Abstract: An accumulator conveyor of the type that includes a plurality of article accumulating zones extending between the infeed and discharge ends of the conveyor. In preferred form, each of the conveyor's zones includes at least one novel power transmission assembly, all of those assemblies being powered by a single flexible drive member, e.g., an endless chain. Each power transmission assembly includes a novel fluid ram which cooperates with a power wheel to move that power wheel into and out of driving engagement with the conveyor's article propelling member(s) within that zone it serves.