67 Muncie M20 stamping questions

[Thomas W.]

I have owned my 67 Corvette since 1986 and I have service documents back to 1981. Sometime between 1967 and 1980 the original M20 transmission or just the case was replaced. My protect o plate displays transmission assembly stamp P7A23 and my VIN sequence number is late January 1967 build. However, the transmission in my car has a 3885010 case but the assembly stamp is P0527. In addition there is no VIN number that I can see on the either side of the case (I do not know if the VIN # might be on the top portion of the case). Also, 111876 is stamped on the driver side of the case just behind the reverse light bracket. If there is no VIN derivative stamp on this case is it possible that this was a GM replacement transmission that might have been installed by a dealer?

Finally, can I learn anything from the "10" stamp and the clock dial pointing to the middle casting dot? Thanks, Tom

[Leif A.]

Re: 67 Muncie M20 stamping questions

The 11 18 76 stamping could be a rebuilders stamp and the date of the rebuild...Nov 18, 1976

[Mark F.]

Re: 67 Muncie M20 stamping questions

I have owned my 67 Corvette since 1986 and I have service documents back to 1981. Sometime between 1967 and 1980 the original M20 transmission or just the case was replaced. My protect o plate displays transmission assembly stamp P7A23 and my VIN sequence number is late January 1967 build. However, the transmission in my car has a 3885010 case but the assembly stamp is P0527. In addition there is no VIN number that I can see on the either side of the case (I do not know if the VIN # might be on the top portion of the case). Also, 111867 is stamped on the driver side of the case just behind the reverse light bracket. If there is no VIN derivative stamp on this case is it possible that this was a GM replacement transmission that might have been installed by a dealer? Finally, can I learn anything from the "10" stamp and the clock dial pointing to the middle casting dot? Thanks, Tom

Hi Tom,

My guess is the "10" is a foundry mold number. As many of these cases they made, they must have had MANY molds (and possibly multiple casting lines) to keep up with demand.
Tracking mold numbers could also have been useful from a QA standpoint.

The "clock" with the middle dot could be indicating this was cast on the 2nd shift.

I'm sure others will chime in, too...

[Thomas W.]

Re: 67 Muncie M20 stamping questions

I appreciate your replies. Leif, I never thought of a rebuild date stamp (11/18/76) but it sure fits the timeline with the long history I have with the car. I have been finishing a number of restoration details over the last few years. My NCRS friends have encouraged me to have my car judged at one of the regional events. The NCRS tech forum has been extremely helpful to me. Thank you!

[Patrick B.]

Re: 67 Muncie M20 stamping questions

This looks like a 1966 Muncie originally built May 27, not the original trans for a 67 Corvette.