Best way to seal AOD pan ?

David Neibert

SCCoA Admin
The Lentech AOD I bought for my 93 has had issues with leaking from the pan since the day it was installed back in 2004. When first installed and filled with fluid I discovered about 2 quarts of fluid on the floor the next morning. Tried snugging up the pan bolts, but all felt tight.

Pulled the pan (Lentech cast aluminum), installed a new gasket (rubber looking one) and used some Permatex ultra blue gasket sealer on both sides of the gasket. When removing the bolts I noticed that about 2/3s of them had a portion of the aluminum threads coming out with the bolts :eek: I ran a tap into all the holes reinstalled and tightened the bolts to about 20-25 ft lbs. Didn't leak nearly as much, but was still dripping from the pan and the leak seemed to be coming from the pan gasket.

After hearing that some Lentech transmissions had been built with pan bolts that were too long, I removed several of the bolts and measured the length to insure I wasn't bottoming out in the bottom of the holes in the tranny before tightening against the pan gasket. The bolt length turned out to be correct, but just to be on the safe side I added a couple washers to each bolt to insure more pressure would be applied to the pan gasket. All that did was remove more aluminum threads from the tapped holes in the transmission. I decided to leave it alone and live with the dripping fluid for the time being.

After a year or so, I decided it was going to be necessary to change over to a full manual VB with a trans brake if I ever wanted it to launch with boost. Great...this is my chance to fix that stupid leaking pan at the same time. I supplied the shop that changed the Valve Body with a set of heli-coils to repair the threads for all the pan bolts and at the same time I switched over to the John Deere hydraulic fluid. I also supplied another pan gasket and filter to make sure the rubberised type gasket was used. I instucted the guy doing the work to use a generous amount of sealer on both sides of the gasket, torque it down good and allow it to sit overnight before adding any fluid.

A week after getting the car back I noticed it was still leaking :mad: It was probably leaking from day one, but since the hydraulic oil looks just like motor oil when on the floor, it took a little longer to notice. I took a look at the pan to see if sealer was used on both sidesof the gasket and it was...I also tried tightening the bolts, they were all about as tight as I dared go (over 30 ft. lbs). At the time I had bigger problems with the car and decided to leave it alone for now. Since then (Oct 2006) it has begun to leak more and also sprang a leak from the filler tube.

Other than bringing the pan to work to make sure the sealing surface is milled flat, I don't know what else would account for the sealing problems. I've got the same pan on my 91 and I never have any problems with leaking on it. Is there some kind of super duper sealer or AOD pan gasket that will seal better, or am I stuck with this leak forever ?

David

PS: I'm also leaking trans fluid from the driveshaft splined yoke (end cap not sealed).
 
On cast alum it is possible you have a hair line crack somewhere. Heat will open the crack but when it is cold it would be hard to see. Sounds like you have covered the gasket and sealer thing.

Ken
 
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I used sealer and a rubberized gasket on my AOD after installing the Lentech and havent noticed any leak.... Might be warped or cracked????? did you straight edge it see??
 
Might not be a bad idea to see if it is just leaking from one spot. Get one of those leak detect kits and run it with the UV light?
 
I take back what I said about the rubberized gasket... I got my parts from the transmission shop here in Lexington, P&S transmission, and he gave me a cork gasket. I have cork gasket on mine and my Sally's and havent noticed any problem with leaking...
 
Dave,

Mine has had a leak everytime I've ever sealed it. It will usually hold for quite a while, but after the car sits for a while, the leak comes back.

Napa sells the rubber pan gaskets.

P.S. Sorry about not having a lift yet
 
The duraprene gaskets (brown fiber) work great on oem pans. The cast aluminum pans seem to be hard to seal. If you could get all the fluid off and run a thin bead of silicone I think it would be best, but what a mess everytime you change it. Kurts has the duraprene gasket which I figured would solve it yet didn't. The pan manufacturers need to put grooves in there to help the gaskets seal better. Smooth surface against smooth surface is hard to seal.
Alan
 
I'm not so sure that the cork gaskets don't work better. :eek: As for torque, 10-15 is as tight as I'd go. 20+ seems too much for the small bolts and the type of gasket. I think its possible to compress the cork too tightly as well and have it crumble + leak. :(
 
Although there would be a risk of warping, you might consider powdercoating the pan first, then make a paper gasket, finally sealing with Permatex red gasket spray on both sides.

The best method in the end may be to dump the cast pan.
 
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I'm not so sure that the cork gaskets don't work better. :eek: As for torque, 10-15 is as tight as I'd go. 20+ seems too much for the small bolts and the type of gasket. I think its possible to compress the cork too tightly as well and have it crumble + leak. :(

I think I'm going to try a cork gasket with a thin coating of Permatex black high temp RTV try this time. BTW, I've always thought the reason for not torquing the pan gasket very tight was to avoid warping/bending the stamped sheet metal.

I will also take a little extra time and inspect the pan for flatness, sealing surface imperfections and cracks, but it looks to be leaking from the gasket area and the filler tube connection.

Thanks for all the suggestions.

David
 
Although there would be a risk of warping, you might consider powdercoating the pan first, then make a paper gasket, finally sealing with Permatex red gasket spray on both sides.

The best method in the end may be to dump the cast pan.

What is the reason for powder coating ? I thought that powder coating acts as an insulator, which would cause the pan to retain heat.

BTW, the sealing surface is milled very smooth and the flange is about 1/4" thick. The wall thickness of the pan also requires that socket head capscrews are used instead of the usual hex head capscrews. It's actually a very nice pan...just wish it wasn't such a pain to seal.

David
 
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>What is the reason for powder coating

Perhaps help to seal the pan itself - may even provide a better seal surface..? I've seen cast aluminum diff covers that were perennial leakers - a few coats of epoxy paint seemed to help. And yep, seems to defeat the reason to run the aluminum in the first place by risking heat retention. That's why I said sometimes you just need to put the darned thing back on the shelf. Tough choice... no leaks or better cooling.

Any chance it came with a lifetime exchange policy? :)

Do you think studs instead of bolts would be helpful?
 
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Okay...now I understand where you were going with the powder coat suggestion. If I thought it was a porosity problem with the casting, I wouldn't hesitate coat the inside with epoxy paint/sealer.

We do the same with transfer case castings after machining and prior to assembly, where I work. In the past we have tried numerous methods of sealing the castings, including graphite impregnation....but the epoxy paint still works best.

No on the warranty and No on the studs because the nuts won't clear the sides of the pan.

David
 
I put a TCI aluminum pan on the c4 and have dropped the thing about 4 times trying to get a perfect seal. You would think that after spending $100 on a lowsy oil pan it would come with a rubber gasket so you wouldn't have this kind of problem.
 
WoW! The problems you guys have with those automatic transmissions!! I don't know...... :p ;) :D

Ira
 
I'm starting to think the sealing surface on the transmission is where my problems are coming from.

David

The flange on my transmission certainly isn't perfect and I had to clearance the inside of the pan to clear around the valve body so the pan would even sit flat on the transmission flange. But between a 1/16" thick paper gasket with RTV on both sides I'm still amazed that the thing leaks.
 
David, is it possible there is a situation where excess (pan) pressure is allowed to build up and/or not bled off properly?
 
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