An adjustable length strut includes a pair of relatively movable members defining a pair of load bearing faces which in part define a closed chamber containing fluent material, the fluent material spacing the faces and means is provided movable relative to the faces to vary the configuration of the chamber and therefore of the fluent material to vary the relative position of the faces. The members and movable means may be variously pistons, cylinders or sleeves slidable on pistons or in cylinders. Such a strut has particular, but not exclusive, application to vehicle wheel brakes as the adjustable element of a wear compensating auto-adjustor or a lock actuator.