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Technical TH350 Fluid level/leak problems

Discussion in 'Traditional Hot Rods' started by MikeG5211, Jul 7, 2019.

  1. MikeG5211
    Joined: Jul 7, 2019
    Posts: 61

    MikeG5211
    Member

    So I am almost a complete beginner here I have a 23 T bucket kit car that I'm trying to finish up getting it on the road. Me and a friend who is much more experienced then me take it for its first real test drive a few days ago and he drives it a bit and says the Tranny is slipping probably due to low fluid.

    Ok fast forward to today and I'm getting ready to take it on another test drive to warm it up and check fluid level but I figure Ill add some fluid first because the first drive I don't think it was registering any fluid on the stick at all. So I'm filling it and it starts leaking out of some hole.

    [​IMG]

    So I'm trying to figure out by googling what this hole is for and I can't find anything
    If its a vent hole or a overflow drain or something, I can't find anything so I call my father who's been a mechanic and owned a shop and he don't know what it is but he suggests just plugging it so I do that which I'm not sure was the right thing to do.
    [​IMG]

    The little thing came out I filled it with epoxy bolted it back on done i think. then I notice more fluid is leaking where the dipstick tube meets the transmission?[​IMG]

    So to start I'm just wondering If Ive just overfilled it or should I not have these leaks and what the hell is that hole for and should I have plugged it or not? thanks.
     
  2. First pic is for the detent cable they are cheap NEW

    Get new o ring for the fill tube
     
  3. MikeG5211
    Joined: Jul 7, 2019
    Posts: 61

    MikeG5211
    Member

    Ok thanks but now I'm even more confused because I don't think this car was ever set up to use a detent cable I thought it was just running on vacuum and the holley vid I just watched says the TH350 needs the cable, if I do even have a TH350 but it sure looks like one? here is the current setup with wider shot of tranny.

    [​IMG]

    [​IMG]
     
    325w likes this.
  4. Your detent "kick down cable" is not present..... Do you know if you have a manual valve body? Your just going to have to "down shift it", or introduce "passing gear" yourself. Looks like you just need a couple of o rings= one for the detent cable block off, and one for the dip stick. Add a lil goop for good measure,- BUT, have everything clean= carb/brake cleaner, let dry, goop, install, wait a day, then go for it..........
    And- at least run a one piece line to the vac mod....... That line needs some attention!:rolleyes:
     
    bonneville bones likes this.

  5. MikeG5211
    Joined: Jul 7, 2019
    Posts: 61

    MikeG5211
    Member

    Well I just googled what a manual valve body is and I have no idea what I have. How would I check?
    Are Th350's not all the same? thanks
     
  6. manual valve body's are normally for racing. You have a vacuum modulator so I would presume that you do not have one.
     
    Bandit Billy likes this.
  7. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 2,865

    427 sleeper
    ALLIANCE MEMBER

    Like JNKYARDDOG 1 said, get a new detent cable, and hook it up! That cable controls the shift points and the line pressure, IIRC. That should take care of the slipping issue. As far as the dipstick tube, if it were mine I'd get rid of that chrome aftermarket tube and get a later model factory tube with the long, grommet-style seal with the dipstick to match. Hopefully that will solve the issues.
    Also, NEVER use any type of sealant on an automatic transmission, ANYWHERE!
     
    Last edited: Jul 7, 2019
    loudbang and squirrel like this.
  8. s55mercury66
    Joined: Jul 6, 2009
    Posts: 4,335

    s55mercury66
    Member
    from SW Wyoming

    The cable on a TH350 only controls the forced downshifts, they will work fine without one, but you will have to downshift manually as mentioned above, if you want to pass someone or show off a bit.
     
    31Vicky with a hemi and squirrel like this.
  9. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    If you just want to get the thing to quit leaking so you can see how it works, then you can ignore the detent cable, plug the hole in the plastic fitting and make sure it has a good O ring on it. Then take out the dipstick tube, and see if it has an O ring, if the O ring is damaged or aged (they get hard and "flat" when old) or if the tube itself is damaged--either deformed, or cracked. Usually just a new O ring will be all it needs, sometimes it will need a new tube-if it needs a new tube, get the later design, it is a LOT less prone to leaking. Make sure the tube and dipstick are a matched set, of course, so you can check the fluid level accurately.
     
    ffr1222k and alanp561 like this.
  10. OLDSMAN
    Joined: Jul 20, 2006
    Posts: 2,422

    OLDSMAN
    BANNED

    The cable only controls forced downshifts, has nothing to do with normal up shifts
     
  11. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    It does have something to do with normal full throttle upshifts, doesn't it? like it delays them? But the trans will generally live a long time without it.
     
    31Vicky with a hemi likes this.
  12. It’s a better transmission and better driving experience with the cable functioning.
     
    olscrounger and squirrel like this.
  13. Leaks on a th 350,,,
    run a deep pan
    with the filter extension
    Keep the fluid level constant accordingly to the new filter location/level.
     
    olscrounger likes this.
  14. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    Yeah, I always make the detent work on my cars, but there are guys who don't, and they seem to live through the experience just fine
     
  15. geoford41
    Joined: Jul 26, 2011
    Posts: 762

    geoford41
    Member
    from Delaware

    Take off the Teflon tape on the inverted flare fitting on the trans cooler tube, it is NOT supposed to be on the fitting, the seal is made by the inverted flare matching up to the brass adapter.
     
  16. OLDSMAN
    Joined: Jul 20, 2006
    Posts: 2,422

    OLDSMAN
    BANNED

    If this was my car I would replace the dipstick tube and kick down cable with the new style. Instead of an o-ring they have a sleeve on them, that seals them much better
     
    47ragtop likes this.
  17. The cable does nothing until the last few millimetres of travel, where a spring load will be felt. This is where the throttle is just about wide open. (just got this info from an auto trans workshop when I set my kickdown up, works fine).
     
  18. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    That sounds right.... But that little bit of travel changes the upshift from about 3500 to about 4500 rpm?

    Sent from my Trimline
     
  19. MikeG5211
    Joined: Jul 7, 2019
    Posts: 61

    MikeG5211
    Member

    Thanks guys, lots of useful information, Ive got the leaks sealed for now. Maybe in the future ill replace the tube entirely but for now a new O-ring did it good. Now I have to fix the shift stick that just broke off :eek:
     
  20. Correct. The full throttle 1-2 will usually be about the same, (whatever the governor allows), and the 2-3 will somewhat lower, without the detent cable . I'm being vague with the numbers intentionally. Lots of different ways to build 350's , but that generally is what will happen.
     

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