Bought new wheel and the are easy to replace. Found why the brok and did a quick fix so it wont happen again. As the wheels age one will pull off then they all get weak and the rack will come off the track, To prevent this. you can put a plastic tie so the wheels cant fall off in the first place, The disign holds them in place with pressure from the plastic but the plastic ages and gets weak. A tie would have to actually break before the wheel can fall off.