Transmission Question

**Jim.M** · 04-04-12, 05:26 PM

I recently took the tranny out of my '69 (small block) and I am trying to figure out if I have an M20 or M21. Here is what I know.... The tranny matches the VIN (...700275) The code is P9M14. I know that the P means Muncie Plant, 9 stands for 1969, M is for August, and 14 is the 14th. The ratio code of A, B, or C is not present. The casting number 3925660 was used for Muncie transmissions that year. I am thinking that since my car is a low production number, the transmission was made in '68. How can I figure out if I have an M20 or M21? Any advice would be appreciated....

**Crimson Thunder** · 04-04-12, 08:16 PM

You can tell by the rings(grooves) around the input shaft. I believe one ring is M20 and two is M21. I need to look it up to be sure.

**Jim.M** · 04-04-12, 11:47 PM

Thanks for the info... Looks like I have an M20.....

**6880 Mike** · 04-05-12, 08:12 AM

It's my understanding the A, B, and C are not ratio codes. They ID the tranny. A for M20, B for M21, and C for the M22. Your VIN indicates you car was assembled in August, 1968 at the beginning of the 69 model year. Your transmission (and everything else on your car) would also have been dated 1968.

**JohnZ** · 04-06-12, 04:06 PM

The A, B, or C suffix code on the Muncie "P"-stamp are ratio codes, and identify the gearset (A=M20, B=M21, C=M22); however, that coding didn't start until the third week of October, 1968, and your transmission was built before that.

**Jim.M** · 04-06-12, 06:41 PM

I wanted to thank everyone for replying. My car is undocumented and the numbers stampped on the block were shimmed off during the last rebuild. I am learning everything about it that I can. I hope to find the build sheet off the gas tank when I pull the body to replace the frame... Thanks again