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Tranny & Axle Gear Question

Discussion in 'The Garage' started by SF87K5, Dec 29, 2002.

  1. SF87K5

    SF87K5 1/2 ton status

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    Ok I cant find where I found what the gear ratio is for a TH400 (all the gears) and what the gear ratio is for a NP205. I have a buddy that will see me his combo out of his K30. I also need to find out what gears I should run also for 37" - 40" tires. I was thinking of 4.56's, I want to crawl and daily drive with it. Or should I just go straight to the 4.88?
    Someone please help. The more the marrier, Thanks for all your help guys
     
  2. Sandman

    Sandman 3/4 ton status Author

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    I know that the 4.88 and a 42" tire work out really well. 4.56 might be fine with 38" tires. Especially with an auto.
     
  3. SF87K5

    SF87K5 1/2 ton status

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    Thanks Sandman, from looking at the gear chart on 4wheelparts.com I will probly go with 4.88 gears.

    More input is welcome on this.
     
  4. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    With 40's and 4.56's you'll be spinning 2700 at 65 MPH and 2850 with 37's at the same speed. So I guess it depends on how much RPM you feel like listening to and how much highway the truck will see.

    First gear on a TH400 is 2.48:1

    Low range on a 205 is 1.96:1

    Rene
     
  5. SF87K5

    SF87K5 1/2 ton status

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    Rene
    I will be doing a lot of highway driveing also. So I think I am going to go with the 4.88 gears.

    Do you know what all the gear ratios are for the TH400 1st-3rd and what the 2wd and 4wd low and high are for the NP205?
     
  6. Batmanjr

    Batmanjr 1/2 ton status

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    TH400:
    1st 2.48:1
    2nd Something inbetween
    3rd 1:1

    205:
    LOW 1.96:1
    High 1:1
    /forums/images/graemlins/thumb.gif
     
  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    With 4.88's your freeway RPM will be 3050 with 37's at 65, and a hair under 2900 with 40's.

    I have 4.56's, 36's and a SM465 4 speed and I wish dearly for an overdrive on the freeway. My target max for freeway is 2500...less would be cool but 2500 is tolerable. It will be much better with 39.5's when I get them this spring./forums/images/graemlins/thumb.gif

    205 has two ranges only...1:1 is high range and 1.96:1 is low range. TH400 is 1:1 high and 2.48:1 first gear. Second is somewhere around 1.6:1 but I'm not sure exactly on that one.

    rene
     
  8. SF87K5

    SF87K5 1/2 ton status

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    Rene,
    Ok for 37" - 40" tires i should go with the 4.56 gears and not the 4.88 gears then.

    Thanks for your help more is welcome.
     
  9. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Yes, numerically higher gears mean more rpm's. 4.88's will spin more rpm's with the same size tire than 4.56's will.

    Rene
     

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