TH 350 Leak

[85/Silverado]

Just installed a New TCI TH350 Tranny and I'm getting a Leak where the Driveshaft Yoke goes into the tranny, My Mechanic installed a new seal yesterday on the tail piece and I still see a little fluid on my garage floor this morning.
Does anyone know what else I can check?

[abig84]

possibly over filled? but i have the same issue with the transfercases on my 86 and 93 chevy, the seal has been changed multiple times and they still leak i finally just gave up and check the fluid regularly. kinda wonder if the yolk gets worn down over time and never seals or something

[geezer#99]

Who installed the tranny?
Make sure the vent is open.

[Shady Rascal]

See if the fluid is weeping out of the little hole in the center of the yoke. You'll have to use a flashlight and look up in there were the u joint lives.

[Ironangel]

Originally Posted by geezer#99

Who installed the tranny?
Make sure the vent is open.

Originally Posted by Shady Rascal

See if the fluid is weeping out of the little hole in the center of the yoke. You'll have to use a flashlight and look up in there were the u joint lives.

Two good points to check! The slip yoke can indeed wear to the point where a new seal will no longer work. You should be able feel a wear line in the yoke if thats the problem. Also take a look at the speedometer cable connection, make sure both these seals are good. It's always a good idea to just install new ones with Transmission changes.

[Shady Rascal]

I was talking about the center hole of the yoke leaking, not the outer surface where the seal rides.



Not my picture....

[85/Silverado]

I just crawled under a took a couple of photos does this help?

[cadillac_al]

The yoke looks a little rusty to me. I usually scotchbrite it when I have it out. You wouldn't think a rebuilt trans would need a new output bushing but who knows. I'll blame the rusty yoke scratching up the seal for now.

[Ironangel]

Originally Posted by Shady Rascal

I was talking about the center hole of the yoke leaking, not the outer surface where the seal rides.



Not my picture....

Good clarification, I knew what you were talking about but perhaps the OP didn't. Cadillac Al makes a good point as well. It dont take much air to blow a drip of transmission fluid right to the back of the tranny, thats why I mentioned the speedometer cable connection. Judging from the pics 85/Silverado posted, it would appear that Shady Rascal may have nailed down the cause of the leak? Good call!

[Shady Rascal]

Now, spray it down with carb spray nice and clean to get all the fluid off. Then smear a dab of silicone on your pinkie finger and snake it up there and smear it on the hole in the center of the yoke.

[cadillac_al]

I forgot about that hole in the yoke. The oil pattern in the tunnel does seem to be toward the back of the yoke. That must be it. How come they don't all leak from that spot?

[YoungPup1977]

Per your pic of the tail housing you provided..... you should have one of these (PIC) on the output shaft. It slides onto the putput shaft after the speedmeter gear. it has an O-ring in the inside of this which fits over the yoke....The short output shaft's of the TH 350's does not have this but the longer output shaft that you have does..... hope this makes sense.

[garyd1961]

Originally Posted by 85/Silverado

I just crawled under a took a couple of photos does this help?

Clean up your yoke. I see rust and it should be shiny smooth. If that's the only leak you have on a TCI trans you are lucky. Most have pan gasket leaks.

[YoungPup1977]

Per the pics provided, it looks to me that the leak is at the U joint area because of the wetness above the drive shaft yoke. The inner seal in the cone is missing (see pic from my previous post) or TCI did not install it at all....without this cone/seal it will leak out the yoke because the yoke has a hole in the end of it....

The design intent of such Cone/seal is to eliminate fluid passing by the inner portion of the output shaft splines and the splines of the yoke. Thanks for listening and Good Luck....



Added a PIC of the other end of this cone showing the inner O-Ring: this slides over the yoke when the yoke is installed into the tail housing

Pull your driveshaft out and take the tail housing off from the case (4 bolts) check to see if you have this cone/seal.....if not Check out Ebay item 122404134815 ....

[cadillac_al]

That's some helpful info Youngpup. I usually only mess with short shaft th350s and haven't seen that cone seal. I guess TCI doesn't pay a lot of attention to small details if that seal is missing.

[GRADYS Performance]

That cone is NOT normally used in a short TH350 output shaft transmission. Take the driveshaft out and silicone or weld the hole in the end of the yoke. Transmission is fine, Rusty yoke/wrong yoke is the problem.

[YoungPup1977]

Originally Posted by GRADYS Performance

That cone is NOT normally used in a short TH350 output shaft transmission. Take the driveshaft out and silicone or weld the hole in the end of the yoke. Transmission is fine, Rusty yoke/wrong yoke is the problem.

The pic's provided, show the tail housing is not a short shaft TH 350. The pics provided show its a medium length output shaft which normally has a cone/seal part on the output shaft.

I always wondered why there is a hole in the yoke, does anyone really know why its there....and why on a short shaft the cone/seal is not provided...

[Captainfab]

I assumed the hole is there to allow air to escape with a tight fitting yoke to output shaft, and/or one that has been lubed or greased as they should be.