# 3885010 off a m20

That's the 1966 -1967 1" Bore Patent Number. Reference: http://www.5speeds.com/casting.html

The 'code' would be stamped in the case flange as something like:

P0101 for a 66 where 'P' is for Muncie and 0101 is the date of Jan. 01.

...or...

P7A01 for a 67 where 'P' is for Muncie, '7' is for 1967, A01 is the date of Jan. 01.

Reference: http://www.chevellestuff.com/generic/muncie.htm

FWIW, the M20, M21, and M22 got a letter suffix to identify them in 1969. Prior to 1969, they could be identified via the number of rings on the input shaft (kinda).

63-65 M20 ~ none
66-74 M20 ~ one
63-73 M21 ~ two
67-74 M22 ~ none

Thanks!

There is an error in the above response[probably a typo].The m21s had one ring and the m20s had 2..some m20s and m21s with replacement inputs had none also like the m22....

Ls6Convertible
Tech Team


posted 01-09-2004 01:48
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There is an error in the above response[probably a typo].The m21s had one ring and the m20s had 2..some m20s and m21s with replacement inputs had none also like the m22....
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Not True Ls6Convertible, 63-65 Muncie M20 (wide ratio) did not have any identifying grooves on the input from the factory!

Dave thats what i said...it is correctly stated above on the early transmissions but where 67 up is listed as 2 rings for m21 and 1 for m20 is where i made the statement that these years[67 up] may have a replacemnet shaft[or an early no ring shaft] so opening the side cover is usually a must to identify these....thanks for the 400hp setup by the way i received it today,cant wait to open it!! !!!

I guess I read it wrong graemlins/clonk.gif

I'm sure you will find the Tri-Power as stated. Enjoy!

Dave Finally opened the tri power boxes.Im not sure which was better, the parts or the wrapping.First time i ever needed a tool set to take apart a cardboard box !!If you are ever unemployed,come see me.. ill have an opening in my shipping department...thanks

Originally posted by Ls6Convertible:
There is an error in the above response[probably a typo].The m21s had one ring and the m20s had 2..some m20s and m21s with replacement inputs had none also like the m22.... Roger, copy...my bad. The 66-74 M20 had the two rings (63-65 still had none) and the 63-73 M21 had one ring. The above doesn't take into account any repairs/rebuild/fixes etc by an outside source, only what was original. redface.gif redface.gif