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Low RPM shifts in a TH400

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BigJohnson, Sep 24, 2001.

  1. BigJohnson

    BigJohnson 1/2 ton status

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    Does anyone know what rpm a TH400 should shift? I have one with 3.08 gears and 31's. When I floor it only gets to 2000rpm in first and then shifts around 1500 to 1200 after that. I have suspected the governor in the junkyard tranny may for a diesel engine. I don't know if there is any difference but it might explain the lack of rpm. I am going to try a governor re-calibration kit.
    Any thoughts on the problem? What kind of rpm change is possible after changing the governor?
    Thanks,
    Jordan
     
  2. Jason73K5

    Jason73K5 1/2 ton status

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    Do you have the kickdown switch hooked up? That and the vacum line are the things that affect shifing from outside the transmission, so you might want to make sure they're working properly.

    73K-5: TBI350/TH-400/NP-203/14FF/D44
    Topless, doorless and no tailgate!
    Fresno, CA
     
  3. EDdaTREE

    EDdaTREE 1/2 ton status

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    If the 400 is like a TH350 there's also an allen-head screw in the end of the modulator where the vac. line goes on. HTH

    09-11-01 "We are AMERICANS we shall not fail"
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    At least on the 200-4R (they are all similar in operation in most respects) you can get some governors that stock, will shift the tranny at 6k, some at 3500, WOT. It's just a matter of playing with them until you get it right. I'd ASS-U-ME that you could have any RPM shift you want, as long as you understnad what modifications are going to accomplish what (weight removal/add, stronger/weaker springs, etc) At least the Th350/400 governors are easy to get to!

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
    No anti-theft measures on your truck? No pity when its stolen
     

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