A method of mounting a first drum and a second drum of a double-drum sequential gear control device for a motor-vehicle gearbox in a predefined relative angular position is provided. In a mounted condition, the first drum is rotatably arranged about a first rotation axis and the second drum is rotatably arranged about a second rotation axis parallel to but not coincident with the first rotation axis. The method includes forming a first positioning hole in a first position of the first drum and forming a second positioning hole in a second position of the second drum. The method also includes arranging the first drum and the second drum in the predefined relative angular position and locking the first drum and the second drum in the predefined relative angular position. The locking includes engaging the first and second positioning holes with a locking device. The method further includes disengaging the locking device from the first and second positioning holes of the first and second drums once mounting of the gear control device is completed.