Brake fluid is one of the most important fluids in a car. Without it, safe driving would be impossible, as the brakes would not work. Brake fluid transmits the force exerted by the driver on the brake pedal onto the wheel brake. In order to ensure it can always handle this, the brake fluid must be changed regularly during inspection or maintenance.
Brake fluid is hygroscopic. That means it absorbs moisture from its environment. If the brake fluid absorbs too much moisture, the wet boiling point is lowered significantly, which increases the risk of total brake system failure under extreme loads.
Example Downhill: If the foot is constantly on the brake, the temperature of the brake fluid rises. When the boiling point is reached, the bound water begins to boil and vapour bubbles form in the brake system.
The Result: No pressure can build up in the brake system = total brake failure!
Brake fluid should be changed every two years. When choosing, manufacturer‘s specifications must be observed because there are different classes:
The higher the DOT class, the higher the boiling temperature and wet boiling point. Higher DOT classes tend to allow for longer maintenance intervals. The DOT standards are based on the American FMVSS-116 standard of the Department of Transportation (DOT).
Dry boiling point: describes the property of the sealed new brake fluid. In this state, the brake fluid is almost anhydrous (substance containing no water). The dry boiling point is usually between 240 and 280°C.
Wet boiling point: determines the property of the brake fluid at the end of its life cycle, at a water content of 3.5% the fluid should be replaced. This defined wet boiling point must not be undercut.
Viscosity: describes the flow rate of the brake fluid. The lower the viscosity, the faster the brake fluid flows through the brake system, and the faster the brake signals are transmitted.