The following describes the development of a wet disk brake for medium duty truck use. It was determined that the most important parameter to allow extended periods of energy absorption of a brake is the heat capacitance. This brake utilizes a hydrodynamic film of oil between interleaved stators and rotors to distribute the heat evenly throughout the entire mass thus effectively increasing the thermal mass of the brake. Tests also indicate that there may be as much as a 50% increase in fuel economy. Road wear tests project the present brake to have a life of 50,000 miles. If other friction materials used in bench tests were used, brake life could be as high as 150,000 miles.