a railcar moving or positioning system incorporating relatively simple mechanical bogey frame side member sensing systems mounted on each dog carriage of a railcar indexing system is disclosed . each sensing system is used to control the operation of a dog mounted on the same carriage . a mechanical follower device is employed to sense the underside of an encountered bogey frame side member . deflection of the follower is used to operate a hydraulic valve which , in turn , is used as a control cylinder to raise or lower an adjacent dog member .