(1) On certain vehicles, the rear axle shaft may not have sufficient strength, and therefore, it may crack due to high stress upon starting and breaking of the vehicle. If this problem is left unattended, the cracks can grow, and in the worst case, the axle shaft might break, which would cause the vehicle to stall. (2) The hub flange caps of the rear axle may not have adequate waterproofing, and they may allow water to enter inside, in which case the splines, which connect the axle shaft and the hub flanges, may rust. If this problem is left unattended, the rust may build up and the splines may wear out, and in the worst case, whereas with no driving force transmitted, the vehicle would stall.