GM produced the Muncie 4-speed passenger car transmission from 1963-74.
Distinguishing features of the Muncie:
Muncie 7 bolt side cover Reverse in tailshaft Al
Saginaw 7 bolt side cover Reverse on cover Fe
Borg-Warner 9 bolt side cover Reverse in tailshaft Al or Fe
Muncie Serial numbers were done in three different variants during its
production run.
A serial # for 63-66 would look like this---P0503N---and decodes thus:
P=code for all passenger car Muncie 4 speed
05=month of build, 5=May
03=day of build
N=night shift
(these early boxes have no year of manufacture on them)
A serial # for 67-68 would look like this---P7T02---and decodes thus:
P=Muncie, like above
7=year of build, 1967
T=month of build (A Jan,B Feb,C Mar,D Apr,E May,H Jun,
K Jul,M Aug,P Sep,R Oct,S Nov,T Dec)
02=day of build
A serial # for 69-74 would look like this---P0C17A---and decodes thus:
P=Muncie, like above
0=year of build, 1970
C=month of build (same codes as above)
17=date of build
A=M20 (B=M21,C=M22)
In addition to the numbers stamped on the case, Chevy had a small
METAL TAG with a part number bolted to one of the transmission
bolts. Parts of this number show up on the build sheet & the
Protect-O-Plate.
1970 Camaro Muncie tag #s:
3952659-RPO M20 w/RPO L34, L48, & Z28
3968011-RPO M21 w/RPO L34 & Z28
3978766-RPO M22 w/RPO L78
3968012-RPO M22 w/RPO Z28
1971-74 Camaro Muncie tag #s:
(will list when I find them)
'63-68 Muncies had a nut threaded onto the end of the shifter forks
that held the shifter ears on them. 1969-74 had a bolt threaded into
the end of the forks.
'63-65 Muncies had 2.56 low in wide ratio and 2.20 in close ratio.
'66-74 wide ratio Muncies had 2.52 low and 2.20 in close ratio.
'65-70 M22s used the coarse spline input shaft. The fine spline input
shaft (26 spline) wasn't introduced until the '71 Camaro (1970 Chevelle
with 454 had the fine spline shaft already in 1970).
'71-74 M20s and M21s had the fine spline input shafts; M20s w/2
grooves, M21s w/1 groove.
The M-22 (prior to 1970) also had a fill plug *AND* a drain plug.
From 1970-74, all Muncies had the drain plug.
Muncies came in different ratios. The 63-66 M20 boxes had 2.56 first
gear. The M20 from 66-74 had 2.52 first gear. M21 & M22 boxes had 2.20
first gear. To determine these ratios from the gears themselves, count
teeth on front cluster gear and main drive gear. Divide these two and
multiply the result by the first gear set which should be 36/17.
(example: M22 has 27/26 X 36/17= 2.20)
GEAR TEETH COUNT
M20 (63-66) 29/24
M20 (66-74) 25/21
M21 & M22 27/26
Gear Ratios ('66-74) Gear Spread
1st 2nd 3rd 4th 1-2 2-3 3-4
M20 2.52 1.88 1.47 1.00 1.34 1.28 1.47
M21&22 2.20 1.64 1.27 1.00 1.34 1.29 1.27
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