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Adjusting the vacuum modulators on a 400 turbo

Discussion in 'The Garage' started by thatK30guy, Nov 1, 2005.

  1. thatK30guy

    thatK30guy 1 ton status Premium Member

    Jan 12, 2001
    Likes Received:
    Anyone done this? I've heard about the procedure being done but never actually done it myself.

    I got a brand new one today for my rebuilt 400 which is waiting to go in my K30. While installing the mod, I noticed the slot in the vacuum plug port and immediately had to ask what others have done to adjust it.

    How many adjustments are there? Where is the best performance at? Turn it all the way left or right and work my way left or right?

    Any info or tips highly appreciated. :bow:
  2. dremu

    dremu Officious Thread Derailer Premium Member GMOTM Winner

    Feb 27, 2000
    Likes Received:
    East of San Francisco
    I've only tweaked the one on my TH350, but I assume it's the same procedure.

    It's a continuous adjustment of shift point; when I bought mine it came with a little booklet describing the process. Basically you drive it, and if you don't like how it shifts, try turning the screw a tiny little bit one way or the other.

    I ended up turning mine a quarter-turn one way, which made the shifts much much harder, reeeeeeeeeeeeevvvvvvvvvvvvv BANG ... so a quarter turn the other way put me back where I was, and another quarter turn made the shifts nice and smooth.

    I suspect the only reason I had to fiddle with mine was because the tranny has some kind of shift kit in it (I got it used, so no firsthand details); otherwise the factory adjustment on the modulator should be pretty close, I'd think.

    -- A
  3. sweetk30

    sweetk30 professional hooker Premium Member

    Nov 1, 2004
    Likes Received:
    horseheads , ny 14845
    thay are vary close out of the box. and vary little bits at a time. mod just adjusts firmness. govenor does the shift times/mph points.
  4. wildbilzrydn

    wildbilzrydn 1/2 ton status

    Jun 27, 2005
    Likes Received:
    Joliet, IL
    [reeeeeeeeeeeeevvvvvvvvvvvvv BANG

    I had a '74 c-20 w/ a 454 and I did the same thing. It was the hardest shift I ever felt in my life. Of course I thought if I was going full throttle it would shift eventually, but I made the mistake of letting up on it a little bit. Scared the crap out of me.

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