C2 Speedometer Drive/Driven Gears

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  • Pete Whelan
    #1

    C2 Speedometer Drive/Driven Gears

    I'm trying to get the correct speedometer drive and driven gears for my '66 Muncie 4 speed transmission. I have a 3.08:1 rear axle ratio. The service part numbers that I found are 3708144 for the drive gear and 3860341 (brown w/18 teeth) for the driven gear. I haven't been able to get either through GM.

    I did notice that there is a 3924098 (which has been changed to 6261794) drive gear that was used on '68-'70 Muncie transmissions. Is this a direct substitute for the 3708144 gear?

    I also found a 3987918 driven gear (brown, unknown number of teeth) that is available from GM. Is this a substitute for 3860341?

    Thanks,

    Pete Whelan
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    • Joe L.
      Beyond Control Poster
      • February 1, 1988
      • 42936
      #2
      Re: C2 Speedometer Drive/Driven Gears

      Pete-----

      The GM #3708144 speedo DRIVE gear is discontinued. This is a steel drive gear that is an interference fit on the shaft. The GM #6261794 is NOT a replacement for the 3708144. The 6261794 is a nylon drive gear which is secured to the mainshaft with a clip. Only 1968-70 Muncie mainshafts are machined for the clip necessary to secure the 6261794 drive gear. I think that you may be able to get a replacement for the 3708144 gear from aftermarket sources. Long Island Corvette may be such a source since they specialize in 63-67 Corvette parts.

      The GM #3860341 speedo DRIVEN gear is discontinued but is replaced by the GM #3987918 which is still available.
      In Appreciation of John Hinckley
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        • Wayne M.
          Expired
          • March 1, 1980
          • 6414
          #3
          Re: C2 Speedometer Drive/Driven Gears

          Pete --- as an addendum to Joe's good info, you should be able to find a used drive gear 3708144 in any respectable transmission shop. It is 1.85" OD, by 0.61" thk. (which distinguishes it from the 3708145 gear for 3.70-and-up diff ratios at 1.765" OD (nominally 1.75") by 0.531" thk. Both drive gears have 8 teeth.

          The brown driven gear has 18 teeth; maybe you should order the 19-tooth (natural color) gear while you're at it [#...919], just in case you have smaller dia. tires, and find that your speedo / odo reads higher than true speed / distance.
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            • Pete Whelan
              #4
              Thank you Joe and Wayne *NM*

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