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th400 transmission ajusting the govener

Discussion in 'Chevy Trucks' started by plummermark2002, Mar 26, 2004.

  1. plummermark2002

    plummermark2002 Member
    Messages: 30

    Can anyone tell me how to adjust the govener on my th400 transmission ? I have a 1982 chevy 3/4 ton pickup, i just changed the transmission from a th350 to th400 and it seams to be shifting real fast, it's already in third at low speed.any help with this would be appreciated, plummermark.
  2. Mebes

    Mebes Senior Member
    Messages: 386

    The governor is usually not adjustable.
    I would suspect that your problem is with the Throttle valve linkage or cable (depending on your setup)
    The throttle valve is connected to the carburetor (or throttle body if fuel injected) and it moves with the throttle linkage giving the transmission an indication of how far you have your foot to the floor so it can adjust the shifts accordingly.
    Check for linkage or a cable that connects to the throttle and the transmission.
    They should move together all the way from idle to wide open throttle.
    I would imagine that you have some slack in there and the carburetor is moving quite a bit before the throttle valve linkage starts to move.
  3. plummermark2002

    plummermark2002 Member
    Messages: 30

    The hookup i have for my transmission has the detent switch above the gas petal that operates the passing gear, i don't have one on the tranny. plummermark2002.
  4. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Thats the way all TH400's are (electric kickdown).

    Check the vaccuum modulator (I'm pretty sure the 400's have those still). First check for vaccuum leaks, and that the source is ok. If the tranny has been rebuilt, it quite possibly has an adjustable modulator. These can be tuned with a hex key down the vaccuum port. Not sure of the proper method. Maybe someone else can help further?

    Governors can be swapped on most trannies... not much experience with the TH400, but on the 700R4 (for example) there are different weight springs available for it which change the shift points. Maybe your governor is from a diesel? Doesn't hurt to try it--your tranny shop may be able to lend you a spare one to try...
  5. Mebes

    Mebes Senior Member
    Messages: 386

    The way the vacuum modulator works is.
    No vacuum (like when the foot is to the floor) late shifts.
    High vacuum (like just off idle) early shifts.

    I don't think that a vacuum leak would cause this problem.
    In my experience I have seen vacuum leaks and disconnected hoses cause late shifting or no shifting at all. (Not early shifting like you described)

    I do think that it could be hooked up to the wrong vacuum port.

    Make sure that you didn't hook up the vacuum modulator to a line with a canister, or after a check valve.

    It should be hooked to a T on the manifold so it can sense true vacuum from the manifold.

    I do agree with the other 3 points that derekbroerse said about the adjustable modulator, diesel transmission, and the governor weights.
    Good luck.