Taken from the april, '92 issue of super chevy. I have found it to be accurate.
FIRST DESIGN MUNCIE
The first design was from 1963 to 1967 and is considered the weakest of the bunch. The cluster shaft is 3/4 inch dia., the selector plate has an internally pressed stud. Input shaft is 10-spline and selector shafts are outfitted with 5/16th inch studs.
Example:
Typical date code
0503N
P-muncie
05-May
03-Third day.
D/N-Day or night shift(not always coded)
There is no year designation on these transmissions.
MONTH
01-January
02-February
03-March
04-April
05-May
06-June
07-July
08-August
09-September
10-October
11-November
12-December
THE SECOND DESIGN
The second design muncie (1967-1968) increased the cluster shaft diameter 7/8ths inch and included the second design selector(side) cover with the larger diameter pin externally pressed in to prevent it from shaking loose from the case. Selector shafts studs increased to 3/8ths inch. The 10-spline input shaft remained.
Typical date code:
P7T02
P-muncie
7-1967
T-December
02-second day
MONTH:
A-Jan.
B-Feb.
C-Mar.
D-April
E-May
H-June
K-July
M-Aug.
P-Sept.
R-Oct.
S-Nov.
T-Dec.
THE THIRD DESIGN(1968-1973)
Due to an increasing number of selector shafts breaking off, the only change made in 1969 was to alter the selector shafts by drilling and tapping them to accept a 3/8ths bolt instead of studded shaft accepting a nut.
Subsequent component changes made in 1970 changed the input shaft to a 26-spline(fine) and increased output shaft diameter to accept a T-400 trans. yoke. The final incarnation of the muncie lasted until 1973 when the transmission was taken out of service.
1969-1973 Typical date code:
P9B08C
P-muncie
9-1969
B-February
08-Eighth day
C-M22
MODEL IDENTIFICATION(1969-1972)
A-M20
B-M21
C-M22
Note: not always stamped
Originally, identifying the transmissions by external markings was simple. The M20(wide ratio) trans. had two grooves cut into the 10-spline input shaft and no fill plug in the case, while the M21(close ratio) had a single groove on the 10-spline input shaft and no fill plug on the case. The M22 had no grooves on the input shaft and was the only transmission to be equipped with a drain and fill plug. Unfortunately, over the years, replacement cases and gears offered by Chevrolet and aftermarket manufacturers did not follow the G.M. assembly line identification system, so trying to use this method to identify a transmission is almost impossible.
To determine close ratio(2.20:1 first gear) or wide ratio(2.54:1 first gear), mark the input shaft and output shaft, engage first gear and spin the input shaft and count how many revolutions the input shaft turns to make one revolution with the output shaft. Just less than 2 1/4 turns is a close ratio, and a little more than 2 1/2 turns is a wide ratio.
M22 transmissions can only be identified removing the selector cover(side cover) and visually identifying the straight cut gears-all other muncie transmissions had conical cut(angle) gears.
The most well known Muncie transmissions are the M20(wide ratio), M21(close ratio), and the M22(rock crusher).
Although not mentioned much, there was also an M23 transmission that was used, beginning in 1970. The M23 is recognized by a 26-spline(fine) input shaft and a large output shaft that requires a T-400 driveshaft yoke.
Although some claim that the M23 is a 'rock crusher', it is indicated that this box was assembled in both wide and close ratio components and also with straight cut gears common to the rock crusher (M22) transmission.
This chart, so far, has been very accurate in identifying the muncie trans. over the years, so I wanted to share. It sure seems alot of the muncies out there have made their homes in the tri-5's, so I think it would be good to have it here for everyone to use.
Jay
FIRST DESIGN MUNCIE
The first design was from 1963 to 1967 and is considered the weakest of the bunch. The cluster shaft is 3/4 inch dia., the selector plate has an internally pressed stud. Input shaft is 10-spline and selector shafts are outfitted with 5/16th inch studs.
Example:
Typical date code
0503NP-muncie
05-May
03-Third day.
D/N-Day or night shift(not always coded)
There is no year designation on these transmissions.
MONTH
01-January
02-February
03-March
04-April
05-May
06-June
07-July
08-August
09-September
10-October
11-November
12-December
THE SECOND DESIGN
The second design muncie (1967-1968) increased the cluster shaft diameter 7/8ths inch and included the second design selector(side) cover with the larger diameter pin externally pressed in to prevent it from shaking loose from the case. Selector shafts studs increased to 3/8ths inch. The 10-spline input shaft remained.
Typical date code:
P7T02
P-muncie
7-1967
T-December
02-second day
MONTH:
A-Jan.
B-Feb.
C-Mar.
D-April
E-May
H-June
K-July
M-Aug.
P-Sept.
R-Oct.
S-Nov.
T-Dec.
THE THIRD DESIGN(1968-1973)
Due to an increasing number of selector shafts breaking off, the only change made in 1969 was to alter the selector shafts by drilling and tapping them to accept a 3/8ths bolt instead of studded shaft accepting a nut.
Subsequent component changes made in 1970 changed the input shaft to a 26-spline(fine) and increased output shaft diameter to accept a T-400 trans. yoke. The final incarnation of the muncie lasted until 1973 when the transmission was taken out of service.
1969-1973 Typical date code:
P9B08C
P-muncie
9-1969
B-February
08-Eighth day
C-M22
MODEL IDENTIFICATION(1969-1972)
A-M20
B-M21
C-M22
Note: not always stamped
Originally, identifying the transmissions by external markings was simple. The M20(wide ratio) trans. had two grooves cut into the 10-spline input shaft and no fill plug in the case, while the M21(close ratio) had a single groove on the 10-spline input shaft and no fill plug on the case. The M22 had no grooves on the input shaft and was the only transmission to be equipped with a drain and fill plug. Unfortunately, over the years, replacement cases and gears offered by Chevrolet and aftermarket manufacturers did not follow the G.M. assembly line identification system, so trying to use this method to identify a transmission is almost impossible.
To determine close ratio(2.20:1 first gear) or wide ratio(2.54:1 first gear), mark the input shaft and output shaft, engage first gear and spin the input shaft and count how many revolutions the input shaft turns to make one revolution with the output shaft. Just less than 2 1/4 turns is a close ratio, and a little more than 2 1/2 turns is a wide ratio.
M22 transmissions can only be identified removing the selector cover(side cover) and visually identifying the straight cut gears-all other muncie transmissions had conical cut(angle) gears.
The most well known Muncie transmissions are the M20(wide ratio), M21(close ratio), and the M22(rock crusher).
Although not mentioned much, there was also an M23 transmission that was used, beginning in 1970. The M23 is recognized by a 26-spline(fine) input shaft and a large output shaft that requires a T-400 driveshaft yoke.
Although some claim that the M23 is a 'rock crusher', it is indicated that this box was assembled in both wide and close ratio components and also with straight cut gears common to the rock crusher (M22) transmission.
This chart, so far, has been very accurate in identifying the muncie trans. over the years, so I wanted to share. It sure seems alot of the muncies out there have made their homes in the tri-5's, so I think it would be good to have it here for everyone to use.
Jay
