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TH400 2nd - 3rd shift is screwed up

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Wheeling Arizona, Jun 15, 2002.

  1. Wheeling Arizona

    Wheeling Arizona Registered Member

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    My TH400 in my 90 Suburban is acting really strangly with it's 2nd to 3rd shift. Sometimes it is normal...around 40-45mph or so. But that is usually good for only one or two shifts. Then the shift point seems to move much higher, like 65mph or so...and the shift is really mushy when it finally shifts. I have even had it in 2nd as high as 70mph as it fluctuates back and forth into 3rd and out. The shift is not crisp at all...almost a drifting into 3rd and out.

    Any ideas?

    --Steve
     
  2. Wheeling Arizona

    Wheeling Arizona Registered Member

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    Starting to suspect a vacuum leak on the modulator. Anybody ever have similar problems? --Help--

    --Steve
     
  3. arq

    arq 1/2 ton status

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    start with the basics, good source of vaccume, pinched/torn lines, modulator, etc etc...

    ARQ.
     
  4. rodzzilla

    rodzzilla 1/2 ton status

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    Had a modulator problem w/a TH350. The shift points were higher, but the were also a lot harsher. How is the fluid?
     
  5. slider

    slider 1/2 ton status

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    Turbo 400's do not have a vacuume modulator, they use a electric switch for kick down. When is the last time the fluid and filter were changed? /forums/images/icons/confused.gif
     

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