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ABS, ADR, TCS, EDL, ESP > < Brake fluid

A4 Cabriolet Mk2

General notes
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 vehicles equipped with ABS.
  WARNING
Rubber parts of brake system (sleeves, seals) are not compatible 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 apparent months later, and then give rise to greater expenses, particularly in vehicles equipped with ABS.
  N47-0016
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 incorrect fluid.
  N47-0013

ABS, ADR, TCS, EDL, ESP > < Brake fluid