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Trans. won't down shift

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Scott73, Jun 21, 2002.

  1. Scott73

    Scott73 Registered Member

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    Trans. won\'t down shift

    The transmission will not always shift down into first. Sometimes it does and sometimes it won't. I can manually put it in first and it works fine. I think I'm going to try changing the fluid and filter and see if this helps. It' a 78 K5 I just bought and it had been sitting for about the last year. Any other suggestions
     
  2. lt61173

    lt61173 1/2 ton status

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    Re: Trans. won\'t down shift

    check the kick down cable & the modulator valve
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: Trans. won\'t down shift

    TH400 or TH350? TH350 probably the kickdown cable is maladjusted or not hooked up, and if TH400, not sure if the solenoid affects 2-1 kickdown or not, although the solenoid DOES affect 3-2 kickdown, but will still kick down without the wiring hooked up, in some cases.
     
  4. Sinful_Nature

    Sinful_Nature Registered Member

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    Re: Trans. won\'t down shift

    K.... Don't mean to throw a question on top of question but currently I'm running with the Kickdown cable not connected and I have no problem with it down shifting. Grant it... if I need quick power it isn't there(like going to pass someone) but help saves on wear & tear and gas.

    Should I be able to do this?

    ~ Russ
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: Trans. won\'t down shift

    Every GM tranny I'm aware of (even the powerglide) has a kickdown function of one type or the other. Don't really NEED to be hooked up, but its kind of nice. Not too big a deal if you have a nice console shifter, but with column shifting, although the downshift usually isn't difficult, going BACK to the higher gear is sometimes tricky.

    You can always manually shift if you need to (like you mention, passing) and IMO, if the tranny can't downshift, you are *wasting* gas...the engine needs to rev a little higher to make more power, and without downshifting, you are decreasing engine vacuum (more throttle opening) without letting that extra gas do any work...thus, intake velocity is decreased, with no benefit. It is the same as not downshifting a manual, just pushing the pedal harder and harder...you'll speed up on flat ground, but not nearly as efficiently as if you downshifted to bring the vehicle speed up, then upshift when speed was sufficient to make the higher gear more effective.
     
  6. Sinful_Nature

    Sinful_Nature Registered Member

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    Re: Trans. won\'t down shift

    K... you just made rethink my position reagrding the kick down cable. To be honest it wasn't hooked up when I did a tranny swap (I guess out of laziness). I was thinking it would save on gas were I know the kick cable isn't on, so I don't hammer the right pedal often. Keeps me in check. But you bring up some valid points... just may have to hook it up again.

    Thanks!

    ~ Russ
     
  7. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Re: Trans. won\'t down shift

    Could be a sticking valve in the valve body. Now could be a good excuse to put in a shift kit. Just hose down the valve body with brake cleaner and compressed air while you have it off.
     
  8. FL84K5

    FL84K5 1/2 ton status

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    Re: Trans. won\'t down shift

    I have this exact same problem with my 700R4. Sometimes it will shift down fine to pass or go up a hill, and sometimes it wont downshift.
     
  9. Scott73

    Scott73 Registered Member

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    Re: Trans. won\'t down shift

    A lot of the time it won't shift in to 1st when I come to a stop. I have to do it manually if I want to take in 1st. If i am at a stop light for a short period of time (20-30 seconds) it will shift down on its own most of the time.
     

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