Muncie Id Help [Archive] - Chevy Nova Forum

: Muncie Id Help


1969BlueNova
5th-November-2009, 10:48 AM
I need help identifying a few thing on a muncie I just bought. The id tag says 3950356 and the vin on the case is 19s708486. Its a m20 if it helps. I got everything else id.

One more question, is there a more desirable side cover to look for mine has 3884685 on it right now.

1969BlueNova
5th-November-2009, 05:05 PM
ttt, No one can help??

fanbelt
5th-November-2009, 05:29 PM
Check this out...www.5speeds.com/muncie2.htm

donnie
6th-November-2009, 12:02 AM
Casting Year(s) Ratio
3831704 1963 Only M20 2.56 1st M21 2.20 1st
3851325 1964 - 1965 M20 2.56 1st M21 2.20 1st
3885010 1965 - 1967 M20 2.52 1st M21 2.20 1st M22 2.20 1st
3925660 1968 - 1970 M20 2.52 1st M21 2.20 1st M22 2.20 1st
3925661 1970 - 1974 M20 2.52 1st M21 2.20 1st M22 2.20 1st

Years Type Ring(s) Ratio Reverse
1963 - 1965 M20 None 2.56 / 1.91 / 1.48 / 1.00 3.16
1966 - 1974 M20 Two 2.52 / 1.88 / 1.46 / 1.00 3.11
1963 - 1974 M21 One 2.20 / 1.64 / 1.28 / 1.00 2.27
1967 - 1974 M22 None 2.20 / 1.64 / 1.28 / 1.00 2.27

Ratio of drop between gears

Transmission 1st 2nd % Reduction 3rd % Reduction 4th % Reduction Reverse
M20 (63-65) 2.56 1.91 25.39% 1.48 22.51% 1.00 32.43% 3.16
M20 (66>) 2.52 1.88 25.40% 1.46 22.34% 1.00 31.51% 3.11
M21/M22 2.20 1.64 25.45% 1.28 21.95% 1.00 21.88% 2.27

Years Type Ring(s) Spline Input Shaft
Tooth Count
1963 - 1965 M20 None 10 24
1966 - 1974 M20 Two 26 21
1970 - 1974 M21 One 26 26
1969 - 1974 M22 None 26 26

There are 7 different input shaft possibilities on a Muncie. All 26 spline inputs came with 32 spline output shafts and all 10 spline inputs came with 27 spline output shafts. It is commonly mistaken that all "fine spline" 26 spline input shafts are M22 transmissions. The M22 transmission has a 20 degree helix angle on the gear set as opposed to a 45 degree angle found on the M20 and M21 and were made with a higher nickel alloy. The straighter angle was designed to produce less end loading of the gear train and less heat but created more noise, thus the nickname "Rock Crusher" was born. Another misconception is if you have a drain plug you have a M22. This was only true when the first M22 boxes were created; all 3925661 castings (1970-1974) had drain plugs.

The M22 was only produced in a close ratio version. It would not have been sold with a 3.31 or higher (lower numerically) rear end ratio unless it has been changed by an owner somewhere along the line.

The date code indicates the particular year the transmission was built for.

Partial or "Concealed" VIN Stamping

Most transmissions since 1962 will also have a CON VIN stamped in the case generally along the top ridge or even on a mounting surface such as the flange mounting the tail shaft to the main case noting the original car it was installed in. An example of the CON VIN is the same that is stamped on the engine pad in all 1968 and later Chevelles, and generally 1966 & 1967 SS396 Chevelles with an alphanumeric set of characters like 7K123456; model year, assembly plant, and vehicle sequence number.

Most plants stamped the CON VIN on the top, while some stamped it on the side near the date code. Characteristics of the VIN stamp, including the location, type size of the stamp, and the method (individual or 'gang' stamped) was chosen by the individual assembly plant.

1963 through 1966

Date codes from 1963 to 1966 included only the month & day. P0101 indicates January (first 01) 1st day (second 01).

1967 and 1968

In 1967 and 1968, the date code got a year designator and a letter designator for the month such as P8A01, meaning 1968 (8), January (A) 1st (01). Note that a Muncie dated with a September to December build date was actually built the prior calendar year. An example would be the date code P8T13, meaning 1968 (8), December (T), 13th. The transmission was assembled December 13, 1967 for the 1968 model year.

1969 through 1974

The 1969 to 1974 Muncie got a ratio designating letter at the end of the date code. An example would be P2C25B. This decodes to 1972 (2), March (C), 25th, M21 (B).

Date Codes: A ~ January, B ~ February, C ~ March, D ~ April, E ~ May, H ~ June
K ~ July, M ~ August, P ~ September, R ~ October, S ~ November, T ~ December

Type Codes: A ~ M20, B ~ M21, C ~ M22

Here is an example from a 1964 Chevelle from Fremont, CA. Note the H103065 stamped on the flange and the date is shown by the P1030 stamping in the upper right of this photo. The CONVIN stamping positively identifies this as a 1964 Fremont Chevelle because the letter "H" was only used in 1964 for Fremont.

1969BlueNova
6th-November-2009, 10:06 AM
Thanks donnie.

1969BlueNova
6th-November-2009, 03:01 PM
ttt, anyone have a thought on the side cover.

crash
7th-November-2009, 10:26 AM
1969 Used a 306 side cover for the standard model year, and 648 for the extended year... Crash

1969BlueNova
7th-November-2009, 06:48 PM
1969 Used a 306 side cover for the standard model year, and 648 for the extended year... Crash

Thanks exact info I was looking for..:D