The objective of this work is to develop an efficient multi-body model of a worm gear reducer in order to predict fluctuating reaction forces at supporting bearings. Noise and vibration in a worm gear reducer system takes place primarily due to axis misalignment, unsteady motor power supply and the twist of a shaft. The dynamical interactions among input and output shafts together with equivalent stiffness, contacting worm and worm-gear and supporting bearings were included in this multi-body dynamic model. The fluctuating reactive forces on the supporting bearings of single- and double-axis reducers were computed for four alignment angles of axes by the model. The fluctuation force on supporting bearings due to misalignment of axes is a major factor for the noise and vibration of a worm gear reducer. The results demonstrate convincingly that a double-axis type worn gear set is more vulnerable to axis misalignment compared to a single-axis type. Therefore, a single-axis reducer fits for a powered wheelchair.