Abstract: A strut (40), whose effective length depends on the relative positions of two strut portions (42,44) adjustable with respect to each other is connected in parallel with a brake actuating mechanism (18). One strut portion (44) has at least one part adjustable transversely of the longitudinal direction of the strut (40) and upon actuation of the brake tends to increase the length of the strut (40). This strut portion (44) has an operable connection with an intermediate member (24) which is supported on one of two structural members (128, 136) transmitting the actuating force independently of the strut (40) for rotation around the axis (B) of the brake actuating device (18) and is rotatable against the frictional resistance thereof only as long as this does not surpass a given value. In this way, the strut (40) is prevented from unnecessary or over-adjustment upon particularly forceful actuation of the brake.

Abstract: In order to reduce the distortion of a servo booster housing in use the booster is provided with one or more force transmitting means which extend through the movable wall for transmitting reaction forces directly from the master cylinder housing to the vehicle bulkhead between which the booster is mounted. This enables a housing of lighter weight to be employed, and an overall saving in weight may be achieved.