I had that with my Craftsman 21hp lawn tractor. I drove one wheel into a hole and bent the tie rod. You can see a video on how to fix this and where to order through repairclinic.com or on youtube. I only replaced the one side, but will do the other to make sure. If you leave this problem too long, your wheel might fall off because there are metal tubes (flange bearings in mine) in each wheel and they will really wear out quickly when the wheels are toes out (facing out a bit). Your wheel/s will then be really loose because of the excess rubbing and actually wear the bearings right down which makes the wheel loose and washers and clamps fall off. That all worked so no need to replace the axle, which seemed not to be bent.