The Dreaded Tranny Pan Leak

Transmission and Drivetrain Tech

  1. 512Stroker

    512Stroker We are all here because we are not all there.

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    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?
     
  2. plumkrazee70

    plumkrazee70 Well-Known Member

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    I was wondering this also. I know the modern tranny pans uses mopar atf rtv.
     
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    • Yunick13

      Yunick13 Well-Known Member

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      Have you checked to make sure the flange on the pan is flat?
       
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      • dartfreak75

        dartfreak75 Restore it, Dont part it! FABO Gold Member

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        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.
         
      • brian6pac

        brian6pac Well-Known Member

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        Spray copper on the pan side, nothing on the trans side.
         
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        • bcschief

          bcschief Well-Known Member

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          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 ?
           
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          • 512Stroker

            512Stroker We are all here because we are not all there.

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            Pan was new when I installed it and it is flat.
            Do you know what the torque is on the pan bolts?
             
          • 512Stroker

            512Stroker We are all here because we are not all there.

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            I have already checked for leaks above the pan several times. It appears to be the dam gasket.
             
          • George Jets

            George Jets 1967 Dart 2 Door FABO Gold Member

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            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
             
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            • jdsduster

              jdsduster Well-Known Member

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              no better gasket than the crush proof.last gasket you will ever put on.period.put it on dry.
               
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              • Dana67Dart

                Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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                • rustycowll69

                  rustycowll69 Well-Known Member

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                  I DO NOT recommend silicone RTV. They make a MOPAR reusable gasket. It came with a factory deep pan on my 02 ram2500. Damn near fool proof!
                   
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                  • RustyRatRod

                    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                    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.
                     
                    Last edited: Mar 17, 2021
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                    • rustycowll69

                      rustycowll69 Well-Known Member

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                      The part number is stamped right in the pan!
                      If you are trying to seal a chrome pan, good luck!


                      20210317_152453.jpg
                       
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                      • JoePole1

                        JoePole1 A dude in a B body FABO Gold Member

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                        • 12many

                          12many Well-Known Member

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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
                           
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                          • fishmens67

                            fishmens67 Well-Known Member

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                            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.
                             
                          • 512Stroker

                            512Stroker We are all here because we are not all there.

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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
                             
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                            • 512Stroker

                              512Stroker We are all here because we are not all there.

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                              Pan is not chromed
                               
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                              • fishmens67

                                fishmens67 Well-Known Member

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                                It can also wick through several of the pan bolts.
                                 
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                                • j par

                                  j par Well-hung Member

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                                  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...
                                   
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                                  • fishmens67

                                    fishmens67 Well-Known Member

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                                    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
                                     
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                                    • brian6pac

                                      brian6pac Well-Known Member

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                                      I pulled a piece of RTV out of a valve body once that wouldn't shift,
                                      Go figure.
                                       
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                                      • rustycowll69

                                        rustycowll69 Well-Known Member

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                                        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 bitch to bust that pan loose without bending the pan, and another bitch 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.
                                         
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                                        • George Jets

                                          George Jets 1967 Dart 2 Door FABO Gold Member

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                                          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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