Test the brakes at various vehicle speeds with light to hard pressure on the brake pedal, avoiding brake lockup and tire slip. Blocking the wheels during braking does not give full information about the effectiveness of the brake compared to braking, when the wheels can turn and the braking distance is shorter. This is due to the fact that when the locked wheel is sliding, the friction coefficient is less than when it is rolling.
Three main factors influence the braking process:
- on different wheels there will be different conditions for the adhesion of tires to the road, which causes different braking forces. Air pressure and tire tread must be the same;
- braking forces on the front and rear axles must be proportional to the vertical loads acting on them;
- misalignment of the wheels can cause the car to pull to the side when braking.
To check for brake fluid leakage, depress the brake pedal with the engine running at idle and the transmission shift lever in neutral. If the pedal gradually sinks at constant pressure, then there is a leak in the system. Visually check for leakage and brake fluid level in the master cylinder reservoir. A slight drop in the brake fluid level is due to normal pad wear. An abnormally low level indicates a leak in the system. In a hydraulic system, both internal and external leakage is possible. If the brake fluid level is normal, check the length of the brake booster rod. If improper stem length is found, adjust length or replace stem.
Check the brake master cylinder in the following order:
- check for damage to the brake master cylinder or for brake fluid leakage around the brake master cylinder. A low brake fluid level can only indicate a leak. It is also abnormal to wet the surface of the brake master cylinder;
- check the pedal linkage connection and stem length. If they are OK, disassemble the master cylinder and check for stretching or swelling of the cylinder seals, then for wear of the rubber parts. If there are swollen seals, non-standard or contaminated brake fluid may be used. If contaminated brake fluid is found, all components should be disassembled and cleaned and all rubber components replaced. All pipelines should also be flushed.
Incorrect brake fluid, or mineral oil or water in the fluid, can cause the brake fluid to boil or damage rubber components. If the main piston seals in the master cylinder are swollen, this means that the rubber components are damaged. This fault can be confirmed by swollen oil seals in the brake drum cylinder piston on the wheels. If rubber wear is confirmed, disassemble all parts of the hydraulic system, wash them with alcohol. Dry the parts with compressed air before assembling. Replace all rubber parts in the system, including hoses. During the operation of the brake mechanism, check the absence of fluid in the gaskets. If fluid is found, replace gaskets. If the brake master cylinder piston seals are in good condition, check for leakage or excessive overheating. If these conditions are not found, drain the brake fluid, fill the brake master cylinder and re-drain the system.
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