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Recalibrating spedo.....

Discussion in 'The Garage' started by 89BlazerK5, Sep 19, 2003.

  1. 89BlazerK5

    89BlazerK5 1/2 ton status

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    i just did an engine rebuild, and i'd like my odometer and spedo somewhat correct. i have a 91 with 4L60, and NP241. i'm assuming it has an electronic sensor?? i have 4.56 gears with 33" tires, so, yeah, my spedo is way off. when it says 85, i'm actually doing 65. can i not change the driven gear in the tcase? or do i have to fix it electronically??
     
  2. BigOrange90Jimmy

    BigOrange90Jimmy 1/2 ton status Premium Member

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    just put 35's on it. mine with a 700/241 setup w/4.56's reads perfect. you'll have to fix it electronically. get a TruSpeed sensor if you're really worried about it.
     
  3. R72K5

    R72K5 Banned

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    certain 92 vehicles got VSS in 92, but was onlylike the caprices and such, should still be cable speedo in 92 on trucks, look for speedo cable through firewall.

    the goal of recalibrating speedo gears ratio is to get fromone mile marker to the next in 60 seconds, if you get to next oen too soon then your cable needs sped up, if you get to next marker too late then cable needsd slowed down
    i think i got them not backwards,

    to change ratio you change the speedo gear tooth counts int he end of the tranny, smaller drive or larger driven to slow cable down, larger drive or smaller driven to speed it up
    do a search on yahoo homepage for speedo gear calibration, theres quite a few internet pages on how to do this

    this subject is asked about ALOT all the time, theres tons of posts about this on this and pretty much probably every automotive forum out there these days
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    '91 is electronic speedo, and is "run" via the toner ring in the 241.

    DRAC (under the dash near the ashtray) is what you recalibrate for changing gear sizes, but I have no idea who can do this anymore, as GM quit selling them some time ago.

    FWIW VSS has been in most of the trucks since '81 or 82. VSS presence has nothing to do with whether the speedo uses cable or electric, just the WAY the vehicle speed is "read" is different.
     

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