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Tires/gear ratios/ OD

Discussion in '1982-Present GM Diesel' started by kennyw, Nov 21, 2004.

  1. kennyw

    kennyw N9PHW Premium Member

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    My '79 K20 now has 4.10 gears, 285/75R16 tires and a SM465/NP205. Looks like I'm spinning 2713 RPM @ 65 mph. I have a fairly worn set of 36 x 12.5 x 16.5's that could bring it down closer to 2487 @ 65. Probably still going to need to add an OD unit at some point in the future but it looks like it would get me down to 1990 RPM @ 65 with the 36" tires (2296 RPM @ 75 mph).

    I'd like to go with the US Gear Dual Range unit between the tranny and tcase to be able to split gears and just starting to gather info on them US Gear Dual Range unit
    Any opinions on this unit? I'm picking up a 32 spline SM465/NP205 combo to rebuild and run with this unit... Going to take some time to save up my pennies and buy it though /forums/images/graemlins/thinking.gif
     
  2. imiceman44

    imiceman44 1 ton status

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    [ QUOTE ]
    My '79 K20 now has 4.10 gears, 285/75R16 tires and a SM465/NP205. Looks like I'm spinning 2713 RPM @ 65 mph. I have a fairly worn set of 36 x 12.5 x 16.5's that could bring it down closer to 2487 @ 65. Probably still going to need to add an OD unit at some point in the future but it looks like it would get me down to 1990 RPM @ 65 with the 36" tires (2296 RPM @ 75 mph).

    I'd like to go with the US Gear Dual Range unit between the tranny and tcase to be able to split gears and just starting to gather info on them US Gear Dual Range unit
    Any opinions on this unit? I'm picking up a 32 spline SM465/NP205 combo to rebuild and run with this unit... Going to take some time to save up my pennies and buy it though /forums/images/graemlins/thinking.gif

    [/ QUOTE ]

    It's a great strong unit, the only problem is the cost.
    I had found one for sale used a while back for a th400 2wd, and I let it go. It was $1200
     
  3. camiswelding

    camiswelding 1/2 ton status

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    Kenny.... unless Im wrong US Gear does not offer a setup for a 4wd application that you spec.... but Gear Vendor does,,, I have also heard the GV has a better reputation...
    about 2750 for one new for your application... I have installed one before and they work very well....
    I have a nice 32 spline sm465 4x tranny...
    cam
     
  4. kennyw

    kennyw N9PHW Premium Member

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    They list it for a SM465/NP208 combo but the bolt up patterns would be the same as the 32 spline SM465/NP205. I want an overdrive that goes between the tranny and tcase that is good in 4wd not one that bolts on the back of the tcase and is only good in 2wd.

    Only problem I could for see is setting up the shifter for the tcase to get around the OD unit on the NP205.
     
  5. Pookster

    Pookster 1/2 ton status

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    Might be cheaper to sell your 465 and get a nv4500.

    I am just wondering how your RPM's are that high with 4.10's and 285's. THen I went and looked it up, and the RPM's between a 33" and a 31" tire aint exactly much!

    With a NV4500, its 1981 RPM with your same setup in 5th gear.

    It just dpeends which one works better for you.
     
  6. kennyw

    kennyw N9PHW Premium Member

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    Problem with the NV4500 is it still has the same terrible gear splits that the SM465 does. I want to be able to split gears as well has have an overdrive. Basically the add on OD unit gives me an 8 spd rather than settling for a 5 spd /forums/images/graemlins/wink.gif
     
  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    For the money of the GV OD you could also look at the ZF6-S650 6 speed. Granny low first, OD 6th with 4 relatively evenly spaced gears in between. No ridiculous drops in rpm when shifting...

    It's on my wish list...and maybe one day I'll begin actively hunting one down for my truck. It'll make much better use of the power I do have, plus help the MPG on long trips. It'll also make for a much quieter ride on the freeway. /forums/images/graemlins/smile.gif

    Rene
     
  8. kennyw

    kennyw N9PHW Premium Member

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    That's another good option I guess. /forums/images/graemlins/thumb.gif
     

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