The bearings themselves are most likely worn too far down to drive the rear. They are replacable. I can't remember what size they are off hand. It may depend on what diff you have. If it is the regular Outlaw Rampage (silver chassis/ black gearcase), and not the Pro (blue chassis/ white gearcase), your diff is an option part. It is either the Kyosho or Thorp (MIP) Dirt Burners brand. When I get home today, I'll take a look at the parts lists and see what I can find.