Rear main seal leak?

Engine, Trans & Driveline

  1. superbird77

    superbird77 Well-Known Member

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    Hey guys, I think I know the answer but you guys know far more than I. My newly rebuilt 383 with about 150 miles on it started leaking engine oil today after a short drive. The oil is leaking from the transmission inspection cover (4 speed car) if I start it up it leaks a drop every two seconds, Turing off the car it eventually stops. After I removed the cover I found oil in it and you can see where oil has flung around inside the bell housing. I can see the end of the crank flange and it looks dry but behind the flywheel and clutch it's all over. I inspected the engine and no oil is leaking from anywhere else. Rear main seal right? Ugh... pic below of inside the cover. IMG_0553.JPG
     
  2. Fran Blacker

    Fran Blacker FBBO Gold Member FBBO Gold Member

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    Only other place inside bell housing are oil gallery plugs.
     
  3. Mike67

    Mike67 Well-Known Member

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    I'm yet to assemble my motor and this is probably one of my biggest worries as I hate leaks...I was browsing trying to figure out which bearings I was going to run and saw this on Mancinis site. I had never heard or seen these before, I'm curious if they work?http://www.manciniracing.com/rbanlemabe.html
     
  4. moparnation74

    moparnation74 Well-Known Member

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    Your 100% positive its oil and not gear oil from the trans?

    Sounds to me it is the rear main seal.
     
  5. superbird77

    superbird77 Well-Known Member

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    It's engine oil, its black, smells like engine oil. Gear oil has that mineral smell to it so I'm 99% sure it's not trans gear oil. Plus it only does it while running. Does anyone know where the gallery plugs are located on a 1969 383 block in case its possibly that?
     
  6. moparnation74

    moparnation74 Well-Known Member

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    I do not know of anyone whom has used that Mike...Good idea to relieve pressure on the seal. My current build I even considered using the original rope seal but I decided to listen to the guys at hughes performance on how to properly install the piton seals. Even though I do not have months of run time. I do not see any problems in the future...

    http://www.hughesengines.com/Upload...in_Seal_Installation_InstructionsJune2006.pdf
     
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    • Fran Blacker

      Fran Blacker FBBO Gold Member FBBO Gold Member

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      If you end up pulling rear main seal cap. The little bumps on inside where oil pan bolts go near rear main cap a friend said always make sure they don't hit the cap. He did motors at a dealership and had a rear main leak on him because of that. It was the only one he had that happen to. He just kissed those nubs on inside just below aluminum main seal cap.
       
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      • Fran Blacker

        Fran Blacker FBBO Gold Member FBBO Gold Member

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        Just above the cam to the left and right.
         
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        • moparnation74

          moparnation74 Well-Known Member

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          PbTV-CAM_19-300x199.jpg
           
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          • superbird77

            superbird77 Well-Known Member

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            Is it common for a rear main seal to go so quickly? Is it just bad luck or maybe improper install?
             
          • Ski 61701

            Ski 61701 Well-Known Member

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            Before you get too carried away and start ripping into the rear main seal. Look real close at the passenger's side rocker arm cover at the rear. Run your finger along the bottom and make sure that is absolutely dry. What happened to me once is I thought I had a rear main leak. I had quadrupled checked everything before putting motor in the car. Well I had oil all over. It wound up being the valve cover gasket leaked ran down the back of the engine and leaked at the inspection cover. I was sick/pissed about having to pull the motor out. But once I found the vc leak got different gaskets and sealed it up. Viola' dry as a bone. I just use oem seal holder. Take .010 off of the end, and i get my dremel tool and gently grind out the nubs that hold the oem rope seal in. Get a Superformance real main seal follow the directions and you are good to go
             
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            • Cornpatch MO

              Cornpatch MO Well-Known Member

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              To know for sure where a oil leak is coming from, there is a special liquid you can put in your motor oil. Run the engine for a short drive, shine a black light on the engine, and the leak will show up as fluoresent yellow. A mechanic used it on mine and showed a bad valve cover gasket and a rear main seal.................................MO
               
            • superbird77

              superbird77 Well-Known Member

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              Thanks for all the help everyone. Let me ask this, to do the rear seal on this will the engine need to come out?
               
            • moparnation74

              moparnation74 Well-Known Member

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              Nope....just remove the oil pan..
               
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              • PurpleBeeper

                PurpleBeeper Well-Known Member

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                Listen to these guys. MAKE 100% SURE where your leak is coming from first.
                1. valve covers, piece of cake
                2. oil galley plugs, pull transmission back, remove clutch/flywheel & use Teflon tape on the oil galley plugs
                3. trans front seal, trans comes out
                4. rear main seal, drop oil pan

                On those grooved bearings, I have one but never used it. When I had a leak in my rear main it turned out I had the rear main seal installed backwards.

                One more thought.... new motor + new seal = "maybe" you've got a bad PCV valve or valve cover breather making you build up pressure in your crank case so oil is FORCED past an otherwise good seal. To check, take off your oil filler cap & run the engine to see if it doesn't leak anymore.
                 
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                • superbird77

                  superbird77 Well-Known Member

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                  If I do need a new rear seal, what brand seal and sealant does everyone recommend?
                   
                • superbird77

                  superbird77 Well-Known Member

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                  I thought of the pcv and breather last night as well, I removed both but it still leaked. Good looking out, sometimes it can be something that minor. Doesn't appear to be my situation but thanks for mentioning it.
                   
                • moparnation74

                  moparnation74 Well-Known Member

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                  Felpro Viton...you can get it at your local parts store Fel 2947...Make sure you get the side seals..
                  http://www.manciniracing.com/subheviremas.html
                   
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                  • AR67GTX

                    AR67GTX Well-Known Member

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                    There's one other slim possibility for the leak which is the rear cam plug (post 9 has a good picture with the plug out). If your cam was installed after that plug was already in place it might have got bumped loose. I managed that once installing a cam on a fairly new Pontiac and got a free lubrication of the entire underside of the car within the first few miles. But it's probably the rear main seal.
                     
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                    • Cranky

                      Cranky Henchman #27 Staff Member FBBO Gold Member

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                      Just tore down a rebuilt 383 that had the rope seal in it. The whole engine was one big greasy mess but the back of the block was dry as a bone. And I don't see how a lip seal can last with the factory knurling on the crank......
                       
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