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Help with CUCV build plans...gears and tires

Discussion in '1982-Present GM Diesel' started by grimjaw, Jan 25, 2007.

  1. grimjaw

    grimjaw 1/2 ton status

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    I have been planning the build up of my M1028. I want a lot from this truck. It will become my DD, but I also want it to be a trail truck, around town pickup and “Oh Crap!” wagon. After looking at every transmission I could think of I think a built 700r4 will work the best. I had thought of a NV4500, but since I would like to add a Banks turbo in the future, an Automatic seems better.

    As you most likely know the M1028 CUCV comes with D60 front and 14BFF rear. There is a limited slip in the front and a Detroit in the rear with the 4.56 gears stock. This and the 6.2L diesel made me first consider going with 37” tires. The problem is 37s are a bit pricey, will need at least 6” if lift to keep the fenders intact, and come in a limited selection. This made me look at 4.10 gears and 35” tires. The tires would be somewhat cheaper and have a wider selection. I am debating whether it would be easier/ cheaper to just swap the whole axles from my 79 K5 or the guts.

    I need to weight the cost, PITA factor and final engine efficiency to see what would be the better plan. Please take a look at the numbers I list below, add any real world experience and let me know what you think.


    700r4 and 4.56 gears with 37” tires
    Road RPMs at Given Speed
    Gear………35mph……………55mph……………75mph
    1………… 4435………………6969……………...9504
    2………….2362………………3712……………...5062
    3………….1449………………2278……………...3106
    4………….1015………………1594……...………2174

    Road Speed at Given RPM in Miles Per Hour
    Gear……….1250rpm……..1750rpm………2250rpm
    1………………10……………..14……………….18
    2………………19……………..26……………….33
    3………………30……………..42…………...…..54
    4………………43……………..60……………….78






    700r4 and 4.10 gears with 37” tires
    Road RPMs at Given Speed
    Gear………35mph……………55mph……………75mph
    1………… 3988………………6266……………...8545
    2………….2124………………3338……………...4552
    3………….1303………………2048……………...2792
    4……….….912….……………1433……...………1955

    Road Speed at Given RPM in Miles Per Hour
    Gear……….1250rpm……..1750rpm………2250rpm
    1………………11……………..15……………….20
    2………………21……………..29……………….37
    3………………34……………..47…………...…..60
    4………………48……………..67……………….86






    700r4 and 4.56 gears with 35” tires
    Road RPMs at Given Speed
    Gear………35mph……………55mph……………75mph
    1………… 4688………………7368……………...10047
    2………….2497………………3925……………...5352
    3………….1532………………2408……………...3283
    4………….1073………………1685……...………2298

    Road Speed at Given RPM in Miles Per Hour
    Gear……….1250rpm……..1750rpm………2250rpm
    1……………….9……………..13……………….17
    2………………18……………..25……………….32
    3………………29……………..40…………...…..51
    4………………41……………..57……………….72







    700r4 and 4.56 gears with 35” tires
    Road RPMs at Given Speed
    Gear………35mph……………55mph……………75mph
    1………… 4215………………6624……………...9033
    2………….2245………………3529……………...4812
    3………….1378………………2165……………...2952
    4…………..964……………….1515……...…...….2066

    Road Speed at Given RPM in Miles Per Hour
    Gear……….1250rpm……..1750rpm………2250rpm
    1………………10……………..15……………….19
    2………………19……………..27……………….35
    3………………32……………..44…………...…..57
    4………………45……………..64……………….82
     
    Last edited: Jan 25, 2007
  2. imiceman44

    imiceman44 1 ton status

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    I am guessing you have a typo in the last chart?
    it's 35" tire not 37" tire and it's 4.10 gears, correct?
     
  3. grimjaw

    grimjaw 1/2 ton status

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    You are correct, I will edit it. Stupid cut and paste.
     
