Most walkers have two wheel bearings per wheel and they can be replaced. You will hear a clicking sound or rubbing sound if the bearings are failing. Sometimes the bearing actually gives out. Before the wheel is ruined these can be replaced. Take off the wheel and put a screwdriver in the bearing opening and pop them out. They will pop back in by finger strength or a slight tap with a hammer. If you replace 1 side it is good to replace both. Things like sand and grit can ruin the bearings so if 1 is ruined they both probably need to be replaced to get the grit out of the wheel. Nova has a 5 pack for their Wheel bearing replacement.