If the pedal effort is noticeably greater than normal when braking, check the brake booster with the vehicle stationary.
You will need: pliers, rubber bulb.
1. With the engine not running, press the brake pedal five to six times. Keeping the pedal depressed, start the engine. The brake pedal should move forward.
2. If this does not happen, check the tightness of the connections of the vacuum booster hose with the check valve..
3. …and the intake pipe, if necessary, eliminate air leaks. If this does not give a positive result, then the amplifier is faulty and must be replaced.
Article based on information from the website [ladaman.ru]
4. To check the vacuum booster for leaks, open the hood and start the engine for 1 minute. Approximately 30 seconds after the engine is turned off, press the brake pedal twice; you should hear the characteristic hiss of air entering the booster.
5. Additionally, check the booster check valve; if it is faulty, the vacuum in the booster vacuum cavity is not maintained when the engine load changes or when it is stopped. To check, hold the valve and disconnect the vacuum hose from it.
6. Remove the valve from the rubber seal of the booster flange and place it on the valve nipple (short, larger diameter) rubber bulb (for example, from a hydrometer)...
7. ...and squeeze it.
8. If the valve is working properly, the bulb will remain compressed. If the bulb straightens out, replace the valve and retest the booster.
9. Reinstall the removed parts in the reverse order of removal.
Note: If a fault is found in the amplifier, replace it with a new one, since amplifier repair work is very labor-intensive, requires appropriate skills and the use of special installation and adjustment equipment.