Designing highly loaded spur and helical gears for truck transmissions that are both strong and quiet requires an analysis method that can easily be implemented and also provides information on bending stress, load distribution, and transmission error. The finite element method is capable of providing this information, but the time needed to create such a model is very great. In order to reduce the modeling time, a preprocessor program that creates the geometry needed for a finite element analysis has been developed. While requiring a minimum of user input, the program generates a three-dimensional model of contacting spur or helical gears using eight node brick elements. Gap elements are used to model the contact that normally occurs between meshing gear teeth as well as the contact that may occur off the line of action due to the teeth deflecting under load. The effects of non-standard geometry such as profile modification, lead modification and tooth errors can be easily included in the model. The preprocessor creates an input file used by a commercially available finite element code. The technique used to develop the preprocessor program is presented. Examples of the geometry created by the preprocessor and finite element analysis results are also given. The preprocessor provides a method in which spur and helical gears can easily be modeled and incorporated in the normal design and analysis procedure.