Brake Fluid: Description and Operation

Brake Fluid

• Brake fluid is hygroscopic, i.e. it has the ability to absorb water and moisture from the air.

If water has been absorbed, the boiling point will drop, i.e., during high braking temperatures the brake fluid may develop steam bubbles and cause the brakes to fail.






Over time, brake fluid will darken in color. Dark-colored brake fluid does not specify anything about its quality. The color forms due to chemical reactions.

The rubber components of the brake system (boots, seals) do not tolerate mineral oil, gasoline, and cleaning agents!

Even the smallest amount on a seal or boot can cause the part to change and thereby affect the function of the brake system. The results of an unclean brake system first show themselves months later, causing increased repair costs, especially on vehicles with ABS.

A = Boot - Original size






B = Boot - Swollen through contact with mineral oil

It is Implied by the Previously Mentioned Points That

Keep containers of brake fluid closed securely. This is to make sure that no oil, dirt or cleaning materials and no humidity can enter the container.

Store containers of brake fluid away from oil (even hydraulic oil) and cleaning fluids to prevent an accidental mixing of both fluids or even filling the brake system with the wrong fluid.

The use of brake fluid approved by Audi is recommended, refer to the Parts Catalog.