Originally posted by Carrameow
In all honesty I think I rebuilt the transmission very well. By saying that, I mean you can only put it back together correctly, and well (it works), or incorrrectly ( it doesnt work). I got Lucky. So I dont think the problem is the Transmission.
That is a pretty fair statement, unfortunately you are seeing in black and white. I would conclude from your statement that you did not put it together correctly BECAUSE it doesn't work.
There are numerous shimming conditions that affect your problem and as you put it, if it were right, it would work.
It's my guess that the 3/4 shift hub is too far from fourth, the output shaft has too much endplay, or maybe third gear is too far from the hub. Other causes would be parts problems such as a worn slider sleeve, worn shift fork, worn third gear dog teeth.