The invention relates to a gear train unit comprising a plurality of planetary gear train stages, which are connected one after the other and which each comprise a ring gear (4, 4a, 4b), a sun gear (2a, 21, 21a) and a plurality of planet gears (3, 3a, 3b) supported on a planet carrier (5, 5a, 6), wherein the sun (2a, 21, 21a) of each following planetary gear train stage is formed by the planet gear carrier (5, 5a) of the preceding planetary gear train stage. The gear train unit comprises a drive element (2), which forms the sun gear (2a) of the first planetary gear train stage, and an output element (17), which is connected in a torsionally rigid manner to the planet gear carrier (6) of the last planetary gear train stage. The gear train unit can be shifted in such a way that either a first or a second gear ratio can be set.