is actuated under load the rolling bodies 4 roll in the thread as a result a comparatively high level of efficiency of 75 to 90 is achieved in contrast given load free actuation of the gearbox 1 the rolling bodies 4 slip i e the balls 4 slip until the brake lining 34 which is assigned to the brake piston 5 bears against the brake disc not illustrated because virtually load free actuation occurs here the balls 4 do not begin to roll until they are under load the gearbox 1 therefore acts at the same time as a re adjustment means if the brake linings 33 34 are worn dispensing with a separate re adjustment device or integrating a re adjustment device and actuation device into a single component is particularly cost effective and at the same time robust so that the rolling of the rolling bodies 4 under load and the slipping in the case of load free actuation of the gearbox 1 are always possible a spring element 10 is provided which maintains a rolling distance for the rolling bodies to roll over the previously mentioned electric motor 7 and the two stage gearbox are accommodated here by a housing 28 which is associated with the drive module 21 and can be closed off with a housing lid 28 a in the illustrated embodiment the two stage gearbox is embodied as a worm gear system 11 12.