A clamp assembly for an injection molding machine includes (a) a clamp cylinder housing and (b) a clamp piston affixed to an end portion of a tie bar and slidable within the housing among a clamping position, a mold break position, and a meshing position disposed axially intermediate the clamping and the mold break positions. The clamp assembly further includes (c) a clamp chamber for urging the clamp piston towards the clamping position when pressurized; (d) a return device for urging the clamp piston towards the meshing position when pressure in the clamp chamber is relieved; and (e) a mold break chamber for urging the clamp piston towards the mold break position when pressurized. The mold break chamber is bounded axially by opposed surfaces of the tie bar and the return device.