Ever since I've installed the 80e, I've had a trans fluid leak out the rear seal. I went ahead and replaced the rear seal when I first did the swap, and it appears its leaking from the seal again already. I also have a little vibration that I didn't have with the 60e. Upon inspection under the truck, I have a lot of play in the slip yoke on the tailshaft. Every time I shake it I can see fluid come out of the rear seal and onto my crossmember. Could all of this be caused by a bad tailshaft bushing? Would the bushing being out cause the premature failure of the seal due to the amount of freeplay back there? Thanks

 

yeah 3 things would cause this from my experience.

Bad bushing inside tailhousing.
Slip yoke to short and not riding all the way inside bushing.
Last something wrong with output shaft. (this ended up being wrong with my last 80e)

also maybe a out of round driveshaft vibration or something to do with rearend. I played hell chasing this issue with my old 80e. It finally let go and i went with another used unit. This one hasnt leaked a drop or had any issues. Hope u figure it out bud.

 

I really appreciate the info man! This trans is a 97 model. It's just been rebuilt, but I'm almost 100% positive its running the original bushing in the tailhousing(looked like the original seal when I replaced it). I'll start with that.
We just did the swap and we measured out the slip yoke before we cut it some, so I hope that knocks that one off of the list.

I did a fresh swing bearing and shimmed the rear end when the 60e was still in(and it knocked out the vibration I had pre-4l80e), so I really hope the last little bit is in that bushing and possibly the angle of the 80e which I could shim some if need be. Thanks man!

 

Bushing definitely sounds bad. You basically need to get a new tailshaft housing, which comes with the bushing already installed.

 

That's exactly what I'm going to do there! Get it in the mail ready to install and when I get some time put a fresh bushing in the other housing. Always good to have a spare one for an emergency.

 

It does sound like the bushing is bad. A couple things to consider. If there is a scratch where the seal rides it will cause a leak. I have seen this area scratched when someone removes the old seal. A thin bead of sealant will fix this problem. Wiggle the yoke with it installed in the tailhousing. If that is loose, and it sounds like it is, that would be your problem. You can't just wiggle the output shaft. The shaft centers inside of the yoke, and the yoke centers inside of the bushing. Without the yoke installed, the output shaft will wiggle all over the place.

 

Finally got around to swapping out the tailshaft housing today. When I pulled the old one off, the bushing fell out in two pieces. It was for sure the problem. Replaced it, shimmed the rear some more and now all the vibration and leaking are gone.
Thanks again to all that replied.