Craftsman riding mower 38" dirve belt problem

[LADDERMAN643]

1989 model - the drive belt keeps jumping off rear pulley above rear axle when stopping and going -guide pins in place on each side of pulley,new belt . Cross reference p/n and is correct belt. Tried adjusting brake and clutch rod - pulley seems tight-belt does ride in v groove below top edge of pulley-so pulley wore out?- all other pulleys tight-when engaging clutch/brake seems like belt to loose and jumps off pulley-belt is routed correctly.please help-open for suggestions

[Restrorob]

If the guide pins are in place PROPERLY the belt will not drop off, Make sure their not bent away from the pulley too far. One should have to loosen these guides to install a new belt.

[LADDERMAN643]

There is a flat bar from one guide to the other guide below pulley that is removeable -maybe its off centered and letting belt off one side -i'll check it thanks !!!!