A mechanical torque converting transmission for producing an output with variable, controllable speed and torque characteristics comprises a rotary input shaft (12) adapted for attachment to a rotary power source and connected to a main drive gear (20). The drive gear is meshed with a plurality of pinion gears (32) which are journaled for rotation on an arm assembly (24). An eccentric device (34) is driven by each pinion gear for creating a centrifugal force that cyclically urges the arm assembly (24) in alternating forward and backward directions with a pulsating motion during each rotation of each eccentric device. A clutch (36) is provided for allowing forward movement of the arm assembly while preventing movement in the backward direction during each eccentric revolution. A resiliently displaceable device (26) interconnecting the arm assembly and an output shaft transforms the pulsating motion of the arm assembly to a smooth rotational motion of the output shaft (28), thereby causing the output shaft to rotate at a different speed and torque from that of the input shaft. Controls can be utilized to activate or deactivate the clutch and also change the phase relationship of the driven eccentric devices in order to vary the transmission output under varying load conditions.