To check the operation of the vacuum brake booster on a car, you will need: a screwdriver, a rubber bulb.
1. With the engine off, press the brake pedal 5-6 times. While holding the brake pedal down, start the engine. The brake pedal should move forward (fail). If this does not happen, check the tightness of the vacuum booster hose on the intake pipe fitting...
2....and on the non-return valve. If necessary, depending on the defect, tighten the vacuum booster hose clamp, replace the clamp or hose.
3. Take out the valve from the case of the vacuum amplifier of brakes and from a vacuum hose.
4. Put on the fitting of a larger diameter (which the valve is inserted into the vacuum booster) rubber bulb and squeeze it. Wherein...
5.... air must escape through the valve. Release the pear. If it remains in a compressed state, then the vacuum booster valve is working. Otherwise, replace the brake booster valve. In the absence of a pear, you can purge the vacuum booster valve with your mouth.