a method of assembling a speed reducer assembly including a housing having a front wall or side defining a bearing shoulder having an inner surface , a back wall or side defining an opening and having an outer face ; a bracket having an inner surface which rests against the back wall face to close the back wall opening and defining a second bearing shoulder having an inner surface , a worm and a worm gear held in meshing contact in the housing , and front and back shims which align the center of curvature of the worm gear with the axis of the worm . the method of aligning the worm and worm gear includes the steps of predetermining the width of the shims and then assembling the speed reducer assembly . to predetermine the width of the shims , the distance from the center of curvature of the worm gear to an axially outer surface of the worm gear assembly is determined . a gauge is provided to determine this distance .