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HELP...Leaky Ass 350 Trans Pan/Gasket

Discussion in 'The Hokey Ass Message Board' started by LesIsMore, Aug 1, 2012.

  1. LesIsMore
    Joined: Apr 8, 2008
    Posts: 449

    LesIsMore
    Member
    from Ohio

    Ok, I have tried just about everything now, still have a leaker. I have a 350 turbo trans, got everything all bolted up and filled with fluid, had a small leak. figured the old gasket was shot so pulled off the old stock steel pan. They are thin and fairly flimsy, so I figured get a nice thick finned aluminum walled one and a nice thick cork gasket to seal it up. A small bead of RTV on top and bottom of cork (maybe thats the problem) got it all buttoned up, followed the pattern, not over tightened or under tightened, it has alan heads, so just hand torqued it. It sits in my garage for a couple weeks, seems to be sealed, I am gone for vacation for a week, come back, nice puddle below. So what now? Any ideas, I hear the 350s all leak, but this is nuts. Try a felpro rubber gasket? I have one,but ist is fairly thin, seems cork would have been better. Or do I have another problem? Its definitely at the seal, nothing from in front or above. Thoughts?
     
  2. JeffB2
    Joined: Dec 18, 2006
    Posts: 8,675

    JeffB2
    Member
    from Phoenix,AZ

    Check around the dipstick tube sometimes seepage there trickles down to the pan and "tricks" you,very common.
     
  3. Deuce Roadster
    Joined: Sep 8, 2002
    Posts: 9,519

    Deuce Roadster
    Member Emeritus

    Also check the shift linkage seal. They are famous for leaking.
    KD tools makes a nice simple tool for changing the seal. Just remove the linkage and pull the seal.

    [​IMG]

    The number is KD 2393 ...
    About 10 or 12 dollars for the tool.
     
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  4. Roothawg
    Joined: Mar 14, 2001
    Posts: 20,725

    Roothawg
    Member

    Mine doesn't leak, so don't buy into that.
    Is there a rubber gasket available like the newer style valve cover gaskets? I started buying those and made leaking valve covers a thing of the past.
     

  5. flamedabone
    Joined: Aug 3, 2001
    Posts: 4,875

    flamedabone
    ALLIANCE MEMBER



    The shifter shaft is right above the panrail, which looks like a pan leak. Look reeeeal close and you can spot it. MAKE NO ATTEMPT to change the shaft seal without the KD tool...if you scratch the case or the shaft trying to get it out any other way, you are fucked.

    Ask me how I know....


    Good luck, -Abone.
     
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  6. squirrel
    Joined: Sep 23, 2004
    Posts: 47,498

    squirrel
    Member

    Leaking like that after sitting a while is not the pan gasket, it's something higher.

    Shift linkage
    Kickdown Cable
    Speedometer Drive
    Governor cover
    Pump O ring
    Rear seal

    are all likely suspects
     
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  7. 48fordnut
    Joined: Nov 4, 2005
    Posts: 3,895

    48fordnut
    ALLIANCE MEMBER

    I have the same problem, went with the alum pan,but you need to put a coating on the pan as its porous. I did and it stopped that leak, now its the shifter seal. Thanks for the tip on the tool D/R.
     
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  8. Roothawg
    Joined: Mar 14, 2001
    Posts: 20,725

    Roothawg
    Member

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  9. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    If you're certain it's the pan gasket, Permatex makes a a special sealant for automatic transmissions.

    http://www.permatex.com/documents/tds/Automotive/81180.pdf
     
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  10. sskustoms
    Joined: Jun 18, 2007
    Posts: 276

    sskustoms
    Member

    What he said ,just happened to my dads 56 changed the o-ring at dip stick tube and fixed it we thought it was a pan gasket at first would leak after sitting a few days
     
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  11. snapper
    Joined: Jan 4, 2004
    Posts: 531

    snapper
    Member
    from PNW

    ..
    Is there a system ck valve for the convertor? I have a 350 trans that has an intermittent 3-5 qt leak if not driven weekly, otherwise dry. It sure makes a mess. Been chasing it for years, dose have a cheap chrome filler tube with new o-ring. Acts like the convertor is leaking back into the pan thus overfilled leak. Any one have a diagnosis?

     
  12. If it is leaking around the dipstick seal and it's an o-ring, you might want to try using the later "boot" style or multi-lip seal.
     
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  13. 48stude
    Joined: Jul 31, 2004
    Posts: 1,167

    48stude
    Member

    Blue RTV isn't compatible with tranny fluid. Bill
     
  14. odins701
    Joined: Aug 9, 2008
    Posts: 390

    odins701
    Member

    The factory doesn't use rtv, so whats up with that? I agree with these fellas, you need to carefully identify the source of the leak. There are much better gaskets available other than cork. Clean, clean, clean equals no leak. look for wetness around the seals above the pan gasket.
     
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  15. Early dipstick tubes ('77-back?) had a "groove" rolled around the end of the tube to locate the o-ring. Later tubes ('78-up?) did not. If I remember correctly you can use the multi-lip seal on either style. But don't try using the o-ring on the later style tube.

