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Gear ratio

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  • Kurt G.
    Very Frequent User
    • April 30, 2005
    • 343
    #1

    Gear ratio

    Can anyone tell me the gear ratio in 4th gear on a '72 M-21 transmission? Trying to figure out half shaft and wheel rpm's. Thanks.
    Kurt Geis
    Chairman, Midway USA Chapter
    Targa Blue 1972, Top Flight and Duntov Award, 2014
    Arctic White 1994, Top Flight, Hrt. of Amer. Reg. 2011
    Arctic White 2013 60th Anniv Special Edition Conv.
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    • David H.
      Extremely Frequent Poster
      • June 30, 2001
      • 1544
      #2
      Re: Gear ratio

      Originally posted by Kurt Geis (43861)
      Can anyone tell me the gear ratio in 4th gear on a '72 M-21 transmission? Trying to figure out half shaft and wheel rpm's. Thanks.
      Kurt,

      The GM Archives Vehicle Information Kit for 1972 (page 129 of 163) shows M21 ratios of:

      First: 2.20, Second: 1.64, Third: 1.27, Fourth: 1.00, Reverse: 2.26.

      Information fits are available for free download at:

      GM Heritage: An Iconic Legacy | General Motors
      http://www.gmheritagecenter.com/gm-heritage-archive/vehicle-information-kits.html
      Explore more than a century of innovation, automotive leadership, and iconic vehicles at General Motors—a legacy that still drives the future of the industry.



      Click on the link then scroll down the page to "Corvette" and click on "Show". Select (click) the year you want to download, "1972" in this case and accept approval of the GM Usage Agreement. The pdf will then download. In your case, "1972", the info is on page 129 (Multiplication Factors are on page 117).
      Judging Chairman Mid-Way USA (Kansas) Chapter
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        • Michael W.
          Expired
          • April 1, 1997
          • 4290
          #3
          Re: Gear ratio

          M20, M21 and M22 are all 1:1 in 4th gear.
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