I rebuilt my '88 700R4 and used the Probuilt modified TransGo shiftkit. Everything turned out pretty well except the oil return plug from the tail housing holds to much oil back to lube the output shaft bushing. I'm not sure if the new output seal is bad, or there is to much oil retained, but fluid is constantly weeping from the seal. Resulting in the need for a pan under the car and fluid all the way down the tunnel. Has anyone else had this problem? I'm thinking of either removing the plug completely, or else drilling a hole in it so that fluid can return to the pan, but at a slower rate than without the plug.

it probably isn't a seal leak at all. you need to check it better. I think you'll find the yolk leaks from the small pin hole under the u joint!!!!!!!!!!! you have to remove the driveline, remove the yolk and u joint, I prefer to weld the inner of the yolk solid so it can't leak again (old school trick). NOTE: when you do this if inside the extension housing there is a thin metal piece that has an o ring that slips over the yolk-it should be removed-just use a hammer and tap it off. hope that helps..just some random thoughts.

Can you elaborate on that at all? I can only assume the hole is a breather to let air in and out of the yoke so it can be slid onto the output shaft and not create pressure or vacuum during suspension travel. Is the O-ring in the yoke? I know there isn't one in the transmission. The yoke slides over the output shaft and through the seal as well as output bushing.
Then again that could be for the 87 and older 700R4s.

Thank you. I'll have to get that done in the next few days.

I've never known the f-body driveshaft yokes to have the bleed hole. This was usually done on truck yokes. So unless you swapped in a different yoke odds are there isn't a bleed.

As for the original question about the tail housing plug. I don't recall installing one when I did the TransGo reprogramming kit. The yoke bushing is usually lubed by oil thrown from the speedo gears. So unless this was removed (speedo pickup/VSS) I'm not sure why the tail housing drain would be plugged.

RBob.

I do know I put a plug in there, but now I'm questioning if I should look at the instructions again. Well, I'll check out the driveshaft and see if it does have a hole or not. Seems like a possibility though. Otherwise I have a 4th gen steel driveshaft I could try and see if that one leaks as well. I'm still holding out for an aluminum one though.

Well, no hole in the driveshaft. I did find that there is some play between the driveshaft and the bushing in the tail. So it's that bit of movement that allows the fuild past the seal. I've got the 4th gen shaft and will see if that is the same size, otherwise I might have to check the bushing and see if that is a bit different in size. Thanks for the help though.

you may have knocked the spring off of the output seal during assembly of the driveline. there is supposed to be a spring to hold the seal tight on the yoke.

I went ahead and pulled the tail housing so I could check the bushing to driveshaft clearance. That is pretty tight. Seal was stiff, so I removed and bought a new one. Driveshaft is straight, took some crocus cloth to it to remove anything that might be creating a burr against the seal. I'll throw it back together tonight and see what happens.

Might just be one of those modified car deals where I have to live with oil down the bottom of it as well as dripping everywhere.

you should replace bushing and seal together. IMO since you've got it off, go to a local rebuilder/ he'll probably have extras laying around as the four wheel drives don't take that bushing during a rebuild and extras accumulate.

I thought about the bushing, but I don't think I even have 500 miles on this one yet.

you haven't mentioned if there was a plug installed by you or not. I'm curious.

Yes, there is a plug installed in the return passage from the tail to the pan(to keep more fluid back to help lube the bushing). It's still in there, and I think I've got the problem fixed with a new(softer) seal.