Insufficient vacuum in the intake manifold, leakage or breakage of the vacuum lines, leaking of the diaphragm, and non-strict air valve closure will all lead to poor operation of the vacuum booster. The brake pedal effort is usually an important signal of complete damage to the vacuum booster. Whether the vacuum booster is working properly can be checked by the following methods.
1 sealing performance inspection
There are two ways to check the sealing performance:
1) Start the engine and turn off the engine after idling for 1 to 2 minutes. The brake pedal is stepped on several times with the usual brake pedal force. The interval between pedaling each time should be more than 5 s. If the brake pedal height is increased gradually at a time, the vacuum booster seal performance is good. Otherwise, the engine vacuum supply condition should be checked. If the degree of vacuum provided when the engine is running is normal, it indicates that the vacuum booster has a poor seal and should be overhauled.
2) Start the engine so that the engine will depress the brake pedal several times after idling for 1-2 minutes, and stop the engine when the pedal is at the lowest position and the pedal effort remains unchanged. If the vacuum provided by the engine is normal and there is no change in pedal height within 30 s, the vacuum booster seal performance is good. If there is a clear rebound of the brake pedal, the vacuum booster has a gas leakage fault.
2 power function check
When the engine is off, use the same pedal effort to depress the brake pedal several times to eliminate the entire residual vacuum of the vacuum booster. After confirming that there is no change in the pedal height, stop the pedal and then start the engine. If the brake pedal is slightly lowered at this time, it means that the boost function of the vacuum booster is normal; if the pedal is not moving, the booster will not help. It should first check whether the vacuum source provides a certain degree of vacuum, and then check the vacuum line, single Directional valve and vacuum booster.