A system has been developed to load the power train of a lab test vehicle with field recorded torques. This loading is accomplished with hydraulically activated axle load brakes which are controlled by an electro-hydraulic servo system. The entire power train is then tested as though the tractor was operating in the field. The advantages of the test system include 24 h/day operation regardless of weather conditions and very consistent day to day loading of the test vehicle. This paper presents the reasons for starting the program and a description of the power train test system.