The brakes will suddenly be hard.

1, due to insufficient power of the brake booster, first check whether the vacuum tube of the brake booster is blocked. 2. The reason of vacuum degree. The reasons that affect the vacuum degree include atmospheric valve seat crack, film fatigue damage, vacuum valve seat crack or vacuum hose single valve failure. 3. Reasons for free travel When the driver steps on the brake pedal, the brake will not start immediately, but there will be a buffer time to make the driver feel more comfortable. After the free stroke is over, the brake enters the effective stroke. During the transmission of the brake pipeline system, the pedal force reaches each wheel. With the gradual increase of pedal strength, the driver's pedaling feeling becomes heavier and the speed becomes slower. The pedal has no free travel or the free travel is very small, which may cause hard braking or excessive pedal force. 4. The reasons of take-off value and take-off point are analyzed from the design point of booster. The take-off value is not only an important reason of braking stiffness, but also a quantitative index of braking stiffness. 5. Clearance value between valve plug and rubber reaction disc. Under normal circumstances, the large air valve and vacuum valve in the vacuum booster are closed. When the driver steps on the brake pedal, the vacuum valve is closed, and when the air valve is opened, there will be a certain gap between the valve plug and the rubber reaction plate. This gap value will affect the take-off value, which can be said to determine the take-off value.