A novel computer simulation program entitled TORAN™ has been developed by the Spicer Clutch Division of Dana Corporation. TORAN™ has been developed for use as an engineering tool for quick and interactive, yet a complete torsional analysis of heavy duty truck drivetrains. This will allow the design and application engineers to examine and predict the behavior of these drivetrains throughout practical ranges of frequencies and torques.TORAN™ is more than just another modification of similar existing programs. The Program, which includes a database of confidential data furnished by drivetrain component and OEM manufacturers and algorithms proprietary to the Spicer Clutch Division. The algorithm accommodates some substantial nonlinearities, such as clutch damper hysteresis and universal joint disturbances. Also included are several new modeling features describing geometrical configuration of axles, torsional properties of tires, etc. The Program can perform a complete modal analysis and evaluate the steady state response to periodic excitations. Furthermore, the special structure of the TORAN™ database and its user friendly interface provide a means for interactive parametric studies for design purposes. The interface allows interactive addition of damper inertias at different locations in the drivetrain and an immediate evaluation of their influence on the drivetrain torsionals.The simulation software involves more than 20,000 lines of computer code in FORTRAN and C and uses OSF MOTIF windowing functions for its user-friendly interface. While the simulation is designed within a UNIX type environment, the user need not be UNIX competent to run torsional analyses. All functions are built to be mouse-click and keyboard operations within the environment provided by the software. Both modeling issues and program features of TORAN™ will be detailed in this paper.