Return of the Transmission Leak
 

My 1972 K10 has a transmission leak. The pan had some kind of reddish-orange silicone bead around a rubber gasket that was leaking, but I removed that, scraped off the gunk, checked the pan for burrs/dents/distortion, and replaced the old gasket with a new cork gasket. Alternately torqued down the bolts supporting the pan, taking care not to over-torque, and refilled with ATF (MD3). Let the truck cool down, sitting overnight, and found that next morning it was leaking once again, with a significant pool on my garage floor. Checked the plug and it was dry, but found ATF all around the seal. Have been told to stay clear of rubber, not to use cork, and all kinds of different things but want to get the answer from people in the know so I am posting the question to you. Where am I going wrong here? What is the best gasket to use? Any guidance you might be able to provide would be greatly appreciated.
Thanks,
AK

Re: Return of the Transmission Leak
 

Could something else be leaking down making it look like the pan gasket? Fill tube seal, detent o-ring, cooler lines?

Often times these old pans are tweaked out must enough they won't seal. When I find one I can't seal with a standard cork gasket and 8-10 foot pounds of torque, I get a new GM pan or a cast aluminum pan and have had no more leaks.

Re: Return of the Transmission Leak
 

Also check the seal around the selector lever shaft!

Re: Return of the Transmission Leak
 

@ Lee H - Cooler lines! I messed with them before, maybe they are not snug, I will check that tonight and work my way down from there.

@ brianthelion02 - I installed a Lokar shifter cable assembly, going to look at that seal around the selector shaft right after I check the cooler lines.

Felt like I have been spinning my wheels, thanks again for giving me some traction here guys.

AK

Re: Return of the Transmission Leak
 

X2 on the selector shaft seal. I chased a trans leak on my CST for several months, only to finally discover that there was a big burr on the selector shaft that was cutting into the seal. It looked exactly like a pan gasket leak...

Took a dremel tool and smoothed it out...new seal...no more leak. The burr was most likely made by me when I changed the seal without the proper tool. I now own the tool...:)

Re: Return of the Transmission Leak
 

Oh yes,that tricky little tool,lol! Most trans shops will do the job really cheaply. Sometimes that seal wont leak on a daily driver ,but let it sit a couple days and the torque converter drains back into the transmission case! All little leaks show up then!!

Re: Return of the Transmission Leak
 

+1

That's where my mystery leak was. It dripped down and onto the seal and made its way from to back along the gasket edge and dripped onto the floor toward the rear.

I was assuming it was the seal since it was wet all along it but the shaft seal was the culprit all along.