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400 trans question (was diesel version)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Steve_87K5, Feb 15, 2001.

  1. Steve_87K5

    Steve_87K5 1/2 ton status

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    I am putting this former diesel 400 trans behind a 350. I will use reman gas torque converter,
    and former owner already has put in a gas shift kit (even though it
    was still behind a 6.2).

    Questions:
    1. Should I change the vac servo (it has a red-black stripe)
    2. Where do I pick off the vacuum for it (using a Qjet) ?
    3. Anything else to change?
    Thanks

    SteveB
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    The vac line can come from anywhere that has manifold vacuum. (not ported, IE EGR and Vac advance) Without seeing your carb, I can't tell which port will work, since they probably had over 100 variations of vacuum fittings on them. Even tapped off the intake would work. I think you'd be ok with the diesel modulator..they only seem to make a maximum 5mph difference in shift timing, at least in my cases. The best thing you could do, if it is shifting too early (which diesels did) is to replace the governor with a gas one..or modify the existing one. Its a little tricky, but can be done. Either that, or when you want to accelerate, hold it in whatever gear you want.



    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  3. Blue85

    Blue85 Troll Premium Member

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    Doesn't the 400 use a spring and weight governor? If so, you will probably just need heavier springs on it to delay the shift points. The 6.2's usually shifted at like 3200rpm, which is really going to kill performance with a gas engine. I think the governor and the modulator are all that you would have to worry about since you are already getting a gas converter.

    <font color=blue>5-lugs: The sign of true weakness.</font color=blue>
     
  4. CK5

    CK5 In my underwear Administrator Premium Member GMOTM Winner Author

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    How can you tell the difference between a gas and diesel version 400?

    Steve
    [​IMG]
    Mall-Running poseur 4x4 with curb-feelers
     
  5. WhiteWhomper

    WhiteWhomper 1/2 ton status

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    What's the matter Steve? Are you getting nervous that your 400/203 in the garage might be a diesel unit?
     
  6. CK5

    CK5 In my underwear Administrator Premium Member GMOTM Winner Author

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    Yep, thats the one question I forgot to ask about. [​IMG]

    Steve
    [​IMG]
    Mall-Running poseur 4x4 with curb-feelers
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    Well if you have a TH400 attached to a 203, if that setup is stock, it could never have been in a diesel truck, right? Not sure how much info the partial VIN has, but maybe the VIN on the tranny would tell you the motor? Worth a shot. The code on the tag on the side of the tranny (like "CG") might be a clue also, although I have no idea who you could ask to deceipher that for you....(although I know that C stands for Chevy, and the last letter is relative strength..A being weak, Z being strong...diesels probably only got one strength rating based on their outfitting)



    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  8. Steve_87K5

    Steve_87K5 1/2 ton status

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    Thanks for the info. Now, back to the solvent,
    cleaning brush and a Miller genuine on the side. What more could you want.

    SteveB
     

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