Manual Transmissions - Group 4.000

3-speed manual transmission w/overdrive [RPO M10]

Standard Saginaw 3-speed transmission

Muncie 4-speed manual transmission. Note the speedometer cable exit on the passenger side. Because the speedometer cable exited on the passenger side, an extra hole was required in the firewall to accommodate the speedometer cable.

Transmission Month Date Codes

P7C09 (March 9) date stamping on a 1967 Muncie 4-speed transmission.

P7H21 (June 21) date stamping.

P7M08 (August 8, 1966) date stamping.

1967 was the first year to have the year stamped in the date code and the month represented by a letter code. Below is a 1966 model year Muncie; note the difference.

P0221 (February 21) date stamping on 1966 Muncie 4-speed transmission.

 
1964 to 1968 Muncie 4-speed transmissions can be identified from later models by the way the transmission arms attach.  Early Muncie side covers had a stud and the shift arm attached with a nut on the stud while the 1969 and later model side covers had a hole and the shift arms attached with a bolt.

Early (64-68) side plate. Note the shift arms are held in place by a nut/stud arrangement. The shifter rods used in the above photo are aftermarket Hurst rods.

Although no M-22 Muncie transmissions are known to be installed in 1967 Chevelles they were installed in Corvettes and the swap is a simple bolt-in affair. Here is a comparison between the M20/M21 gear set and the M22 gear set.

M20/M21

M22

The Saginaw 4-speed transmission was also used and shown for "M20 PROD V-8 ENG & R.P.O. L30". Easily identified by the reverse gear being on the main case instead of the tail housing.

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 3.55 or higher (lower numerically) rear end ratio unless it has been changed by an owner somewhere along the line. This transmission is a carry-over from 1966 with no major changes. Although the M22 was available in the Chevelle model, records indicate that no Chevelle was ever fitted with one in 1967 and only 20 L88 427/430hp Corvettes were so equipped.

The serial number is a date code and indicates the particular year the transmission was built for. Serial numbers from 1963 to 1966 included only the month and day. P0101 indicates January (first  01) 1st (second 01). In 1967 and 1968, the serial number 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 December build date it was actually built the prior 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. The 1969 to 1974 Muncie got a ratio designating letter at the end of the serial number. An example would be P2R25B. This decodes to 1972 (2), October (R), 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

Assembly Date Code Location

Manual transmission part numbers