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.
Vacuum booster operation
The vacuum created during engine operation is transmitted through a rubber hose and check valve 1 to cavity A1.
Since cavity A1, through the central hole in the connector 22 and the holes in the connector flange and piston 10, constantly communicates with the cavities AZ and A5 , then a vacuum is also created in these cavities.
When the brake pedal is not depressed, cavity A5 communicates with cavity A4, which, in turn, through the holes A6 in the thrust cover is connected to the cavity A2.
Consequently, vacuum is created in all cavities A1, A2, AZ, A4 and A5 of the amplifier.
Check valve 1 holds the highest vacuum in the booster that is generated when the engine is running.
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 cavities A4 and A2.
Then piston 17, moving diaphragm 18, lifts it off the valve body seat 15,
As a result, atmospheric air, passing through the filter 14, holes in the body 15, enters the diaphragm 18 and further through the radial drillings there are 15 valves in the body - into cavity A4 and through holes A6 into cavity A2, that is, to pistons 5 and 10.
Atmospheric air enters cavities A4 and A2 until the diaphragm 18 valves under the influence of the reaction washer 20 sits simultaneously on the saddles of the piston 17 and housing 15, blocking the air supply.
Thus, the following action of the system is carried out through the reactive washer, i.e. the force generated by the amplifier is directly proportional to the force, applied by the driver to the brake pedal.
As the force on the pedal increases, piston 17 compresses reaction washer 20, moves diaphragm 18 away from the seat in 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 driver’s foot and from pistons 5 and 10 of the booster is transmitted through the reaction washer to pusher 3 and then to the pistons of the main cylinder.
When the pedal is released, piston 17 moves away from diaphragm 18, allowing it to move onto the seat in body 15.
In this case, the access of atmospheric air is stopped, and the rarefaction through the resulting end gap between piston 17 and diaphragm 18 is transferred from cavity A5 in cavity A4, A2.
cavities A1, A2, AZ, A4and A5 will again communicate with each other, and the pistons under the action of 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 negative pressure stored in the amplifier by the check valve allows 2-3 effective braking of the car.
If there is no vacuum in the booster, pushrod 3 will only be affected by the force applied by the driver to the brake pedal.
Removing the vacuum booster
- 1. Loosen fastening clamp 1 and disconnect hose 3 from non-return valve 2 of vacuum booster.
- 2. Remove brake master cylinder
3. Remove cotter pin 1, unscrew fastening nut 2, remove axle 5 and disconnect pusher 4 of booster from lever 3 of brake booster, while removing plastic bushings 6.
4. Unscrew 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.
1. Press the brake pedal to the stop several times with the engine off and, holding 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.
2. To check the tightness of the vacuum booster, you must open the hood and start the engine for 1 minute.
Approximately 30 seconds after the engine has been turned off, depress the brake pedal 2 times, while a characteristic hiss of air entering the amplifier should be heard. Otherwise, replace the amplifier.
3. Blow out the hose with check valve at both ends. Air must only pass through the side of the non-return valve. Otherwise, replace the non-return valve.
Installing a vacuum booster
1. 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 bolt1.
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.