Press the brake pedal vigorously at least five times with the engine off. Then start the engine with the pedal depressed. With a working vacuum booster, the brake pedal should drop noticeably. If this does not happen, check the tightness of the vacuum connections.
Disconnect hose from vacuum booster. Start the engine. Put your finger on the end of the hose and check for vacuum.
If there is no vacuum, check» hose for tightness and mechanical damage. Replace hose if damaged. Tighten the hose clamps.
On a diesel engine, disconnect the vacuum hose from the vacuum pump and check with a finger for pressure.
If there is a vacuum, measure its magnitude. Replace vacuum booster if necessary.
Attention: At the same time, it is imperative to replace the non-return valve in the vacuum pipeline, since the penetration of gasoline vapors through a defective valve may damage the diaphragm in the vacuum booster.