I've had this mower, which I got at Home Depot, for probably 5 years. Recently the front right wheel has begun locking up (it's self-propelled). It only locks going forward, not backward. I've tried disassembling the gearbox inside the wheel and it all seems fine. It seems that it has something to do with play in the axle connecting the front wheels. That's why it locks when it rolls forward... but not sure why just one wheel locks. Any ideas on how to deal with this?