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If the last character is an "A" it is a wide ratio, M20, tranny. My 1969 differential is a 3.36 with an M20. If I had to guess without seeing the actual last part of your number I would say you have a close ratio.
VS
If the last character is an "A" it is a wide ratio, M20, tranny. My 1969 differential is a 3.36 with an M20. If I had to guess without seeing the actual last part of your number I would say you have a close ratio.
VS
I see a stamped number P9R26 which means Muncie 1969 October 26. The VIN number is stamped next to that date code and reads 19S707020. 1 = Chevy, 9 = 1969, S = assembly plant = St. Louis, remainder of number 707020 is the cars sequential build number.
Sorry but there is nothing to identify the ratios of Muncie's as each of the casting numbers for the cases, side covers and tail housing were the same for all three ratios.
Hi c,
I'm not sure if you're saying theres no way to identify this transmission from the stamp, or transmissions in general?
Doesn't the last character of the transmission's assembly stamp typically indicate what the transmission is?
The suffix letter indicates the first gear ratio.
A = 2.52:1 Wide Range M20
B = 2.20:1 Close Range M21
C = 2.20.1 Close Range M22
It appears there was a poor 'strike' on C3's transmission case… the P is very heavy and then each ensuing character is lighter until the last character can't even be seen.
Looks like a C to me. That means you have a M22 "Rock Crusher". Most of the ones I've seen have a very audible whine or howl depending on the personality of the transmission. It's caused by the lack of a helical cut to the gears. Straight cut gears are stronger but a lot louder.
Here is an example using my October 24th 1969 build date car.
P9R13A
P - Muncie
9 - 1969
R - October
13 -13th day of the month
A - M20
A is an M-20
B is an M-21
C is an M-22
The problem is the "A, B, C" designation stamp on the Muncie trans was only started in the later part of the 69 run and I can't remember the month it took place. I think it was either Sept or Oct of 69. Before that the letter designation (A, B, or C) stamp for trans type was not used.
To me, from what is visible your stamp looks to be P9R26 but kind of fades out.
Last edited by CanadaGrant; 09-24-2017 at 12:11 AM.
A couple more identifiers would be the number of rings cut into the input shaft. The wide ratios would have 2 rings while the close ratio M22 had none. I see in the picture there is a drain plug on the main case which was unique to the M22 but the plug itself would have a P stamped on it. The wide ratios did not have a drain plug drilled and installed.
You could open the side case and look at the gears but without a real M22 or M20/M21 to compare it to you may not be able to determine the gears are cut helical or straight as it's not that great of a difference in the tooth angles. But if you have a strap wrench and felt marker you can mark one tooth on the output and input shafts then count the number of turns of the input compared to output.
A couple more identifiers would be the number of rings cut into the input shaft. The wide ratios would have 2 rings while the close ratio M22 had none. I see in the picture there is a drain plug on the main case which was unique to the M22 but the plug itself would have a P stamped on it. The wide ratios did not have a drain plug drilled and installed.
You could open the side case and look at the gears but without a real M22 or M20/M21 to compare it to you may not be able to determine the gears are cut helical or straight as it's not that great of a difference in the tooth angles. But if you have a strap wrench and felt marker you can mark one tooth on the output and input shafts then count the number of turns of the input compared to output.
Good luck c3.
I understand that sometime in 69 drain plugs were installed on all 3 Muncies. I am not sure when but my Oct 24th 1969 built has the original M20 and it has a factory drain plug.
Looking at the larger picture the build date looks like P9R20 to me, which is Oct. 20th 1968 for an early 1969 model year Corvette, the A-B-C coding didn't start until Oct. 26th 1968 calendar year, so this trans just missed being A-B-C coded...
The factory drain plugs started the end of July/August of the 1969 calendar year(start of the 1970 model year)...
If the P9R26 date and the stamped 19S707020 VIN says assembly date is 1969 I don't see how it could be correct for a 1968 car. Am I missing something??
If the P9R26 date and the stamped 19S707020 VIN says assembly date is 1969 I don't see how it could be correct for a 1968 car. Am I missing something??
1969 Corvette VIN 07020 was built in Nov. 8, 1968. The transmission is dated October 26 (P9R26), which fits for a November built car.
This also aligns with what he has, "Looking at the larger picture the build date looks like P9R20 to me, which is Oct. 20th 1968 for an early 1969 model year Corvette, the A-B-C coding didn't start until Oct. 26th 1968 calendar year, so this trans just missed being A-B-C coded..."
A couple more identifiers would be the number of rings cut into the input shaft. The wide ratios would have 2 rings while the close ratio M22 had none. I see in the picture there is a drain plug on the main case which was unique to the M22 but the plug itself would have a P stamped on it. The wide ratios did not have a drain plug drilled and installed.
You could open the side case and look at the gears but without a real M22 or M20/M21 to compare it to you may not be able to determine the gears are cut helical or straight as it's not that great of a difference in the tooth angles. But if you have a strap wrench and felt marker you can mark one tooth on the output and input shafts then count the number of turns of the input compared to output.
Good luck c3.
Originally Posted by CanadaGrant
I understand that sometime in 69 drain plugs were installed on all 3 Muncies. I am not sure when but my Oct 24th 1969 built has the original M20 and it has a factory drain plug.
Originally Posted by crash-ent.
Looking at the larger picture the build date looks like P9R20 to me, which is Oct. 20th 1968 for an early 1969 model year Corvette, the A-B-C coding didn't start until Oct. 26th 1968 calendar year, so this trans just missed being A-B-C coded...
The factory drain plugs started the end of July/August of the 1969 calendar year(start of the 1970 model year)...
Hope this helps... Crash
Originally Posted by VERYSOON
My October, 1969, Muncie M20 has a drain plug. I feel certain that the tall 3.70 gear has a close ratio M21. Mine is 3.36.
VS
The OP picture is actually showing the fill plug.
And yes, while an October 1969 built transmission would have a drain plug, an October 1968 built transmission would not.
09-23-2017, 11:15 AM
My M20/21 4 speed transmission