    Seal GM# 1259475 should be less than $4.00 at most GM dealers.

    1259475.jpg
     
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  16. 48fordnut
    Joined: Nov 4, 2005
    Posts: 3,895

    48fordnut
    ALLIANCE MEMBER

    went to O'rileys after looking up seal, @ .79cents and it is pioneer part no 760014-5[​IMG]
     
  17. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,426

    Von Rigg Fink
    Member
    from Garage

    if someone told you all TH350's leak they are a LIER!:eek::D

    i see you have many replies as to where to look for the issue, hope you find it and prove to have a th350 that doesnt leak
     
  18. saltflats
    Joined: Aug 14, 2007
    Posts: 10,457

    saltflats
    Member
    from Missouri

    May want to pull the flywheel cover and make sure the front pump o ring is not leaking.
     
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  19. squirrel
    Joined: Sep 23, 2004
    Posts: 47,498

    squirrel
    Member

    He might have done it over a year ago when the thread started?
     
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  20. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,161

    Mr48chev
    ALLIANCE MEMBER

    Saltflats got bored this morning and started on the back page rather than the front.
     
  21. saltflats
    Joined: Aug 14, 2007
    Posts: 10,457

    saltflats
    Member
    from Missouri

    Yeah and I haven't even been in the beer yet.
     
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  22. Atwater Mike
    Joined: May 31, 2002
    Posts: 10,352

    Atwater Mike
    ALLIANCE MEMBER

    Well, Hey! I hadn't heard of that dipstick seal until now, either.
    That's what happens when one devotes all his time to blacksmithing and fabbing brackets.

    LOL Thanks for that tip!
     
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  23. elba
    Joined: Feb 9, 2013
    Posts: 622

    elba
    Member

    NEVER use a cork gasket or sealer. Go to a good transmission shop and buy a black neoprean gasket. Clean parts and make sure the holes on the pan are not dimpled. Use hammer as necessary. Install gasket and pan ( no sealer ) and torque the bolts to 13 ft lbs. Torque twice. Use original bolts if you have them. If using allen head, place a good OD washer on the allen bolts.
    Also, as mentioned above, the boot on the dipstick tube is much better than the o ring.
     
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  24. B.A.KING
    Joined: Apr 6, 2005
    Posts: 3,697

    B.A.KING
    Member

    lol...... I always heard that the torque converter would drain down,push fluid out the front pump seal after setting for 3-4 weeks. any truth to this year old mystery????
     
  25. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,793

    tfeverfred
    Member

    Cork works fine. Just don't over torque and tighten the bolts in a pattern. Just like valve cover gaskets. Hey! It's traditional!;)
     
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  26. Commish
    Joined: Jan 9, 2010
    Posts: 379

    Commish
    Member
    from NW Ok

    My theory on that is that the torque convertor seal will deform slightly and let a quart or two out when setting for long periods on some cars. Tolerances are probably borderline on the ones that do, a little tighter on the ones that don't. Usually top them off and fire them up and drive them and they won't leak a drop.
     
  27. txturbo
    Joined: Oct 23, 2009
    Posts: 1,771

    txturbo
    Member

    Old thread I know....but just an FYI.
    I use to work at a transmission shop back in the late 80s. I have a lot of experience fixing leaks and fixed a lot of leaky Turbo 350s that nobody else could seem to fix. The shift shaft seal is a very common leak point and it does appear to be leaking from the pan gasket when it leaks. The steel pans are also a common leak point because the bolts usually get over tightened trying to stop a leaking pan gasket when its actually the shaft seal. Over tightening the pan bolts when using a cork gasket puckers the bolt hole until it makes contact with the trans case making it impossible to keep the pan from leaking. So now you have two leaks. Once I figured this out I started using the black paper gaskets and every steel pan I encountered I would flatten out the pucker around the bolt holes. When installing you just need to snug the bolts up. They don't need to be that tight. Never had another one leak after that.
    When replacing the shaft seal its best to use the tool because the sharp edge on the shoulder of the shaft at the end of the threads will nick the new seal almost every time. Its very difficult to install a seal without damaging it without the tool.
     
    Last edited: Dec 31, 2013
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  28. 325w
    Joined: Feb 18, 2008
    Posts: 5,449

    325w
    ALLIANCE MEMBER

    The use of OE dip stick tubes help cure leaks also. You can cut the tube to fit. Put heat shrink on the cuts as you adjust to fit. When done cut holes in the heat shrink and tack weld. Remove the shrink and finish weld. Measure the tube before you start. When done remeasure and cut dip stick down the same amount as you removed.
     
  29. B.A.KING
    Joined: Apr 6, 2005
    Posts: 3,697

    B.A.KING
    Member

    mine does that, let it set for a month,it leaks about a quart. if I go out and start it up,about once a week, bring it up to operating temp, not a drop.
     
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  30. unkledaddy
    Joined: Jul 21, 2006
    Posts: 2,865

    unkledaddy
    Member

    FARPAK..........love 'em!
     

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