Two opposing hydraulic rams simultaneously drive bearings onto bearing seats at opposite ends of an axle assembly on which wheels inside the bearing seats are already in place. Wheel support dollies initially position and support the wheel and axle assembly between the opposing rams. The rams are adjusted vertically to opposed positions concentric with the axle. As the rams act upon the bearings, the axle and its supporting dollies can move axially off its center position if greater resistance is encountered in mounting one bearing than in mounting the other. Sensing means mounted on the wheel support dollies monitor the movement of the axle and stop the flow of driving fluid to the ram which has pushed the axle off center until the opposite ram recenters the axle.