Abstract: An accumulator mechanism for stopping a carrier on an inverted power and free conveyor system when it approaches a stopped preceding carrier. A pivot arm on a leading trolley for each carrier has a retractable trolley dog which is normally driven by a chain dog projecting from a drive chain. The accumulator mechanism includes an actuator lever which is pivoted to mounting plates and carries a cam roller that acts in a cam slot formed in a pivot plate. When the actuating lever is pivoted due to contacting a preceding carrier, the cam roller acts within the contour of the slot to pivotally displace the pivot plate. The pivot plate then pulls a lift link upwardly to pull on the pivot arm and retract the trolley dog from the chain dog. The slot is arranged to effect lost motion of the cam roller in the slot to accommodate over travel.