I just experienced a problem with my right front wheel bearing, and when I took it apart I had a little surprise. It looks like at some point the ball bearings were rolling between the hub surface and the back race, rather than between the two races. If you compare the pictures of the hubs, you can see the bearing "track" in the right picture, while the left one is normal. The really odd thing is I haven't had the front wheel bearings apart for several years, and somehow it just came loose recently. There was a cotter pin, so the only things I can think happened are either the spindle threads are so worn that the castle nut was able to skip threads, or maybe this damage was done to the hub before and the race was able to move in the hub over time due to the uneven mating surface.
