Real odd TH 350 behavior at speed (downshifting?, neutral shifting? kickdown?)

Discussion in 'Transmission & Driveline Topics' started by 70SSRS350, Nov 23, 2016.

  1. 70SSRS350

    70SSRS350 Veteran Member

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    Hi guys,
    In these days I'm experiencing a real odd/funny/unsafe/you name it "behavior" of my Th350.
    My automatic transmission knoledge ends at the oil level check, so any advice is welcome.

    While at speed of 50-55 mph with transmission in D position, if I progressively push down the accelerator pedal (not floor it!), the car starts to accelerate fine. But at 60-65mph it seems to downshift (in first!) or to shift in neutral, the tach spin to 5500rpm, the engine roared.
    I still don't understand if it downshift or it shift to neutral because It scared me so much that my right foot move back by itself.....
    Well, after 1 second of terror, I gently re-apply the throttle and the car runned fine.
     
  2. 70SSRS350

    70SSRS350 Veteran Member

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    Forgot to say:
    If I drive normally, in traffic, hill's road, or slow driving (lever in D position) the car (and the trans) runs fine, no problem at all.
    If I floor it from still, no problem at all.
    If I drive at a constant speed (50-60 mph), no problem.
    The issue happen only during a slow acceleration at speed.
    If I Shift manually moving the lever, the trans seems to work fine.
     
  3. 70SSRS350

    70SSRS350 Veteran Member

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    A friend of mine talked me about a kickdown problem, is it possible?
    Kickdown worked at (about) half throttle?
     
  4. 70SSRS350

    70SSRS350 Veteran Member

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    Anyone?
     
  5. rchydzik

    rchydzik Veteran Member Lifetime Gold Member

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    Kickdown at highway speed really should not happen until full throttle. I would check the kickdown linkage at the carburetor. At full throttle, the kickdown should be pulled out. Not until then. There should be a sliding connection on the cable to accommodate that.
     
  6. 70SSRS350

    70SSRS350 Veteran Member

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    Many thanks for replay, I've found some informations on the web to adjust the kickdown linkage, I'll start checking it.

    http://www.chevelles.com/forums/33-transmission-driveline/65854-adjusting-kickdown-cable-th350.html
    http://www.chevelles.com/forums/148-2005/95549-how-correctly-adjust-kickdown-cable-th350.html

    It looks pretty easy to do, I hope very much it solves!
     
  7. bigdav160

    bigdav160 Veteran Member

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    Perhaps the governor is going bad? Usually though, they go to first and do not upshift when the gear on it goes bad.
     
  8. 70SSRS350

    70SSRS350 Veteran Member

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    One week ago I found some spare time to adjust the kickdown linkage on the carb and this strange issue vanished.
    To be honest there was no big difference on the linkage (or cable position) from before and after adusting it.
    Anyway the problem seems to be solved, the trans now downshift correctly at highway speed.

    I'm a bit unsure of WHY the kickdown linkage needed to be readjusted....
    Some time ago, before this problem, I put a 1/2" phenolic carb spacer under the carb, is it possible that the spacer misplaced the kickdown linkage?
     

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