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Gear change/Speedo

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by TwoCrowsDesign, Mar 1, 2002.

  1. TwoCrowsDesign

    TwoCrowsDesign 1/2 ton status

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    I just swapped a 3.73 rear into my Blazer, replacing a 3.42. Of course now the speedo is whacked. I assume that when I go to larger tires the speedo will change again. Will 33's get me close to accurate? What will 35s do? Running 31's right now which were stock along with the 3.42 gears.

    Thanks,





    John
     
  2. TXsizeK5

    TXsizeK5 1/2 ton status

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    33"s will get you closest to stock.

    31/3.42 = 9.06
    31/3.73 = 8.31
    33/3.73 = 8.85
    35/3.73 = 9.3
    Thats how i look at it... you are getting most power with 31s and 3.73 of course and with 35s it will
    have less umph than stock though but your spedo wont be too far off... id settle with 33's.

    87 Custom Deluxe
    305/Sm465/ NP208
    4.56 , 6"susp, 35" BFG Muds, CatCo Cat & Series 40 delta flow 3" tips.
     
  3. TwoCrowsDesign

    TwoCrowsDesign 1/2 ton status

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    Thanks, that makes sense. Hmmm, 4.11s huh?

    John
     
  4. jimmy88

    jimmy88 1/2 ton status

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    Just pick the size tire you want, then change the plastic gears in the transfer case. My parts guy printed out a list of all the gears with the color codes and tooth counts. The math sucks but its worth it for a accurate speedo. Cost me $3.20 for the drive gear, $7.60 for the driven gear and $20.29 for the sleeve for the driven gear when I switched to 4.56 and 33's about two years ago. I still got the printout let me know if you want a copy.

    Jim

    88 Jimmy, D60, 14Bolt FF, 700R4, NP241
     
  5. Thunder

    Thunder 3/4 ton status

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    <a target="_blank" href=http://www.tciauto.com/tech_info/speedo_gears.htm>Speedo gear info and formulas</a>

    <a target="_blank" href=http://coloradok5.com/gallery/Thunders-Blaze> Blazer pics</a>

    <font color=blue>Nevada... Where the pavement ends and the west begins
     
  6. TwoCrowsDesign

    TwoCrowsDesign 1/2 ton status

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    Thanks, I'll tke a copy if its not too much trouble.



    John
     
  7. jimmy88

    jimmy88 1/2 ton status

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    Great link, don't forget to use the loaded diameter of the tire when you use the TCI calculator.

    88 Jimmy, D60, 14Bolt FF, 700R4, NP241
     

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