A hybrid drive train significantly improves energy efficiency of ground vehicles. While numerous auxiliary hybrid power sources have been researched, few are capable of the energy and power density of a flywheel coupled with a continuously variable mechanical transmission. The primary challenge of a flywheel hybrid system is a transmission capable of coupling a high speed flywheel to the drive train of the vehicle. A novel solution to this challenge is a switch-mode continuously variable transmission that utilizes a rapidly switching clutch to transmit power. This system, the mechanical analog of a DC-DC boost converter circuit, utilizes a flywheel, a high frequency clutch, an anti-reversing ratchet, and a spring to vary the output torque. The switch-mode continuously variable transmission is demonstrated through an idealized finite difference model, created from the dynamic system of equations. The model is used to demonstrate the system behavior in a passenger car subjected to road loads in various conditions. The output of the model demonstrates pulses in the output torque as a result of the rapidly switching clutch. This output ripple in is smoothed to an acceptable level by the torsion spring. From this preliminary analysis the on-off continuously variable transmission offers an efficient, energy dense, and power dense hybrid vehicle drive train alternative.