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Discussion in 'The Garage' started by 86454K30, Dec 31, 2006.

  1. 86454K30

    86454K30 1/2 ton status Premium Member

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    delete........thanks
     
    Last edited: Jul 5, 2007
  2. HarryH3

    HarryH3 1 ton status Author

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    An adjustable modulator only moves shift points by a small amount. The governor is the main control for shift points. At what RPM does the 2-3 shift happen? If it's also that low, then perhaps someone swapped in a Turbo 400 from a diesel application. They're programmed to shift at much lower RPM than the ones for a gas application.

    Also make sure that the kickdown switch is working. It helps keep the trans in lower gears when the throttle is floored.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Stock modulators I've seen are not adjustable, at least TH400.

    Not worth it, since the modulator is mainly used to control shift firmness, and as noted, only changes shift RPM/speed a small amount. You can modify/change the governor yourself if so inclined.
     
    Last edited: Jan 2, 2007
  4. 86454K30

    86454K30 1/2 ton status Premium Member

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    shifting Th400

    Ok I adjusted the modulator...and as both of you said nothing happened. The truck has been sitting for a yr or 2 and only driven periodically. The transmission only has about 10K on it could I have a problem with a "sticky" governor? This the original trans for this truck also not a diesel one. I appreciate your feedback.

    Thanks

    Larry:bow:
     
  5. 86454K30

    86454K30 1/2 ton status Premium Member

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    Btw the 2-3 shift is at about 23-2400rpms. Shouldn't the 1-2 shift be about 1800rpms?
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    IIRC messed up governor won't allow upshift at all, but I could be mistaken.
     
  7. k204dr

    k204dr 1/2 ton status

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    is the modulator new? maybe you have a vacuum leak in the line to it.
     
  8. diesel4me

    diesel4me 1 ton status Premium Member

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    hmmm...

    I think every modulator has an adjustment screw inside the vacuum hose nipple(and some come out an get sucked into the vacuum hose!--(I learned that is why stock GM modulator steel vacuum lines have that restriction in them where they connect to the manifold!--so that screw wont get sucked into the engine!..)..
    ..adjusting them usually only changes shift points and firmness by 5-10 mph at best though..you need a dinky regular screwdriver to adjust them..

    If the modulator isn't getting enough vacuum,it will make the tranny upshift much later,and much harder..I'm talking going into second gear at 35-50 mph instead of 15-20 like it should,and you have to wind up the motor pretty hight before it will shift..also,if vacuum is low or absent,the tranny will feel like its free wheeling when you back off the throttle,almost like you put ot in neutral..if its acting like that,I bet its the vacuum isn't getting to the modulator..

    If the govenor gear is stripped,you'll only have low and reverse--it wont upshift at all..or it'll try too,then go back into low again..:crazy:
     
  9. 86454K30

    86454K30 1/2 ton status Premium Member

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    Hey thanks for all your input, before I got all worried I checked to see if it had vacuum at the modulator(what I should have done first)..no vacuum but I had it at the manifold...somonehad replaced the hard line with a braided stainless line apparentyl it is either plugged or broke inside...I replaced with a new rubber hose and it works great, though now I have to go back and adjust the modulator I screwed with. I seem to forget to look at the easy stuff first.

    Thanks

    Larry
     

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