To reduce the force applied to the brake pedal, a two-chamber vacuum booster is installed between it and the main brake cylinder, triggered by a vacuum in the engine intake pipe
The amplifier consists of a body 11, a body cover 6, a thrust cover, in which pistons 5 and 10 with diaphragms 7 and 8 are installed.
On the threaded end of the piston connector 22, the secondary piston 5 is attached with a nut, and the piston 10 and the diaphragm 18 are attached to the flange part of the connector using six bolts that are screwed into the valve body 15.
In the body of 15 valves, the pusher 16 with the piston 17 and the filter 14 is fixed with two screws 19.
Piston 10 has a reactive washer 20, through which the total force is transmitted to pusher 3 from pusher 16, directly connected to the brake pedal, and from both booster pistons.
To ensure the release of the system, a gap is required between the pusher 3 and the primary piston of the main brake cylinder.
The clearance is provided by the adjusting bolt 4.
The head of the bolt must be recessed by 1.35-1.65 mm relative to the mating plane of the cover to which the master cylinder flange is attached.
Operation of the vacuum brake booster
The vacuum created during engine operation is transmitted through a rubber hose and check valve 1 to cavity A1.
Since the cavity A1 through the central hole in the connector 22 and the holes in the flange of the connector and the piston 10 constantly communicates with the cavities AZ and A5, a vacuum is also created in these cavities.
When the brake pedal is not pressed, the cavity A5 through the gap between the valve diaphragm 18, the piston 17 and the radial holes of the connector 22 communicates with the cavity A4, which, in turn, through the holes A6 in the thrust cover is connected to the cavity A2.
Consequently, a vacuum is created in all cavities A1, A2, AZ, A4 and A5 of the amplifier.
Return valve 1 keeps the greatest negative pressure in the amplifier, which is formed during engine operation.
When you press the brake pedal, the piston 17, under the action of the pusher 16 associated with the pedal, touches the diaphragm 18 of the valves and interrupts the communication of the cavities A1, AZ, A5 with the cavities A4 and A2.
Then the piston 17, moving the diaphragm 18, tears it off the seat on the valve body 15.
As a result, atmospheric air, passing through the filter 14, holes in the housing 15, enters the diaphragm 18 and then through the radial drillings in the valve housing 15 - into the cavity A4 and through the holes A6 into the cavity A2, that is, to the pistons 5 and 10 .
Atmospheric air enters the cavities A4 and A2 until the diaphragm 18 of the valves, under the influence of the reaction washer 20, sits simultaneously on the piston seats 17 and housing 15, blocking the air supply.
Thus, the follow-up action of the system is carried out through the reactive washer, i.e. the force created by the amplifier is directly proportional to the force applied by the driver to the brake pedal.
When the force on the pedal is increased, the piston 17 compresses the reactive washer 20, moves the diaphragm 18 away from the seat in the valve body 15 and additional atmospheric air again enters the pistons 5 and 10, which increases the effect of the amplifier.
The force from the drivers foot and from pistons 5 and 10 of the amplifier is transmitted through the reaction washer to the pusher 3 and then to the master cylinder pistons.
When the pedal is released, the piston 17 moves away from the diaphragm 18, allowing it to move to the seat in the housing 15.
In this case, the access of atmospheric air is stopped, and the rarefaction through the resulting end gap between the piston 17 and the diaphragm 18 is transferred from the cavity A5 to the cavities A4, A2.
The cavities A1, A2, AZ, A4 and A5 will again communicate with each other, and the pistons under the action of the spring 21 will return to their original position and braking will stop.
The booster is ready for new braking.
In the event of an engine stop, the vacuum stored in the amplifier by the check valve allows 2-3 effective braking of the car.
If there is no vacuum in the booster, only the force applied by the driver to the brake pedal will affect the pusher 3.
Removing the vacuum brake booster
Loosen the clamp 1 of the fastening and disconnect the shlang 3 from check valve 2 of the vacuum booster.
Remove the brake master cylinder
Remove the cotter pin 1, unscrew the fastening nut 2, remove the axle 5 and disconnect the pusher 4 of the booster from the lever 3 of the brake booster, while removing the plastic bushings 6.
Unscrew the four fastening nuts 1 and remove the vacuum booster 3 from the bracket 2.
Checking the vacuum booster
When increasing the force on the brake pedal, it is necessary to check the performance of the vacuum booster.
Depress the brake pedal to the stop several times with the engine off and, keeping the pedal depressed, start the engine.
At the same time, due to the pressure drop in the cavities of the booster, the brake pedal should move forward.
If this does not happen, check the tightness of the vacuum booster hose connections and, if necessary, eliminate air leakage.
If this still fails, then the amplifier is defective and needs to be replaced.
To check the tightness of the vacuum booster, open the hood and start the engine for 1 minute.
Approximately 30 seconds after the engine has been turned off, press the brake pedal 2 times, while a characteristic hiss of air entering the amplifier should be heard.
Otherwise, replace the amplifier.
Blow out the hose with check valve at both ends. Air must only pass through the non-return valve.
Otherwise, replace the non-return valve.
Installing the vacuum brake booster
Install the vacuum booster in the reverse order of removal.
Before installing, check the gap between the end face of the vacuum booster cover and the adjusting bolt 1.
The gap should be 1.35 - 1.65 mm. If the gap differs from the specified one, unscrew the lock nut 2 and, turning the adjusting bolt 1, set the required gap.
Then tighten locknut 2.