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What speedometer gear do i need?

Discussion in 'The Garage' started by FarmRig, Jun 14, 2006.

  1. FarmRig

    FarmRig Guest

    Yes i put 33''s on my truck recently and did the calculater on line and its going to be about 5mph off. What gear do i need? Thank you.
     
  2. kp texan

    kp texan 1/2 ton status

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    What transmission and rear end gears do you have?
     
  3. FarmRig

    FarmRig Guest

    4spd manual and 3:42 in the rear. Its a K10. Thank you.
     
  4. FarmRig

    FarmRig Guest

  5. randy88k5

    randy88k5 1/2 ton status

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  6. uberbeans

    uberbeans 1/2 ton status

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    What about for sm465?
     
  7. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    The tranny doesn't have a tailhousing or speedo gear in a 4x4 . The speedo gear is in the transfercase regardless of auto or manual .
     
  8. uberbeans

    uberbeans 1/2 ton status

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    So how do I calibrate it?
     
  9. randy88k5

    randy88k5 1/2 ton status

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    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.

    You can use this chart, but I would always want to count the teeth myself:

    [​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/speedometer_calibration_______va.htm in addition to what I posted above.
     
    Last edited: Jun 19, 2006
  10. FarmRig

    FarmRig Guest

    Thank you randy88k5
     
  11. Smitty

    Smitty 1/2 ton status

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    Pay attention to the tooth count on the driven gear. There are two different sleeves for the driven gears; one is for gears with less than 40 teeth and the other one is for gears with more than 39 teeth. I just installed a 40 tooth driven gear in mine and had to purchase the new sleeve.
     

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