Q for you '69 MY Muncie Assy. Date Gurus

[Wayne M.]

As 1969 model year production extended from August 1968 to December 1969, am I correct in assuming that there will be 2 months (Aug '68 and Aug '69) in which the assembly code will be P9M23, except that the Aug '69 assy. date code will have the suffix A, B or C [wide ratio, close, or M22], as the ratio codes were supposedly introduced Dec 1, 1968 ?

How about December 1968 versus December 1969 ? Could you have 2 months with identical assy. dates and ratio codes (ie. P9T05A) ? So without the VIN derivative stamping, or if missing, you could not tell the true assembly vintage ?

[Mark #28455]

Re: Q for you '69 MY Muncie Assy. Date Gurus

The code for trans type started late October 1968, so those three months are easy to tell apart, leaving November and December as the toughies. You can also look at the date codes on the castings to verify the year (side cover, input collar, etc). The 1969 model year was a fluke because of the strikes so the dating system did allow some overlap of the date codes for the Muncie trans. There wasn't a problem with the TH400 as those used a Julian dating system.

As you have likely noted, a common e-bay scam is to add a "C" to the code for an early trans and attempt to pass it off as an original M22, except the original Muncie stamps have a non-standard width (about 2/3 as wide as a "regular" stamp of that height, so the added letter looks much fatter.

All in all, it's the old "buyer beware".

Good luck,
Mark

[Joe L.]

Re: Q for you '69 MY Muncie Assy. Date Gurus

Mark-----

Unfortunately, although there are some "date codes" on Muncie cast components, they do not generally include a year. Consequently, they are pretty much useless in determining the actual date that the component was cast.

[Joe L.]

Re: Q for you '69 MY Muncie Assy. Date Gurus

Wayne-----

Way back in my memory, I seem to recall that there was some way that this was handled in terms of coding. Even if I'm correct in this recollection, though, I don't recall what the method was.

Actually, I wouldn't be surprised to see very late 1969 Muncies with 1970 model year transmissions. There were only 2 differences with respect to 1969 and 1970 Muncie transmissions. First, the 1969 models used the GM #3925660 main case (although it's possible that a few M-22s used the 3925661). 1970 models all used the 3925661 main case which was fitted with a drain plug. The 3925660 and 3925661 main cases are identical except for the drain plug used for all '661' cases.

The other difference in the 1970 transmissions was the fact that the side cover was re-designed to incorporate provisions for the TCS switch. This switch was only installed on California-delivered cars, though, and a plug was installed on non-California cars. So, there'a absolutely no fundamental reason that a 1970 model transmission could not have been used on a 1969.

It's also very possible that a run of the 1969 transmissions was built prior to September, 1969 and that inventory was used for Corvettes (and Camaros) built in the final months of 1969. So, it may be that there were no 1969 model year transmissions built in the period after normal 1969 production ended.

It would be very interesting to hear from folks with Corvettes built in the October-December 1969 period and learn what the transmission codes are on their cars. It would also be intersting to learn if those cars have '660' or '661' main cases.

[Dennis D.]

TCS

Joe

I thought all 70's had TCS.

[Joe L.]

Re: TCS

Dennis-----

Yes, that's correct; I "mis-spoke". I was getting my TCS and EEC mixed up. All 1970 Corvettes had TCS, but only California Corvettes for 1970 got EEC.

[Donald S.]

Re: Q for you '69 MY Muncie Assy. Date Gurus

Joe,

On my November 69 built Corvette, the transmission code number is:
P (Muncie HD 4-speed)
9 (1969 Model year)
R (October)
13 (Day)
B (Close range M-21)

The transmission is original to the car and has the drain plug you mention. I'd have to check the casting numbers; which side would they be located on, passenger or driver side? The car is in the garage stored for the winter and if I'm "going under" I'd like to do it once. It's mighty cold out there!
Don Smith #28087

[Joe L.]

