Checking the performance of the vacuum booster (VAZ-2109)

Press the brake pedal 5-6 times with the engine off to create a vacuum in cavities A and B (see figure 78) the same pressure, close to atmospheric. At the same time, by the force applied to the pedal, determine whether the valve body is jammed. Stop the brake pedal in the middle of its travel and start the engine. With a serviceable vacuum booster, the brake pedal should "go forward" after starting the engine. If the pedal does not "go forward", check the fastening of the hose tip, the condition and fastening of the tip flange in the booster, the hose to the tip and the nipple of the engine intake pipe, since loosening the fastening or damaging them sharply reduces the vacuum in cavity A (see figure 78) and the efficiency of the amplifier.

[The article is taken from the website: VAZbook]