The present invention provides a releasable skate retarder for railway cars. The retarder includes a plurality of spring packs including springs which bias shoe carrying beams toward running rails, trapping wheels of a railway car entering the retarder between the shoes and the running rails, and applying a frictional force to the railway car wheels for stopping the railway car and retaining the railway car in the retarder. The retarder is operable in a release mode in which an operating mechanism moves the shoe beams to a release position in which the spring force is released, allowing the railway car to move freely through the retarder. The retarder is operable in a service mode in which the operating mechanism moves the shoe beams outwardly, allowing the insertion of shims which cause the shoes to be repositioned closer to the running rails to compensate for shoe wear. In one embodiment, the operating mechanism includes a plurality of rams and a common operating member which couples the rams to the spring packs, for drawing the shoe beams inwardly when operating in the release mode and for pushing the spring packs outwardly when operating in the service mode.