Manual Transmissions - Group 4.000
| TRANSMISSION GEAR RATIO | 1ST | 2ND | 3RD | 4TH | REV |
| Saginaw 3-speed w/overdrive *=locked in O.D. |
2.85 *1.995 |
1.68 *1.176 |
1.00 *0.700 |
n/a | 2.95 |
| Saginaw Standard 3-speed Manual (L6/283) | 2.85 | 1.68 | 1.00 | n/a | 2.95 |
| Saginaw Standard 3-speed Manual (327) | 2.54 | 1.50 | 1.00 | n/a | 2.63 |
| B-W H.D. 3-speed Manual (L6/283) | 2.86 | 1.72 | 1.00 | n/a | 2.86 |
| B-W H.D. 3-speed Manual (327/396) | 2.41 | 1.57 | 1.00 | n/a | 2.41 |
| Saginaw M20 | 3.11 | 2.20 | 1.47 | 1.00 | 3.11 |
| Saginaw M21 | 2.54 | 1.80 | 1.44 | 1.00 | 2.54 |
| Muncie M20 | 2.52 | 1.88 | 1.46 | 1.00 | 2.59 |
| Muncie M21 | 2.20 | 1.64 | 1.28 | 1.00 | 2.26 |
| Transmission Gear Ratio Drop Between Gears | |||
| Saginaw 3-speed w/overdrive *=locked in |
1st to 2nd - 41.05% * 1st to 2nd - 41.05% |
2nd to 3rd - 40.48% * 2nd to 3rd - 40.48% |
3rd to O.D - 30% |
| Saginaw Standard 3-speed Manual (L6/283) | 1st to 2nd - 40.94% | 2nd to 3rd - 40.48% | |
| Saginaw Standard 3-speed Manual (327) | 1st to 2nd - 40.94% | 2nd to 3rd - 33.33% | |
| B-W H.D. 3-speed Manual (L6/283) | 1st to 2nd - 39.86% | 2nd to 3rd - 41.86% | |
| B-W H.D. 3-speed Manual (327/396) | 1st to 2nd - 34.85% | 2nd to 3rd - 36.31% | |
| Saginaw M20 | 1st to 2nd - 29.26% | 2nd to 3rd - 33.18% | 3rd to 4th - 31.97% |
| Saginaw M21 | 1st to 2nd - 29.13% | 2nd to 3rd - 20.00% | 3rd to 4th - 30.50% |
| Muncie M20 | 1st to 2nd - 29.40% | 2nd to 3rd - 22.34% | 3rd to 4th - 31.50% |
| Muncie M21 | 1st to 2nd - 25.45% | 2nd to 3rd - 21.95% | 3rd to 4th - 21.88% |
3-speed manual transmission w/overdrive [RPO M10]
Standard Saginaw 3-speed transmission
Muncie 4-speed manual transmission. Note the speedometer cable exits on the passenger side. Because the speedometer cable exited on the passenger side of the Muncie 4-speed a hole was required in the firewall to accommodate the speedometer cable and grommet. The regular hole for Saginaw 4-speed, all 3-speeds & automatic transmissions under the steering shaft was simply blocked with a rubber plug. This operation was done on the final assembly line and not at Fisher Body.
Note this Powerglide firewall without hole.
Transmission Month Date Codes
| A - January | E - May | P - September |
| B - February | H - June | R - October |
| C - March | K - July | S - November |
| D - April | M - August | T - December |
P7B17 (February 17) date stamping on 1967 Muncie 4-speed transmission.
P7C09 (March 9) date stamping on a 1967 Muncie 4-speed transmission.
P7H21 (June 21) date stamping.
P7M08 (August 8, 1966) date stamping.
1967 was the first year to have the year stamped in the date code and the month represented by a letter code. Below is a 1966 model year Muncie; note the difference.
P0221 (February 21) date stamping on 1966 Muncie 4-speed transmission.
The year, plant, and sequence number was also stamped on the transmission.
1964 to 1968 Muncie 4-speed transmissions can be identified from later models
by the way the transmission arms attach. Early Muncie side covers had a
stud and the shift arm attached with a nut on the stud while the 1969 and later
model side covers had a hole and the shift arms attached with a bolt.
Early (64-68) side plate. Note the shift arms are held in place by a stud/nut
arrangement. The shifter rods used in the above photo are aftermarket Hurst rods.
Although no M-22 Muncie transmissions are known to be installed in 1967 Chevelles they were installed in Corvettes and the swap is a simple bolt-in affair. Here is a comparison between the M20/M21 gear set and the M22 gear set.
M20/M21
M22
The Saginaw 4-speed transmission was also used and shown for "M20 PROD V-8 ENG &
R.P.O. L30". Easily identified by the reverse gear being on the main case instead
of the tail housing.
