C-2 Tranny tail housing codes

[Hector G.]

I recently had my M-21 rebuilt. I am familiar with the fact that the transmission has an assembly date and that the cars serial #s are on the tranny's main housing. My specific question is, does the tranny have a casting date? If so, where is it, and how can I decipher the code? In addition, does the tranny's tail housing have a casting date? I have located some letters and numbers [CM 2]. Is this the casting date? What does it signify?

I'm new at this but I did spend some time searching for past discussions on this topic. While there are discussions re: the assembly date and serial #s, I was unable to find anything on point. Thanks in advance for your help.

[John H.]

Re: C-2 Tranny tail housing codes

Hector -

Muncie tailshafts are dated using a cast-in circle about 1/2" diameter, just forward of the speedo gear adapter; the number in the top half of the circle is the month, and the number of dots in the bottom half of the circle is the week. Another adjacent circle shows the drawing change number.

[Hector G.]

Re: C-2 Tranny tail housing codes

John,

Thank you. Your insight and knowledge is greatly appreciated. I'm sitting at home and the transmission in question is three feet away from me. Yes, my wife is very understanding. I've explained the significance of this tranny to my wife. I did locate the code on the tailshaft housing in the exact spot you indicated. In regard to the "drawing change" number what does that signify? In my case the letters CM appear on the upper half of the circle and the number 2 appears on the lower half of the circle. In regard to the transmission case, there is also a cast-in circle 1/2 in diameter. However, the number 12 with two dots below it appears 1/2 inch outside of the circle. Was someone just having a bad day? In addition there is a larger number 2 approximately 1/2 an inch to the left and slightly above the number 12. Do you know what this number signifies? Also, there is a diamond shape symbol stamped on the top of the transmission case, where it meets with the case intermediate plate. Does this mean anything? Would you expect the casting date on the main housing to be near in time to the date on the tailshaft housing? Finally, just below the GENERAL MOTORS CORP. casting on the main housing,there are the letters "IS" with the numbers "12-3". They appear quite different from any of the other casted letters and numbers in that they have the appearance of being hand cast. By that I mean, it is as if these letters and numbers were written by hand. They are each a 1/2 inch in height. What is the significance of this information? Thanks John for your help.

Hector

[John H.]

Re: C-2 Tranny tail housing codes

Hector -

The "CM" is the most recent drawing change level in effect in the tooling at the time the housing was cast, and the "2" signifies a deviation in effect at the same time (a change made in production, but not yet officially released on the drawing). Can't help you on the other issues you noted.

[Hector G.]

Re: C-2 Tranny tail housing codes

Thanks John.