| Manual Transmission |
Input shaft
markings |
1st |
2nd |
3rd |
4th |
5th |
6th |
Muncie M-20/M-21
Close ratio |
1 groove |
2.20 |
1.64 |
1.28 |
1.00 |
*** |
*** |
Muncie M-20 / M-21
Wide ratio 1963-65 |
No groove |
2.56 |
1.91 |
1.48 |
1.00 |
*** |
*** |
Muncie M-20 / M-21
1963-65 only |
2 grooves |
2.52 |
1.88 |
1.46 |
1.00 |
*** |
*** |
Muncie M-22
Close ratio |
1 groove |
2.20 |
1.64 |
1.28 |
1.00 |
*** |
*** |
Borg Warner T-10
Close ratio |
*** |
2.20 |
1.64 |
1.31 |
1.00 |
*** |
*** |
Borg Warner T-10
Wide ratio |
*** |
2.54 |
1.75 |
1.51 |
1.00 |
*** |
*** |
Borg Warner Super T-10
Close ratio |
2 grooves |
2.43 |
1.61 |
1.23 |
1.00 |
*** |
*** |
Borg Warner Super T-10
Wide ratio |
3 grooves |
2.64 |
1.75 |
1.33 |
1.00 |
*** |
*** |
| Borg Warner T-56 6 spd |
*** |
3.36 |
2.07 |
1.35 |
1.00 |
0.80 |
0.62 |
Richmond T-10
4 spd #13040000070 |
*** |
2.43 |
1.61 |
1.23 |
1.0 |
*** |
*** |
|
Richmond T-10
#13040000069 |
*** |
2.64 |
1.75 |
1.34 |
1.0 |
*** |
*** |
Richmond T-10
#13040000072 |
*** |
2.88 |
1.91 |
1.33 |
1.0 |
*** |
*** |
Richmond T-10
#7021090 |
*** |
2.64 |
1.60 |
1.23 |
1.0 |
*** |
*** |
Doug Nash(Richmond)
5 spd manual |
*** |
3.27 |
2.14 |
1.57 |
1.23 |
1.00 |
*** |
ZF-6 Corvette 6 spd
93 & up incl
ZR-1 |
*** |
2.68 |
1.80 |
1.31 |
1.00 |
.075 |
.050 |
The primary Muncie 4-speed
transmission was marketed under Regular Production
Option (RPO) M20. M20 was the generic RPO for a 4-speed,
so note that the Saginaw 4-speed was also marketed under
RPO M20, but with slightly different gear ratios in a
significantly different case. In addition to the M20, a
close-ratio 4-speed was sold as M21, and a Heavy-Duty
close-ratio 4-speed was sold (at a much higher price and
much more limited application) as M22.
The buyer had
no choice as to the transmission manufacturer; use of
the aluminum-case Muncie or the cast-iron-case Saginaw
was determined for you by the factory as a function of
your model. M21 and M22 transmissions were even more
limited to specific models, with details of the
limitation depending upon the model year.
To
distinguish between Muncie types, if the Muncie was
built after 21-Oct-1968, the plant assembly-date stamp
contains one of three letters at the end of the build
code:
A = 2.52:1 Wide Ratio (M20)
B = 2.20:1 Close
Ratio (M21)
or
2.42:1 HD Close Ratio (MC1
3-speed)
C = 2.20:1 HD Close Ratio (M22 4-speed) aka,
"The Rockcrusher"
This suffix was used on all Muncie
assembly plant stamps from 21-Oct-1968 through 1974. See
the transmission decoding FAQ for other details. The
assembly plant stamp is normally located on the
passenger side of the transmission, arranged vertically
just in front of the tailhousing joint.
If the input
shaft is visible, the number of circumferential grooves
on the input shaft will also generally indicate the
Muncie type. Be careful, as 1963-65 M20 Muncies are like
later M22s in that they have no input shaft grooves;
however, the early M20 has only a 7/8-inch diameter
cluster pin, while the M22 has a 1-inch pin.
To
distinguish an early (pre-suffix) M22 from the other
Muncies when the transmission is on a car, note that all
M22s had the lower, forward, passenger-side maincase
boss drilled and tapped for a magnetic drain plug. This
wasn't done (by the factory) for M20/M21 until 1970.
While this boss could be drilled for a plug on a M20
after it left the factory - if the boss is undrilled
then the case definitely was not part of a M22.
The
M22 gears have a shallower mesh angle to reduce thrust
load and heat. If the gearbox cover is removed, the
difference in the angle between the M22 gears and the
gear angle used in the other Muncies is discernable.
Note in the photo below that on the M20/M21 the bottom
of the next tooth starts below the top of the preceding
tooth (i.e., they overlap), whereas on the M22 the angle
is such that the teeth actually have a small gap between
the top of one tooth and the bottom of the
next.
| Transmission |
First |
Second |
Third |
Fourth |
| GM Saginaw |
2.54 |
1.50 |
1.00 |
-- |
| GM Saginaw |
2.84 |
1.68 |
1.00 |
-- |
| GM Saginaw |
3.11 |
2.20 |
1.47 |
1.00 |
| GM Saginaw |
2.85 |
2.02 |
1.35 |
1.00 |
| Warner T-16 |
2.41 |
1.57 |
1.00 |
-- |
| Warner T-16 |
2.86 |
1.71 |
1.00 |
-- |
| Warner T-10 |
2.54 |
1.92 |
1.51 |
1.00 |
| Warner T-10 |
2.10 |
1.64 |
1.31 |
1.00 |
| Warner T-10 |
2.54 |
1.89 |
1.51 |
1.00 |
| Warner T-10 |
2.36 |
1.78 |
1.41 |
1.00 |
| Warner T-10 |
2.36 |
1.76 |
1.41 |
1.00 |
| Warner T-10 |
2.73 |
2.04 |
1.50 |
1.00 |
| Warner T-10 |
2.36 |
1.62 |
1.20 |
1.00 |
| B-W Super T-10 |
2.64 |
1.61 |
1.23 |
1.00 |
| B-W Super T-10 |
2.64 |
1.75 |
1.33 |
1.00 |
| B-W Super T-10 |
2.88 |
1.74 |
1.33 |
1.00 |
| B-W Super T-10 |
3.44 |
2.28 |
1.46 |
1.00 |
| B-W Super T-10 |
2.23 |
1.77 |
1.35 |
1.00 |
| B-W Super T-10 |
2.43 |
1.61 |
1.23 |
1.00 |
| B-W Super T-10 |
2.43 |
1.76 |
1.47 |
1.00 |
| B-W Super T-10 |
2.64 |
2.10 |
1.60 |
1.00 |
| B-W Super T-10 |
2.64 |
2.10 |
1.46 |
1.00 | |
|
| |