When the engine is not running, the vacuum decreases, therefore, the reinforcing effect also disappears. Thus, for example, when towing, it is necessary to apply significantly more force when depressing the brake pedal to achieve the usual effect.
You can check the correct operation of the amplifier as follows:
- Press the brake pedal several times and then keep it pressed. If you then start the engine, the pedal should go down a little more. In this case, everything is fine;
- leave the engine running. Then press and hold the brake pedal again. Stop the engine - the pedal should not rise;
- start and stop the engine again. Press the brake pedal several times. At the first press, the pedal travel should be the greatest and should decrease with each subsequent press.
If the booster is not working properly, the vacuum hose is probably leaking or the non-return valve in the vacuum hose is defective.
You can check this by disconnecting the hose from the amplifier. When working correctly, a suction action should be felt at the end of the hose. When installing a new valve, pay attention to its correct position. If the amplifier is faulty, it is replaced as an assembly.
Self-repair of the amplifier is not possible, because this requires a special tool. But repairing the amplifier is unlikely to be taken to the service station. The failure of the amplifier does not mean a complete failure of the brakes. However, the required pedal force to maintain the same braking distance will increase markedly, especially for a minibus.