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Speedo Calibration

Discussion in 'Technical Q&A' started by tomberlin, Jul 3, 2005.

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  1. tomberlin

    tomberlin Formula Junior
    Silver Subscribed

    Apr 9, 2005
    854
    Bethesda
    Full Name:
    tom berlin
    #1 tomberlin, Jul 3, 2005
    I took the gps out for a ride in my 308 and the speedo's off by 10%. Any electrical wizzards out there ever figure out how to calibrate them? Do they read voltage or frequency?
    Cheers,
    Ton
     
  2. gerritv

    gerritv Formula 3

    Jun 18, 2001
    1,400
    St Catharines
    Full Name:
    Gerrit
    #2 gerritv, Jul 3, 2005
    Last edited by a moderator: Sep 7, 2017
    hi
    They read pulses (aka frequency). On GT4 and I assume early GTS/GTB, the sender generates 4 pulses per rev. This is divided by 32 to drive the odometer. The speedo itself is fed current relative to the frequency input. Inside the speedo (at least of the early cars) there is a small potentiometer that you can use to adjust the calibration.

    Sorry for the blurry picture, but you can see the trimmer in top RH corner.

    Gerrit
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  3. docweed

    docweed Formula Junior

    Dec 8, 2004
    452
    Morgantown,WV
    Full Name:
    Chuck Stewart
    #3 docweed, Jul 3, 2005

    FYI Gerrit is correct. I have a 308 with the speedo and odom in Km. I asked to have it changed to mi/hr. They can change the speedo but not the odom. It has something to do with the pulse. Check out www.paspeedo.com if you need more help..(Palo Alto speedometer, Inc.)
     

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