Audi A4

since 1994 release

Manual of the car


Audi A4
+ Running gear
+ Regular servicing
+ Engines
+ Turbo-supercharging
+ System of an exhaust
+ Cooling system
+ Fuel tank and fuel pump
+ Air filter and channels of absorption
+ System of injection
+ Coupling
+ Transmission and main transfer
+ Suspension bracket of wheels and steering
- Brakes
   Independent work on the brake system
   So the brake system works
   Check of brakes
   Brake fluid
   Check of level of brake fluid
   Check of the brake system on tightness and existence of damages
   Replacement of brake fluid
   Disk brakes
   Measurement of thickness of overlays of forward disk brakes
   Check of a condition of brake disks
   Replacement of overlays of disk brakes
   Back disk brakes
   Measurement of overlays of back disk brakes
   Emergency brake
   Check of idling of the lever of the emergency brake
   Main brake cylinder
   Brake amplifier
   Check of the brake amplifier
   Works on hydraulics of the brake system
   Pumping of the brake system
   The help at malfunctions
   ABS and EDS
   What does ABS?
   Function of separate knots
   Electronic system of distribution of brake effort (EBV)
   Violations in work of the ABS system
   Electronic blocking of differential (EDS)
+ Wheels and tires
+ Electrotechnical equipment
+ System of ignition
+ Lighting
+ Alarm equipment
+ Tools and devices
+ Heating and ventilation
+ Body details
+ Salon
Search of malfunctions
Technical characteristics

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Brake fluid

Between a motive compartment and a windshield in the so-called moisture catching box a tank with brake fluid (1), the main brake cylinder (2) and the brake amplifier (3) are placed. In the photo marks of level of filling of a tank "MOVE" and "MIN" are well visible.

This liquid, yellowish, poisonous and aggressive in relation to an automobile varnish, does not corrode metal and rubber details. She remains rather zhidkotekuchy at –40 °C and, despite the zhidkotekuchest, about about 260 °C possess extremely high boiling point.

But brake fluid has very unpleasant property: it willingly absorbs water, it "is hygroscopic". Water, for example due to humidity of atmospheric air, can really get into brake fluid: through a broad tank or through microscopic untight sites in brake hoses or in rubber cuffs. Such absorption of water leads not only to corrosion of metal details of the brake system, but also causes bystry decrease in a boiling point of brake fluid. At the content of water in only 2,5% its boiling point is only at 150 °C. Near the warmed brakes vials of steam in hydraulic liquid can be formed. They contract – the pedal of a brake can deeply fail, sometimes the leg presses just in emptiness! In this case bystry pumping of liquid a brake pedal sometimes helps. This effect is especially dangerous at a car stop after strong load of brakes. Because of a lack of a head wind everything, being in an environment of brakes, is warmed even stronger. And approximately only in half an hour temperature of brake fluid goes down to normal.

Therefore the plan of maintenance orders preventive replacement of brake fluid every two years. Brake fluid has to meet the FMVSS 116 DOT 4 specification. All liquids with such designation it is possible without fear to mix.