That's one of my problems the rear wheels wont roll and the shifter is stuck on the third gear it won't move it all it could be the brake is stuck on but I noticed both transaxle mounting brackets are broken
I've looked for new ones of those and can't find any so it looks like I'll be using 2 L brackets and make those work or something with the same thickness of metal I can tell the transaxle mounting brackets broke from someone shifting to hard to many times.
It's the mounting brackets on each of the front side of the transaxle alot of people leave those on the frame of the mower instead of taking them off while taking off the transmission