General information
Depending on the vehicle modification, different brake mechanisms may be installed (see Specifications).
The brake system is divided diagonally into two independent hydraulic circuits and consists of a master brake cylinder (MBC) with a vacuum booster, a vacuum hose, brake hydraulic lines and brake mechanisms. If one of the circuits fails, (for example, as a result of a breach in the seal) the second continues to function in normal mode, providing adequate braking of the car. The fluid pressure in both circuits is created by a tandem-design master brake cylinder (MBC). The MBC is activated when the brake pedal is depressed. The brake fluid reservoir is fixed to the MBC.
The brake booster accumulates part of the vacuum created in the engine intake manifold. On diesel and petrol engines of 1.8, 2.0 and 3.6 l, additional vacuum for reliable operation of the vacuum booster is created by a vacuum pump.
The parking brake is a traditional cable-operated type from a lever, acting on the rear brakes.
The procedures for bleeding and checking the brake system, as well as replacing the brake fluid, are described in Sections 8-9 of Chapter 1.
When checking the brake system, the wheels are driven by a single-axis roller dynamometer at a maximum speed of 6 km/h. During the test, the transmission must be in neutral. When the ignition is off, the auxiliary functions of the brake system do not work. On AWD models, a single-axis roller dynamometer must be used, on which the roller for each wheel rotates in different directions - this prevents the transfer of braking forces to the transmission line. In this case, the measurement is only taken for the wheel rotating forward, i.e. the test must be carried out twice. If the specified dynamometer is not available, follow the following sequence for testing on a conventional single-axis roller dynamometer. Place the front wheels on the rollers, turn off the engine, wait about two seconds and check the front brakes. Start the engine, wait about 5 seconds (until a sufficient vacuum is created) and install the rear wheels on the rollers. Turn off the engine, wait about two seconds and check the rear brakes. Start the engine and wait about 5 seconds (until a sufficient vacuum is created).
The ABS or ESP system with various additional functions is installed as standard. A description of ABS/ESP and their functions is presented in Section 24 of the Chapter "Control Bodies and Operating Techniques".
To monitor the operation of the brake system and the ABS/ESP system, the corresponding indicator lamps in the instrument cluster are used (see Section 13 of the Chapter "Controls and Operating Techniques").
Security measures
Brake fluid is a highly toxic and chemically aggressive compound and when in contact with body panels it destroys the paintwork.
The dust generated during the wear of brake pads may contain asbestos, which is harmful to human health - do not inhale it under any circumstances when cleaning the brake mechanisms!
Working with the brake system requires special cleanliness and strict adherence to instructions. If you do not have the necessary experience, it is advisable to contact a service station.
Note: When driving on wet roads, you should periodically press the brake pedal to remove moisture from the brake discs. As the wheel rotates, moisture is thrown off the brake discs by centrifugal force, but a silicone film, rubber abrasion products, grease and other contaminants remain, reducing braking efficiency!
Corroded disc brakes create a shaking effect when braking, which does not disappear over time. In this case, the discs should be replaced.
The burning of dirt onto the surface of the brake pads leads to the formation of grooves on the surface of the brake discs, which leads to a decrease in braking efficiency.
When checking on a roller dynamometer, the transmission must be in neutral. In this case, the maximum test speed must not exceed 6 km/h.
Notes on carrying out repair work on the ABS/ESP system
When performing any repair work on the ABS/ESP, the first step is to determine the cause of the malfunction using a diagnostic tool connected to the vehicle's diagnostic connector (see Chapter 5).
Observe general safety precautions when working with brake fluid. After performing work in which the brake hydraulic circuit was open, air should be removed from the hydraulic system (pump it up, see Chapter 1). Maintain impeccable cleanliness, never use additional parts containing mineral oils.
Thoroughly clean the connections and surrounding area before disconnecting the brake lines. Do not use aggressive detergents, gasoline, solvents, etc.
Place the removed parts on a clean surface and cover them.
After separating the control unit from the hydraulic modulator, use transport protection for the connector contacts.
If repairs cannot be made immediately, cover or cap exposed components.
Use only lint-free cloth.
Unpack spare parts only immediately before installation. Do not work with compressed air or move the vehicle when the system is open.
When painting a vehicle, the ABS/ESP electronic control unit may be exposed to a maximum temperature of 95°C for a short period only. Exposure to a temperature of 85°C is permitted for approximately 2 hours.