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?


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Joel Adams
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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?  

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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 ??

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John Sigmund

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?

 



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Joel Adams
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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???

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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.


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

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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.



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Joel Adams
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Well I drained and dropped the pan tonight.  Inspected the gasket I put in a few weeks ago - it's a flexible, black material, kind of like hard rubber, very thin.  (not much thicker than the rubber of a bicycle tire tube).  Inspected the pan and found a low spot on the bolting rim that is (what a surprise) right where I was seeing most of the seeping.  I lightly ball peened the rim in that area and got it to look a little better with a straight edge.  lightly peened some of the bolt holes that were slightly mushroomed, too.  Then installed pan with my new, reusable, much thicker, ATP gasket.  Also, the holes have grommets - on the old gasket the bolts fit in the holes very tight, I'm wondering if that could be some of my problem, too.  (gasket twisted a little as I was tightening bolts??)  Anyway, tomorrow I will fill it and test drive and hope for the best!  Thanks for the help.  

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Ah yes....the cheesy inner tube gasket...  Never seen one of those things actually work...too thin, and mooshy to seal anything. Add in a slightly disfigured pan surface, and you have a recipe for leakage.
The new gasket should fix it up nicely.  

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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Go things put back together last night and drove it to work today - Knock on wood ....no seeping yet.  Time will tell.  Thanks again for the help.  

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