P/N 3925660 Muncie case markings

[JGraft]

Hi CRG experts,

I recently removed reportedly an M20 transmission from my 1968 Camaro and are trying to determine the authenticity of it.  1. With the "US PATENT NO 3088330", the last "0" is a different font size. 2. With the "GENERAL MOTORS CORP.", the "P" is also a noticeably different font size. 3. The assembly information is marked "P8A24c" where the "C" is in a lower case instead of upper case. Relative to item 3 I found via CRG info the "C" or M22 identifier production began 10/21/68 which is much later than the assembly date stamp identified. 4. In the casting circle there is no raised bumps and no number to indicate the week and month the housing was cast.

18L333116 is stamped onto the top surface of the case.

Please see attached photos.

Thx,
Jeff

[JGraft]

photo of assembly info.

[JGraft]

VIN # stamping.

[bertfam]

All you posted is normal. That's not a lower case C but what we believe to be a place card holder for the gang stamp (and there are lots of main cases without the date code circle or the "bumps").

Here are three other examples of the place holder. The top one is a 67 with what appears to be a partial 3 or 7. The middle one (like yours) is a 68 with what appears to be a partial E. There were other place holder characters used like the bottom one which appears to be a partial K or maybe an X

Ed

[bcmiller]

Ed is spot on, as usual.

There are several thoughts about the extra characters or partial characters at the end. Placeholder probably makes the most sense. Could also be for some unknown internal tracking for the person doing the assembly or for a specific shift. I have asked around trying to find someone that worked at the Muncie assembly plant, but haven’t found anyone. I did find someone that did assembly of the Borg Warner units prior to 1965.

[cook_dw]

First time I’ve seen a placeholder with a broken K vs the more common broken E.  I had noticed a timeframe where the place holder was used but that K one shoots that in the foot.

[bertfam]

Here are a few service transmissions with something I can't figure out!

Ed

[cook_dw]

Broken “M”.?.

[bcmiller]

It’s also possible that the last partial character is an inspection mark.

Would have to look over the whole case to see if it has any.

I have seen all kinds of Muncie inspection marks. Hearts, diamonds, etc.

[bertfam]

Here are a few, but I've also seen clovers and hearts.

1. Arrow Head
2. Triangle
3. Circle with a 2 in it AND a triangle split in half
4. A square with a 3 in it

Ed

[JGraft]

Thankyou for the response CRG experts, so is the consensus this case is authentic? There are no other markings of any kind anywhere else on this case.

Thx,
Jeff

[bertfam]

Yes, it's genuine GM!

Ed

[bcmiller]

Thankyou for the response CRG experts, so is the consensus this case is authentic? There are no other markings of any kind anywhere else on this case.

Thx,
Jeff

Case and markings are real.

Can’t tell if your transmission is an M22 based on the pics. Post a picture of the input shaft. Might need to have the side cover off too, but let’s start by looking at the input shaft.

[bertfam]

Bryon, he originally stated it's an M20 at the very top of the page

Ed

[bcmiller]

Says reportedly an M20.

I don’t see anything in those pics that proves anything.

[JGraft]

Thx everyone, input shaft has 2 rings, and internal helical gears, not 17 degree straight cut, also counted 1st gear teeth, it's definitely an M20.

[bcmiller]

10-4 thanks.