ID a Muncie
The Muncie 4-speed transmission was used with many different GM models and engine combinations from 1963 through 1974.
The main difference between the Muncie and the Borg-Warner is that the Muncie has a 7-bolt side cover and the Borg Warner
has a 9-bolt side cover.
Muncie 4-speeds were produced in two different ratios wide ratio (M-20) and close-ratio (M-21).
An extra heavy duty close-ratio version (M-22) was also offered on many of the big-block high-performance models.
The choice of transmission was dictated by the engine size and rear-axle ratio. Axle ratios of 3.73 and lower (numerically higher)
came with close-ratio transmissions, while axle ratios of 3.55 and higher (numerically lower) used wide-ratio transmissions.
In addition, many GM high-performance engines came with M-22 “Rock-Crusher” in the 1970-73 years, however an early
version of the M-22 was available as early as 1965 in Corvettes.
The main internal
differences in the 3 types of transmissions are listed in the parts below.
All other components interchange, with the exception of production upgrades and changes.
For example, 1963-65 synchronizers, blocking rings, etc. do not interchange with 1966 and newer
versions, and therefore the transmission must be stock or interchanged as a unit.
Casting: 3925660 Years: 1968 - 1970 Ratios: M20 2.52 1st , M21 2.20 1st, M22 2.20 1st
Casting: 3925661 Years: 1970 - 1974 Ratios: M20 2.52 1st , M21 2.20 1st, M22 2.20 1st
Year 1966-1974 Type: M20 Rings: Two Ratio: 2.52 / 1.88 / 1.46 / 1.00 / 3.11
Ratio: 2.20 / 1.64 / 1.28 / 1.00 / 2.27
Year 1967-1974 Type: M22 Rings: None Ratio: 2.20 / 1.64 / 1.28 / 1.00 / 2.27
Example 170N553721 P0E08C
1= Norwood Assembly Plant, unit #1
70 = 1970
N = Norwood
553721 = the last 6 digits of your VIN
P = Muncie
0 = 1970
E = May
08 = day
C = M22 (A=M20, B=M21, C=M22)
A = January, B
= February, C = March, D = April, E
= May, H = June