A brake has been designed for use on a class 8 tractor trailer which utilizes a hydrodynamic film of fluid between a series of rotors and stators to reduce wear and increase energy rejection capability. The hydrodynamic film brake or HFB was constructed and tested on a brake dynamometer and demonstrated a very low parasitic loss at all speeds and a high energy rejection rate. Deceleration rates of a 10,450 kg (23,000lb) inertially simulated axle were 6 M/S2 (20 ft/s2) with the application of 0.618 MPa (90 PSI) air pressure. These tests demonstrated the feasibility of meeting the braking requirements for class 8 vehicles with a wet disc brake. Test results indicated very low wear rates for in service operation and good heat rejection characteristics. Design objectives were to produce braking capabilities which will retard a 36,000 KG (80,000 LB) truck traveling 96 KPH (60 MPH) down a 6% grade for up to 4 minutes without the use of engine retardation and without exceeding brake temperatures of 230 C (450 F).