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Speedo Help

Discussion in 'The Garage' started by sgarrison, Aug 22, 2006.

  1. sgarrison

    sgarrison 1/2 ton status

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    Hi guys, I could use some help with my speedo problem. I have a 700R4/208 in my '83 blazer with 4.88 gears and 36" tires. My problem is my speedo reads really fast. Does any body know the PN/color code of the "slowest" speedo gears? I went to my Chevy dealer and all they could tell me was that those axles(14FF&D44) never came under a Blazer and they never came with 4.88 gears. I already have a reduction box on the Transfer case and it helps a little. Any help?
     
  2. ryan22re

    ryan22re 1/2 ton status

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    My guess is that the closest you will get is a speedo gear setup (drive and driven gear) from either a 3.73 or a 4.10 truck. To get exactly back to stock you'd have to have the speedo gears from a 3.9something ratio which wasn't available. No ideas on colors though.
     
  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Just take your rig to a speedo shop and about $100.00 later it will be accurate to 100 MPH.
     
  4. mudbog42

    mudbog42 1/2 ton status

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    Yeah take it to a speedo shop. Mine was about 15-20MPH faster than I was going when I got my lift and gears put in (86 K-5 6"lift and 4:88 gears). I think it costs me like $70 or something and its right on now
     
  5. 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.
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Just as an FYI, almost all GM speedo gears (drive and driven) have the tooth count cast into the edge of them. Not supposed to go by color on used gears because it is said they can change color.

    Also, the "sleeve" (first picture in above post) is not the same for all speedometer gears. The difference in tooth count is sometimes made up by offsetting the gear a hair (for larger diameter) and the wrong driven gear in the wrong sleeve will tear up the gears. I believe that is universal for all GM transmissions/t-cases that use removable gears, but I'm not certain.
     

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