The booster is part of the tandem brake master cylinder assembly kit. It is not disassembled and repaired only by the manufacturer.
The booster works on the basis of vacuum taken in cars with a gasoline engine from the suction pipe, and in cars with a diesel engine from a separate vacuum pump. The pressure during the test is 0.08 MPa.
The brake booster only works when the engine is running. When driving with the engine stopped, the brakes work, but to achieve the desired braking effect, it is necessary to press the pedal with more force.
The amplifier consists of a chamber composed of two firmly connected steel stampings - a cover and a bottom. Piston assembly is nested inside. It consists of a plastic piston, there is also a control valve with steel segments, a support and a lining that ensures the progressiveness of the amplifier. The following parts of the piston assembly are: the button acting on the THV piston and the piston with diaphragm. There is a spring inside the booster chamber that returns the piston assembly to its original position after the end of braking. The chamber is sealed. The booster is controlled by thrust from the brake pedal.
The operation of the amplifier proceeds as follows: when you press the brake pedal with your foot, the control valve is pressed into the plastic piston and the button acting on the THV piston is driven through the steel segments and the lining.
With increasing resistance on this piston, the rubber part of the control valve sits on the plastic piston seat.
As a result, there is a break in the connection between both volumes of the amplifier chamber. With further movement of the control piston, the volumes of the amplifier on the side of the cover are connected to the atmosphere. The difference in pressure on either side of the piston assembly causes it to move further, the movement is transmitted by the button on the THV and increases the pressure in the brake fluid system. Therefore, the degree of boost depends on the force developed by the pedal and on the vacuum created in the booster.
The required braking characteristic is achieved by the mechanical transmission of the steel segments through which this force is transmitted.
When the brake pedal is released, the spring returns the piston assembly to its original position and the vacuum is immediately equalized in both volumes of the amplifier chamber.
In case of violation of the tightness of the amplifier or in the case of an idle engine, it remains possible to mechanically control the brakes, naturally without amplification.
Examination
1. With the engine off, press the brake pedal several times with your foot to remove the remaining vacuum in the system.
2. Then press the pedal again and hold it in this state.
3. Then start the engine.
4. If the amplifier is working, the pressed pedal should still settle by about 10 mm.
5. If the pedal does not fail, it is necessary to visit the service in order to establish the cause of the malfunction.