the actuating unit according to the present invention , as shown in fig1 includes a vacuum brake power booster 1 and a master brake cylinder 2 , which is preferably a tandem - type master cylinder , inserted after the vacuum brake power booster . the vacuum brake power booster 1 includes a booster housing 3 , formed by two housing halfs 20 , 21 connected to each other , in which the housing half 20 , represented on the left side , supports the tandem - type master cylinder 2 , while the housing half 21 , represented on the right side , is fastened to a vehicle body wall 45 of an automotive vehicle with fastening means 27 , 28 provided at its periphery . in a cylindrically - formed extension of the right housing half 21 , which is not shown in detail , a control housing 8 , including a control valve 9 which can be actuated by an input member 4 being in axial abutment against an actuating pedal 30 , is slidably guided in a sliding ring seal 16 . on the end remote from the input member 4 the control housing 8 supports a movable wall 5 which is formed by a diaphragm plate 22 and a rolling diaphragm 23 being in abutment against it . moveable wall 5 subdivides the interior of the brake power booster housing 3 into an evacuable vacuum chamber 6 and a working chamber 7 . control valve 9 permits a connection between the working chamber 7 and the vacuum chamber 6 or the atmosphere . as can be seen ( especially from fig3 ) the control valve 9 is preferably formed by two sealing seats 10 , 11 which have an annular design , are arranged coaxially to each other and interact with an elastic , rotationally symmetrical valve body 12 . valve body 12 can be a disc valve , for example . sealing seats 10 , 11 are in abutment against valve body 12 when the vacuum brake power booster 1 is in a release position . the first sealing seat 10 , the opening of which allows a connection between the two chambers 6 , 7 , is provided in the control housing 8 . the second sealing seat 11 , the opening of which allows a ventilation of the working chamber 7 , is provided on a valve piston 15 . valve piston 15 is guided on a continuous and centrally positioned force - transmitting bolt 14 and is in force - transmitting connection with the input member 4 . valve piston 15 has a resetting movement which is limited by a transverse member 17 being , in a release position , in axial abutment against a sliding ring seal . the sleeve - shaped valve piston 15 is in force - transmitting connection with an elastic reaction disc 13 , which preferably has an annular design . valve piston 15 is positioned in a cylindrical recess of the control housing 8 and allows the transmission of the actuating force introduced at the input member 4 , on the one hand , and also of the boosting force generated by the movable wall 5 onto a pressure plate 26 , on the other hand , which interacts with a master brake cylinder piston 29 . the force - transmitting bolt 14 , which preferably extends axially through the control housing 8 , is screwed in a closure element 38 with the end closest to the tandem - type master cylinder 2 . closure element 38 closes the tandem - type master cylinder 2 and is fastened to the left booster housing half 20 by means of fastening screws 24 , towards the outside . the other end of the force - transmitting bolt 14 is anchored to the pedal assembly 44 . actuating pedal 30 is pivotally supported on pedal assembly 44 . pedal assembly 44 is fastened to the booster housing half 21 ( illustrated on the right side of the drawing ) by means of the mounting element 31 , 32 , so that actuating pedal 30 causes a transmission of the reaction forces resulting from the pressure generated in the tandem - type master cylinder 2 directly from the master cylinder 2 to the vehicle body wall 45 . referring now to fig2 and 3 , the force - transmitting bolt 14 extends through the range of action of the actuating pedal 30 between two parallel arms 42 , 43 of the actuating pedal 30 arms 42 , 43 are spaced from each other , while the reaction disc 13 and the pressure plate 26 are arranged on a tubular sleeve 25 , which is guided slidingly on the force - transmitting bolt 14 and receives a seal ring 48 in its radial enlarged portion 47 . certainly the actuating pedal can be designed in another way , as for example a pedal with an opening that receives the force - transmitting bolt 14 or a pedal with a flat arm interacting with a slotted force - transmitting bolt . in the embodiment of fig3 the output force of the vacuum brake power booster 1 to the tandem - type master cylinder piston 29 is transmitted by two rod - shaped elements 18 , 19 , which are arranged symmetrically in parallel to the force - transmitting bolt 14 between the tandem - type master cylinder piston 29 and the pressure plate 26 . in the embodiment of the present invention illustrated in fig3 the end of the force - transmitting bolt 14 closest to the master cylinder 2 is screwed in a bowl - shaped part 40 , which is screwed to the booster housing half 20 by means of the fastening screws 24 , which fasten the master cylinder 2 to the booster housing half 20 . to this end the bowl - shaped part 40 is provided with a radial collar 41 which serves as an abutment for a resetting spring 39 biasing the movable wall 5 in opposition to the actuating direction . alternatively , force - transmitting bolt 14 and the part 40 can be connected also in other ways , as , for example , a connection by way of indentation , a bayonet connection and the like . a one - piece version of the bowl - shaped part 40 with the booster housing half 20 closest to the master cylinder is also possible . in the embodiment of the present invention that is illustrated in fig4 the actuating unit 1 , 2 is fastened to the vehicle body wall 45 by means of the mounting elements 31 , 32 , which retain the pedal assembly 44 . the vehicle body wall 45 is clamped in between the right booster housing half 21 and the pedal assembly 44 . the force - transmitting bolt 14 has a hollow - cylindrical section 34 which protrudes from the control housing 8 and provides , in the illustrated section , two radially opposed axial slots 35 , 36 . this embodiment provides that the output force of the vacuum brake power booster 1 is transmitted to the tandem - type master cylinder piston 29 by means of a bolt - shaped element 33 which is formed , in the illustrated example , by an axial extension of the master cylinder piston 29 . the part 33 , which is guided in the section 34 of the force - transmitting bolt 14 , is in axial abutment against a transverse pin 37 guided in the slots 35 , 36 and positioned perpendicularly in a cylindrical projection 49 of the pressure plate 26 , so that the two parts 33 , 37 are in a force - transmitting connection . experts working in the relevant field are familiar with the function of the actuating unit 1 , 2 according to this invention which therefore does not have to be discussed in detail . the preceding description is exemplary rather than limiting in nature . the purview and scope of this invention is to be limited only by the appended claims .