Re: Q for you '69 MY Muncie Assy. Date Gurus

Don-----

Excellent information. That definitively says that the 1969 versions of the transmission were still being produced and so-coded (for Corvettes and, presumably, Camaros) even after the 1970 model year production had started for other models. Also, the normal nomenclature was being used with no change to designate the longer production run. In other words, a transmission with exactly the same coding would have resulted for a transmission built on October 13, 1968 as for one built on October 13, 1969, EXCEPT for SUFFIX coding (which beagn on October 21, 1968). Presumably, then, transmissions manufactured between October 21, 1968 and December 31, 1968 would have had the EXACT same coding as those built between October 21, 1969 and whenever the 1969 model year transmission production ended for Corvettes (probably early December, 1969 but continuing much longer for Camaros).

The transmission main case casting number is found on the upper portion of the right (passenger) side of the main case. It's very prominent and large and quite easy to make out. I'm betting that yours will be a 3925661. If so, that fact could be used to discern many of the late 1968 built 1969 model year transmissions from the late 1969-built 1969 model year transmssions, depending upon when the change from the 660 to the 661 actually occured in this late 1969 period.

[Donald S.]

Re: Q for you '69 MY Muncie Assy. Date Gurus

Joe,

Congatulations! You are correct, it is 3925661.

Looking at the transmission casting, I remembered your post a few days ago regarding the "finish" on some of the aluminum pieces. This thing looked like it was cast in someones basement! The casting number looked as if it was added to the mold because it was of a different "font" from the rest of the wording under it. As a matter of fact, I'm taking your word that it's a "1" at the end because it was completely illedgible! However it's 392566 for sure.
As I stated before, it has a drain plug also.

Don Smith #28087

[Joe L.]

Re: Q for you '69 MY Muncie Assy. Date Gurus

Don-----

That's even more interesting. The 1968-69 case was GM #3925660. The 70-74 case was GM #3925661. Thus, both cases have the 392566 "prefix". However, what may have been done is that for these 1969 transmissions they used the 3925661 case but either obliterated the last digit or ground it off and re-stamped it with a "0" which may have been done too crudely to be discernable with the transmission in the car.

They couldn't "obliterate" the drain plug, though. While the '660' cases used for M-22 applications during 68-69 had the drain plug, most '660' cases did not. The fact that your late-build 69 has the drain plug with an M-21 is convincing enough proof that what you have is really a '661' case, whether or not the last digit of the casting number is legible.

I can tell you that the last digit on my original '660' case (and, others that I have) is VERY legible and the last digit on some '661' cases that I have are very legible, so it's not as if these were customarily illegible.

This brings up another issue, though. While I don't know if this feature is judged as it's not in the JG, if it is so-judged some folks with late 1969s found with the '661' main case and/or drain plug (which feature is easily discerned on the judging field), may be "dinged" for an incorrect configuration (unless they have an M-22). That would appear to me to be unjustified just from the little that we now know. I certainly hope that folks with late 1969s have not gone out and purchased "correct" '660' transmission main cases without drains in order to re-stamp and make their cars "correct".

[Donald S.]

Re: Q for you '69 MY Muncie Assy. Date Gurus

Joe,

I have the same "problem" with my water pump. Since I'm not the original owner (but have owned the car for all but seven of it's 36 years) I was confident that the water pump was original to the car. The casting number is 3940960 with a casting date of J289 which I translated to October 28th 1969, perfect for my November 19th build date. The JG states only the 3856284 as being correct.
It was several years ago that you had noted that it was liklely this pump would have started showing up in late production 1969.
Fortunatly I didn't conform to the JG and still have that pump on the car.

In regards to the transmission, the right side of the car is currently parked tight to the wall, (making it difficult to squeeze my frame underneath), and the lighting wasn't the best, but the last digit was obviously not as visible as the rest. Maybe this was an interum change until they got the "official" number on the casting plate.
When the weather improves, I'll be able to get the car up high enough and get a better look as to what happened to that last digit. I tried to get a couple of digital pics, but the speedometer cable kept getting in the way!
Thanks!
Don Smith #28087

[Jack H.]

Reason for lack of thorough info...

on transmissions is NCRS policy NOT to risk life/limb by crawling that far under cars on the judging field to verify numbers/dates (can be a REAL BEAR on a side exhaust car!). Different story during non-restored car judging (Star/Bowtie). There, the car is put on a lift to give both mechanical and chassis teams a clear and safe view of the undercarriage...