1. Phenomenon: When the car is running, the brake pedal will be stepped to the end quickly, the car cannot immediately slow down and stop. Its brake
The deceleration is small and the braking distance is too long.
(1) The free stroke of the pedal is too large.
(2) The brake fluid in the brake master cylinder is insufficient, or the compensation hole is blocked, the master cylinder cup, the aprons are aged, swollen, deformed or damaged
(3) The piston and cylinder of the brake master cylinder are excessively worn and the oil is leaking loosely. The oil return valve is poorly sealed and the oil outlet valve spring is broken.
(4) The brake cylinder aging, swelling, and piston stuck, the cylinder piston and the cylinder body are excessively worn, and the oil leaks loosely.
(5) The brake shoes are badly worn, the brake clearance is too large or the clearance is reversed.
(6) Brake drum is out of round, grooved or worn too thin, oil on brake shoe surface, ablation hardening, exposed rivets, etc.
(7) The air infiltrates into the hydraulic brake system, or the temperature of the brake system is too high, the brake fluid in the pipeline vaporizes, forming an air resistance.
(8) The tubing is deflated, the joint is loose and leaking, the brake hose is aging, cracked or blocked.
3. Diagnosis and elimination
When the hydraulic brake system of the car is not working properly, the "three-foot brake" (light pedal, quick pedal and continuous pedal) can be used.
"Foot feeling" method to quickly diagnose. The specific exclusion steps are as follows:
1. First foot brake: light pedal. Use the toes or forefoot to lightly press the brake pedal. (1) If the brake resistance is felt only when the pedal is stepped to two-thirds of the whole journey, it means that the free stroke of the pedal is too large and should be adjusted. (2) When lightly depressing the brake pedal with the forefoot. a) If you feel that the pedal is harder than before when you step on the brake pedal, or even you can't move it, it means that the brake master cylinder and the cylinder of the pump are swollen and deformed, which will cause them to freeze or cause precipitation and blockage due to the brake fluid being used for too long. The pipeline. The brake fluid and brake cup should be replaced, and the brake pipeline should be cleaned. b) If the brake pedal feels soft and elastic when it is depressed, it means that there is air or brake fluid heated and vaporized in the hydraulic brake line. The pipe joints should be tightened and deflated according to the requirements of different models. c) If the brake pedal is released after the pedal is depressed, and the pedal cannot return to its original position at this time, the oil return valve or oil return hole of the master cylinder is also blocked. If there is always a sound of "flutter" and "flutter" at this time, it means that the brake master cylinder has been overturned. The oil return valve or oil return hole of the master cylinder should be cleared, and the master cylinder cup should be reassembled or replaced.
2. Second foot brake: quick pedal. That is, quickly depress the brake pedal with the sole of the foot. (1) If the hydraulic brake system equipped with a quick self-locking joint appears to be effective when the "light pedal" brake pedal is present, and the brake is ineffective when the quick pedal is pressed, it means that the quick self-locking joint is reversed or the joint Caused by improper adjustment of the two spring forces. In this way, when "quickly stepping" the brake pedal, the self-locking phenomenon occurs in the joint ball, and the brake fluid cannot pass through. In this case, it should be reassembled, and the spring force of the compression spring at the oil end should be appropriately lowered. (2) If you feel that the free travel of the pedal is small during "Quick Pedal", the brake is effective, but when the brake pedal is slowly depressed, you feel that the free travel is large and the brake is ineffective. Aging and wear out too much. Keep the pressure on the brake pedal unchanged. At this time, if you feel that the pedal continues to move down, it means that there is leakage in the brake line. First, check externally whether the brake pipe is broken or loose at the pipe joint, and then check whether there is leakage of brake fluid at the dust jacket of the master cylinder push rod and wheel brake cylinder. If there is no leakage of brake fluid, It means that the master cylinder or sub-cylinder cup is aging and cracked or stepped on, and should be replaced.
3. The third foot brake: continuous pedaling, that is, stepping on the brake pedal several times in a row. (1) If the brake pedal is pressed several times in a row, the pedal is always in the end and there is no reaction force, it means that the cause of the failure is the lack of brake fluid in the reservoir chamber of the master cylinder, and the oil inlet and the vent hole of the reservoir cover are blocked; or mechanical connection The mechanism falls off; or the brake cup is broken or overturned. At this time, the brake fluid should be added to the reservoir, the ventilation hole should be cleared, and the brake cup should be replaced. (2) If the brake pedal is stepped on several times in a row, the pedal can be raised and the braking performance is improved, then the free stroke of the pedal and the wheel brake clearance should be checked.