1970 Muncie date code question

[David L.]

I have a Muncie 4-speed M21 transmission with a 1970 Corvette V.I.N. that I bought at a swap meet in Thompson, CT back in the 1990's. I bought the transmission for my 1970 Camaro SS350 project that has since been abandoned. The stamping on the main housing is "P0T30B" (Muncie, 1970 model year, December, 30th, M21) which makes the assembly date as December 30, 1969. The casting numbers on the housing are "3925661", "9", and "12". Does the large "12" represent December and the "9" represent the year 1969?
Dave

[Mark F.]

Re: 1970 Muncie date code question

I have a Muncie 4-speed M21 transmission with a 1970 Corvette V.I.N. that I bought at a swap meet in Thompson, CT back in the 1990's. I bought the transmission for my 1970 Camaro SS350 project that has since been abandoned. The stamping on the main housing is "P0T30B" (Muncie, 1970 model year, December, 30th, M21) which makes the assembly date as December 30, 1969. The casting numbers on the housing are "3925661", "9", and "12". Does the large "12" represent December and the "9" represent the year 1969? Dave

Hi Dave,

I'm pretty sure the "9" is the casting mold number (not a year code).
not sure what the 12 is (and notice the "1" is larger font than the "2")...

[Bill B.]

Re: 1970 Muncie date code question

Dave,

The marking are somewhat confusing to me. The "70S407318" appears to be the VIN from a 1970 Corvette manufactured in March of 1970. The "P0?30B? is strange, where the "?" is expected to be a letter "A" thru "G" for the 1970 Corvette model year. It looks more like a "T" or "F", but if an "F", that wouldn't normally fall in the expected production range (F = June), according to my information. The "30" refers to the day of the month. The 3925661 main case casting code of 3925661 does refer to transmissions of 1970 - 1974 vintage.

Perhaps others may offer better info on this one.

[Bill B.]

Re: 1970 Muncie date code question

Unless I'm wrong, according to a "P0T30B" stamping, the transmission was supposedly manufactured December 30, 1970, which would make it destined to go into a model year 1971 vehicle. I do not believe the "0" was a model year designation, but rather manufacturing year designation, unless someone at the plant started changing the gang stamp incorrectly, and then the transmission was "lost in the system" for a while before being installed in that March '70 Corvette ...

(edit - Late breaking info - According to an article by Paul Cangialosi, Muncie transmissions with a December build date were marked with a next year ident, for some reason. To quote: One important point is that if you have a Muncie dated with a December build date it was actually built the prior year. An example would be the date code P8T13. This is for a 1968 production car. The T stands for December and 13 is the day.
So ... with this info, it does make sense and a 2 to 3 month delay from build to vehicle installation does not appear to be out of the ordinary. Also, without knowing the first 4 digits of the VIN known, it might not even be a Corvette partial VIN, but it WAS definitely a St. Louis build vehicle. (Most likely was a Corvette)

[Patrick B.]

Re: 1970 Muncie date code question

The digit after the P refers to the model year not the calendar year. Your trans was made in December 1969 for the 1970 model yeay.

[Bill B.]

Re: 1970 Muncie date code question

Patrick, thanks for the correction and to Jack Morocco for catching an important typo.

Further investigation on this provided some additional detail:

During the 1963 thru 1966 Muncie build period, there was no year info provided. The second and third digits after the "P" represented the month it was assembled and the 4th & 5th digit the day

Apparently starting around the 1967 model year, they started using a single second digit that represented the model year, not the actual year it was assembled, with the 3rd letter representing the month and the 4th & 5th digits representing the day.

The letter suffix (A, B, C) was added starting 1969 to indicate M20, M21 or M22.

Thanks again Patrick & Jack!

[Tom P.]

Re: 1970 Muncie date code question

This is the correct answer.

[David L.]

Re: 1970 Muncie date code question

This is the correct answer.

Tom,
What exactly "is the correct answer"?

The stamping on the main housing is "P0T30B" (Muncie, 1970 model year, December, 30th, M21) which makes the assembly date as December 30, 1969. The casting number on the housing are "3925661". There is no question in my mind that the transmission has a 1970 Corvette partial V.I.N........"70S407318"......where the number "0" is the model year 1970 and the letter "S" is for St. Louis where Corvettes were assembled for many years.

Here is my question once again:
Does the large "12" casting number represent December and does the "9" casting number represent the year 1969 on the main housing? I have never seen numbers like this on a Muncie.......but I have not seen every Muncie transmission that was ever built either.
Dave

[Tom P.]

Re: 1970 Muncie date code question

The digit after the P refers to the model year not the calendar year. Your trans was made in December 1969 for the 1970 model yeay.

I failed to quote the above reply, which is correct information.
The 9 and 12 in circles, such as on various cast alum parts has been discussed and debated for many years without a definitive conclusion. But as explained above, the P0T30B is valid for Muncie, 1970, Dec 8, M21. Thus, assembled in Dec 69 for installation in a 70 model.

[David B.]

Re: 1970 Muncie date code question

Looking at earlier Muncie case prints indicates the 9 and l2 are die status & date markers which must appear in that area. The 9 being the status marker. Earlier cases with a circle had the month at top and week below (date marker). In this case I would guess 1 is January and 2 is the second week. Are you sure Stamp #s are not P0130B? Therefore January 30th. ??

[Patrick B.]

Re: 1970 Muncie date code question

Looking at earlier Muncie case prints indicates the 9 and l2 are die status & date markers which must appear in that area. The 9 being the status marker. Earlier cases with a circle had the month at top and week below (date marker). In this case I would guess 1 is January and 2 is the second week. Are you sure Stamp #s are not P0130B? Therefore January 30th. ??

[Tom P.]

Re: 1970 Muncie date code question

Looking at earlier Muncie case prints indicates the 9 and l2 are die status & date markers which must appear in that area. The 9 being the status marker. Earlier cases with a circle had the month at top and week below (date marker). In this case I would guess 1 is January and 2 is the second week. Are you sure Stamp #s are not P0130B? Therefore January 30th. ??

The letter for the Month on Muncie main cases did not follow the same format as it did on other GM castings, such as blocks, heads, etc.
I was A-Jan, B-Feb C-Mar, D-Apr, E-May, H-Jun, K-Jul, M-Aug, P-Sep, R-Oct, S-Nov, T-Dec .
I don't know why it was different on Muncie cases, you will have to ask GM why it was different (good luck).