MUNCIE TRANS INDENTIFICATION
Case casting numbers, relating production years and ratios available
Casting: 3831704 Years: 1963 Only Ratios: M20 2.56 1st , M21 2.20 1st
Casting: 3851325 Years: 1964 - 1965 Ratios: M20 2.56 1st , M21 2.20 1st
Casting: 3885010 Years: 1965 - 1967 Ratios: M20 2.52 1st , M21 2.20 1st, M22 2.20 1st
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
Ratios of the M20 , M21 , M22
Year 1963-1965 Type: M20 Rings: None Ratio: 2.56 / 1.91 / 1.48 / 1.00 / 3.16
Year 1966-1974 Type: M20 Rings: Two Ratio: 2.52 / 1.88 / 1.46 / 1.00 / 3.11
Year 1963-1974 Type: M21 Rings: One 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
Input Shaft Tooth and Spline Count Related to Year
Year 1963-1965 Type: M20 Rings: None Spline: 10 Tooth Count: 24
Year 1966-1970 Type: M20 Rings: Two Spline: 10 Tooth Count: 21
Year 1970-1974 Type: M20 Rings: Two Spline: 26 Tooth Count: 21
Year 1963-1970 Type: M21 Rings: One Spline: 10 Tooth Count: 26
Year 1970-1974 Type: M21 Rings: One Spline: 26 Tooth Count: 26
Year 1967-1970 Type: M22 Rings: None Spline: 10 Tooth Count: 26
Year 1969-1974 Type: M22 Rings: None Spline: 26 Tooth Count: 26
Reading Serial and VIN Numbers
Serial numbers for Muncie 4 speeds always begin with the letter "P". P stands for Muncie. Why.... I have no idea. The serial number is a date code the transmission was built for a particular year. Serial numbers from 1963 to 1966 included only the month and day. P0101 would indicate January 1st. From 1967 to 1968 the serial number got a year designator and a letter designator for the month such as P8A01, meaning January 1st 1968. One important point is that if you have a Muncie dated with a December build date it was actually built the prior year. An example would be the date code P8T13. This is for a 1968 production car. The T stands for December and 13 is the day. To confirm this simply look at the VIN number. It will usually begin with a 18S101350 or a 28N12950. This means the Muncie was assembled December 13, 1967 for the 1968 model year. The VIN number will usually be a low number. 1969 to 1974 Muncies got a ratio designator at the end of the serial number. An example would be P4D23B. This equates to April 23, 1974, M21 ratio.
Month Code Chart
January Letter: A May Letter: E September Letter: P
February Letter: B June Letter: H October Letter: R
March Letter: C July Letter: K November Letter: S
April Letter: D August Letter: M December Letter: T
Ratio Code Chart
Letter: A M20 Ratio
Letter: B M21 Ratio
Letter: C M22 Ratio