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speedometer correction ?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by K5DRAGER, Nov 30, 2001.

  1. K5DRAGER

    K5DRAGER 1/2 ton status

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    I have a 90 that came with 3.42's and 31 inch tires I'm going to 4.56's and 35's what do I need to do to correct the speedometer. This is my first daily driver so I'm new to this speedo correction thing. Thanks
     
  2. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color=blue>Theres a gear in the output of the t-case that spins a cable that hooks up to your speedometer. When you put on bigger tires, you cover more ground in a revolution of the driveshaft than you do with smaller tires (more circumference). I dont know how much of a difference in teeth you need. Anyone know how to calculate this? My truck came with 31s and 3.07s and I have 4.10s and 36s now, How many teeth does my gear need to be?
     
  3. K5DRAGER

    K5DRAGER 1/2 ton status

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    So the 241 case is still a mechanical speedo cable and not a electric one ? Like I said I'm not used to this, I always had 205's in everything else and didn't really care about the speedo.
     
  4. jwduke

    jwduke 1/2 ton status

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    Check this out- <a target="_blank" href=http://www.speedometershop.com/>http://www.speedometershop.com/</a> It may be of help! Good luck!

    1 ton '87 Chevy SWB in the making!
     
  5. 90K5

    90K5 1/2 ton status

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    '89 was the last year for the machanical speedo, so we're out of luck there. You'll have to get a Vehicle Speed Sensor Buffer, which somehow recalibrates the speedo. I think Superlift makes them, but they are kinda expensive, something like $120, and it goes on the back of the speedo I think.

    90K5
     
  6. chevyfumes

    chevyfumes Court jester

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    Watch for the muzzleflash!
    You can also calculate for tire siz and gears and figure how far your off and then if the MPH is 55 and your speedo say's 47 then you would't have to spend any dough... I think I'm right at about a mile an hour evry ten miles an hour so 10MPH is 11 and 70 is 77

    <font color=blue> I'd rather have a bottle in front of me, than a frontal lobotomy!
     
  7. K5DRAGER

    K5DRAGER 1/2 ton status

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    Thanks 90K5 I was leaning towards that but wasn't sure and kinda wanted to know before calling some of these company's.
     
  8. 90K5

    90K5 1/2 ton status

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    no problem. I am not going to fix mine, I calculated all the speeds, and what they really equal, and made a little chart I keep in my center console...

    90K5
     
  9. GRINCH

    GRINCH 1/2 ton status

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    In 90 they use a DRAC connected to the ECM. I had a speedo shop in Norther Ga. do mine. It cost 60 bucks. It's a small box under the dash next to the ash tray.

    The Few, The Proud, The K5 Blazer
     

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