Originally Posted by Chadborne
Also, the number above the GM U.S. patent number is 3885010 which I understand is the casting number for 1965-1967. Is this true?
Other numbers that are stamped in the transmission are 3884685 and 3846429. Any idea what these are?
3885010 = Maincase number for 1966-67 ... M20, M21 or M22.
3884685 = Sidecover number for 1966-67-68 ... M20, M21 or M22.
3846429 = Tailhousing number for 1964-65(until Feb '65) ... M20, M21 or 1965 ... M22.
There is a build date on the passenger side of the rear maincase, reading in a vertical position. That will help determine a specific manufacturing date. There will be no A,B or C suffix code, as that started with the 1969 model year. Otherwise, it sounds like you have a transmission using various parts, and the only way to tell what you actually have is to open the sidecase and count teeth.
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P7B01 = Build date = 4 speed Muncie, 1967, February 1st