So I have an issue with my 3311x5s. When I put it in 1st gear it won't move. Second gear it moves but very very slow. Reverse works good. I have no idea where to start. There is gear oil in the case... I just received a yoke that I haven't installed yet...
A couple of things I would check.
Gear shift adjustment - If the clutch is partially over the hole in the drive disc, it won't pull well and the disc won't last.
Worn yoke - This is most likely. Check the slot in the yoke that rocks back and forth when clutching. They get notches worn in them and don't hold as much tension against the drive disc as needed.
Drive disc - I have seen the actual drive disc get worn in one speed area, but this is rare.