forget to adjust its drive from time to time (see «Parking brake actuator adjustment»).