TH350 leak - stopgap measures?

Discussion in 'The "Juice Box"' started by -JJH-, Apr 2, 2019.

  1. -JJH-

    -JJH- "Works like a Buick" - a Finnish proverb

    Hi all,
    I have a TH350 tranny on my '70 GS, that has been leaking/seeping fluid for a couple of years now. The leak is not a major one - we're talking about a few drops of fluid on a piece of cardboard, after shutting down the engine and letting the car sit for a while. Looking underneath the car, it appears that the leak is coming between the torque converter and transmission housing - torque converter seal gone bad?

    Another thing I noticed last autumn, before storing the car for a winter - when all warmed up, on gear and idling, I get some odd rattling or resonance sound, that disappears if I blip the throttle just a bit ie. alter the RPM's slightly.

    Other than that, the tranny works nicely and smoothly, and fluid being free of odd smells and contaminants.

    Now, I am planning on rebuilding the car within few years and at that time, I am planning on getting an overdrive transmission. Hence, at that time I am thinking about storing up the current, original TH350, without rebuilding. Considering this, would there be some 'snake oil' / stopgap solution that I could/should try to stop the slight leak for time being?

    I know these 'transmission fix' liquids are not necessarily the best solution, but I am looking for some cheap interim solution that could carry me through few years and few thousands miles.


  2. telriv

    telriv Well-Known Member

    Try a pint of DOT111 brake fluid. That's what most of the sealers have in them. I've been doing it for years & telling others with good results. IF it doesn't work it only cost you a couple bucks & it WON'T harm anything.

    Tom T.
  3. Ken Warner

    Ken Warner Stand-up Philosopher

    Dot3 in a transmission?
    On purpose?
  4. -JJH-

    -JJH- "Works like a Buick" - a Finnish proverb

    Wow, I did find the same info on a couple of websites, too; recommending to top up the tranny with brake fluid. Should work, if the leak is really a minor one (as looks like in my case).

  5. 1972Mach1

    1972Mach1 Just some guy.....

    We used to use the brake fluid trick at the Dodge dealer I was working at in the late early 2000s. Works like a champ for a while.
    BUICKRAT likes this.
  6. TORQUED455

    TORQUED455 Well-Known Member

    Many times, a leak in that area is just the pan gasket. I’ve had excellent luck with Duraprene gaskets. Make sure you retorque once after getting the trans hot.
  7. knucklebusted

    knucklebusted Well-Known Member

    The trick we used to use was Type-F fluid instead of Dexron III because Type-F causes seals to swell a bit. Never heard of the brake fluid trick and not sure I'd want it in my transmission.

    Doesn't brake fluid and oil turn to a gel?
  8. 1970 STAGE 1

    1970 STAGE 1 Well-Known Member

    Trans - X will fix seal seepage. It will also help sticking valve bodies.. Magic stuff.
  9. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    Ive done dozens of pump gaskets on th350s. Yank the trans and replace. One day job..
  10. Fox's Den

    Fox's Den 22 years of racing the same 355 Buick motor

    They do tend to leak on a 350 trans after a while and will leak more after sitting for a few weeks or so. I have had to get it replaced a couple times now. I just do it when I have to pull trans for what ever reason to change convertor and so on. The noise you hear could be a cracked flywheel. I ended up putting in a 2004r trans and it has been very good. I have a lockup convertor that I can lock up manually. TA has a SFI flywheel for those and I have had it for over 20 years now
    What is great is I can lock up in 3rd gear driving at 40-45 mph. With my 373 gear I run at 2200 rpm at 65 mph which is great.
    The only thing I had to do was move the trans mount back to the next holes and get a new driveshaft. That was easy too just take a measurement and send to company of your choice and they make one, cost was not bad on that either.

    The 2004r trans has been in my car since 2005 and still does not leak and sits all winter. Best improvement I ever did.

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