Chosen Solution
I have a craftsman 917.289272 made by husqvarna. I first replaced the drive belt but it happened with the new one. Both times it happened when I had a trailer hooked up and had the parking brake on so I could dismount from the mower while it was still running. When I released the parking brake the belt jumps off and lodges underneath the pulley.
@dix , Tom, I recommend inspecting the belt first for correct size and routing. If belts keep coming off check belt guide/keeper/guard for out of adjustment. The keepers/guards should be about a 1/8 inch away from the pulleys to keep belt from falling off when belt goes from load to no load(slack). If keepers/guards are not close to pulleys to retain in pulley groove they can pop off and should be adjusted. Also found in a repair forum to check transaxle bolts for missing/loose/sheered off when this happens the transaxle is allowed to tilt forward allowing belt to slip off rear pulley. Good luck. I hope this helped you out, if so let me know by pressing the helpful button. http://www.ssbtractor.com/wwwboard/view_…
Similiar to theL Plaff above. I found that the front upper brace on a husqvarna YTH2348 had broken off near the bolts that fastens it to the axle drive unit, it also had bent and cracked around the four bolts that fastens the axle to the frome near both wheels. all was streightened and welded, it fixed the belt problem.
