a pinion gear 8 is attached on the top end of output shaft 7 so to be constrained to rotate therewith the pinion gear 8 has an external toothing which makes a driving connection with drive cables 9 that have spiral shaped toothing and which are coupled to the part to be displaced i e in this case the cover of the sliding lifting roof an input shaft 10 is supported in the bearing bore of housing bottom pan 5b coaxial to output shaft 7 the input shaft is composed of a lower shaft portion 10c a collar 10a with a larger diameter located in a center pan of the input shaft and an upper shaft portion 10b adjacent to collar 10a upper shaft portion 10b has on its periphery axially running serrations 14 that mesh with an internal toothing 12 that are shaped to complement it and provided on the inner side of a hollow space 11 of output shaft 7 serrations 14 and internal toothing 12 make possible an axial shifting of input shaft 10 with respect to axially stationary output shaft 7 without interrupting power transmission therebetween upper shaft 10b of input shaft 10 further has on its end facing output shaft 7 a hollow space 13 into this hollow space 13 and into hollow space 11 of output.