69 Muncie Build Date and Drain Plug

[Brian Bates]

I am doing some research on late 69 Muncie transmissions. Since the 69 model year was extended for the Corvette did the stamp of the assembly date remain with a 9 in the second position through December 1969? It would seem like the Muncie factory would need to know what model car the transmission they were building was for. They would need to switch the second character of the stamp from a 0 to a 9 for Corvette boxes only.

Additionally, I understand that M-21's have a drain plug beginning with the 1970 model. The same question applies to this application based on model usage.

I am looking at an M-21 with the following info: P0M29B, no VIN stamp, cast #3925660, and a drain plug. I realize that this may not be a Corvette box but the August 29th build date would assume it could have been.

[Joe L.]

Re: 69 Muncie Build Date and Drain Plug

Brian-----

Interesting point regarding date stamping inasmuch as, a you mention, transmissions are one of the few components that are date stamped according to MODEL YEAR and not CALENDAR YEAR. My 69 was built in mid-September 1969, so I'll check it this evening. My vague recollection, though, is that it has a "9" in the model year position of the stamping.

As far as the transmission which you are looking at, I always thought that, except for M-22s, the drain plug didn't start for all transmissions until the introduction of the 3925661 main case. As I recall, this occurred in mid or late 1970 or, perhaps, for 1971. However, yours is obviously not one of those since it is the '660' main case, so I am somewhat surprised. But, perhaps the general application of the drain plug started earlier. However, I can tell you for sure that my '660' main case M-20 trans which was built just about the same time as the one you are looking at, DOES NOT have the drain plug.

Also, I believe that by 1969 just about all, if not all, GM cars had a VIN derivative stamped into the main case of the transmission. The fact that yours doesn't may indicate that it was originally a SERVICE transmission. A SERVICE transmission may have had a different PART NUMBER than the PRODUCTION PART NUMBER for the application serviced. That may explain the addition of the plug. For example, a SERVICE transmission may have serviced several applications, including some which were originally equipped with a drain plug(perhaps some other GM car-line besides Chevrolet). So, the drain plug was added to all of the SERVICE transmissions to enable one part number to SERVICE a wide range of original applications.

[Wayne M.]

Re: 69 Muncie Build Date and Drain Plug

Joe --- This bit about the '67-up tranny assembly date code using the MODEL year (rather than the calendar year) bugs me. I realize (now) that Colvin's book mentions this, but neither the engine or the differential dating follows this pattern.

After all, the model year was readily identifiable in the VIN derivative (for original installations), and I just can't picture Muncie slowing down production to avoid exceeding the end of a model year.

1969 Corvette production is a poor year to test the validity of this, as the model year (end) almost matched the calendar year, but for other years ('67,'68 and '71 thru '74) it would be interesting if a few others could report the trans assy codes for (say) Sept thru Dec cars, or trans assy month codes M thru T; (protect-o-plate code will do)

(From Missouri until shown otherwise)

[Bob Lanham #32271]

Re: 69 Muncie Build Date and Drain Plug

This is interesting to me. I wrote down everything I could and took a couple of photos of my 69 trans when I was wrestling it last week. I couldn't really figure out what it was based on the NCRS spec guide, but it does have a drain plug. It also has a plug higher up on the trans which I assume is the filler plug. Does this mean my trans is most likely not original? Could it be original, but be from the 1970 run? Mine was built in Oct 69 and the head castings indicate they are for a 454 and were built in Sept 69. This is a 427/390. I'd be interested to know if anyone else has anymore info on the trans or heads.