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  1. #1
    Join Date
    Dec 2017
    Location
    Jasper, Al
    Posts
    5

    speedometer gear?

    Speedometer gear?
    I'm doing a 4R70W swap into my 69 Mach 1. 27" tall tire, 3.25 gear. 8 tooth drive gear in the trans.
    The various online gear calculators come up in the middle at between ~19-20 teeth on the driven gear, If its 19.4, should I round down to 19 or up to 20 teeth? If I went with a 19 would the speedometer read low or high?

  2. #2
    Join Date
    Apr 2006
    Location
    KCMO
    Posts
    9,122
    The calculators are your best source to figure it out.
    Error on the 19 so at least you are not speeding and don;t know it.
    5% error is acceptable according to my state.

  3. #3
    Join Date
    Apr 2018
    Location
    Ga
    Posts
    10
    This thread might help you-- stangnet.com/mustang-forums/threads/need-help-with-a-aod-swap-speedo-and-wiring.404552/

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