Muncie M21 ID Tag....?

[Ken's67]

I'm working with a number matching 1967 Corvette.
327 350HP with a Muncie M21 Tranny. The casting numbers on the transmission are correct, and the stamp date code and VIN numbers are also correct. Here is the problem: The ID tag that was on the transmission is: 3890563 I think the correct tag number should be: 3880853 (M21 Close Ratio L79). I was unable to find anything about 3890563 tag number. If someone swapped tags, this number should still be a valid "Muncie" part number, yes? I can't find any info on it. Any help?
Thanks Ken

 

[61 Silver]

Transmission TAG

http://www.ncrs.org/cgi-bin/archivesearch/search2.pl

I typed your tag number into the NCRS archives and there was reference to this tag. You may want to type in the above URL to read the answers.

The transfer of the URL did now work correctly, so up-load the NCRS site, second archive and type your number and click search.

 

[JohnZ]

3880853 is the correct assembly number for the M-21 used only with L-79 (M21AB ECL code); M21AA (tag 3880855) was used only with non-L88 BB's (L-36/68/71/89). 3890563 is a '68 or '69-released part number.

 

[Ken's67]

Here is something that someone talked about on the NCRS forum....

"the speedometer gear set installed in the transmission. These were installed at the transmission assembly plant in Muncie, IN, and not at the vehicle assembly plants. So, each different possible speedometer gear set (probably at least 10) times the number of basic trans possibilities (3) gives quite a number of different units which much each be identified by a seperate and distinct part number. ...

Can this part number "3890563" be only for a M21 (L-79) with a 3.55 rear end gear? (to get the correct speedo gear in the tranny)
I see from the link that "61 Silver" put up, that other '66 and '67 owners have the same number tag. I don't thinkthis number it for a '68 and '69.

 

[JohnZ]

The quote referred to deals only with the speedo DRIVE gear (the one pressed on the output shaft at Muncie) - there were two different drive gears - both had 8 teeth, but were two different diameters, to mesh with two different diameters of plastic DRIVEN gears, each of which had different ranges of tooth counts to match up with different axle ratios; the plastic driven gears were installed at St. Louis. The only physical difference between the 853 and 855 transmission assemblies was the diameter of the Muncie-installed steel drive gear on the output shaft.

For 1967, the L-79/M-21 combination was only available with 3.70 and (optional) 4.11 axles. The big-blocks with M-21 were available with 3.08, 3.36, and 3.55 axles as standard and optional depending on which engine was chosen, which required a different range of driven gears (thus the other DRIVE gear).

3.70 was an option with L-71 and as "special order only" with the L-36 and L-68, and a 4.11 axle was available as "special order only" with L-71; in those cases, the 853 Muncie normally used only with L-79 was used, as it had the correct DRIVE gear to be compatible with that range of axle ratios and their associated driven gear tooth counts.

 

[Ken's67]

Yes JohnZ, good point.
I assumed it was a M21 tranny, it maybe a M20.

I'm sure that the rear end is original, with a "AN2267" (3.55 posi. Feb. 2 1967) stamped on it.

Someone was telling me that the 3870354 would have been used with a 3.36 rear end, not a 3.55. the listings all assume the base configuration for the engine combination, and is not complete for all combinations possible. The Base combination for the L-79 with a M-21 is a 3.70 rear axle, which would correspond to the 3880853 number. We need to find information for the additional numbers.
Ken

 

[Ken's67]

The correct answer on the tag info.!

I like to thank Joe Lucia in coming up with the answer. (I think)
Here is what he said.
......As has been suggested, the list of PRODUCTION part numbers for the transmissions found in the AIM is seriously incomplete and, in some cases, inaccurate. There were MANY more numbers used in PRODUCTION than were shown in the AIM. Also, sometimes the part numbers shown in the AIM for a certain application were also used for other applications. The "controlling factor" was what rear end ratio that the car had and which 4 speed was to be installed (M-20, 21 or 22). Other than the model of the transmission, the installed speedo gear combination was the ONLY difference between these transmissions.

Anyway, GM #3890563 was the PRODUCTION part number for a 1967 M-20 Muncie used with 3.55:1 rear gear ratio. It was used only with L-79 for 1967 Corvettes since the M-20/3.55:1 combination was not used for any other engine option. However, the GM #3890563 was used for other 1967 Chevrolet applications with M-20 and 3.55:1 gears. The GM #3890563 was never available in SERVICE, though.....

Thanks again to all for the help. Ken