Abstract: A conveyor system comprising a track along which a plurality of carriers are movable. Each carrier includes a pusher dog that is movable into and out of position for engagement by a pusher lug of a conveyor chain. Each carrier is provided with wheels, and a pivoted anti-back up cam member which is normally urged by gravity in a direction to hold surfaces thereof out of engagement with the track. Each carrier further includes an actuator operable when it engages a preceding carrier or an obstacle to move the pusher dog out of engagement with the pusher lug. A spring is provided between the actuator and the anti-back up cam member so that when the actuator is operated to move the pusher dog, the cam member frictionally engages the track.