1. The reason for the loss of braking efficiency may be poor operation of the vacuum booster. To quickly check it, press the brake pedal several times with the engine off to remove the vacuum in the booster, and then, holding the pedal, start the engine. If the pedal drops slightly after starting the engine, the vacuum booster is working properly.
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..
Note: The throttle assembly has been removed from the photo for clarity.
3. …and with the booster. Replace or repair the faulty hose. If the hose is in good condition, the vacuum booster must be replaced (see "Replacing the vacuum booster").
4. Check the functionality of the check valve (see "Checking the operation of the brake booster"). If the check valve is faulty, replace it.
If braking is accompanied by beating and pulsation of the brake pedal, you should first check the condition of the front disc brakes.
5. After jacking up the car, remove the front wheels one by one and inspect the brake discs. The thickness of the brake disc should be at least 23.0 mm, the disc surface should be even and smooth on both sides. If the disc surface is rusty in places, which usually happens after the car has been parked for a long time with un-dried brakes, try cleaning the working surface with fine sandpaper. If this procedure does not help, you will have to send the discs for grinding or replace them with new ones.
6. Check the mobility of the brake piston. To do this, try to move the piston with a screwdriver. If the piston cannot be moved, it is jammed in the brake cylinder.
Attention! Jamming of the brake cylinder piston leads to constant braking of the corresponding wheel when the pedal is released and skidding of the car when braking.
If braking is accompanied by jerking of the car and creaking in the area of the rear wheels, if the rear of the car skids during intensive braking, check the condition of the drum brakes of the rear wheels.
7. After placing the car on a jack, remove the rear wheels one by one, remove the brake drums (see "Removal and installation the brake drum") and measure the diameters of their working surfaces. The inner diameter of the drum should be no more than 230.2 mm, the working surface of the drum should be flat and smooth, without ring marks and clearly visible ovality (the ovality, which should be no more than 0.5 mm, can be determined by the unevenly worn working surface of the drum). If the inner diameter of the drum is larger than the permissible value, the ring marks are very deep or uneven wear of the working surface is clearly visible, the drum will have to be replaced with a new one.
Note: If the vehicle is equipped with rear disc brakes, check the disc thickness in the same way as you did for the front brake (see point 5). The brake disc thickness should be at least 9 mm.
Note: The parking brake operates the rear brakes via cables that connect the parking brake lever and the brake shoe control mechanisms. Many drivers try to use the parking brake as little as possible to extend its "life," but achieve the opposite result. If you do not use the parking brake, dirt and moisture stagnate in the cable sheaths, the cables become covered with rust, stop moving, and break. Therefore, use the parking brake when necessary, but do not forget to adjust its drive from time to time (see "Adjusting the parking brake drive").
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