Brake Fluid; General Notes - Audi A8 2003 Workshop Manual

5

Brake fluid

5.1

General notes

Brake fluid is hygroscopic, i.e. it has the tendency to absorb water
and moisture from the atmosphere
The boiling point decreases as the water content increases, which
means a considerable rise in brake fluid temperature can lead to
formation of vapour bubbles and brake failure.
The colour of the brake fluid becomes darker over the course of
time. A dark brake fluid colour is not an indication of its condition.
The change in colour is caused by chemical reactions and may
occur within a short period (several weeks), particularly in vehi‐
cles equipped with ABS.
WARNING
Rubber parts of brake system (sleeves, seals) are not com‐
patible with mineral oil, fuel and cleaning agents.
Even minute quantities coming into contact with a seal or sleeve
will affect the component and could impair brake operation. The
consequences of a contaminated brake system only become ap‐
parent months later, and then give rise to greater expenses,
particularly in vehicles equipped with ABS.
A = Sleeve (original size)
B = Sleeve (swollen due to contact with mineral oil)
Summary of the above mentioned points:
Always keep brake fluid containers properly sealed. This is the
only way of preventing contamination by oil, dirt, cleaning agents
or moisture.
Brake fluid containers should be kept completely separate from
oils (including hydraulic fluid) and cleaning agents to prevent any
mixture of fluids or even filling of the brake system with an incor‐
rect fluid.
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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
Audi A8 2003 ➤
Brake system - Edition 03.2013
17
5. Brake fluid