tranny fuild comming through the center of the yoke

jojo66 · 04-05-2008, 10:52 PM

okay having more problems with this car. tranny is a th400 and there is a pretty severe leak. we replaced the rear seal and it stopped for a while but now theres even more fluid comming out. The fluid is actually comming out of the center of the yoke. I have never seen this or even heard of this.Why is this happening? what caused this? and how do i make it stop? FYI i can see straight through the yoke, isnt there suppose to be a plug in there? if so what is the plug called? Someone please help me cause this car is making me lose my mind and i'm close to abandoning all hope...

oldsconv · 04-28-2008, 04:44 PM

Had the exact same problem years ago when I put in a rebuilt TH400 (like an idiot - never saved the original trans). It turns out some years of TH400 had yokes with no hole and a normal output spline. Other years, the output spline shaft had a groove that accepted a thin o-ring and the yoke (with a hole) slid over the shaft and the o-ring sealed it inside the yoke. Mine leaked just like you said even with the new outer seal and it turned out the o-ring on the shaft was missing, so I added a new o-ring. I think you have to take out rear seal and see if the shaft has a groove for an o-ring, OR fill in the yoke hole with silicone, but I prefer to do it right with the o-ring. If there is no groove on the output shaft for an o-ring, I think you need to seal the yoke hole. Put in a new rear seal after you do this (don't try to re-use the one you took out in this operation)/.

Thanks, Pete

kaz442 · 04-29-2008, 09:56 AM

I just weld the hole up. Silicone will work but for how long? One little spot weld and you done. JKaz

70oldsW30 · 04-29-2008, 12:22 PM

I'd suggest replacing the o-ring like oldsconv said. Once handy little feature of that hole is that it lets air out of the pocket that is formed inside the yoke when it slides up on the output shaft. If the splines on the output shaft and yoke are all clean it will go right on but if you've ever tried to put one on that has some fluid on it with no way to vent the air you can't even push the yoke over the output shaft. I would be concerned that even if it went on clean that it might naturaly get some trans fluid in there (that is what is happening), capture some air that can no longer get out and every time the yoke had to slide over the shaft enough (about a hundred times in a trip to the grocery store, maybe?) it would push on the output shaft a little bit - or a lot. Don't know just what that would wear on the inside but I sure wouldn't like to find out with any of my VIN matching transmissions. I figure that Oldsmobile engineers put that little hole there for a reason and it wasn't to let the fluid drain out of the back of the transmission.

04-05-2008, 10:52 PM	#1 (permalink)
jojo66 Junior Member Join Date: Dec 2007 Posts: 6	tranny fuild comming through the center of the yoke okay having more problems with this car. tranny is a th400 and there is a pretty severe leak. we replaced the rear seal and it stopped for a while but now theres even more fluid comming out. The fluid is actually comming out of the center of the yoke. I have never seen this or even heard of this.Why is this happening? what caused this? and how do i make it stop? FYI i can see straight through the yoke, isnt there suppose to be a plug in there? if so what is the plug called? Someone please help me cause this car is making me lose my mind and i'm close to abandoning all hope...

04-28-2008, 04:44 PM	#2 (permalink)
oldsconv Junior Member Join Date: Apr 2008 Posts: 5	TH400 tranny leak Had the exact same problem years ago when I put in a rebuilt TH400 (like an idiot - never saved the original trans). It turns out some years of TH400 had yokes with no hole and a normal output spline. Other years, the output spline shaft had a groove that accepted a thin o-ring and the yoke (with a hole) slid over the shaft and the o-ring sealed it inside the yoke. Mine leaked just like you said even with the new outer seal and it turned out the o-ring on the shaft was missing, so I added a new o-ring. I think you have to take out rear seal and see if the shaft has a groove for an o-ring, OR fill in the yoke hole with silicone, but I prefer to do it right with the o-ring. If there is no groove on the output shaft for an o-ring, I think you need to seal the yoke hole. Put in a new rear seal after you do this (don't try to re-use the one you took out in this operation)/. Thanks, Pete

04-29-2008, 09:56 AM	#3 (permalink)
kaz442 Member Join Date: Sep 2007 Location: NJ Posts: 25	I just weld the hole up. Silicone will work but for how long? One little spot weld and you done. JKaz __________________ 72 442 conv. 455 +.060 th400 3.31 12 bolt 70 F85 490 stroker, th400 3.73 12 bolt 87 Buick GN

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04-29-2008, 12:22 PM	#4 (permalink)
70oldsW30 Member Join Date: Apr 2008 Location: houston Posts: 35	I'd suggest replacing the o-ring like oldsconv said. Once handy little feature of that hole is that it lets air out of the pocket that is formed inside the yoke when it slides up on the output shaft. If the splines on the output shaft and yoke are all clean it will go right on but if you've ever tried to put one on that has some fluid on it with no way to vent the air you can't even push the yoke over the output shaft. I would be concerned that even if it went on clean that it might naturaly get some trans fluid in there (that is what is happening), capture some air that can no longer get out and every time the yoke had to slide over the shaft enough (about a hundred times in a trip to the grocery store, maybe?) it would push on the output shaft a little bit - or a lot. Don't know just what that would wear on the inside but I sure wouldn't like to find out with any of my VIN matching transmissions. I figure that Oldsmobile engineers put that little hole there for a reason and it wasn't to let the fluid drain out of the back of the transmission.