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th400 kickdown

Discussion in 'Chevy Trucks' started by bodhidexter, Aug 6, 2004.

  1. bodhidexter

    bodhidexter Junior Member
    from ma
    Messages: 11

    i have a th400 trans my question is about the kickdown/passing gear it appears to be controled by engine vacuum . is this accurate? also is the signal timed or full vacuum and how does it work?
  2. ratlover

    ratlover PlowSite.com Addict
    from IL
    Messages: 1,325

    it should have a switch deal for kickdown
  3. wfd44

    wfd44 Senior Member
    from Maine
    Messages: 369

    TH-400's use electric kickdown. The vacuum canister is the vacuum modulator - it controls shifting relative to engine load.
  4. Mebes

    Mebes Senior Member
    Messages: 451

    The vacuum modulator should be hooked to a vacuum port on the intake manifold.

    When the throttle is closed the vacuum is high because little air is entering the engine.

    As you depress the accelerator pedal the carburetor opens up letting more air and fuel into the engine causing a loss of vacuum.

    The vacuum modulator on the transmission senses this change in vacuum, and responds by increasing pressure in the parts of the transmission that control when and how hard the transmission shifts.
  5. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Is it me, or have we answered this same question about three times since Spring? Not that I mind answering questions or helping people out but it might be a good idea to read thru a few of the posts first... ;)
  6. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Meh.... not so bad.... they're a few pages back...

    You're forgiven.... this time :p