If you have one piece rear axles then Dave is correct, there must be a locking collar pressed on after the bearing is pressed on. The backing plate is actually the bearing retainer so in order from the out side in it should be : Dust shield, outer axle seal, backing plate, bearing race / bearing, locking collar. The inside axle seal goes in the axle housing its self. If you have 2 piece axles the the the order is the same, just no locking collar. It is important that the axle bearing race is positioned so that the bearing is in the housing first, then the race goes in(factory or 2 piece axles). If the race is installed in the housing, then the bearing it can fail in such a way that the axle will come out of the housing.