Usually caused by a worn shift fork that never pushed it all the way into position in the first place.
Yeah, but only on deceleration usually, so if you keep you foot in it they're fine. Dad used to modify the main drive gear where the synchronizer drum slid over it. A little arc ground into the splines on the correct side, fixed with no parts needed.
usually the jumping out of gear issue is caused by the sides of those little synchro teeth, and what they mate against, being worn on the sides. Reshaping them can help.
The Jalopy Journal
