axially during this axial movement the shift rail 32 preferably adopts three positions namely two axial end positions each corresponding to an engaged transmission ratio and a central position between the end positions which corresponds to a neutral setting of the transmission fig2 shows a sectioned view of the servo assistance device 10 according to the invention in a neutral position the servo assistance device 10 comprises a control rod 20 and a piston rod 22 as well as a cylinder 34 and a piston 36 the control rod 20 of the servo assistance device 10 is arranged to move axially within the piston rod 22 and co operates via a gearshift linkage with a shift lever see fig1 the piston 36 and the piston rod 22 are connected fixed to one another or made as one component the piston rod 22 co operates with means for shifting the gear type variable speed transmission see fig1 a valve 56 consists of valve pistons 40 48 and valve slides 38 46 the valve pistons 40 48 are arranged fixed on the control rod 20 so that actuation of the control rod 20 actuates them too along their axes and also in the axial direction relative to the control rod 20 between the valve pistons 40 48 the valve slides 38 46 are also arranged to move axially the valve slides 38 46 are held axially apart from one another by a spring element 54 and each rests against a valve seat of the piston rod 22.