Audi A4, S4

since 2000 release

Repair and operation of the car

Audi A4, S4
+ Introduction
+ Governing bodies and methods of safe operation
+ Current leaving and service
+ Engine
+ Cooling systems, heating and air conditioner
+ Power supply systems, release and decrease in toxicity of the fulfilled gases
+ Systems of electric equipment of the engine
+ Manual box of gear shifting
+ Automatic transmission
+ Coupling, power shafts and differential
- Brake system
   Removal of air from brake system
   Removal and installation of front brake shoes
   Removal and installation of blocks of brake mechanisms of back wheels
   Check of thickness of a brake disk
   Removal and installation of a brake disk / support
   Adjustment of the parking brake
   Removal and installation of the switch of a stoplight
   Removal and installation of a brake hose
+ Suspension bracket and steering
+ Body
+ Onboard electric equipment

Brake system

Main data

The brake system consists of the main brake cylinder, the amplifier of a brake and disk brake mechanisms of lobbies and back wheels. The hydraulic brake system has two contours operating diagonalno. One contour influences on forward right/back left tormoza, the second contour works on forward left/back right tormoza. At refusal of one of contours, for example, owing to liquid leak braking of the car is carried out by other contour. Liquid pressure in both contours is created by the doubled main brake cylinder operating from a brake pedal.

The tank with brake fluid is in a motive compartment, over the main brake cylinder. It supplies with brake fluid all system.

The amplifier of a brake at the petrol engine accumulates part of the vacuum created in the soaked-up engine pipeline. When pressing a pedal of a brake the effort to it decreases owing to the strengthening action of vacuum. As the diesel engine has no necessary vacuum on absorption, models with the diesel engine have the special vacuum pump. The vacuum pump is installed ahead on a head of cylinders and is set in motion from a camshaft.

The car has as ahead, so behind disk brakes with a floating bracket of a support. At such design one piston provides pressing of both brake shoes to a brake disk.

At the movement on wet roads it is necessary to press periodically a brake pedal for drying of disk brakes. Owing to the centrifugal force arising in the course of the movement of the car, water is dumped from disks. However there is a thin film of products of wear of rubber, greasing and the pollution interfering effective operation of brakes.

Dirt and water on a surface of brake shoes lead to formation of furrows on a surface of brake disks that reduces efficiency of braking.

When cleaning brake system dust which can do harm to health of the person therefore it is impossible to inhale brake dust is emitted.

ABS/amplifier of the emergency braking / EBV/EDS

Works with electronically controlled elements of brake system and system of the movement are allowed to be made only to the experts having the corresponding preparation.

ABS: The anti-blocking system interferes with blocking of wheels at sharp braking of the car. It promotes controllability preservation by the car in the course of braking and increases traffic safety.

Amplifier of the emergency braking: The electronic system of the amplifier on the basis of the speed of movement of a pedal of a brake and pressure upon a pedal distinguishes an emergency. In such situation the amplifier automatically during milliseconds increases the brake pressure set by the driver to border of blocking of wheels.

EBV: The system of electronic distribution of brake effort by means of ABS hydraulics distributes brake effort between lobbies and back wheels. As the electronic EBV system works significantly more sensitively, than the regulator of brake effort operating mechanically, is used significantly the bigger range of regulation.

At the movement on a straight line back brakes participate at full capacity in braking process. To provide stability of the car as well when braking on turns, it is necessary to reduce participation in process of braking of back brakes. Via sensors of number of turns of ABS the EBV system receives information, whether the car directly moves or does turn. At turn implementation braking by back brake mechanisms decreases. Thanks to it back wheels can keep the maximum lateral coupling with the road.

EDS: The electronic blocked differential, at start-off from a place brakes the turned wheels. Thanks to it the torque is redistributed on the "pulling" wheels.

The electronic blocking differential works at start-off from a place and is switched off automatically at achievement of the speed of 40 km/h. Advantages of this system are lack of negative influence on road performance and preservation of comfort of management at start-off of the car from a place.

Instructions on ABS/EBV/EDV systems

The scheme of safety in the electronic control unit watches that the system with any defect (for example, break of a cable) or at too low working voltage (battery tension lower than 10 V) was disconnected itself. It is displayed on the dashboard by fire of control lamps. The usual system of braking remains thus efficient. The car when braking behaves as if ABS is absent.

If during the movement control lamps of ABS and brake system burn, at strong braking back wheels since distribution of brake effort failed are blocked.

If during the movement the control lamp of ABS lights up:


  1. Stop the car, switch off the engine and again start it.
  2. Check battery tension. If tension lower than 10.5 In, charge the battery.

If control lamps light up in a start of motion and after a while die away, it specifies that at first battery tension at first was too low. Then it raises owing to battery charging from the generator.

  1. Check, whether plugs of the battery are reliably fixed and whether there is a reliable contact.
  2. Lift and install the car on supports, remove wheels and check electric wires of sensors of number of turns for existence of external damages (a place of mastications). More careful inspection of ABS/EBV/EDV systems has to be carried out in conditions HUNDRED.

Before carrying out electrowelding works it is necessary to rasstykovat the socket of the control unit of hydraulics in a motive compartment. The socket undocks at the switched-off ignition. When coloring the control unit can quickly be exposed to temperature not above +95 °C and during longer time (no more than the 2nd hour) temperature not above +85 °C.