  4. imiceman44

    imiceman44 1 ton status

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    Happens to all of us :D
    Anyway, my vote goes to the 37" tires on your stock gearing, much less to hassle with, a lift is easy.
    Now if you don't want to have it to tall because you want to DD it, then I understand, but my personnal thoughts on this, i would go with a mild lift, and cut the fender lips and roll them for a finished look.
    I have done that on my blazer and my waggy, looks good, didn't lift it too much and stuffed bigger tires with no gear change.
    :D
    Or if you feel like doing more refined body work, you can cut a slice off the fenders in between the lips and the area you are keeping and then reweld the lips. :D
     
  5. kennyw

    kennyw N9PHW Premium Member

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    I'd also suggest you go with 37's and a couple inches of lift and trim as required. That is my plan for my M1028 except I'm running surplus HMMV 37 X 12.5 X 16.5 tires on H1 beadlocks. My truck is a dually to start with so I don't even have to recenter the H1's.

    I also have a once well built 700R4 in my truck now that the PO installed... and I'm lucky that the internals welded together enough that I can still move it around the yard. Don't count on any 700R4 lasting long if you tow with it. Go 4L80E (use a diesel wiring harness and computer from a 1991 K20 burb or K30 crewcab) or NV4500 if you want overdrive.
     
  6. grimjaw

    grimjaw 1/2 ton status

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    Is your m1028 a 14bff or d70 rear?

    If I go with 37's I will use a set of Humvee 37's for fitment. Later I think I want the Truxus MT radials. They come in 37x12.5x16.5.




    NV4500 and 4.56 gears with 37” tires
    Road RPMs at Given Speed
    Gear………35mph……………55mph……………75mph
    1………… 8131………………12777……………...17423
    2………….4406……………….6924…………….....9441
    3………….2420……………….3803…...………......5187
    4…..……..1449………………..2278……...…...…..3106
    5………....1087……………….1708……...…...…...2329

    Road Speed at Given RPM in Miles Per Hour
    Gear……….1250rpm……..1750rpm………2250rpm
    1……………….5………………8……………….10
    2………………10……………..14……………….18
    3………………18……………..25…………...…..33
    4………………30……………..42……………….54
    5………………40……………..56……………….72
     
  7. BKinzey

    BKinzey 1/2 ton status

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    I've read for the 6.2 1850rpm is optimum so you may want to keep that in consideration when looking at tires / gearing.

    HMMWV tires. Aren't the bias ply 36" and the radials 37"?
     
  8. grimjaw

    grimjaw 1/2 ton status

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    my goal is between 1750 and 2250rpms.


    you are correct. I currently have the 36" Bias on my K5. I can get a set of 50%or less tread 37's cheap locally to play with.
     
  9. kennyw

    kennyw N9PHW Premium Member

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    I have a D70 rear.

    [​IMG]

    PO did a lot to the truck that I need to redo/undo but luckily the only part of the drivetrain he touched was installing the 700R4.
     
  10. imiceman44

    imiceman44 1 ton status

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    One small problem for him is that he wants to use the 700R4, so he can't get the RPM's down that much without killing the 700R4 but since it has the overdrive it will help a little in the mileage.
     
  11. AJMBLAZER

    AJMBLAZER Better to be lucky than good. Premium Member

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    [​IMG]

    [​IMG]

    That's my M1008 on a stock suspension and 36x12.5-16.5 RT/II's straight off of a HMMWV using GM 16.5 wheels.
    They rub some but not horrible. No damage to the tires or the body so far. The place I got the truck from trimmed the back of the front fenders a little and also took the bottom edge off of the front of the front fenders.
    Would I wheel like this? No. I feel if I flexed it all that hard I'd crease a fender or damage the tire.

    I'm thinking of a 4" lift spring in the front in the short term and then later on replacing it with something like a 2-3" lift spring and a 1" zero rate aal to space the front axle forward. I just want to get the tires away from the rear of the fenders and towards or at the center of the wheel wells.


    Oh yeah, we've recently discussed HMMWV surplus tires but the MT radials aren't the greatest tire in the world. They'd be pretty good for a daily driver but depending on how hard you want to whump on them their sidewalls are notoriously thin.
    Also, the 36" and 37" heights are a mind game...for all intents and purposes they're practically the same height.



    There was a M1008 on Ebay last fall that I kick myself for not spotting before I got mine. Went for less than I paid for mine too. Built turbo 6.5L, 4L80E, NP205, 6" lift, 36" HMMWV tires, AC, cruise, tilt, etc. All the creature comeforts, plenty of beef and the guy let it go for probably what the engine cost him.:eek1:
     

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