Abstract: A power transmitting mechanism for starting a load which is either of high inertia or of high starting torque and which is to be driven at a high speed through a high reduction ratio. The load has a main power source and also an axuiliary power source which initially turns over the load from a zero speed condition. After the load has been turned over by the auxiliary starting means and through a high reduction ratio, the main power source acts to slip the overrunning clutch and bring the load up to speed. The auxiliary power source has a hydraulic coupling retarder which acts to retard the auxiliary power source during its initial operation and thereby reduces its kinetic energy during its initial operation and decreases the large torque pulses which would otherwise occur in the mechanism during the start-up. The mechanism includes hydraulic control means for controlling the sequencing of the fluid fill of the hydraulic coupling retarder.