Fig. 6-2. Brake booster: 1 - tip mounting flange; 2 - amplifier body; 3 - rod; 4 - lid; 5 - piston; 6 - amplifier mounting bolt; 7 - distance ring; 8 - valve spring support cup; 9 - valve; 10 - valve support cup; 11 - return spring support cup; 12 - protective cap, 13 - protective cap holder; 14 - pusher; 15 - air filter; 16 - valve return spring; 17 - valve spring; 18 - housing cover seal; 19 - seal retaining ring; 20 - thrust plate; 21 - buffer; 22 - valve body; 23 - diaphragm; 24 - valve body return spring; 25 - rod seal; 26 - master cylinder mounting bolt; 27 - rod seal collar; 28 - adjusting bolt; 29 - hose tip; 30 - valve, A - vacuum cavity; B - a channel connecting the vacuum cavity with the internal cavity of the valve; C - a channel connecting the internal cavity of the valve with the atmospheric cavity; E is the atmospheric cavity of the engine, since loosening or damage to the hose and flange 1 sharply reduces the vacuum in cavity A and the efficiency of the booster.
Stop the brake pedal in the middle of its travel and start the engine. If the vacuum booster is working properly, the brake pedal should "go forward" after the engine starts.
If the pedal "does not go forward", check the fastening of tip 29, the condition and fastening of flange 1, the hose to the tip and the fitting of the engine intake pipe, since loosening of the fastening or damage to the hose and flange 1 sharply reduces the vacuum in cavity A and the efficiency of the booster.
In case of spontaneous braking of the car, check the vacuum booster for leaks with the engine running. Start with the brake pedal released and then pressed at a fixed position. The "suction" of the protective cap 12 to the valve body tail and the hissing of sucked-in air indicates insufficient tightness of the booster.
Even if the protective cap is not suctioned, check the condition of the seal 18, for which:
- carefully remove and then slide the protective cap 12 off the flange of the hole on the cover 4;
- with the engine running, shake the protruding tail of the valve body in the transverse direction with a force of 29.4-39.2 N (3-4 kgf), while there should be no characteristic hissing of air passing into the amplifier through the seal 18 of the cover.
If the vacuum booster is leaking, disconnect the pusher 14 from the brake pedal, remove the protective cap 12 and apply 5 g of TSIA-TIM-221 grease between the seal and the flange of the cover and the valve body, then check the condition of the air filter 15, replace it if necessary and reinstall the protective cap.
If this does not eliminate the air leak, then the vacuum booster must be replaced.