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  1. #1
    Join Date
    Feb 2009
    Location
    Huntington Beach, CA
    Posts
    22

    Default highway speed issues.

    Just got my m715 in jan. and is going to be my everyday driver, it has a ford 460/c6 combo in it. and i just got back today from a trip out to the desert to do some off roading.

    off road the thing is a wonderful.
    getting to the off road some 180 miles from my house was not so wonderful.
    top speed of around 50-55 at 3000rpms. and gear oil leaking out of the t-case everywhere.

    was curious what the best options are to go about getting much more manageable highway speeds but still have it crawl rocks well.

    -over drive unit bolted to the back of the c6 tran.?
    -no doubt reading around on the fourm i will have to change the t case?? to a np205 will it be able to handle the highway speeds?
    -and should i change the stock axle gears?

    alot to think about already and i just bought it...

    dan

  2. #2
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
    Posts
    11,533

    Default

    The NP205 is a great swap.

    What you do about getting more speed does depend on how much more speed you are looking for...want to do 60 all day? Or 70? At what kind of RPM?

  3. #3
    Join Date
    Feb 2009
    Location
    Huntington Beach, CA
    Posts
    22

    Default

    i would like to cruise on the freeway at 75 doing no more than 2800 rpms. as to keep the gas milage reasonable.

  4. #4
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
    Posts
    11,533

    Default

    OK...

    With stock tires, that means you need:
    axle gears of 4.56, which is the lowest numerically the stock axles can take without a carrier change.

    AND a .83 overdrive.

    This equates to 2806 RPM (approx.) at 75 MPH.


    If you go to a true 38 inch tire:
    4.56 gears
    AND
    .93 overdrive
    results in 2813 RPM at 75 MPH.

    With a spring over and 39.5 in tires:
    4.56 gears
    AND
    .96 overdrive
    results in 2794 rpm at 75 mph.

    Without changing the axle gears:

    With a stock tire:
    .65 overdrive
    results in 2829 RPM at 75 MPH.

    With a true 38 inch tire:
    .72 overdrive
    results in 2804 RPM at 75 MPH.

    With a spring over and 39.5 in tires:
    .75 overdrive
    results in 2810 rpm at 75 mph.



    Then you HAVE to beef up the brakes over stock...at least in my book...stock brakes at 75, especially the single line master, wouldnt cut it.

    Handling on these trucks isnt that great either...speed like that would be a little nerve racking in my mind...for a long trip anyway...more than was intended stock...

  5. #5
    Join Date
    Dec 2006
    Location
    Auburn, AL
    Posts
    251

    Default

    I think this is a little more than you were looking at, but the vehicle (stock) was really never designed to do what you (and myself) want to do with it.

    The drive train is happiest at lower RPMS. Mine screams, leaks, and is generally unrully at higher speeds. There's a lot of reasons for the unrulliness, but it's not happy.

    If I were going to try to keep it sort of stock, I would change the gearing on the diffs and swap out the t-case for a 3:1 low. I am not a fan of the NP200. This solution requires a fair amount of work and not an inexpensive route, but I think you will be happier in the long run.

  6. #6

    Default

    Body swap, if high speed and daily driving is your thing. Even with brake upgrades and gear changes your still working with 40 year old equipment. Find a 97 f350 with the 460 and the auto and bolt your body to it.

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