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Speedo corretion options?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BillyBob, May 16, 2004.

  1. BillyBob

    BillyBob 1/2 ton status

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    What can I do to kinda get an idea as to how slow I'm really going? I kinda can't get a good sense of speed becuase of how high the truck is. Should I just get a speedo gear for the gear ratio of my diffs? I don't think it'll help much since I have 35's. though I do think some K-20s did come w/ 35s and 4.10s. /forums/images/graemlins/1zhelp.gif
     
  2. K5MONSTERCHEV

    K5MONSTERCHEV 1/2 ton status

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    You can get a reduction box, take it to a speedo hop and have it recalibrated or, what I did was when I put in my Auto Meters, I used the elcetronic speedo, this way I can recalibrate it when I switch my tires, its really easy too, I just push a button, drive 2 miles and push it again, DONE! And it is accurate!
     
  3. marine_enlisted

    marine_enlisted 1/2 ton status

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    I know I saw a website that talked all about speedo correction somewhere. Try a Google search for speedometer correction and see what it has to say. My speedometer is off too and I have found three ways to figure it out two are free and one can cost you a lot. #1 drive by one of those litle radar trailers that the cops put on the shoulder sometimes in school, construction, and residential areas and compare it's reading with your speedo. #2 Get beside someone at night with a stock vehicle and look at their speedo needle or just have a friend drive beside you and tell you how fast you're going. #3 go on a road trip with your cruise set at 65 and wait for the friendly police man to pull you over and tell you how much over you were going, and do the math. I have done all three, but I forgot a couple of weekends ago and State Trooper Shaw was kind enough to pull me over and tell me I was going 78 while my cruise was at 65. That cost me $119.00for that bit of knowledge, probably could have bought the gears to re-cal my speedo for that price. /forums/images/graemlins/doah.gif

    I have thought about asking a policeman if they can clock me so I can see exactly what my speed is again after I do my gear swap, but tha would probably not work here in this busy area. I know that the State Troopers in Iowa would do it for us. Maybe you could make a call to your local law enforcement? /forums/images/graemlins/dunno.gif
     
  4. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    You forgot the easiest way (IMO) for checking speedo. The odometer...check the exact reading on the odometer and run by 10-25 milemarkers and see how far off it is, then do the math. My speedo and odometer read 25% slow.

    Rene
     
  5. Blue85

    Blue85 Troll Premium Member

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    You just need to change one or both of the small plastic gears in the tailhousing of your transfer case. If you do a web search, you will come up with a site that lists all of the available gears for Chevy 4x4s. This One lists the driven gears, which they refer to as "Large Gears"

    Go Here to calculate what you need.

    You can also use the ratios of your existing tires to stock and your existing gears to stock to find the ratio of teeth between the gear you have and the one you need. Try to work it out so that you only have change the driven gear (and not the drive gear) if possible and the swap is super easy. Just use common sense: deeper gears make the cable turn faster, so you need more teeth on the driven gear or less teeth on the drive gear, etc.
     

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