Abstract: A power and free conveyor system wherein a train of track supported trolleys includes a lead trolley normally driven by an overhead power chain. The train moves through a transfer area wherein the lead trolley is disengaged from the power chain; and, in order to complete the transfer, a trailing trolley is provided with a secondary or transfer dog which engages the power chain while the lead trolley is undriven. The transfer dog is pivotally connected to one end of an operating arm which is pivotally mounted on a lower portion of the trailing trolley, and the other end of the operating arm supports a cam follower. An actuating cam extends below the track in the transfer area, causing the transfer dog to rise into a transfer position so as to engage the power chain and thereby propel the train through the transfer area.