Pull off the chains, remove the drive shaft and unbolt the gearbox from the side mount. There is a bearing cage underneath the mower above the windrower wing. Remove the fasteners. Then you need to try to remove the locking collar from the bearing and pull off the bearing from the gearbox shaft. My advice? Crack the bearing collar and the bearing its probably rusted and worn out anyways. Buy a new bearing at TSC or your dealer or online. After that, you can pull out the gearbox and slip off the old belt and install a new one. If your mower has a 1 way slip clutch, be carefull NOT to drop and lose the springs and pins from the slip clutch cage. Examine them for wear and replace them if they are worn or flat spotted.
Then put her back together. While you are at it, check out the wobble box bearings for excessive freeplay, put a new knife bushing in and check the chain tensioners for wear. They are just stamped steel sprockets. Be sure to install the chains so that the rolls are in correct position such that the chevrons are in register. You might even consider new chain because these units are notorious for stretching chains because of the way some pto snap clutches work (engagement is not gradual). The new chains might save you from developing fast wear rate on the roll sprockets.
