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how to fix Speedo problem

Discussion in 'The Garage' started by badmix, Nov 5, 2006.

  1. badmix

    badmix 1/2 ton status

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    How did you guys (if ya did at all) fix the speedo issue with early K5s (80s) mines an 84, when ya did bigger tires and gears.

    I had 2:73 gears and 31" tires, now I have 4:10s and 32s , my speedo is off by about 20mph. What is the fix for this.
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I've seen ratio boxes added between the speedo and the speedo hole on the T-case. i am going to head down to a local tranny and drivetrain place and ask about them soon. I'll have my truck mobile by Tuesday and should get a chance to get true speed with my GPS so I know ecatly how far off the speedo is. With the 465 and old 205 it was off by a solid 25% slow...

    I'll be interested to see if my new 205 gets the speedo closer to the mark or not.

    Rene
     
  3. Slapperbar

    Slapperbar Retired Navy NDT Examiner Premium Member

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    On a TH350 you can change the drive and driven gears for the cable. Should be the same for the 'case.
     
  4. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    http://coloradok5.com/forums/showthread.php?t=121705

    and I fixed the link to TCI , since they changed the pages

    I got to update again with the 4.56 . And I need a 48 tooth driven gear , which doesn't exist . So I need to change my drive gear to 15 tooth gray ( mine is 18 tooth blue ) so I can run a 39 tooth driven gear to correct .

    Looks like a little fun for me !!
     
  5. badmix

    badmix 1/2 ton status

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    Okay, so new plastic gears, but how hard are they to change. I dont wanna tear tranny or Xfer case apart jus to correct speedo?
     
  6. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Simple , one just unscrews the speedo cable , take off the hold down screw to remove the driven gear .

    Drive gear isn't as easy , but can be done with case in the truck . I have never done one , but have assembled a 208 , so I will finger it out on the spot :thumb:
     
  7. randy88k5

    randy88k5 1/2 ton status

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    I posted this in a previous thread ( http://coloradok5.com/forums/showthread.php?t=176781 )

    .....

    OK, I will describe how to do it. This is not the only way, but it is the way I would probably do it.

    Note: this is not really a "calibration" like you would find on much newer computer controlled cars. Those you can just plug into a computer and reset your tire/gear size and it will read correctly. You have to physically change the small plastic gears to get the correct reading with our rigs.

    First, you need to know your exact tire diameter. Get the measuring tape.

    Find your current gear ratio. Actually count the teeth or use the driveshavt vs. wheel spin method.

    Know what transfer case you have.

    Now, you have to count the teeth of your current drive and driven speedometer gears. Find where the speedometer cable goes into. It looks like this:
    [​IMG]

    Now remove the hold down bolt and gently rock the sleeve loose from its hole. When it comes out, it will contain the driven gear, which looks like: [​IMG]

    count the teeth.

    If you look into the hole, you can see the drive gear:
    [​IMG] [​IMG]

    count the teeth.

    http://www.bgsoflex.com/speedo1.html

    then...

    http://www.tciauto.com/tech_info/speedo_gears.htm
    [​IMG]

    Now, using the calculator (speedometer rev/mile being 1000) and resource page I posted above, find out which combination will work for you to give you the correct reading on the speedometer face. You might need to swap both drive and driven gears.

    Images and some good info found at http://www.transmissioncenter.net/sp...n_______va.htm in addition to what I posted above.
     
  8. gmc4cw

    gmc4cw 1/2 ton status GMOTM Winner

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    put bigger tires on. :D
     

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