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How to get highway speeds out of a M1028????

Discussion in '1982-Present GM Diesel' started by grimjaw, May 5, 2006.

  1. grimjaw

    grimjaw 1/2 ton status

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    I just bought a nice M1028(6.2L/400/205/4.56 and 32" tires) and I am trying to plan the best way to have it all. Good power offroad, able to drive on the interstate, and good mileage are my wish list.

    The first item on the change list is the tires. I guess I will need to go to 35 to 37 inch tires to help with the rpms.

    Now the real debate is the lack of overdrive.

    1 - I could swap to much higher gears, something like 3.42s or 3.73s.

    2 - I could replace the th400 with a built 700R4

    3 - Or I could get a Gear Venders type OD... really pricey.

    So far it looks to me that plan number 2 is the best overall. Are there better ways of getting to 2000 - 2200 rpms at speed?

    I am always grateful for any good advice. Thanks.
     
  2. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    You could also go up to a taller tire to make the gearing higher . Try some 35's . Or if want some load carrying ability , some taller tires for 16 inch rims which come in d or e ratings .

    I would do this WITH a 700r4 as well .

    You would have great low end with 4.56 and the first in the 700r4 ( and converter ) . And with the OD and a taller tire , you'd sip fuel on the highway .
     
  3. grimjaw

    grimjaw 1/2 ton status

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    The working plan is to get a BTO level 3 700R4 or its equal and run 35 to 37 inch tires on recentered hummer wheels. This is not 'cheap' but looks like the best plan with an Auto (the wife, said must be auto).

    I am not sure on transfer cases yet. My one requirement is NO chain drives. A 203/205 doubler would be great but I am not sure if there is an adapter for the 700R4.
     
  4. surpip

    surpip 1 ton status

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    ya there is alot of people have done that
     
  5. crawlink5

    crawlink5 1/2 ton status

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    I mounted my 203 from the TH350 straight to the 700r4 back when I made that swap. 1978 th350/203.
     
  6. grimjaw

    grimjaw 1/2 ton status

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    After a little research the th350 to np203 adapter with a spacer will will for a 700r4 to np203. Best of all they are not rare at all.
     
  7. crawlink5

    crawlink5 1/2 ton status

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    I did forget to mention that the 700r4 had an Advance Adapters short shaft in it. So no spacer was needed
     
  8. grimjaw

    grimjaw 1/2 ton status

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    That would be the best way, but the spacer is alot cheaper. If money is not a real issue at the time I order the 700R4 I will get the short shaft installed.
     
  9. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Without overdrive you'll need 40's to even get close to workable rpm's on the freeway. My truck spins at 2600 rpm on the highway with 40's, with 35's on it I avoid the highway altogether...

    A 700R-4 and 37's will get the R's down to ~2000 at 70 mph.

    Rene
     
  10. uao85

    uao85 1/2 ton status

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    I just bought an m1008 that I will be swapping in a built 700r4, revamping the motor to the tune of 300+ hp and 550+lb/ft, and maybe adding a turbo or a propane kit, and adding a set of 36" hummer tires, beadlocks. I am going with a 700r4 because I also travers the hwys ever so often.

    Remington
     

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