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Thread: Vaccum line on the th400

  1. #1
    Join Date
    Dec 2006
    Location
    Oxford, Ohio 45056
    Posts
    175

    Default Vaccum line on the th400

    Where do I connect the vaccum line that is on the th400 tranny. I have a 502
    with Edelbrocks Fuel injection? Also what does the vaccum do?

    Thanks
    Chris

  2. #2
    Join Date
    Mar 2004
    Location
    northern Arizona
    Posts
    1,025

    Default

    iirc, the vacuum is used to help the kickdown - I can check tomorrow to see where mine plugs in on my J-10

  3. #3

    Default

    Wow.

    Anyone want to kick in and get Elohim a service manual????

    It goes to the modulator, on the passenger side of the trans, and you'll probably want to hook that to the base of the throttle body... although, Edelbrock's install instructions should have a section dealing w/vac. connections.

    From TCI's site:

    What does the vacuum modulator do?

    Answer: The vacuum modulator is a canister that contains a diaphragm and a calibrated spring. The diaphragm senses changes in engine vacuum due to throttle position/load changes and transfers the diaphragm motion to the modulator valve in the transmission. The calibrated spring opposes the diaphragm movement. This provides the means for the transmission to adjust internal pressures based upon torque demand by the engine.

  4. #4

    Default

    Vacuum line controls line pressures for shifts , kickdown is the electrical connection on left side of trans . Vacuum line could go to carb or manifold , has to be a constant vacuum source , not a ported vacumm . Kickdown is just a 12 volt source wired into a switch on throttle pedal . I ran without the kickdown hooked up for a couple of months , would downshift at part throttle but not a good full throttle kickdown .

  5. #5

    Default

    Quote Originally Posted by fasteddie View Post
    Vacuum line controls line pressures for shifts , kickdown is the electrical connection on left side of trans . Vacuum line could go to carb or manifold , has to be a constant vacuum source , not a ported vacumm . Kickdown is just a 12 volt source wired into a switch on throttle pedal . I ran without the kickdown hooked up for a couple of months , would downshift at part throttle but not a good full throttle kickdown .
    x2

    It wont up shift without the vac hooked up......

  6. #6
    Join Date
    Jan 2007
    Location
    Fort Smith, Arkansas
    Posts
    911

    Default

    Short answer, the vacuum controls the shift response, etc. On a stock vehicle, I've seen them Tee'd in with the vacuum advance for the distributor. I don't know if that will work properly with your set up though. You can also adjust the modulator if you want a little different response. With all the work on your truck, you may have done some mods to the tranny too which might warrant you playing with the modulator. I have never bothered with any adjustment. Also, I don't remember an electrical kickdown with the TH400. I thought all were mechanical hooked to throttle linkage via the cable encased in the hard black tubing.

  7. #7

    Default

    The 350TH is cable operated, while the 400TH is vacuum, no electrical controls on those two. Probably thinking of the later 4L60E and 4L80E trans.
    This post is closed-captioned for the hearing impaired.

  8. #8
    Join Date
    Dec 2006
    Location
    Oxford, Ohio 45056
    Posts
    175

    Default

    Lokar sells an electric kickdown for the TH400. I suppose I will purchase it.

  9. #9
    Join Date
    Mar 2004
    Location
    northern Arizona
    Posts
    1,025

    Default

    The 400 has an electrical kickdown, the switch is mounted under the dash on the J-trucks and is activated by the gas pedal.

  10. #10

    Default

    I must be getting old.


    Anyone see where I parked my car?
    This post is closed-captioned for the hearing impaired.

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