My 91 4wd suburban with a 4L80e is leaking around the pan - I can see seepage from the pan/transbody interface.  I just recently did a pan drop to try to solve the same issue, although now it seems to be worse.  Any thoughts?  I may have slightly overfilled it, but probably no more than 1/2 quart.  Is that enough for leakage from the top of the pan?  I used a fel-pro gasket that is installed dry - no silicone.  The instructions did call for some light grease on one side of the gasket but I assumed that was just to assist with placement so I did not do that (I just used some of the bolts to keep the gasket in place as I was installing the pan.)  Could that be my problem?  I torqued all the bolts in a criss-cross pattern.  

|UPDATED|7/5/2015 11:44:21 PM (AZT)|/UPDATED|

Grease is good.  Did you check the gasket surface on the pan with a straight edge to see if it was flat?

Need to first determine if it IS the pan leaking. Check the selector(shifter linkage) shaft that sticks out of the ds of the trans, the filler tube seal, cooler lines, and the electrical connector....all of these places can leak, and seep around the pan, making it appear to be a pan gasket leak.
What type of gasket did you use? Cork, "farpack", black paper?

Thanks guys.  Joel, I double checked the stuff you mentioned and I'm 95% sure it's the pan gasket.  Entire driver's side is pretty dry - electrical connector and selector are dry.  On the passenger side there are the oil cooler lines (totally dry) and the dipstick/filler tube.  It could be the filler tube, but it does not look like it.  Worst case seeping is at front and back of tranny.  In fact, most is going on to the t-case skid plate and dripping through a hole in that.  At the front, it is dripping down the bell housing and falling off at it's low point.  The seeping is between the pan and the gasket, not the gasket and the tranny case which kind of tells me it is not coming from above?  

Dave, not super familiar with '91 suburban tranny, but if it is a stamped steel pan, did you tap back the mounting holes with a ball peen hammer ??

Sounds like a reusable gasket, Dave. Not many problems with those at all. Could have a buggered up spot on the pan somewhere I suppose....What of gasket did it have on it when you removed it the first time?

 

Joel, I don't think it's a reusable one - it didn't have that bead of rubber or silicone or whatever.  But I did just order an ATP reusable from Amazon.  Guess what I'm doing this weekend???

Most of the factory, and aftermarket reusable gaskets don't have the red/orange bead of rubber...most are all black. That just happened to be the pic I had. Reusable gaskets for the 4L80 are stiff. Actually rubber coated steel.
Cork gaskets are of course flimsy, and the Farpack gaskets are kinda in between...not stiff, but not floppy.
The pan rail itself doesn't have to be perfect....the gasket will fill in any minor defects. If the pan has any bent spots, or large dings, then you'll need to flatten it out as best you can. Check the surface of the trans well, too, for any gouges, or leftover gasket pieces.
You could get a later model(deeper) pan, and deep filter for it, too. The late/deep pans are made a little better(thicker steel), and have fewer issues with leakage.

I got the ATP reusable pan gasket today - no instructions.  Assuming it goes on totally dry?  

ALL gaskets should be installed dry, with very few exceptions....imho. The re-usable gaskets can be installed with fluid on them, and they will still not leak, so they don't have to be perfectly dry when changing fluid, tho it is better to be clean & dry.

I'm bettin your leak/seep is something other than the pan, Dave, unless your pan is messed up. 1/4" overfull won't hurt anything, but it certainly can cause the fluid to spew out of the vent when it gets hot. Trans fluid expands as it gets hot, which is why there is a "Cold" and "Hot" marking on the dipping stick. Hot fluid should be in the middle, between the cold and hot limits. A little over is fine, as far as operating functions go.

My only suggestion is to use some brake cleaner, and spray the whole thing off...get it nice and clean. Drive it, let it sit overnight, and look for seepage/trails.