A transmission (15) utilizes oscillating torque to vary the mechanical power transmitted to a load (17). An arm assembly (29) is rotatably coupled to a frame (23). At the ends of the arms are eccentric masses (31), rotatably coupled thereto. An input shaft (25) rotates the masses about the ends of the arms. The rotating masses produce an oscillating torque that causes the arms to oscillate. The arms are coupled to an output assembly (33). The output assembly utilizes one way clutches (107, 109), with one clutch reversed relative to the other clutch. The one way clutches convert the bidirectional rotation of the arms to unidirectional rotation for the load. The output speeds of the transmission are controlled by providing at least two side by side rotatable masses (95, 97) and varying the phase of one of the masses relative to the other mass. Varying the phase changes the center of the gravity of the masses, thereby affecting the torque applied to the arms.