1970 Z28 M21 stock speedo gears - 3:73 rear gear

Discussion in 'Original Drivetrain Topic' started by 70lt1z28, Nov 14, 2017.

  1. twozs

    twozs Veteran Member

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    hopewell jct ny
  2. 70lt1z28

    70lt1z28 Veteran Member Gold Member

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    Beavercreek, Ohio, USA
    Twozs, thanks for your help. I certainly listen to anyone's posts when they are trying to help. I think the 1973 AIM is completely relevant to the conversation.

    For "visual correctness" does anyone know for sure if the adapter is a yes or no?

    I may just use the following chart for the final say:

    http://nastyz28.com/threads/muncie-speedo-bullet-and-adapter-1970-z28.310766/page-3#post-3551087

    Using that chart with 3.73, 25.9 (from here: https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=45) and doing the math results in 2.909 X 0.8241 = 2.397. Which is very close to stock 8 tooth drive/19 tooth driven natural color 2.375 ratio. This makes some more sense now.

    Wanted to add for others the part numbers are 3987919 for the 19 tooth natural colored driven gear.
     
    Last edited: Nov 15, 2017
  3. COPO

    COPO Veteran Member Lifetime Gold Member

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    Ontario, Canada
    My 70 Z28 with 3.73 uses the factory 19 tooth bullet gear with the SW .8241 reducer, plus my tail shaft uses the plastic gear and not the steel.
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    Last edited: Nov 15, 2017
    70lt1z28 likes this.
  4. FlaJunkie

    FlaJunkie Veteran Member Lifetime Gold Member

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    Mine used the metal gear with no box on the outside. 3:73 gears. M21.
     
  5. 70lt1z28

    70lt1z28 Veteran Member Gold Member

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    Yours is a pretty early 70, isn't it?
     
  6. FlaJunkie

    FlaJunkie Veteran Member Lifetime Gold Member

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    Mar 24, 2001
    Rockledge, Florida
    02C production, Norwood.
     

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