Phenomenon: When the car is driving, the brake pedal is stepped to the end, and the brake suddenly fails.
1. There is no brake fluid in the master cylinder.
2. The master pump cup is damaged or overturned.
3. The sub-pump cup is damaged or overturned.
4. The brake pipeline is severely broken or the joint is out of joint.
Diagnosis: The reason for the poor braking performance of the hydraulic brake system can generally be based on the brake pedal stroke (commonly known as high and low), the soft and hard feeling when stepping on the brake pedal, the stability after stepping on the brake pedal, and the braking When the pedal increases in height to judge.
1. Generally, the pedal height during braking is too low and the braking performance is poor. If you brake with two or more feet in a row, the pedal height will increase and the braking performance will improve, indicating that the gap between the brake drum and the friction plate or the master cylinder piston and the push rod is too large.
2. When the brake is maintained, if the height of the pedal drops slowly or rapidly, it means that the brake pipeline is broken, the joint is not well-sealed, or the cylinder cup is not properly sealed, the return spring is too soft or broken, or the master cylinder cup , The apron is not well sealed, the oil return valve and the oil outlet valve are bad. You can first step on the brake pedal to observe whether there is any leakage of brake fluid. If the exterior is normal, check the sub-cylinder or master cylinder for failure.
3. When braking for several consecutive feet, the pedal height is still too low, and after the second foot braking, the master cylinder piston is not returned to its position. When the brake pedal is stepped on, the master cylinder push rod and piston will hit the sound, yes The master cylinder cup is broken or the return spring is too soft.
4. The pedal height increases slightly when braking for several consecutive feet, and there is a sense of elasticity, indicating that air has penetrated into the brake pipeline.
5. After several consecutive feet, the pedals are all pressed to the bottom, and there is no reaction force on the pedals, indicating that the brake fluid in the master cylinder reservoir is seriously depleted.
6. When braking with several feet in a row, the pedal height is low and soft, and the vent hole of the screw plug of the reservoir in the main oil inlet is blocked.
7. When braking with one or two feet, the pedal height is appropriate, but the braking performance is poor if it is too hard. Check whether the gap between the friction piece of each wheel and the drum is too small. If the gap is normal, check the surface condition of the drum wall and friction plate. If it is normal, check whether the brake shoe spring is too hard, whether the master cylinder or sub-cylinder cup is swollen, and whether the piston and cylinder wall fit loosely. If everything is normal, check whether the brake hose is aging and not smooth.
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Link to this article：Analysis on the Causes of Sudden Failure of the Braking of Automobile Maintenance Vehicles
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