Took the car out of storage last week and found a puddle of tranny fluid. I had the tranny fluid, filter and gasket changed just before it went to storage last year. I had two small leaks last year so the mechanic dropped the pan inspected the surronding areas and it all looked good. We changed the gasket and it still had a small leak before it went to storage. Any ideas what is causing the leak? Everything above and surronding the pan looked dry at the time.

Sounds like your going to have to get under it and see where the fluid is coming from. Main things I have seen on these are pan gasket which you have already changed, front seal, rear seal and the side seal. The worst one being the front seal because trans would have to come out to do. If its frt seal you usually have fluid hanging on the converter/flywheel cover. But a pan leak could also show up on cover as well. i would remove that cover, clean everything real good and drive it for a few miles. then look to see what is leaking. Side seals will leak down the trans and many people think its the pan because it comes down and drops from the edge of the pan. If that's your leak it can be fixed in the car but you'll need a special tool. I may still have mine if you need to borrow one. The rear seal you would have to pull driveshaft to replace but not a terrible job to do. Hope this helps, I'm sure more suggestions will come from this group. Best of luck. Rodney

Assuming it is a 400 trans, a couple of things...
The 400 has an issue with the o-ring that seals the outer diameter of the pump shrinking with age. If it sits for extended periods, the fluid will drain back out of the torque converter, raising the fluid level in the pan. The level will get high enough to be above where the o-ring seals the pump, and, with a shrunken o-ring, it will not seal, and fluid seeps out. It can run down the pan rails, appearing to leak from the pan. The only cure is to remove the trans, and replace the o-ring, and pump gasket.
It's also possible the trans pan is not flat where the gasket sits. Other leak areas include the shifter shaft seal, electrical connector, governor cover, modulator, and cooler lines.
I would suggest cleaning/drying the trans off well, driving a few miles, then check to see if you can determine where the fluid is leaking.

I had the same issue with my 73 TH400. If the car sat for more then a week the oil would leak out of the pan gasket. After many attempts at replacing the gaskets and seals I discovered the casting had lots of porosity in the pan seal flange. I finally fixed the problem by replacing the trans with the 200-4R OD.

Hope you get yours fixed soon.

 

 

 Check and or replace the speedometer gear "O" ring. Mine was bad, leaked. after replacement it was good.

I have had a similar problem and just changed out a chrome dip stick back to a stock one, which replaces the oring on the dip stick tube. I believe that is where mine was leaking from.

That's where mine was leaking from.  If you change the o ring, inspect the speedo gear.  The little o ring is spring loaded, and if it's failed, the metal spring may have grooved the gear shaft.  If it's grooved up, replace it (it's cheap).  Be careful you don't drop the gear in the transmission when it's going back together, very easy to do!

Thanks for the suggestions there are a few that I never checked. When I have time I will bring it in and take a better look. I will keep you posted.

It never ends with cars like mine that sat idle for five years. :) Mine has leaks from o ring seals, and just about every location mentioned except the pan. No leaks there. When the tyranny is dropped I could go ahead and have it rebuilt. Is that a good idea? If so, any suggestions? The tranny shifts smoothly but probably is completely original. Clunks when first put in gear but nothing more. My mechanic put trans x in it to seal the leaks. (Didn't work). Does that change anything?

You answered yer own first question with the 2nd statement..."My mechanic put trans x in it to seal the leaks"....
You really have no choice, now, but to have it rebuilt.
Putting something in a trans to stop it from leaking(other than new seals) is just silly, imho(NO disrespect to anyone who has, or will continue to do it). You might get the leak to slow down for a while, but it ain't gunna FIX it. That stuff works on the principal of swelling the rubber parts/seals, in hopes that the swelling will make a tighter seal. All that stuff really does is soften/swell the rubber parts....but then there's nothing to keep the seals from continuing to swell....right up until the point where they just fall apart....now you have a really BIG leak.   And usually, a trans that no longer functions at all.....
I can tell when a trans has had some kind of seal swelling compound poured into it...I can smell it, for one, but it's the rubber stuff that is now 50 times larger than it should be that tells the tale. O-rings simply fall off of the components....they are now better suited for use as rubber bands than seals.
Ya need a more practical reason for never using that stuff? Well....you'll never be able to correct what should have been a MINOR repair after putting that stuff in the trans....the trans will ALWAYS have to be completely disassembled and rebuilt if it has some sort of miracle stop leak juice in it...


Otay...rant over....sorry...... I shouldn't get so wound up over it...it's actually good for business.....