Checking the technical condition of the brake system
The brake system is checked on a dry, clean and fairly flat area with good coverage. Reliable check of a condition of brake system on damp or covered with mud (including dry sand) the site will be difficult due to the different grip of the tires with the coating. An uneven surface is also not suitable for checking the brake system due to strong vertical vibrations of the wheels.
The brake system should be checked at different braking intensity and different vehicle speeds. In all cases, blocking and slipping of the wheels must be avoided. Locking the wheels does not mean effective braking because the braking distance is longer compared to braking at the traction limit when the braked wheels continue to rotate. This is due to the fact that the blocking of the wheel is accompanied by a drop in the adhesion of the tire to the road surface.
The vehicle's braking system is designed to reduce the likelihood of wheel lockup in most of the cases most commonly encountered during normal operation, with the exception of fairly rare emergency braking with extremely large deceleration. Braking the car without locking the wheels not only shortens the braking distance, but also maintains the stability and controllability of the car.
At high decelerations, the brake pedal becomes more «tough».
External factors affecting the operation of the brake system
Tires
Tires with different contact and grip will brake differently. Tires must be maintained at the same air pressure. Tires located on the same axle should have approximately the same tread depth.
Vehicle load
When the vehicle is unevenly loaded, those wheels that carry a large proportion of the load require more braking torque than the others. To brake a fully laden vehicle, higher brake pedal forces are required.
Wheel alignment
Violation of the correct angles of installation of the wheels, especially the camber and longitudinal inclination of the axis of rotation, leads to the withdrawal of the car to the side when braking.
Brake fluid leaks
With the engine idling and the transmission in neutral, depress and hold the brake pedal with constant force. If the brake pedal is slowly lowered, this may be due to brake fluid leaks. The entire brake system should be inspected for leaks. Check the brake fluid level in the reservoir. A slight drop in fluid level may be due to normal brake pad wear. A large drop in level may indicate fluid leaks. In a hydraulic brake drive, both internal and external fluid leaks are possible. Keep in mind that even if this test passes, the system may still have small leaks. If the brake fluid level is normal, check the length of the vacuum booster tappet. If the length of the pusher differs from the norm, it is necessary to adjust or replace the pusher. Check the adjustment of the service brake system and the parking brake.
Checking the Master Cylinder
The checks below are not guaranteed to detect all possible node failures.
Check for cracks in the cylinder body and traces of brake fluid on the outer surface of the cylinder. Leaks are indicated by droplets of brake fluid falling into the brake booster chamber. Humidification of the cylinder from the outside is permissible.
Check for binding in the pedal drive and the length of the pusher. If no problem is found, remove and disassemble the cylinder.
Check the condition of the cylinder and piston seals If the seals are swollen or elongated, the brake fluid may be unsuitable or contaminated with foreign matter. In this case, it is necessary to completely disassemble the cylinder and flush all parts. Rubber parts must be replaced. You should also flush the entire hydraulic brake system.
Unsuitable or contaminated brake fluid
The use of non-recommended brands of brake fluids, as well as the ingress of mineral oil or water into the hydraulic drive, leads to a decrease in the boiling point of the working fluid and failure of rubber seals.
Swelling of the outer sealing covers on the main or wheel brake cylinders indicates the failure of the internal rubber seals. If signs of swelling of rubber parts are found, it is necessary to disassemble and completely flush the entire hydraulic drive with alcohol. Before assembling, it is necessary to dry all parts of the hydraulic drive with a jet of compressed air to prevent alcohol from entering the brake system. Rubber parts, including brake hoses, must be replaced. You should also check for traces of brake fluid on the brake linings. If the pads are heavily soiled, they must be replaced. If the brake master cylinder seals are OK, overheating of the brake fluid is a possible cause. If there is no overheating, drain the brake fluid, flush the system with fresh brake fluid, fill in new brake fluid and bleed the air from the hydraulic drive.