This thesis presents a drive train model that is designed for use with heavy-duty agricultural and construction vehicles. The drive train model is part of an overall vehicle dynamics model that was developed for a real time vehicle simulation. A drive train contains all the components that transmit the torque produced by the engine to the drive wheels of the vehicle. These components include the engine, clutch, transmission, drive shaft, differential and the drive wheels. The tractive force at the tire/ground interface is a function of the torque at the drive wheel. The tractive force is used to calculate the rate of change of the vehicle longitudinal speed. Commercially available vehicle dynamics models require many input parameters. This can be very costly in both time and money. The drive train model in this thesis has only 12 input parameters. The drive train model handles real time inputs from the simulation operator. These include the steer angle, throttle, brakes, transmission gear ratio and clutch position. The drive train model assumes that there is no slip at the drive wheel/ground interface. Thus, the drive wheel spin rate is always directly proportional to the longitudinal speed of the vehicle. This assumption enables the drive train model to use the longitudinal speed of the vehicle as calculated by the vehicle dynamics model as the primary input. The drive train model contains a clutch between the engine and transmission. The clutch is either locked or slips. When the clutch is locked, the engine spin rate is always directly proportional to the vehicle longitudinal speed. When the clutch slips, the engine spin rate and the longitudinal speed are both functions of the torque carrying capacity of the clutch. The thesis includes simulated results of maneuvers exercising the drive train model. These simulations call for steering, using the clutch, throttle position changes and gear shifts. Continuous shifting from forward to reverse is also shown.