Brake system technical condition check

GENERAL INFORMATION.

The brake system should be checked on a dry, clean and sufficiently level surface with a

good surface. A reliable check of the brake system on a wet surface or a surface covered with dirt (including dry sand) is difficult due to

varying tire grip on the surface. An uneven surface is also unsuitable for checking the brake system due to strong vertical wheel vibration. The brake system should be checked at different braking intensities and at different

vehicle speeds. In all cases, avoid wheel lock-up and skidding.

Wheel lock-up does not indicate effective braking, since the braking distance is longer than when braking at the limit of grip, when the

braked wheels continue to rotate. This is because wheel lock-up is accompanied by a drop in tire grip on the road surface. The vehicle brake

system is designed to reduce the likelihood of wheel lock-up

in most cases, the most common situations in normal operation,

except possibly for relatively rare emergency braking with extremely

high deceleration. Braking the vehicle without wheel lock-up not only

shortens the braking distance, but also ensures vehicle stability and

steerability.

At high decelerations, the brake pedal becomes firmer.

External factors affecting the brake system operation.

1) Tires. Tires with different contact and grip with the road will brake

unevenly. Maintain the same air pressure in all tires. Tires

on the same axle should have approximately the same tread depth.

2) Vehicle load. When the vehicle is loaded unevenly, the wheels carrying a larger share of the load

require a greater braking torque than the

others. Braking a fully loaded vehicle requires greater

force on the brake pedal.

3) Wheel alignment angles. Incorrect wheel alignment angles, especially camber and caster of the steering axis, cause the vehicle to pull to one side during braking.

The brake system is equipped with a BRAKE warning indicator, which is

located on the instrument panel. When the ignition key is turned to the START position, the BRAKE indicator should light up. After the key is returned to the RUN position, the

indicator goes out. The BRAKE indicator comes on in the following cases:

– when the parking brake is applied (ignition on).

– when the brake fluid level in the master cylinder reservoir drops. With the engine idling and the transmission in neutral, press and hold the brake pedal with constant force. If the brake pedal slowly sinks, the possible cause is a brake fluid leak.

Inspect the entire brake system for leaks. Check the brake fluid level in the reservoir. A slight drop in fluid level may be

caused by normal brake pad wear. A significant drop in level may indicate a fluid leak. Both internal and external fluid leaks are

possible in the hydraulic brake system. If the brake fluid level is normal, check the length of the vacuum booster pushrod. If the

pushrod length differs from specification, adjust or replace the pushrod.

Check the adjustment of the service brake and the parking brake.

The following master cylinder checks do not guarantee detection of all possible assembly faults.

1) Check the cylinder body for cracks and for traces of brake fluid on its

outer surface. Leaks are indicated by drops of brake fluid. Wetness on the outside of the cylinder is

permissible.

2) Check the pedal linkage for binding and check the pushrod length. If

no fault is found, remove and disassemble the cylinder. Check the

condition of the cylinder and piston seals. If the seals have swollen or elongated,

the possible cause is unsuitable or contaminated brake fluid.

In this case, the cylinder must be completely disassembled and all parts must be

washed. Rubber parts must always be replaced.

The entire brake hydraulic system must also be flushed.

Using non-recommended brake fluid types, or allowing mineral oil or water to enter the hydraulic system, lowers the boiling point of the fluid and causes rubber seals to fail.

Swelling of the outer rubber boots on the master or wheel cylinders indicates failure of the internal rubber seals.

If signs of rubber part swelling are found, disassemble and thoroughly flush the entire hydraulic system with alcohol. Before assembly, dry all hydraulic system parts with a stream of compressed air to prevent alcohol from entering the brake system. Rubber parts, including brake hoses, must be replaced. Also check for traces of brake fluid on the brake linings. Replace linings if heavily contaminated. If the master cylinder seals are in good condition, the possible cause is overheating of

the brake fluid.

If there is no overheating, drain the brake fluid, flush the system with fresh brake fluid, fill with new brake fluid and bleed air from the hydraulic system.