553 Brake Systems Technician Handbook Brake Fade Normally, the heat generated during braking is absorbed by the brake drums and rotors and dissipated into the surrounding air. But during heavy braking it takes just seconds to increase the temperature of a rotor to several hundred degrees Fahrenheit. And it takes much longer for the rotor to cool. When repeated braking generates more heat than the components can absorb, the brakes begin to fade. There are three kinds of brake fade. Mechanical Fade Mechanical fade typically occurred on drum type brakes as the drum overheated and expanded away from the brake shoes. Braking then required much greater pedal effort to compensate.
Friction Material Fade Friction material fade affects drum brakes as lining fade and disc brakes as pad compound fade. Overheating reduces the lining or pad ’ s coefficient of friction, reducing the brake’s ability to stop the vehicle. Hydraulic Fade Hydraulic fade occurs when un-dissipated heat brings the brake fluid to a boiling point, creating gas bubbles inside the brake tubing. Because gases compress under pressure, overheated brake fluid does not transmit brake pressure to wheels. Brake fade is the primary reason for weight limits on towing. It is also the reason that trailers over a certain weight are required to have their own brakes. Technical Training 7