Abstract: A power and free conveyor transfer system includes a number of drive trolleys operating within a free track and being selectively propelled by endless drive chains within a vertically aligned power track. Each drive trolley includes a trolley housing body to which are rigidly attached a pair of downwardly extending lateral arms, each with a rearward facing drive surface. A pivotable drive member is attached to the front end of the trolley housing and extends backward and downward between the lateral arms with a drive dog forming a portion thereof. The drive trolley design facilitates transfer of each drive trolley between non-synchronous delivering and receiving power tracks in a conveyor transfer zone. Within the transfer zone, the delivering and receiving power tracks are at different elevations and approach each other from a relatively large angle to minimize the potential for mechanical interference or jamming.