Abstract: A clutch hydraulic slave cylinder comprising a cylinder body, a primary piston sealingly reciprocable relative to the body and co-operating with the body to form a first fluid chamber within said body, and a secondary piston sealingly reciprocable relative to the primary piston and co-operating with the primary piston to form a second fluid chamber. the second fluid chamber is connected to the first fluid chamber through a valve means. The primary piston is biased by a spring means from a fully retracted condition to an at-rest condition in which it can exert a pre-load on a clutch bearing, and said valve means is open when the primary piston is in the fully retracted condition, and is closed when the primary piston is in the at-rest condition.

Abstract: A hydraulic annular slave cylinder (16) for a motor vehicle clutch having an annular body (21) with inner and outer cylindrical sidewalls (22, 23) having a fluid chamber (55) formed therebetween. The inner sidewalll (22) extends axially beyond the outer sidewall (23) and a piston member (41) is sealingly slideable on the radially outer surfaces of the two walls (22, 23). A clutch release bearing (60) is mounted concentrically of the piston member (41) and fluid chamber (55).