The car has three independent braking systems: service, spare and parking.
The service brake system is hydraulic, dual-circuit (divided into front and rear circuits), with a vacuum booster, a pressure regulator and a sensor for an emergency drop in the level of brake fluid in the reservoir.
The spare system is formed by each circuit of the working system.
If one of the brake circuits fails, the second circuit provides braking to the vehicle, albeit with less efficiency.
The parking system is mechanical, with a cable drive from the hand lever to the brake pads of the rear wheels.
The front wheel brake mechanism is disc, with automatic adjustment of the gap between the pads 7, Figure 2, and the ventilated disc 6, with a floating caliper.
The movable bracket is formed by a caliper 5 with a two-piston working cylinder. The 4-shoe guide is bolted to the steering knuckle.
The movable bracket is bolted to the guide pins 3 installed in the holes of the guide shoes. The guide pins are greased and protected by rubber boots.
Pistons with O-rings are installed in the cavity of the working cylinders. The elasticity of these rings maintains an optimal clearance between the pads and the ventilated disc.
When braking, the pistons, under the influence of fluid pressure, press the inner pad against the disc, as a result of the reaction force, the caliper moves on the fingers and the outer pad is also pressed against the disc, while the pressing forces of the pads are the same.
When releasing the pistons, due to the elasticity of the O-rings, they move away from the pads, a small gap forms between the pads and the disc.
The main brake cylinder of the "tandem" type of the hydraulic brake drive is installed in the engine compartment directly on the vacuum brake booster.
It consists of two separate chambers connected to independent hydraulic circuits.
The first camera is connected to the rear brakes, the second to the front ones.
On the main cylinder through rubber connecting bushings 6, a reservoir 1 is installed and fixed to the cylinder with a screw 4, the inner cavity of which is divided by partitions into three compartments.
Each of the two main compartments feeds one of the chambers of the master brake cylinder, and the third compartment feeds the master cylinder of the hydraulic clutch release.
When you press the brake pedal, the pistons of the master brake cylinder begin to move, the working edges of the cuffs overlap the compensation holes, the chambers and the reservoir are disconnected, and the displacement of the brake fluid begins.
A sensor 3 of the brake fluid level is installed in the upper part of the reservoir.
When the liquid level falls below the permissible level in the instrument cluster, the warning lamp for the malfunctioning state of the brake system lights up.
The flange for connecting to the vacuum brake booster is sealed with a rubber ring.
The vacuum booster installed between the pedal mechanism and the main brake cylinder, when braking due to the vacuum created by a vacuum pump driven from the engine camshaft, through the rod and piston of the first chamber of the master cylinder, creates an additional force proportional to the force from the pedal.
The vacuum booster is connected to the vacuum pump through a hose and a check valve, which holds the vacuum in the booster when the engine is stopped.
An adjusting bolt with a lock nut is screwed into the front end of the booster pusher, which provides the required clearance for the correct operation of the master brake cylinder.
Rear wheel brake drum with automatic adjustment of the gap between the pads and the drum.
The brake pads 4 are driven by one hydraulic slave cylinder 10 with two pistons 22.
The optimal clearance between the drum 5 and the pads 4 is maintained by mechanical regulators located in the working cylinder and represented by split steel elastic thrust rings 23 installed with an interference fit into the cylinder.
Shaped shanks of the pistons 22 enter the shaped holes of the thrust rings.
As the pad linings wear out, the thrust rings move along the cylinder mirror to its outer holes, allowing the pistons to also move further outward and limiting their reverse movement into the cylinder under the action of the return springs, which compensates for the increasing clearances between the brake pad linings and the drum.
The brake pressure regulator adjusts the brake fluid pressure in the working cylinders of the rear wheel brakes, eliminating the possibility of locking the rear wheels earlier than the front ones.
The regulator is fixed to the frame and through a load spring reacts to the load taken by the rear axle.
The parking brake system is mechanical, with a cable drive from the lever installed in the driver's cab to the brakes of the rear wheels.
