Brake Fade Explained: Why and What To Do
Once you understand the cause of a fading brake pedal you will see how easy it is to avoid it in the future. Brake pedal fade can occur for two primary reasons. The most common is the over heating of the brake fluid to a point where the fluid actually boils and turns to gas. The other common scenario is the over heating of the brake pad friction material to a point where it simply disintegrate from the pad backing plate.
Boiling brake fluid: This occurs when the brake fluid that is located in the area next to the caliper piston reaches such high temperatures that it starts to boil and turn from a none compressible liquid to a compressible gas form. Once the liquid turns to gas, this gas can be compressed making the pedal feel spongy and soft. In severe cases the pedal can be depressed to the floor without applying adequate pressure to the pads to stop the vehicle. After the fluid cools the gas will return to a non-compressible liquid and the brakes will feel normal once again. To reduce the possibility of this situation, especially on a driving school weekend, completely flush your brake system with a high quality, HIGH boiling point dot 3 or 4 brake fluid. We recommend the ATE Super Blue, or TYPE 200. Both of these products have a boiling point that is 122 degrees above DOT 4 specifications.
This feature is what makes this product an excellent choice for racing conditions. Both the Super Blue and the Type 200 are compatible with all of the BMW and Mini Cooper brake systems. An important factor to remember is that as the brake fluid heat cycles it will break down and reduce the boiling point values. This is why it is important to flush the fluid after every 2nd track event, or after a brake fade condition occurs. Another reason brake fluid brakes down is when it is exposed to moisture. This occurs if the fluid is old, stored in an open container, or is left in service for too long. We recommend flushing the system once a year in dry climates, and no more than 6 months for areas with extreme weather conditions. When flushing brake fluid, make sure you replace all the old fluid. This is best accomplished by bleeding the brakes starting at the right rear caliper and working your way to the nearest caliper to the master cylinder. Always flush until the fluid comes out crystal clear (or Super Blue) and never reuse the fluid from the waste container. Two full quarts should flush most any vehicles hydraulic system.
Brake pad failure: The pad friction material consists of 2 components. Those components are the actual organic/asbestos powder and the glue or binder material that is mixed with the powder that is used to compress the material into the shape of the friction pad. The specific formulas of these compounds are what determine the operating temperature range of the brake pad. For example street pads will only function well from a cold situation to a specific temperature, while race pads work poorly at colder temperatures with better stopping power when heated. There are no pads that work well in all conditions.
Street pads compounds: This material will work well from the first morning cold stop to a moderate temperature. Once you exceed the temperature range the binding material (the Glue) will simply melt down and vaporize. This vapor becomes trapped between the pad and the rotor surface making the pad glide on a blanket of vapor. This condition is also a brake failure condition. This can be avoided by using slotted or cross-drilled rotors, which allow the gas to escape. Once the pad begins floating on the gas barrier, additional pedal pressure will be required to slow the vehicle that increases braking temperatures to further destroy the pad. This added temperature will also begin boiling the brake fluid at an early point in the driving experience. This is why most street pads will not last more than 1 or 2 days at a driving school event.
Race pad compounds: These compounds are designed to operate at a much higher temperature. The friction material is more aggressive to the rotors, however this aggressive material will stop the vehicle with less pedal pressure in a shorter time frame, which keeps the heat generation to a minimum. The binder material (the glue) has a much higher melting point that keeps the pad in-tact for the duration of the day. Less melt down translates to less gassing of the pads. The only down side is poor cold braking, more brake dust, and possible squeak.
For street driving we recommend the Mintex Red Box compound, for light track the Mintex 1144, for heavy track the Mintex 1166.