drewt

Hi folks- the TH350 transmission in my 70 Cutlass developed a leak which appears to be coming from the extension housing rear seal. I dropped the driveshaft and tried to pry out the seal, but it won't budge. I think I need to pull the housing off to get a better shot at it. Apparently there's an o-ring seal between the housing and the trans case that I thought I should replace at the same time, but I can't find a replacement anywhere. any ideas? I'm not sure what kind of problems I'm going to encounter removing the extension housiing (trans in the car)-any advice?

Lady72nRob71

The gasket that goes in between the EH and case is available at rockauto for a whopping 46 cents:
ATP Part # SO22 {Housing to Case O-Ring, Square-Cut #1358899}
TH-350, 350C; Housing to Case O-Ring

It is under the 1972 listing, but not the 1970. Crossreferencing shows this to be used from 64-94.

I thought the output seal just pried out once the driveshaft is out.
I am sure someone here knows for sure. I have never been in that deep in a tranny before (yet)...

70 cutlass s

It does, but sometimes you have to use a hammer and chisel to get them out. Just becarefull not to hit too hard and damage the mating surface for the seal.

joe_padavano

The trick to removing a difficult seal without pulling the tailhousing is to drill three small holes in the metal part of the seal and screw in sheet metal screws to pry or pull on. Use grease on the drill to catch the chips.

drewt

Thanks for the input, I guess I ought to try harder to get it out before removing the housing.

71supreme

Hey all,

I am looking to do this same operation on my 71, and I have 2 questions.

1) the book says to apply a non hardening sealer can someone recommend one?

2) How do I remove the driveshaft? do I have to/ should I replace the u-joints?

Thanks!

~Mike

Lady72nRob71

Pull and shove the joints, feeling for looseness. If you had a vibration problem at speed, any looseness could be the problem. If you find none of that, then you could reuse your existing joints. I never replaced any, but I am sure many others have.

I have used Permatex gasket sealer with good results. Follow directions carefully and clean mating surfaces with alcohol and you should be in good shape.

drewt

I ended up removing the extension housing rather than try to pry out the seal and damage something else. It was a piece of cake. Changed the o-ring seal between the housing and the trans, which I found at NAPA. Seems okay for now

Lady72nRob71

Good job! I am sure the o-ring needed replacement soon anyway. Better to be careful and do the job slowly to avoid buggering something up...