When acting on the lever 1 through the system of cables 2,5,8 and levers 7, the brake pads are pressed against the drums, braking the car.
Lever 1 is fixed in the raised position using a ratchet mechanism consisting of a pawl and a toothed sector.
When the lever is raised, the switch located on the lever mounting bracket turns on the warning light in the instrument cluster.
The hydraulic brake system is integrated into a single unit with metal pipes and hoses.
The system is filled with DOT-4 brake fluid.
The travel of the brake pedal with the engine running should be approximately 50 mm.
Too small stroke indicates an incorrect initial setting of the brake pedal, a maladjustment of the vacuum brake booster or a seized working cylinder, which causes increased fuel consumption and accelerated wear of the brake pads.
Too large a working stroke is a sign of excessive clearances in the pedal mechanism or a violation of the tightness of the hydraulic drive of the brake system.
If the travel is reduced by repeatedly pressing the pedal, i.e. it becomes stiff in the air system.
If the full pedal travel begins to increase, the system is leaking.
If the brake pedal always vibrates when braking, the brake discs are most likely warped.
Unfortunately, in such a situation, they only need to be changed, and both at once.
If, when braking, the machine begins to pull to the side, check the working cylinders: they may need to be replaced.
If a knock appears in the front suspension that disappears during braking, check the tightening of the caliper mounting bolts.
After replacing the brake pads, before starting the movement, be sure to press the brake pedal several times - the pistons in the working cylinders must snap into place.
As an option, the vehicle is equipped with a brake system with automatic locking of wheels (ABS)
Possible malfunctions of the brake system and remedies
- Rejection reason
Extended brake pedal travel:
- Leakage of brake fluid from the working brake cylinders
Replace defective brake cylinders, rinse and dry pads, discs and drums
- Air in the brake system
Remove air by bleeding the system
- Damaged rubber O-rings in the master brake cylinder
Replace the cylinder assembly
- Damaged hydraulic brake hoses
Replace hoses and bleed system
- Increased runout of the brake disc (more than 0.15 mm)
Grind or replace the disc if the front brake discs are less than 30.0 mm thick.
Insufficient braking performance:
- Oiling of brake pads lining
Rinse and dry the pads
- Seizure of pistons in the working cylinders
Eliminate the causes of seizure, replace damaged parts
- Complete wear of the brake pads
Replace brake pads
- Overheating of the brakes
Stop and cool the brakes
- The use of substandard pads
Use original pads
- Violation of the tightness of one of the circuits (accompanied by a failure of the brake pedal)
Replace damaged parts, bleed the brake system
- Violation of adjustment of the rod of the vacuum brake booster
Adjust the stem
Incomplete release of all wheels:
- There is no free play of the brake pedal
Replace the brake master cylinder
- Increased protrusion of the vacuum brake booster rod
Adjust the stem
- Swelling of the master cylinder rubber seals due to the ingress of gasoline or oil
Flush and bleed the entire hydraulic drive system, replace rubber parts.
- Violation of the position of the front wheel brake caliper when loosening the mounting bolts
Tighten the mounting bolts
- Incorrect adjustment of the parking brake system
Adjust the parking brake system
Skidding or drifting to the side when braking:
- Seizure of the working cylinder piston
Check and repair piston sticking in cylinder
- Tube blockage due to dented or obstructed
Replace or clean tubing
- Dirty or oily discs, drums and brake linings
Clean brake parts
- Wheel alignment angles are violated
Adjust the wheel alignment angles
- Different tire pressures
Set the required tire pressure
- One of the brake circuits does not work
Replace damaged parts and bleed the system
Increased effort on the brake pedal when braking:
- Defective vacuum booster
- The hose connecting the vacuum booster is damaged or its fastening is loose
- Swelling of rubber cylinder seals due to substandard brake fluid
Replace cylinders, flush and bleed system
Squeak or vibration of brakes:
- Greasing of friction linings
Scrub with a wire brush and detergent with warm water
- Wear of linings or foreign inclusions in them
- Excessive runout due to brake disc wear
Grind or replace the disc.