transmission pan sealing

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David Dickerson

David Dickerson

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I have a 727 gasket sealing issue. Have tried every gasket imaginable including the plastic double bead sealing type with no real luck. (Rubber, cork, steel core with rubber, silicone) all leak. I have an aluminum pan that I had machined totally flat, a steel aftermarket pan, and even a steel pan from a newer model tranni. They all leak! All gasket surfaces totally clean before sealing. Major area of leakage seems to be near the dip stick part of the flange. You can even see part of the sealing bead on the plastic gasket in this area. I contacted Permatex, and they recommended The Right Stuff Grey (one minute gasket maker) Wanted to check here before trying my final resort with a more permanent gasket that will make things difficult to remove if it does leak. Have drained fluid probably 10 times. Have posted this problem before and tried every ones recommendations. Really wondering what people think of Permatex's recommendation or if you have any other solution other than epoxying the pan to the tranni. That would do it!!!
 
You may look at what the motorcycle community uses to seal engine cases. I once had an old classic m/c that had a case leak I couldn't stop. A buddy gave me a tube of 'Honda Bond 4' and after applying the sealant it stopped the leak.

A thin coat on both surfaces applied with your gloved finger is all it takes. It doesn't dry completely so you can later separate the pieces.

Good luck as oil leaks are a P.I.T.A.!
 
Fluid could be leaking down and collecting on the pan so it looks as if its the pan gasket. Try stuffing some rags around suspect areas above the pan. To keep dropping the pan and resealing is not working. Could try oil dye and UV light method also.
 
I went through the same hair-pulling exercises with what I thought was my 727 pan gasket. Turns out it was the shift shaft seals leaking all along that would migrate down and really look like it was the pan leaking.
 
I myself always get a filter kit a NAPA the black gaskets. You put all the bolts through to keep the gasket in place while installing. That is why the holes are smaller and hold the bolts. Do not use any sealant and make sure you dry both surfaces with brake clean.

I agree with the tube o-ring or lever seals leaking also.

Yama-bond and Honda- bond are the only sealant to use on a trans if you need to. We build two strokes. That is what is used to seal case halves. They must be sealed tight they run off of the fuel compressed through the transfer ports from the bottom of the piston going down. They need to be sealed tight . That stuff works.
 
You need to get under there with a roll of paper towels, a mirror, and a pillow. Your neck is going to get tired. Wipe off and wait. Repeat.
 
69 M-CODE CUDA said:
I went through the same hair-pulling exercises with what I thought was my 727 pan gasket. Turns out it was the shift shaft seals leaking all along that would migrate down and really look like it was the pan leaking.
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Same here, the shift shaft seal took me 15 mins to replace with the trans in the car. There’s a speciality tool that makes it easier.
 
You should never have to use sealant. Almost a sure bet it ain't the gasket that is leaking or even weeping. Definitely isn't from the pan bolts. Don't let frustration get in the way of a calm process of elimination approach. There are a few areas of the trans where weeping or leaking can occur. The obvious and already mentioned dipstick tube oring and shift shaft seals. Front pump seal. Also, the band adjusting nut/bolt on the left side can leak (mine does I've discovered and it collects on the excellent non leaking Moroso pan gasket I'm using) Leaks can also eminate from the rear band lever pivot pin. The extension housing mating surface and the speedometer pinion. Hit all the accessible areas with some brake cleaner and monitor the areas. Angle of the trans can cause drips to show up far away from the actual leak. Pretty sure you'll find the source.
 
12many said:
You should never have to use sealant. Almost a sure bet it ain't the gasket that is leaking or even weeping. Definitely isn't from the pan bolts. Don't let frustration get in the way of a calm process of elimination approach. There are a few areas of the trans where weeping or leaking can occur. The obvious and already mentioned dipstick tube oring and shift shaft seals. Front pump seal. Also, the band adjusting nut/bolt on the left side can leak (mine does I've discovered and it collects on the excellent non leaking Moroso pan gasket I'm using) Leaks can also eminate from the rear band lever pivot pin. The extension housing mating surface and the speedometer pinion. Hit all the accessible areas with some brake cleaner and monitor the areas. Angle of the trans can cause drips to show up far away from the actual leak. Pretty sure you'll find the source.
Click to expand...
Here's another possible location. The access panel in the tailshaft to the snap ring.
upload_2019-9-7_20-41-6.png


upload_2019-9-7_20-42-48.png


Old one had an extra hole - surely that didn't help it seal.
upload_2019-9-7_20-47-9.png


I couldn't remember where I put the gasket material, but I have 904 pan gaskets that came in various filter kits for 727/9xx transmissions.
So that's what I used for gasket material.
upload_2019-9-7_20-47-54.png
 
Been fighting this with a very slow drip. Absolutely dry above the pan rail. Tried a Moroso deep pan and Blue gasket. Still a slow drip and dry above the rail. Must be a scratch on the pan rail. I will pull and recheck, 8 quarts of new fluid ticks me off and not eager to drop it just yet! It seeps at the front between the center bolts at the rail. Very frustrating as the old deep Mopar steel pan never leaked until resto. I also wonder if the case may have a leak at the part line. It is dead center of were the seep is.
 
I have always used the old cork gaskets with no sealant. You need to retighten the bolts after a week or two and than you are good to go. I’ve had more trouble with the dipstick o ring than anything. Sounds like you have a problem with your case.
 
66jim said:
Fluid could be leaking down and collecting on the pan so it looks as if its the pan gasket. Try stuffing some rags around suspect areas above the pan. To keep dropping the pan and resealing is not working. Could try oil dye and UV light method also.
Click to expand...
Well, I feel like an idiot with all the money I spent on pan leaking solutions. Since I had the tranni all painted, I didn't really see any signs of oil anywhere except at the pan edge. First tried the paper towels and lo and behold, oil soaked back near tailshaft. Put in the die and found a leak coming from one of the bolts attaching the tailshaft. Tightened and problem solved. Happy but pissed I wasted all that time and money, but that's the hobby. Thanks for the ideas. Now I can focus on my rear main leak and pinion seal leak. LOL
 
Here is a good one I have seen a few times. See if there is a bot hole to hold down the dipstick. I have seen them missing and also no sealer on the bolt. It will drive you nuts looking for it.
 
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