A gearbox for a tap changer. The gearbox has an input drive shaft arranged to be connected to a motor. The gearbox also has a diverter switch drive output with a diverter shaft. The diverter switch drive output is arranged to be connected for actuation of breakers in a diverter switch of the tap changer. The gearbox further has first and second selector arm drive outputs arranged for actuation of a tap selector of the tap changer. It also has reduction gear means connecting the input drive shaft to the diverter switch drive output and to each of the selector arm drive outputs. Further the gearbox has timing connection means arranged to connect the reduction gear means to each of the selector arm drive outputs. The invention also relates to a tap changer having such a gearbox and to a transformer provided with such a tap changer.