I think I know the answer to this, but I wonder what every thinks. Third gear has been acting up for a while now. It has started vibrating bad when I shift into the third (MN6). Now, tonight, when I put it in 3rd, there is no gear there. It is just like it is still in neutral. I believe I must have broke something in the transmission. It shifts fully into gear, but it is like there is simply no gear there.

I'm guessing the transmission now needs some major work, but I'm hoping there is an easier solution. I have a Hurst shifter, and I know there have been similar problems, but it usually effects 3 gears at once. Does anyone have any ideas on this one?

 

No your right the trans has to come out.
You broke something, I can sit here & name parts but a tear down & inspection is what you need.
Then a rebuild, might as well upgrade it while your in there IMO.

 

That was my fear. However, this does give me a chance to upgrade it while I'm in there. I'll also change the clutch if I have to go in there.

I was just holding on to some hope that it could have been simpler than that.

 

dunno about the shifter, but if it's got any adjustments check those first. Could be dammaged 3/4 slider keys or 3rd gear itself. Like wrencher said, pull it out and inspect then order yourself a synchro rebuild kit, snap ring kit, and whatever other parts you'll need.