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Highway speeds w/TH400 and 6.2L

Discussion in '1982-Present GM Diesel' started by AzzKicker, Sep 19, 2002.

  1. AzzKicker

    AzzKicker 1/2 ton status

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    How do you all do it!!! Today was my first time driving 55+ with my new Diesel and I swear it sounds like engine is gonna blow!!!! I'm seroiusly thinking of a doing a TH400 to 700R4 conversion. Do i just need to get used to it. will the truck be fine. It chugs along EASILY at 60-65, its just teh sound of the engine about blow that worries me LOL.
     
  2. 6.2L Jimmy

    6.2L Jimmy 1/2 ton status

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    Do you do alot of highway??
    I have a 700r-4 mated to my 6.2L and I love it.And you can install steeper gears and not have to worry too much about rpm's on the highway. /forums/images/icons/wink.gif
    Mike
     
  3. jeffro

    jeffro 1/2 ton status

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    Correct me if I'm wrong, someone. I figure if the governer is set right you could put the pedal to the metal and leave it there all day.
     
  4. AzzKicker

    AzzKicker 1/2 ton status

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    no i dont do a lot of higheway, nothing more than 20-30 miles on higheway per week. Like if i have to go to the Ranch its about 23miles away, and thats the farthest i'll go. And thats maybe once or twice a week.


    How do you know if Governer is set right. I still cant figure my tranny it, its acting funny in the sense tha it shifts at right time, but it shifts hard, and sometimes it shifts right depending on how I have the pedel, if I'm easing up it shift hard, but if I JUST lay on the FOOT real heavy it accelerates fast and shifts BETTER.
     
  5. jeffro

    jeffro 1/2 ton status

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    I'm not very familiar with the TH400, but on a 700r4 that would indicate a stretched out TV cable. It could be something similar, like kickdown linkage.
     
  6. arveetek

    arveetek 1/2 ton status

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    The governor on a 6.2L is set around 3600 rpm. You're still a long way away from that with your setup. Don't worry about running that fast down the highway. Lots of people do it. You just have to get used to the sound.

    The GM diesels aren't like the Cummins or other diesels that can run up to the governor all day long...you don't want to do that with the 6.2L. It's hard on it. Most people don't even know there is a governor on them, since they're set so high. I hit the governor with my '81 when I'm towing a trailer. I hit it in first and second gear.....second gear I hit the governor at 55 mph with 4.10 gears, have no idea where the governor might be in third gear. So don't worry about it.

    The 400 doesn't have any kickdown cables or linkages. It does use a device called a VRV that is attached to the side of the injection pump. This controls vacuum that is sent to the transmission. The first thing you need to do is make sure your vacuum pump and vacuum system is working properly with no leaks, and then you may need to adjust your VRV by loosening two screws and rotating one direction or the other. You may want to get a Haynes repair manual for better instructions on how to do this.

    Casey
     
  7. Txstruck

    Txstruck Registered Member

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    I have the 6.2L/TH400+NP208/4.56 gears and when im going down the highway, its 60 mph tops for me and she is screamin pretty loud! But I dont worry about going any faster so im ok with it. Had enough speeding tickets in my younger yrs.
     
  8. u2slow

    u2slow 1/2 ton status

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    TH400 doesen't have a kickdown?

    Mine does - there's a switch on the skinny pedal with a wire that runs down to the left side of the TH400. I know its a kickdown since some of my extraneous under-dash wiring snagged it and I was stuck in 1st gear for a while /forums/images/icons/shocked.gif (I had the pan off and the governor out before I figured it out tho /forums/images/icons/mad.gif )

    Mine rumbles away down the highway too - I'm quite sure they're 4.10's in the back of my Burb. I just put 33's on the back, and I'll be swapping in a 3.73 full-float pretty soon to improve the highway economy further.
     
  9. AzzKicker

    AzzKicker 1/2 ton status

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    OMG!!!!! i just checked under my tranny and looked where you said and my wire was disconnected!!!! Maybe thats my whole problem!!! I'll have to check tomorrow!!!!! nevermind, i cant wait, I'm gonna go check now lol
     
  10. arveetek

    arveetek 1/2 ton status

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    Sorry, I should have been clearer.

    The TH400 doesn't have any kickdown cables or linkages, or any TV cables like the 700, 350, and other transmissions. It does use a VRV to control shift points, and it does have an electric kickdown switch located down by the accelerator.

    Casey
     
  11. imiceman44

    imiceman44 1 ton status

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    I was going to say something a couple of days ago and then I thought maybe because you had it with diesel, but I have a th400 on my Jeep wagoneer and a gas engine, and it has the electric switch at the gas pedal for kick down, and when it was disconnected, it wasn't downshifting, and at the same time, the vaccum hose to the modulator also started leaking, I thought for sure my tranny is dying, luckily after I got really frustrated, I decided to check everything religiously and I found both problems and it runs fine. /forums/images/icons/smile.gif
    And as for the th400 on the diesel, my friend has it on his dually and I can tell you you feel it's too loud because it is too loud but you can still drive at highway speeds.
    Just do like I did, I bought some ear plugs /forums/images/icons/smile.gif
    IceMan
     
  12. AzzKicker

    AzzKicker 1/2 ton status

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    nah /forums/images/icons/wink.gif I'm just putting in a good stereo /forums/images/icons/smile.gif
     

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