Brake Bleeding: Service and Repair
Bleeding brake system or replacing brake fluid
A. Vehicles without ASR
Screw off cap and drain chambers in brake fluid reservoir down to a brake fluid level of approx. 10 mm. Observe note on brake fluid
Do not completely drain brake fluid reservoir to prevent air from getting into brake system.
With bleeding unit
Renew brake fluid or bleed brake system with filling and bleeding unit
Observe operating instructions of unit manufacturer.
Allow approx. 80 cc of brake fluid to flow out at each brake caliper so that the lines and pressure cylinders in the brake calipers are filled with new brake fluid. Start bleeding at right rear brake cylinder.
Without bleeding unit
Fill brake fluid reservoir up to "maximum mark" with brake fluid. Pump old brake fluid out of each caliper by pumping brake pedal
Note: Close bleed screw each time brake pedal is depressed and allow brake pedal to return slowly so that air is not sucked in through the bleed screw threads and a sufficient quantity of brake fluid can flow back into the system out of the brake fluid reservoir.
Start bleeding at right rear brake cylinder.
Correct brake fluid level in brake fluid reservoir.
Screw on cap
Note: Assure that the vent hole in the cap (arrow) is not clogged.
B. Vehicles with ASR 1st version
Ignition OFF
Drain pressure reservoir drain at bleed screw "SP3".
Screw off cap and drain chambers of brake fluid approx. 10 mm. Observe Note on brake fluid.
If completely drained the entire brake system must be bled (ASR vehicles: 500 cc brake fluid per wheel).
Connect filling and bleeding unit (observe operating instructions of unit manufacturer).
Allow approx. 80 cc of brake fluid to flow out at each wheel brake to renew brake fluid or following work on brake system.
After repair to master brake cylinder or hydraulic unit allow approx. 500 cc of brake fluid to flow out at each wheel brake.
Open bleed screw(1) until clear brake fluid flows out without bubbles.
Start engine.
Open bleed screw(2) until clear brake fluid flows out without bubbles.
Open bleed screw "SP3" until clear brake fluid flows out without bubbles.
If the bleeding operation with bleed screw SP3 "takes too long with the engine running, the charging pump switches off (no more brake fluid exiting at bleed hose, indicator for "ASR "illuminates). In this case shut off engine and start again. Continue bleeding operation.
Shut off engine.
Disconnect filling and bleeding unit, correct brake fluid level in brake fluid reservoir.
Screw cap on, assure that the vent hole in the cap is not clogged.
C. Vehicles with ASR II
Ignition OFF
Drain pressure reservoir at bleed screw "SP3
Screw cap off and drain chambers of brake fluid reservoir down to brake fluid level of approx. 10 mm. Observe Note on brake fluid
If completely drained the entire brake system must be bled (ASR vehicles: 500 cc brake fluid per wheel).
Connect filling and bleeding unit (observe operating instructions of unit manufacturer).
Allow approx. 80 cc of brake fluid to flow out at each wheel brake to renew brake fluid or following work on brake system.
After repair to master brake cylinder or hydraulic unit allow approx. 500 cc of brake fluid to flow out at each wheel brake.
Start engine.
Open bleed screw "SP" until clear brake fluid flows out without bubbles.
Close bleed screw "SP". Wait for charging operation for pressure reservoir (charging pump can be heard running for approx. 30 seconds).
Shut off engine.
Disconnect filling and bleeding unit, correct brake fluid level in brake fluid reservoir.
Screw on cap, assure that the vent hole in the cap is not clogged.
Notes on brake fluid
Use specified brake fluid only, refer to Specifications
For all bleeding operations the brake fluid exiting through the bleed hose should be clear and free of bubbles under all circumstances.
In the course of the operating time the boiling point of the brake fluid decreases due to continuous absorption of moisture from the atmosphere. For this reason steam bubbles can form in the brake system when the brakes are subjected to high loads. It is therefore necessary to renew the brake fluid once each year
When correcting the brake fluid level assure that the original brake fluid level is not exceeded to prevent the brake fluid reservoir from being overfilled after replacing the brake pads.
Handle brake fluid with care
a) Fill brake fluid only into containers from which the fluid cannot be consumed by mistake. (Lethal dose approx. 100 cc).
b) Even slight quantities of mineral oil lead to failure of the brake system, because the rubber parts decompose. Particular attention is required for brake fluid which is colorless or yellow, because the risk of mix-up is highest. If mineral oil is found in the brake system or the presence of mineral oil is suspected, thoroughly flush the entire brake system including the brake fluid reservoir with brake fluid. All brake parts with rubber components as the master brake cylinder, brake calipers, brake hoses, etc., which have come into contact with mineral oil, must be renewed.
c) Do not allow brake fluid to come into contact with the vehicle paintwork, because it contains constituents, which act as solvents on the paint.
d) Brake fluid is highly hygroscopic, i.e. it absorbs moisture from the air, which reduces the boiling point. For this reason store brake fluid in well-sealed storage vessels only.
e) Do not reuse brake fluid pumped out while bleeding, because it can contain foreign particles and/or water, which would contaminate the brake system.
f) Used brake fluid must be disposed of as special waste. Brake fluid, which is not contaminated with oil, can be recycled.
This requires separate collection and storage of the brake fluid.