What transmission was used on a 70 z28

Discussion in 'Transmission & Driveline Topics' started by 1973camaro406, Apr 16, 2015.

  1. 1973camaro406

    1973camaro406 Veteran Member

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    What transmission was used on a 70 z28? Was it the m-22 or the m-21? I always assumed it was the m-22
     
  2. Double J

    Double J Veteran Member

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    Both could've been used it just depends on what box you checked when you ordered the car.
     
  3. 1973camaro406

    1973camaro406 Veteran Member

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    So no way to tell what the original was other than a build sheet?
     
  4. Gary S

    Gary S Administrator Lifetime Gold Member

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    70 Z28 could be ordered with TH400, M20, M21, or M22. The matching VIN will be on the tranny if it is the original one.
     
  5. 1973camaro406

    1973camaro406 Veteran Member

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    Interesting really
    I don't have original tranny so it's up to me lol
    I'll prolly go with 21. It seems 22's are very high in price. Thank you!
     
  6. Camaro-Chevelle

    Camaro-Chevelle Veteran Member Lifetime Gold Member

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    What is the rear differential gear ratio?
     
  7. Peter Wilson

    Peter Wilson Veteran Member

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    rear gear ?

    I don't think the rear gear has any bearing on it being an M21 or M22 . a local 70 Z28 has the original 12 bolt 4.10 gear rear in it and an M21 , he has the GM of Canada documentation on it and it was delivered new that way . My 71 had a 3.73 gear and an M21 when new , I know of a 71 with a 10 bolt 3.73 and original M22 .
     
  8. Camaro-Chevelle

    Camaro-Chevelle Veteran Member Lifetime Gold Member

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    M21 and M22s are better suited when used with 3.55 and numerically higher gears.

    The M20 Gear Ratios are:
    First 2.52, Second 1.88, Third 1.46, Fourth 1.00.

    The M21 and M22 Gear Ratios are:
    First 2.20, Second 1.64, Third 1.28, Fourth 1.00.

    Since the M21 and M22 have a higher (Numerically Lower) first gear than the M20, it will not work well with 3.07 and 3.31 gear sets.
     
  9. COPO

    COPO Veteran Member Lifetime Gold Member

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    The Muncie M21-M22, works best with 3.73, 4.10 lower gears.
    A M20 will work also but you will be shifting sooner thru 1-2-3 gears.
    Any Muncie (M20, M21, M22) could be ordered with the std 3.73 in the 70 Z28, and optional 4.10 rear.
     
  10. Camaro-Chevelle

    Camaro-Chevelle Veteran Member Lifetime Gold Member

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    What I don't understand is a M21 being ordered with a 3.31:1 12 Bolt in a 68 L79 Malibu. I owned this car and it is all original. I also had the original window sticker. Please look at the window sticker from Bill Simoni's Chevrolet - Buick in Loudonville, Ohio. It is the fifth item down and it is marked Baltimore Window Sticker.

    http://www.chevellestuff.net/1968/misc/paperwork.htm

    Look at lines 2 and 14 on the window sticker. Line 2 shows 6M21AH for the 4 Speed Close Ratio Transmission. Line 14 shows 6G80KA for Positraction with a 3.31 gear set. You would think that the car would have been better suited with a M20.
     

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