Thread: 350TH trans leak

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Any one know the cure for the trans gasket leaking on a 350TH? I have tried rubber gaskets and cork gaskets. Replaced the pan and it still leaks.I even checked the pan to make sure it was level on the gasket surface.I was told not to use any silicone or RTV with the gasket.Your help would be greatly appreciated! Thanks!!

I just had the same problem with mine and I found out that the pan had been overtightned so the gasket had flatten out. I replaced mine with another cork gasket and no silicone and it stopped leaking. You sound like you already done all this and even though you say the pan is not warped, measure it with a level and I'll bet you'll find out that it's warped.

I have used 350 trans for a lot of years the only time I problems with them leaking were, 1 chrome dipstick tube, 2 chrome pan, 3 pan bent from being over tightened,( like valve covers ). I always use a cork gasket with "Form-a-gasket" applied lightly to both surfaces. Hope this helps

Thanks! I will pull the pan and check it again. It is a new aluminum pan. I checked it before I put it on for being level. But, I will check it again. It's not leaking out of the dip stick tube. Just one corner in the back. Just enough to make it messy. It was leaking by the speedo gear and I fixed that. Thanks again!

I had the same issue,as you can see from my past post, I tried everything several times.... I bet I checked the pans flatness a dozen times! The problem was resolved when I replaced the pan that I knew was ok....

Good Luck..

jc

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"I recently installed a new (rebuilt) TH350 in my 29 and have been unable to isolate the source of a leak at the pan. I have replaced the gasket and set the bolts to spec and still have a leak? Any ideas?

o No apparent housing cracks
o Pan is flat and straight
o Cleaned gasket mating surfaces
o New OEM gasket
o Bolts toqured to 13 foot pounds
o Gasket installed dry per spec"
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Hi,
I recently had my 350 trans rebuilt, mostly because it leaked like a sieve.
I thought it was the filler tube, so I had it fixed. No luck. It turned out to be the 'Intermediate Clutch 1-2 Accumulator Piston' seal. It has an O-ring seal and it was deteriorated bad. Anyway, that was the cause of most of the fluid leakage. It is located on the passenger side of the trans. About 2 or 3 inches wide and held in with a snap ring. You might check it out. Clean it off real good then drive it awhile and check it again.

Gary B.
Taylor, Arkansas
Check out my website!

Also take a look at the shifter shaft. If the seal around it is leaking, it will sometimes run along the pan rail and drip off at a corner making the leak seem like it is coming from the pan or even the front seal.

Thanks to all for the advice!! I have a bunch of things to check out. Really appreciate the help!

Originally Posted by Steel Warrior

Thanks to all for the advice!! I have a bunch of things to check out. Really appreciate the help!

if the pan is flat try going to a trany shop and ask for a durapreen pan gasket torque to 10 ft pounds