SM465 3rd gear problem

[arejayeye]

My transmission is falling out of gear in 3rd. This mainly just happens when I hit a bump in the road. Any ideas?

 

[Pender1]

Fairly common issue on these transmissions. Worn shifter fork. Requires a rebuild.

edit: some claim it's 3rd gear backing off a bit and that you need to machine a snap ring slot to keep it on but nobody has shown proof that is what's happening.