Brake Fluid: Description and Operation
Brake fluidGeneral notes
Brake fluid is hygroscopic, i.e. it has the tendency to absorb water and moisture from the atmosphere
An increase in water content in the brake fluid causes its boiling point to drop. A reduced boiling point can cause vapor bubbles to develop as the fluid heats up under intense braking. In this condition the brake is likely to fail completely.
The color of the brake fluid becomes darker over a period of time. A dark brake fluid color is not an indication of its condition. The change in color is caused by chemical reactions and may occur within a short period (several weeks), particularly in vehicles equipped with ABS.
CAUTION: Avoid any contact of rubber components of the brake system (sleeves, sealing rings) with mineral oil, gasoline and cleaning solvents!
Even very small amounts of the above substances will transform structure and dimension of a sealing ring or sleeve enough to adversely affect brake function. The effects of a polluted brake system will not be noticed for several months until they have caused damage that requires extensive servicing, especially on vehicles installed with ABS.
A = Sleeve (original size)
B = Sleeve (swollen due to contact with mineral oil)
The above mentioned points require special rules for handling:
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.