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speedo drive gear

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by docgab, Dec 9, 2004.

  1. docgab

    docgab 1/2 ton status Premium Member

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    Hello all,
    So I was trying to order a speedo drive gear for my 78 K5, th350, np203. As soon as i call up they ask me "color code/number of teeth?" I have no idea. My t-case doesnt have a speedo gear right now so i have no idea what to order. I have 4.11 ratio in the back and am running 35 inch tires. I called an auto parts store and the chevy parts desk and neither could tell me which i needed. Can any of you gurus help a guy out? Thanks.
     
  2. pauly383

    pauly383 Daddy383 Staff Member Moderator

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  3. scrappyk5

    scrappyk5 1/2 ton status

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    you can change colors not only as what gear ratio , but also what size tires you have on. since yours did not have one in it, you might have to buy a couple different ones. they are not that expensive.
     
  4. k5floyd

    k5floyd 1/2 ton status

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    i think it would involve knowing the engine rpm, what gear your in, axle ratio, and tire dimeter and/or circumference to find what rpm the tire is turning. but from there im not good enough at math to figure the rest out
     
  5. k5floyd

    k5floyd 1/2 ton status

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    and pauly383k10, i know a bunch of math to find what drive and driven gear you need given you had a previously accurate speedo(which would require the drive and driven speedo gear) but if you know any easier way, id like to hear it, as i have a 208 and changed gears and tires, and my speedo is now way off. thanks
     
  6. docgab

    docgab 1/2 ton status Premium Member

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    Hey, thanks for the input all. It is much appreciated!
     
  7. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    this is the post that got me curious , got me searching and found out what to do with 208's , just use 700r4 gears . Look at my reply in this thread , #10 . With my 18 tooth gear in case , my 32.5 inch tall tires , and my 3.73 gears , I come up with green 42 tooth gear needed http://coloradok5.com/forums/showthread.php?t=121705
     
  8. docgab

    docgab 1/2 ton status Premium Member

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    OK. This one knocked the cobwebs out of my head. I was looking for an easy way to tell what I needed as far as a DRIVEN gear goes. I guess I need to tear into my x-fer case and see what drive gear I have then? It all makes sense now. lol
     
  9. k5floyd

    k5floyd 1/2 ton status

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    tci's website helps alot, definately saves you from any mental stress doing the math yourself. thanks pauly
     
  10. BrianDamage

    BrianDamage 1/2 ton status

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    yep

    you may be able to remove the cover from where the driven gear usually goes and see it from there
     

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