The Dreaded Tranny Pan Leak

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512Stroker

512Stroker

We are all here because we are not all there.
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Freedom, MO
SBM 727, Hughes 3000 stall, steel stamped plus 2 quart pan.
This will be the thrid pan gasket I have tried, I cant keep it from seeping between the pan and the gasket. First gasket was cork, second gasket is stiff rubber like with ridges in it, still leaks. All gaskets were installed clean and dry, no sealant used.
What trick am I missing here? Sealant?
 
I just rebuilt a 999(904) and used a good gasket that came from b&m and its leaking almost instantly i was hoping once it heated up it would seal but so far no luck still leaking like a seave.
 
Maybe it's the shift shaft seals. Is it leaking on the drivers side at about the middle point of the pan or possibly fluid is running to the back corner of the pan ?
 
bcschief said:
Maybe it's the shift shaft seals. Is it leaking on the drivers side at about the middle point of the pan or possibly fluid is running to the back corner of the pan ?
Click to expand...
I have already checked for leaks above the pan several times. It appears to be the dam gasket.
 
Here is same what I do for valve covers as well as the tranny pans.

Clean pan surface and tranny surface, bolt thread holes and bolts and threads with Brake Parts Cleaner to remove any trace of oil or oily solvents.

Then apply thin layer if black RTV Gasket Maker to both tranny and pan gasket surfaces and a thin layer to both sides of new cork pan gasket.

Then coat bolt theads with Aviation Sealer (like Hi Tack) to seal threads to the case.

Assemble the pan onto the tranny with light but snug torque to the pan bolts, tightening them evenly as you go around 3 times.

Let sit overnight to let RTV cure. Put in your tranny fluid, check when warned up and leave a pint low on the 727s so that you are not overfilling it.

Check when idling in neutral. Leaving the tranny 1 pint low leaves room for torque converter drain back so the fluid level does not go above the shift shaft seals and forces the fluid out.

Can seal the nut and band adjustment bolt threads with Aviation Sealer too as fluid will seep from there also if unsealed.

Never leaks as long as your shift shaft seals are good. Same for 904s too.

If your front seal at the torque converter is leaking, well that is another story . . .

20200802_202253.jpg
 
Sealant doesn't go on transmission pans. Ever, ever, ever. Period. Make absolutely 100% SURE the pan rail is straight and the bolt holes are not distorted. Don't say "It's a new pan" just frikkin DO IT. How hard is that? Seriously? Next get the best gasket money can buy. That would be this. Rubber with a steel core. Put it on CLEAN CLEAN CLEAN and DRY.

Moroso 93110 Moroso Transmission Pan Gaskets | Summit Racing

Lastly torque to spec and DON'T over torque. Finally, come back after a few heat cycles and re-torque WHEN COLD. If it's the pan gasket that's leaking, that should solve it. But beware, like others have said, transmission leaks can be tricky. Sometimes a pan gasket leak ends up being a dipstick tube leak, of shaft seals, or something else, so inspect it very closely.
 
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Don’t forget to check the low/reverse band lever pin/shaft bore on the back of the case for a possible leak. I’ve had leaks there, bad (O-ring) cleaned with degreaser and packed some ultra rtv in there to solve that after thinking maybe the shift shaft and gasket was the source only to have been that shaft and bore.

E143B4CB-EFD8-4DFE-B905-3C99E62952AC.jpeg
 
I went through 2 different new pans and several gaskets with sealant only to find the dipstick was seeping.
It was hard to see, but it wicked around the pan making it look like the pan gasket was leaking.
put a new O-ring on and it was fixed.
 
RustyRatRod said:
Sealant doesn't go on transmission pans. Ever, ever, ever. Period. Make absolutely 100% SURE the pan rail is straight and the bolt holes are not distorted. Don't say "It's a new pan" just frikkin DO IT. How hard is that? Seriously? Next get the best gasket money can buy. That would be this. Rubber with a steel core. Put it on CLEAN CLEAN CLEAN and DRY.

Moroso 93110 Moroso Transmission Pan Gaskets | Summit Racing

Lastly torque to spec and DON'T over torque. Finally, come back after a few heat cycles and re-torque WHEN COLD. If it's the pan gasket that's leaking, that should solve it. But beware, like others have said, transmission leaks can be tricky. Sometimes a pan gasket leak ends up being a dipstick tube leak, of shaft seals, or something else, so inspect it very closely.
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Listen Boozo (nice Picture) I did not think a step by step explanation was necessary so he ya go.
When I said that "its Flat" I should have said that after the first gasket I set the pan gasket surface down on a piece of polished marble and could not pass a .004 feller gauge between the pan and the stone. I figured that that straight for a stamped pan. I do not believe that I have over torqued the bolts as I have secured many pans that have not leaked, but rest assured that when I have the pan off I will check the bolt holes.
Thanks
 
I wish somebody told me I wasn't supposed to use rtv!...
I foolishly put a bunch of "the right stuff" on both sides of the cheap Court gasket that came with the rebuild kit and never had a leak...
I'm not recommending that only because I don't want Rusty fat mod yelling at me...
 
j par said:
I wish somebody told me I wasn't supposed to use rtv!...
I foolishly put a bunch of "the right stuff" on both sides of the cheap Court gasket that came with the rebuild kit and never had a leak...
I'm not recommending that only because I don't want Rusty fat mod yelling at me...
Click to expand...
I tried the right stuff, only to find the tube was seeping.
That stuff was hard to get off, so I didn't use it on the next new pan install. lol
Even had the good Moroso gasket on there one time. Damn leaky dip stick tube. lol
 
I pulled a piece of RTV out of a valve body once that wouldn't shift,
Go figure.
 
I've been watching these trans/transfer case breakdowns on youtube and it's amazing how many units' pickups are plugged up with fugitive silicone boogers.
That being said, my Intrepid auto trans came with silicone from the factory, but the factory has a robot which deposits the PERFECT size bead of silicone for the factory assembly. It never leaked from the pan, BUT it was a real ***** to bust that pan loose without bending the pan, and another ***** to clean all that old silicone off.
If there is a reusable pan gasket, I highly recommend it. IMO, it's worth the extra money.
 
Good trick for any sealed RTV surface is to loosen up the bolts then spray Brake Parts Cleaner on it a couple times over a 20 minute period to let it soak in, keeping it wet.

It starts softening up the RTV and it comes apart easy. Makes it easy to clean the surfaces down clean to the metal too. Trick is to keep it wet and it softens right up.

Weather it is valve covers, oil pans, intake manifolds, timing covers, etc. makes life easier for cleaning up the RTV.
 
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