1966 Chevelle

Manual Transmissions - Group 4.000

File Photo
3-speed manual transmission w/overdrive [RPO M10]

File Photo
Dash mounted lever to activate the Overdrive unit.

File Photo - 07/16/2011
The Chevelle 300, 300 Deluxe, and Malibu came standard with a 3-speed manual column shift transmission.

File Photo
Standard Saginaw 3-speed transmission

File Photo
Heavy Duty full synchromesh 3-speed Borg Warner T16 delivered as the standard transmission when the SS396 series was ordered.

The special 3-speed H.D. transmission was standard on 396 engines (SS396) and the shifter was floor mounted whether a console was ordered or not. The M13 was optional with other engines after March of 1966.

Courtesy Seb Dotson
Borg-Warner T16 H.D. 3-speed transmission stamped W1124, matching invoice on SS396 sold December 27, 1965.

File Photo
File Photo
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.

File Photo

File Photo - 02/04/2009

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

File Photo
P0221 (February 21) date stamping on 1966 Muncie 4-speed transmission.

11/24/2009
Partial VIN stamping from Flint.

File Photo
P7C09 (March 9) date stamping on a 1967 Muncie 4-speed transmission; (1967 was the first year to have the year stamped in the date code and the month represented by a letter code).

File Photo  File Photo
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.

File Photo
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 Ratio 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.If you are lucky and find the transmission tag (generally found on a lower bolt of the side cover), it will help identify a 1966 Muncie transmission. Unfortunately these metal tags are often discarded when repair or maintenance work is performed.

Engine Tag Number
RPO L34/L35 3870357 - M20
RPO L78 3890534 - M20 (after 11/5/65)
Optional 3879668 - M21 (prior to 11/5/65)
Optional 3877459 - M21
Optional 3890567 - M22 (prior to 11/4/65)
Optional 3879993 - M22 (limited sales)
Production V8 3884602 - 4 speed
RPO L30 3884603 - 4 speed
RPO L35 3890533 - M13
RPO L34/L78 3890536 - M13
File Photo


File Photo

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 Muncie (P), 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 examples:  
B-W H.D. 3-speed/Muncie 4-speed:  W1025/P1025 P (Muncie) or W (Warner), 1025 (October 25)
Saginaw 3-speed overdrive S (Saginaw) 10 25 (October 25)

TRANSMISSION GEAR RATIO 1ST 2ND 3RD 4TH REV
Saginaw 3-speed w/overdrive - *=locked in 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 1.56 1.00 n/a 2.41
Borg-Warner H.D. 3-speed Manual (L6/283) 2.86 1.72 1.00 n/a n/a
Borg-Warner H.D. 3-speed Manual (327/396) 2.41 1.57 1.00 n/a 2.41
Muncie M20 2.52 1.88 1.46 1.00 2.59
Muncie M21/M22 2.20 1.64 1.28 1.00 2.26
Saginaw M20 (283 built after March, 1966) 3.11 2.20 1.47 1.00 3.11
Saginaw M20 (327 built after March, 1966) 2.54 1.80 1.32 1.00 2.54

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 - 38.58% 2nd to 3rd - 35.89%  
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%  
Muncie M20 1st to 2nd - 25.39% 2nd to 3rd - 22.34% 3rd to 4th - 31.51%
Muncie M21/M22 1st to 2nd - 25.45% 2nd to 3rd - 21.95% 3rd to 4th - 21.88%
Saginaw M20 (283) 1st to 2nd - 29.26% 2nd to 3rd - 33.18% 3rd to 4th - 31.97%
Saginaw M20 (327) 1st to 2nd - 29.13% 2nd to 3rd - 26.67% 3rd to 4th - 24.24%

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 unreadable

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.