Muncie 4-speed Identification
| Casting | Year(s) | Ratio | ||
| 3831704 | 1963 Only | M20 2.56 1st | M21 2.20 1st | |
| 3851325 | 1964 - 1965 | M20 2.56 1st | M21 2.20 1st | |
| 3885010 | 1965 - 1967 | M20 2.52 1st | M21 2.20 1st | M22 2.20 1st |
| 3925660 | 1968 - 1970 | M20 2.52 1st | M21 2.20 1st | M22 2.20 1st |
| 3925661 | 1970 - 1974 | M20 2.52 1st | M21 2.20 1st | M22 2.20 1st |
| Years | Type | Ring(s) | Ratio | Reverse |
| 1963 - 1965 | M20 | None | 2.56 / 1.91 / 1.48 / 1.00 | 3.16 |
| 1966 - 1974 | M20 | Two | 2.52 / 1.88 / 1.46 / 1.00 | 3.11 |
| 1963 - 1974 | M21 | One | 2.20 / 1.64 / 1.28 / 1.00 | 2.27 |
| 1967 - 1974 | M22 | None | 2.20 / 1.64 / 1.28 / 1.00 | 2.27 |
| Years | Type | Ring(s) | Spline | Input Shaft Tooth Count |
| 1963 - 1965 | M20 | None | 10 | 24 |
| 1966 - 1970 | M20 | Two | 10 | 21 |
| 1970 - 1974 | M20 | Two | 26 | 21 |
| 1963 - 1970 | M21 | One | 10 | 26 |
| 1970 - 1974 | M21 | One | 26 | 26 |
| 1966 - 1970 | M22 | None | 10 | 26 |
| 1969 - 1974 | M22 | None | 26 | 26 |
There are 7 different input shaft possibilities on a Muncie. All 26 spline inputs came with 32 spline output shafts and all 10 spline inputs came with 27 spline output shafts. It is commonly mistaken that all "fine spline" 26 spline input shafts are M22 transmissions. The M22 transmission has a 20 degree helix angle on the gear set as opposed to a 45 degree angle found on the M20 and M21 and were made with a higher nickel alloy. The straighter angle was designed to produce less end loading of the gear train and less heat but created more noise, thus the nickname "Rock Crusher" was born. Another misconception is if you have a drain plug you have a M22. This was only true when the first M22 boxes were created; all 3925661 castings (1970-1974) had drain plugs.
The M22 was only produced in a close ratio version. It would not have been sold with a 3.55 or higher (lower numerically) rear end ratio unless it has been changed by an owner somewhere along the line. This transmission is a carry-over from 1966 with no major changes. Although the M22 was available in the Chevelle model, records indicate that no Chevelle was ever fitted with one in 1967 and only 20 L88 427/430hp Corvettes were so equipped.
| Engine | Tag Number |
| RPO L34/L35 | 3870357 - M20 |
| RPO L78 | The L78 was installed in very limited numbers (reported 612 units sold) and no transmission information is available for this engine. |
| Optional | 3877459 - M21 (prior to 01/05/67) |
| Optional | 3879668 - M21 |
| Optional | 3879993 - M22 (None reported ever being installed in the 1967 Chevelle) |
| Production V8 | 3901103 |
| Production V8 - Optional | 3901104 |
| RPO L30 | 3890553 - M20 |
The serial number is a date code and indicates the particular year the transmission was built for. Serial numbers from 1963 to 1966 included only the month and day. P0101 indicates January (first 01) 1st (second 01). In 1967 and 1968, the serial number got a year designator and a letter designator for the month such as P8A01, meaning 1968 (8), January (A) 1st (01). Note that a Muncie dated with a December build date it was actually built the prior year. An example would be the date code P8T13, meaning 1968 (8), December (T), 13th. The transmission was assembled December 13, 1967 for the 1968 model year. The 1969 to 1974 Muncie got a ratio designating letter at the end of the serial number. An example would be P2R25B. This decodes to 1972 (2), October (R), 25th, M21 (B).
