Technical GM TH350 Tail Shaft Leak FIX?

Ok guys, I'm back in the saddle, but it looks like you've all left me at the starting line. I'll try to catch up with all of your great input.

Mark,
I had already started a test my local transmission guy suggested, so, I'll start your test tomorrow. As I posted above, I had:
1) drained the tail housing
2) drained the pan
3) added 4 quarts to rule out the possibility that I had somehow overfilled it.
4) I parked it last night with the front end jacked up since that is the scenario that guarantees a leak.
5) Today, no leak....... good news? ......nah
I ran it to warm up, and checked the fluid level and it read very low, just barely at tip of dipstick. Thinking my dipstick being an aftermarket model, might be giving a false level reading, I drove up my street just far enough to know that it wanted to slip in low & second gear, confirming that it was actually low.
6) I added 34 Oz of fluid to bring it just into the low end of the full cross hatch.
7) I kept it running and parked it with the back end uphill for just about 5 minutes.
8) Bringing us to now, I turned it around, parked for the night with the back end down hill.
I will do Mark's test tomorrow .

Addressing some of the other responses from today:
1) I had already confirmed that the vent is clear.
2) I had already inspected the extension housing lip seal.
3) I have confirmed no leak from the speedo.
Thanks all for the great input, I'll watch for new responses this evening, and will post status again tomorrow.

 

Extension housing lip seal
Bushing could be bad
Aftermarket dip stick?
How much fluid did you have in the trans ?
I have seen it just like your describing a driveline swap happens and a random dip stick gets used resulting in “fun times”

 

It doesn't have some sort of mondo trans cooler that could hold a lot of fluid and drain back to the trans?

 

Extension housing lip seal and bushing were both replaced, and are good. I'll know better tomorrow, but, I think the dipstick is probably good. It's 32 1/2 inches long.

 

Today's results:
I wear a size 11 shoe, and would say my tranny didn't leak a huge amount overnight except that I drove around running reads and had to add another 28oz to get to where the truck was driving and shifting like it should, AND, the dipstick was showing full. I'm going to get going with Mark Yac's suggested test unless someone see's something in what I've done that I'm blind to.

 

I would replace the seal and use some sealer around the seal where it fits into the tailhousing.

 

This pic didn't upload

 

Saltflats,
Thanks for responding,
I have replaced the seal and used sealer twice, but the third time might end up being a charm.

 

Odd looking U'Joint

 

I would pull the seal out and look at the seal mounting surface inside the extension housing for out of round or and nicks and gouges that the fluid could pass through.

Use the loctite flange sealant it’s in two types a red and a purple colour that’s what I use in situations like this.

Also your yoke seems to be in too far
Is it flared at the end and when your driving bottoming out on the seal ?


Aftermarket pan oem pan?
Someone else I’m sure will chime in but I’m guessing there is probably more then 2 different dipstick and tube lengths depending on what car the trans came out of originally.

I know you have added fluid to get it “just right”
How much fluid did you add?
a TH350 should take between 10-12 litres of fluid ( a litre is just shy of a quart for you “traditional “ guys !

 

Ok, Drivers Meeting:
Tonight's guest Speaker, introducing Mark Yak...Yah, ...Deafening Applause

When I popped the tail housing back about 1/2 inch, I only lost about a teaspoon of fluid.

 

Very well said,LOL

 

That is odd looking. Might be the picture angle, but seems there's lots of that bearing cup exposed at the inside of the shaft yoke. Is that u-joint centered where it's supposed to be? Correct u-joint?

 

While we wait for our guest speaker to check in, let me go back to my original post. Should I be using this sleeve/bushing and O-ring in groove at bottom outside?

ACDELCO part # 8654063 pictured below:

• 
  My brother in law has a 77 chevy truck with a th350, and he swears it has a sleeve or bushing in the tail housing, around the tailshaft with an O-ring on the inside of the sleeve/bushing. I haven't been able to find anything like that. Also, when I have replaced the tail housing seal, I have used cheap AC-Delco seals. Does anyone know if there is a gold standard brand or type that would work better?

 

That sleeve would press fit to the output shaft inside the tailhousing, then the yoke would slind in and out and the o ring would seal the weep hole in it.

 

I'm kinda at a loss here. The U joint does look very strange.
I suppose I might rig up a dial indicator on a magnetic base and place the tip right on the yoke behind the seal.
Rear jacked up like before, start it and put it in low ,and raise it up and have a look /see.
Something is pumping the oil out there. The seal should handle it if everything is running true.

 

Mark,
My leak isn't happening when I drive the truck, no blow back. It only leaks when the truck is parked with the rear down hill. Also, the tail housing seal doesn't sustain any damage over time. What are your thoughts about seal quality, and if a sleeve/bushing exists with an O-ring on either the inside or outside of the sleeve? The only one I have found is the one pictured above and I'm not sure it would work on a th350 application.

 

Okay then..Next test
Park it like you normallywould, but with e- brake on and wheels chocked, trans in neutral. Hopefully you can slide under there with some brake kleen in hand. Grab the front of the shaft and see if you can move it any up and down and in a circle.
Spray it off and try it again and observe.
Seems obvious to me that the seal lips are not staying in constant contact with the yoke, for whatever reason.

 

Thanks everyone on the HokeyAssMessageBoard for helping me troubleshoot my LeakyAssHousing. The solution ended up being installing one of these:

For more on the fix, take a look at:
http://www.73-87.com/7387garage/drivetrain/yokeleak.htm
Again,
Thanks to all, you guys are the bestest!!

 

So it was leaking through the new yoke then? Not the seal?

 

Mark,
Here is the story on my truck. I bought it 12 years ago, Up the road a piece from you, in Phoenix, Az. It was rust free, but engine and tranny were both pretty tired. The transmission leaked from the tail housing seal and thru the yoke. I drove it infrequently, so I just parked it with front end downhill. Last year I decided to start actually working on it. I bought a recently rebuilt transmission (the one currently in it) from a guy about 75 miles from me. I drove the truck to pick the transmission up, and made it about 50 miles, when the engine gave out. I called the guy with the transmission and told him I wouldn't be coming. He graciously offered to bring the transmission the remaining 25 miles to where I was broken down with a blown engine . We loaded the transmission in the bed of my dead truck, and I had the truck and myself towed back to my place. A friend of mine won a complete 350 crate engine at a local cruise-in/car show, and being a diehard Ford guy, he sold the engine to me. If you are buying any of this, now is where it gets really sketchy. I planted the brand new GM 350 crate motor and rebuilt TH350 transmission in the truck. The engine runs great, the transmission shifts great, and WTF, the transmission leaks exactly like the original one, and even I didn't believe that, but it brings us to my original post, and IMHO, the answer to your question. When I replaced the yoke, bushing and seal, the leak thru the yoke was fixed. When I added the sleeve and O-ring, even though it is specifically designed to remedy a leak thru the yoke, it also helps stop the seal leak because the yoke slides inside the sleeve and the O-ring is inside the sleeve and around the yoke. That's my story and I'm sticking to it. Sorry for the long story, and thanks again for the help.

 

I'm just glad u found and fixed it...

 

ME TOO....... BIG SMILE'"

 

Glad you got it fixed. Thanks for the update, and thus, closing out the story.