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Technical TH350 Pan leak

Discussion in 'The Hokey Ass Message Board' started by MrChainsaw, Oct 13, 2015.

  1. MrChainsaw
    Joined: Jul 19, 2014
    Posts: 3

    from Michigan

    I'm at my wits end with this thing. I have Chevy 350 trans that will not stop leaking. I first replaced the gasket with a cheap rubber one ( I didn't know better). Leaked. So I figured the pan could be warped so I bought a new Mr Gasket pan with the cork gasket that came with the kit. applied a small amount of a brush on gasket sealant with a small bead of RTV on the pan side, let it set up over night and then torqued snug. LEAKED. Pulled it again, cleaned and scraped all surfaces, and bought a fel pro gasket, and applied dry with no sealant, torqued to 10 ft lbs. LEAKS! Any input on this time vampire would be appreciated. Thanks.
  2. Chrome pan? if so sand the mating surface.
  3. you sure it is the pan? dipstick tube o-ring, shift lever seal, front seal and cooler lines can all seep and look like the pan is leaking.
    scrap metal 48 and squirrel like this.
  4. travisn706
    Joined: Oct 28, 2013
    Posts: 49

    from Georgia

    Make sure it is not coming out of the kick down cable, or fill tube, all leaks look the same
    squirrel likes this.

    Joined: Dec 7, 2007
    Posts: 66


    Just a thought. You didnt mention it, but could there be a crack in the case vertical to the gasket mating surface that would make the leak look like it coming from the pan/gasket.
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 51,452


    also the accumulator cover, governor cover, speedo gear, front pump seal or O ring, etc.
  7. Same problem here. Is it the deeper dish pan and matching gasket? Fel Pro from memory like a deeper dish pan. I could be wrong?
  8. 48stude
    Joined: Jul 31, 2004
    Posts: 1,238


    tranny fluid will attack and break down Blue RTV . It actually tells you this on the directions. I found this out the hard way:D. Bill
  9. Engine man
    Joined: Jan 30, 2011
    Posts: 3,480

    Engine man
    from Wisconsin

    I too would believe that the leak is elsewhere. The seal for the shifter shaft is very close to the pan and those seals tend to leak. Clean the surface above the pan with brake cleaner and apply masking tape. If fluid flows over the tape, it's coming from higher up. Permatex makes a sealer specifically for transmission fluid.

    270dodge likes this.
  10. squirrel
    Joined: Sep 23, 2004
    Posts: 51,452


    RTV doesn't belong anywhere near an automatic transmission....
  11. Donut Dave
    Joined: Jul 9, 2007
    Posts: 421

    Donut Dave

    I chased my tail for 3 months replacing the after market tranny pan, several pan gaskets. Determined the tiny shifter selector seal was the problem. Purchased a seal remover from NAPA for less than $10 and a $4 seal, took about 10 minutes, life is good!!!!
  12. unkledaddy
    Joined: Jul 21, 2006
    Posts: 2,865


    Make sure that your TH350 isn't overheating.
    What kind of trans cooler do you have, and how long have you been running it?
    If you are certain that it's not overheating, and the leak is at the pan itself then get
    yourself a Farpak gasket available at most transmission shops. Also, make sure that
    the pan flange is nice and straight and when you put it together don't over-torque it.
    Farpak is the NUTZ!
    You can also get one of those UV penlights with additive to put in your transmission
    fluid. That will tell you exactly where she's leaking.

    Good luck.
    Last edited: Oct 13, 2015
  13. k9racer
    Joined: Jan 20, 2003
    Posts: 3,091


    On oil leaks I use a spray from Permatex Part Number 82099. Works vary well.
  14. Them dipsticks are notorious for leaking.
  15. Put the pan back on. Clean the pan lip around the transmission and spray it with dry foot powder. It will show a trail where the fluid is coming from. I have used it for years to detect cracks and stray leaks. Last one was from the front pump gasket-seal that looked like a pan gasket leak.
  16. elba
    Joined: Feb 9, 2013
    Posts: 628


    Check the dip stick o-ring, kick-down o-ring, and shift selector seal. I use the black neoprene gasket with NO sealer. Make sure pan is flat at holes and torque bolts to 13 ft. lbs.
    They make an after market dip stick tube that doesn't have an o-ring but a tapered thimble seal that works really good.
  17. LWEL9226
    Joined: Jul 7, 2012
    Posts: 326

    from So. Oregon

    You got that right . . . . .

    Lynn W
    gimpyshotrods likes this.
  18. unkledaddy
    Joined: Jul 21, 2006
    Posts: 2,865


    What color is that stuff?........... and I wonder if it can stop a small leak at the rear of the intake manifold where I didn't get quite a big enough silicone bead?
  19. I had that happen on a van and I couldn't get enough in after the fact when I could see it plain as day
  20. X2, most common cause of leak that I have found in the dip stick tube "O" ring.
  21. MengesTwinCustoms
    Joined: Oct 16, 2009
    Posts: 279


    You could get Aluminum oil pan with new gasket and no sealer
  22. gimpyshotrods
    Joined: May 20, 2009
    Posts: 20,481


    I like thick cast aluminum pans. Hard to distort.
    LWEL9226 likes this.
  23. k9racer
    Joined: Jan 20, 2003
    Posts: 3,091


    It is a spray and is clear. We use it on our circle track cars all the time. Also on quite a few highway cars. It will seal over oil that is leaking. I also use it on house hold leaks. Good stuff. a little high price though.. Bobby..
  24. wibble_1979
    Joined: Sep 25, 2012
    Posts: 109


    Anaerobic gasket maker by permatex. Put it on both sides of the gasket. Surfaces don't need to be perfectly dry either. Probably already seen it on a transmission. It's a thick red opaque goop works every time. If you use it and there is still a leak it's not from there.
  25. wibble_1979
    Joined: Sep 25, 2012
    Posts: 109


    Aerobic gasket maker. Not flange sealent. There diffrent

    Attached Files:

  26. unkledaddy
    Joined: Jul 21, 2006
    Posts: 2,865


    What about the vacuum trick where you suck the sealant into the void? I've never tried it but some swear by it.
    Absolutely.........with a Farpak gasket. Unless the trans is running too hot that combo is leak proof!
    Ask me how I know.
    Thanks K9 I may just give it a try.
  27. panheadguy
    Joined: Jan 8, 2005
    Posts: 1,053

    from S.E. WI

    Just fixed a leak on one at the kick down cable. Found a tear in the "O" ring. Hard to believe it would leak that much.
  28. Same as putting a big band aid on the transmission, take it apart and seal it properly......

  29. Did you know there are two types of TH350's The ones that leak, and the ones that are going to leak!
    I really struggled with one, and tried different pans (steel/alum), gaskets(comp/cork), gasket tack, torques, washer head bolts, fill level...
    I never did completely get it solved. I wondered if the case had a slight crack.
  30. squirrel
    Joined: Sep 23, 2004
    Posts: 51,452


    The kickdown cable itself will leak...there are about a dozen places besides the pan that you need to check before you need to even consider replacing the pan gasket.

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