Craftsman Tractor Throws Drive Belt In Reverse

My 2008 YTS4000 24hp 46" Craftsman #917-289281 lawn tractor is consistently throwing the drive belt off the transaxle when you try to go in reverse. I replaced the belt thinking it might be the problem, but it throws the new belt as well. The transaxle seems to work fine going forward. But the reverse is very touchy and gives off a groaning noise when it works without throwing the belt. I tried feathering the reverse pedal, thinking I was accelerating in reverse too fast, and it would start to slowly go in reverse, then without changing the position of the pedal, all of a sudden lurches quickly to full speed in reverse and throws the belt. Tractor has 497 hours on it. All pulleys seem to be fine, they spin freely. Any suggestions?

I use my RaptorSD for most of my mowing, but I have a fenced in area for the dogs that has a 48" gate, and the RSD won't fit. Was keeping the Craftsman to mow that area, tow a cart and do leaves with since it has a 3 bin bagger.

Check the front transmission support bracket to make sure the bolts haven't came out or broke off. Without the bracket attached the transmission will rock and throw the belt. This motion also will crack the frame where the axles bolt.

Thank you ILEngine. Both bolts going from the front of the transaxle to the torque bracket were sheared off. So I am ordering new bolts and will have to remove the transaxle to get access to try and extract the bolts. Too bad they did not make it so the bolt went clean through the transaxle with a nut on the bottom - that would be too easy to fix! They had to make it screw into the transaxle case. Any tips or watchouts?

ILEngine, you were right about cracking the frame. The frame mounts for the tranny were cracked on both sides. Removed the transmission tonight and having a local shop remove the broken bolts from the holes. Will reinforce the cracked mounts with washers on top and bottom. Thanks for your help!

Finally put the transmission back on the tractor. Shop drilled out screws and went through the entire transmission so now it mounts with a nut and bolt instead of a screw. Much stronger now. We also drained the transmission fluid and refilled with Mobil 1 5W50 oil as recommended by TuffTorqs, the transmission manufacturer. Tractor works as it should now. But one problem. I re-installed the mower deck and the blades won't engage. Starting new thread for that.