Bare with me on this question.

With the suspension loaded, how much farther can the driveline yoke go into the transmission before it bottoms out? If you don't have 3/4" or at minimum 1/2", the driveline can force the mainshaft forward.

 

Yeah, I you're correct... I bought it from a parts car, the seller claimed that the transmission worked before the motor went. It did not appear to have been gone through, at least not in the last decade so I made the assumption that things must have worked previously. Everything inside was actually in overall pretty good shape, bearings all looked and felt fine but I decided to go through with the rebuild anyways as this is the one automotive project I have yet to tackle and saw it as a good learning experience. Which it has... I've learned how to pull a transmission out and tear it down quickly
I'm still confused to why it would work from a period of time... and then suddenly stop.

 

Hmm... you bring up an interesting point. I'll have to check. I did just do the re-speed steering conversion at the same time. The new engine mounting might be slightly too far back, I also installed front coilovers... the ride height change could alter the angle of the driveshaft and therefore the depth it goes into the transmission possible?

 

...also can I check the yoke depth with the suspension at full droop?

 

Because of the angle of the control arms, full droop causes the driveline to move foward in a state that isn't seen in normal driving conditions. Can't hurt to check in both positions. Typcially one measures with the suspension loaded. The 3/4" is enough to accomodate 99% of driving situations. For it to force the mainshaft forward so hard that it locks the trans up a bit, tells me if that's the reason, you're very tight at ride height.

 

Yeah that's what I figured. Appeared to be plenty of fore-aft allowable when I slipped the driveshaft back in, but that was at full droop. I'll jack up the back axle tonight and take a look.

 

13B engine or 12A?

13B engines mount 3/8" forward. If you bought a 12A crossmember from Re-Speed with a 13B engine, that might be your issue? Notice anything else further back like the shifter, or getting the trans mount lined up?

 

No I had a little bit of an issue getting the trans mount lined up the first time but it wasn't way off. It's a 12A engine with the 12A crossmember. I just got done unbolting the back end of the driveshaft and slipping it all of the way forward with the rear end on jackstands. It looks like there's 1/2" of forward give.
I'm just wondering though, with normal suspension travel, would it shift it forward more than half an inch? If it had though... why would have happened at a moment when I was cruising steadily down a well paved road? If this turns out to be my issue I owe you a beer (Or a whole case for that matter)

 

1/2" SHOULD be enough for standard driving. To push forward that far, you'd damn near have to jump the car. Still racking my brain at what else it could be. Very hard to troubleshoot without seeing/feeling for one's self of course.

 

Yeah that's what I was thinking. It would seem that if the two shafts were binding together... they would have done so immediately. I don't understand what would cause things to shift over time. Vibration? Clutch splines sticking on the input shaft and pushing it back? (which doesn't seem possible since that input shaft bearing is prevented from moving aft by that external snap ring)
What I'm also really baffled about is the original trans... so when this problem first cropped up, I took the original trans (which had worn synchros but otherwise was fine) and swapped the aft case portion and tailshaft from the rebuilt trans onto that. (Tailshaft bushing was worn on my original trans) After doing so and installing it in the car, it made that loud bearing noise which it had never done previously. Could it be somehow related to how I'm installing the rear half of the case? There's no instructions in the FSM specific to re-installing the back half of the case, just putting the gears back together and the front bearings and cover.

 

its possible a snap ring popped out too, happened to a friend of mine. same symptom, test drive started ok, and then it locked up.

i also heard about one where the case bolts weren't tight, so the whole trans fell apart! oops...

i've done a few of these, and i agree that its hard, there are a lot of little parts and they all need to be right.