Press the brake pedal 5-6 times with the engine off to create in cavities A and B (see fig. 78) the same pressure, close to atmospheric pressure. At the same time, by the force applied to the pedal, determine if the valve body is sticking. With the brake pedal stopped in the middle of its travel, start the engine. With a working vacuum booster, the brake pedal after starting the engine should «go ahead». If the pedal is not «goes ahead», check the attachment of the hose tip, the condition and fastening of the tip flange in the amplifier, the hose to the tip and the engine inlet pipe fitting, as loosening or damage to the fastening sharply reduces the vacuum in cavity A (see fig. 78) and efficiency of the amplifier.