Muncie transmission calendar 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

 

Main case casting numbers

1963……………………………………..3831704

1964 -65……………………………….3851325

1966 -67……………………………….3885010

1968 -70……………………………….3925660

1971 -74……………………………….3925661

Rare 1964……………………………...3839606

Very rare 1964 -65………………….3864848

*some 1970’s made match 1971 models sue to mid year changes.

Side cover plate casting numbers

1963 -65……………………………….3831707

1966 -68……………………………….3884685

1969…………………………………….3950306

1970 -72……………………………….3952648

1973 -74(?)……………………………335308

 

Tail Housing Casting numbers

1963……………………………………3831731 with speedometer housing on driver side

1963-66………………………………9779256 with speedometer housing on passenger side

1964……………………………………38346429 with speedometer housing on driver side

1965 -70………………………………3857584 with speedometer housing on passenger side

1971 -1974…………………………..3978764 with speedometer housing on passenger side

*some 1970 may be the same as 1969 models due to mid year changes.

Muncie transmission Identification Ratio Guide

Gears Spline Groove Spline

Series 1st   2nd   3rd   4th   Input   Input   Output

M20: 1963 -65 2.56 1.91 1.48 1.00 10 none 27

M20: 1966 -70 2.52 1.88 1.46 1.00 10 two 27

M20: 1971 -74 2.52 1.88 1.46 1.00 26 two 32

M21: 1963 -70 2.20 1.64 1.28 1.00 10 one 27

M21: 1971 -74 2.20 1.64 1.28 1.00 26 one 32

M22: 1965 -70 2.20 1.64 1.28 1.00 10 none 27

M22: 1971 -72* 2.20 1.64 1.28 1.00 26 none 32

Some 1970 Chevelle’s may have 26 spline Inputs or 32 spline outputs.

Where to find the Production Code or Build Date

  • 1963 -64 are stamped on the left hand side of the case to the lower rear of the side cover

  • 1965 -1974 are stamped on the right hand side of the case on the vertical boss pad of the case just ahead of the tail housing

Identifying codes

  • 1963 -66 codes follow a 5 digit format starting with a P followed by the month and day the transmission was stamped. For example P0421 reads: Muncie four speed aluminum for passenger car April 21st.

  • 1967 -74 Production codes will start with a P followed by a number for the year, a letter for the month, and two numbers for the day. For example P7C05 will read: Muncie four speed aluminum for passenger car 1976, March, 5th.

  • 1969-1974 codes include a suffix letter at the end to aid in identification of transmission ratios. A = 2.52 1st gear wide ratio M20, B=2.20 1st gear close ratio M21, C = 2.20 first gear Rock Crusher M22. One example code would be ( P0E21 A ) which reads: Muncie four speed aluminum for passenger car, 1970, May, 21st, ratio M20.