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
Type Codes: A ~ M20, B ~ M21, C ~ M22 (1969 and newer)
Assembly Date Code Location
| Transmission | Code Location |
| 3-speed (except Heavy Duty) | Left side of main case, on boss below and to the rear of the side cover. |
| 3-speed (Heavy Duty) | Right side of main case, just in front of extension housing. |
| 4-speed | Right side of main case, just in front of extension housing. |
| Date code example: | |
| Muncie 4-speed: P7D01 | P (Muncie), 7 (model year), April (D) 01. |
| TRANSMISSION GEAR'S RATIO | 1ST | 2ND | 3RD | 4TH |
| GM Overdrive 3-speed with OD Locked in | 1.995 | 1.176 | .0700 | n/a |
| GM Standard 3-speed Manual (L6/283) | 2.85 | 1.68 | 1.00 | n/a |
| GM Standard 3-speed Manual (327) | 2.54 | 1.50 | 1.00 | n/a |
| GM H.D. 3-speed Manual (L6/283) | 2.86 | 1.72 | 1.00 | n/a |
| GM H.D. 3-speed Manual (327/396) | 2.41 | 1.57 | 1.00 | n/a |
| GM Muncie (M20) 63-65 | 2.56 | 1.91 | 1.48 | 1.00 |
| GM Muncie (M20) 66-74 | 2.52 | 1.88 | 1.46 | 1.00 |
| GM Muncie (M21/M22) 63-74 | 2.20 | 1.64 | 1.28 | 1.00 |
| GM Powerglide | 1.76 | 1.00 | n/a | n/a |
| GM Turbo Hydramatic 400 | 2.48 | 1.48 | 1.00 | n/a |
| Transmission Gear Ratio Drop Between Gears | |||
| Standard 3-speed (L6/283) | 1st to 2nd - 41.05% | 2nd to 3rd - 40.48% | |
| Standard 3-speed (327) | 1st to 2nd - 40.95% | 2nd to 3rd - 36.71% | |
| H.D. 3-speed (L6/283) | 1st to 2nd - 39.87% | 2nd to 3rd - 41.87% | |
| H.D. 3-speed (327/396) | 1st to 2nd - 34.85% | 2nd to 3rd - 36.31% | |
| M20 (early) | 1st to 2nd - 25.39% | 2nd to 3rd - 22.51% | 3rd to 4th - 32.43% |
| M20 (late) | 1st to 2nd - 25.39% | 2nd to 3rd - 22.34% | 3rd to 4th - 31.51% |
| M21/M22 | 1st to 2nd - 25.45% | 2nd to 3rd - 21.95% | 3rd to 4th - 21.88% |
| Powerglide | 1st to 2nd - 43.19% | ||
| Turbo Hydramatic 400 | 1st to 2nd - 40.32% | 2nd to 3rd - 32.43% | |
Manual transmission part numbers
| Part Number | Reference | Fitment |
| 3901103 | AIM - M20/A1 | RPO M20 with production V-8 engine |
| 3901104 | AIM - M20/A1 | RPO M20 - Optional |
| 3890533 | AIM - M20/A1 | RPO M20 with RPO L30 327/275hp engine |
| 3870357 | AIM - M20/A1 | RPO M20 13817-867 & RPO L35 396/325hp engine |
| 3879668 * | AIM - M20/A1 | RPO M21 |
| 3879993 | AIM - M20/A1 | RPO M22 |
| 3873892 | AIM - M10/A3 | RPO M10 3-speed with overdrive |
| * 3879668 was 3877459 - revised in 1967 but date uncertain | ||
Muncie 4-speed Casting Numbers
Main Case
| 3831704 | 1963 Only small 6207NR Front Bearing ,Pat. Pending, 7/8" Bore |
| 3839606 | 1963 - 1964 Regular Bearing Pat. Pending, 7/8" Bore |
| 3864_____ | 1964 Milled off last 3 digits 7/8" Bore Patent Pending |
| 3851325 | 1964 -1965 7/8" Bore Patent Pending Mostly 1964 |
| 3851325 | 1964 –1965 7/8" Bore Patent Number |
| 3885010 | 1966 -1967 1" Bore Patent Number |
| 3925660 | 1968 – 1970 1" Bore Patent Number |
| 3925661 | 1970 – 1974 (some early 1975 cars) 1" Bore Patent Number |
Tail Housing
| 3831731 | 1963 "Thin Fin Tail" Driver speedometer 27 spline |
| 3846429 | 1963 "Thin Fin Tail" Driver speedometer 27 spline |
| 3846429 | 1963-1965 Regular thick web, driver speedometer, 27 spline |
| 9779246 | 1964 – 1965 Pontiac Catalina Long Tail Driver Speedo 27 Spline |
| 3857584 | 1966 – 1970 Passenger side speedometer, 27 spline |
| 3978764 | 1970 – 1974 passenger speedometer, 32 spline output |
Side Cover
| 3831707 | 1963-1965 Early side cover stud type shift shafts |
| 3884685 | Cover issued with "584" tail stud type shift shafts |
| 3950306 | Short boss with bolt on type shift shafts - no switches |
| 3952642 | Long boss bolt on type w/ TCS switch on 3-4 |
| 3952648 | Short boss bolt on type w/ TCS switch on 3-4 |
| 335308 | Long boss bolt on type with neutral safety switch. Some have a boss for the switch that is cast but not machined on 1-2. |
