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Thread: Speedo Gears

  1. #1
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    Default Speedo Gears

    Here is a good resource for fixing your speedometer after a rear end swap or tire change:

    http://www.transmissioncenter.net/sp...____va.htm#400

  2. #2
    Administrator 88hurstolds's Avatar
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    Stock TH2004R with a 3.73 rear end use a 10 tooth drive (governor) gear PN 8639906 (Green) and a 30 tooth driven gear PN 561035 (Blue) with a 26" tire however 29 tooth gear should be used with a 26" tire, PN 403999 (Green).
    Why GM chose gears that would make the speedometer read less is beyond me, my guess is to compensate for tire wear since it corresponds to a 25.1" tire???


    For a 27" tire use a 28 tooth driven gear PN 410731 (Yellow gear) with the 10 tooth drive gear
    For a 28" tire use a 27 tooth driven gear PN 410417 (Black gear) with the 10 tooth drive gear
    For a 29" tire use a 26 tooth driven gear PN 25502669 (Brown gear) with the 10 tooth drive gear

    For half sizes you will need to change to a 11 tooth drive gear:
    26.5" -11/31
    27.5" -11/30
    28.5" -11/29
    29.5" -11/28
    30.5" -11/27
    31.5" -13 PN 8634934 (White)/31 PN 403417 (White)


    For 3.42 rear end ratio you will need an 11 tooth drive gear PN8634965 (Orange) with a 30 tooth driven gear PN 561035 (Blue) for a 26" tire
    26.5" -10/26
    27" -11/28
    27.5" -12 PN 8634935 (Red)/30
    28" -11/27
    28.5" -12/29
    29" -11/27
    29.5" -12/28
    30" -13/30
    30.5" -12/27
    31" -13/29
    31.5" -13/26



    For 3.08 rear end ratio you will need a 13 tooth drive gear PN8634934 (White) and a 31 tooth driven gear PN 403417 (White) with a 26" tire
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