A modular drive system for a zero turn radius vehicle having a central gear box with a vertical input shaft, a central drive train that powers a variety of left and right side drive mechanisms, and a power take off mechanism having a clutch and brake assembly. The vertical input shaft is a through-shaft design that allows the central gear box to be mounted with either end of the through-shaft oriented in an upward direction. A screw-on filter acts in conjunction with a charge pump to remove debris from the central gear box's hydraulic fluid.