How Do You Know What Muncie You Have
Muncie iv-speed Manual (Grouping four.000) - Casting Numbers
| Casting | Year(s) | Ratio/M20 | Ratio/M21 | Ratio/M22 |
| 3831704 | 1963 But | M20 two.56 1st | M21 2.20 1st | due north/a |
| 3851325 (1) | 1964 - 1965 | M20 two.56 1st | M21 2.20 1st | n/a |
| 3885010 | 1966 - 1967 | M20 2.52 1st | M21 two.20 1st | M22 2.20 1st |
| 3925660 | 1968 - 1969 | M20 2.52 1st | M21 2.20 1st | M22 2.20 1st |
| 3925661 | 1970 - 1974 | M20 ii.52 1st | M21 two.xx 1st | M22 2.20 1st |
| (1) The M22 case casting is unknown at this fourth dimension | ||||
| Years | Type | Ring(due south) | Ratio | Contrary |
| 1963 - 1965 | M20 | None | 2.56 / 1.91 / i.48 / 1.00 | two.64 |
| 1966 - 1975 | M20 | 2 | ii.52 / 1.88 / 1.46 / 1.00 | two.59 |
| 1964 - 1975 | M21 | One | ii.xx / 1.64 / ane.28 / 1.00 | 2.26 |
| 1967 - 1972(2) | M22 | None | 2.20 / 1.64 / 1.28 / 1.00 | 2.26 |
| Saginaw M20 | ||||
| M20 | I | 2.54 / one.eighty / i.44 / ane.00 | ||
| Ratio of driblet betwixt gears | ||||||||
| Manual | 1st | 2nd | % Reduction | 3rd | % Reduction | quaternary | % Reduction | Reverse |
| M20 (63-65) | 2.56 | 1.91 | 25.39% | i.48 | 22.51% | 1.00 | 32.43% | 2.64 |
| M20 (66>) | 2.52 | 1.88 | 25.40% | 1.46 | 22.34% | 1.00 | 31.51% | ii.59 |
| M21/M22 | two.20 | 1.64 | 25.45% | 1.28 | 21.95% | ane.00 | 21.88% | 2.26 |
| Years | Type | Ring(s)/Groove(southward) | Input Splines | Output Splines |
| 1963 - 1965 | M20 | None | 10 | 27 |
| 1966 - 1970 | M20 | Two | ten | 27 |
| 1971 - 1974 | M20 | Two | 26 | 32 |
| 1963 - 1965 | M21 | One | 10 | 27 |
| 1966 - 1970 | M21 | One | 10 | 27 |
| 1971 - 1974 | M21 | One | 26 | 32 |
| 1965 - 1970(ane) | M22 | None | 10 | 27 |
| 1970 - 1972(two) | M22 | None | 26 | 32 |
(1) All M22 applications except 454 engine.
(two) All 454 Chevelle applications. The M22 was produced in 1973 and 1974 for other GM divisions.
All wide ratio transmissions are designated M20 and close ratio transmissions are designated M21 or M22 depending on the gear fix. From 1963 to 1965 the close ratio M21 was ordered nether the M20 RPO lawmaking and the manufactory decided whether to install a wide ratio M20 or close ratio M21 depending on the rear axle ratio specified. From 1966 on, the client could determine the manual selection.
There is strong testify the Saginaw M20 wide ratio transmission did not appear before February/March of 1966, so all M20 four-speeds are assumed to be Muncie earlier this appointment. If anyone as documented proof, such as a warranty menu (Protect-O-Plate) showing a Saginaw coded M20 (R) prior to February/March of 1966 is encouraged to ship a readable prototype of the warranty carte du jour for verification.
The M20 and M21 have the aforementioned cut to the gears, the M22 is a straighter cut resulting in a greater strength. Since the M20 and M21 look the same i way to tell them apart (aside from the grooves on the input shaft) is the molar count on the cluster gear.
1963-1965:
M21/M22 molar count - 27, 22, 19, 17
M20 tooth count - 29, 22, xix, 17
1966-1974:
M21/M22 tooth count - 27, 22, nineteen, 17
M20 tooth count - 25, 22, 19, 17
At that place are 7 different input shaft possibilities on a Muncie. All 26 spline inputs came with 32 spline output shafts and all x spline inputs came with 27 spline output shafts. Information technology is normally mistaken that all "fine spline" 26 spline input shafts are M22 transmissions. The M22 transmission has a twenty degree helix angle on the gear set every bit 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 rut but created more racket, thus the nickname "Rock Crusher" was built-in. Another misconception is if yous 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 bleed plugs.
Partial or "concealed/confidential" VIN Stamping
Nearly transmissions since 1962 will likewise take a CON VIN (concealed or confidential VIN, fractional VIN, or VIN derivative - whichever term one likes) stamped in the case mostly along the acme ridge or fifty-fifty on a mounting surface such as the flange mounting the tail shaft to the main case noting the original auto it was installed in. The stamped CON VIN is the same that is stamped on the engine pad in all 1968 and later Chevelles, and generally 1966 & 1967 SS396 Chevelles with an alphanumeric prepare of characters similar 7K123456; model yr, associates plant, and vehicle sequence number. The engine and transmission were stamped at the same time past the final associates constitute
Almost plants stamped the CON VIN on the top while some stamped it on the side well-nigh the appointment code. Characteristics of the VIN stamp, including the location, blazon size of the postage, and the method (individual or 'gang' stamped) was chosen by the individual assembly establish.
1963 through 1966
Date codes from 1963 to 1966 included only the month & day; such as P0110 indicates Jan (01) 10th day (10).
1967 and 1968
In 1967 and 1968, the date code got a year designator and a letter designator for the month such as P8A01, significant 1968 (8), Jan (A) 1st (01). Note that a Muncie dated with a September to December build date was actually congenital the prior agenda twelvemonth. An instance would be the engagement code P8T13, meaning 1968 (8), December (T), 13th. The transmission was assembled December 13, 1967 for the 1968 model year. Likewise a P8S28 stamp means 1968 (8), September (S), 28th of the calendar year 1967 for a 1968 Chevelle. See 2d example below.
1969 through 1974
The 1969 to 1974 Muncie got a ratio designating letter at the stop of the date code. An example would be P0C25B. This decodes to 1970 (0), March (C), 25th, M21 (B).
Notation: The ratio designation alphabetic character didn't appear until around October 1, 1968 for the 1969 model year and so any Muncie in a 1969 Chevelle dated August (M) or September (P) would probably not take the A, B, or C designation.
| Date codes: | |||
| A ~ Jan | B ~ February | C ~ March | D ~ Apr |
| East ~ May | H ~ June | K ~ July | M ~ August |
| P ~ September | R ~ October | S ~ November | T ~ Dec |
Type Codes: A ~ M20, B ~ M21, C ~ M22
1964
Hither is an instance from a 1964 Chevelle from Fremont, CA. Note the H103065 stamped on the flange and the date is shown by the P1030 stamping in the upper right of this photograph. The VIN derivative stamping positively identifies this equally a 1964 Fremont Chevelle considering the letter of the alphabet "H" was simply used in 1964 for Fremont.
Another Fremont instance equally noted past the leading "H" in the VIN derivative.
1966
Note 1966 date format, February 24
1967
1967 Muncie coded P7S29 for November 29, 1966.*
1967 Muncie coded P7T21 for December 21, 1966.*
* Annotation the extra smaller "seven" or peradventure "v" subsequently the dates. The exact significant of this character is non known; there are suspicions, but no facts. If you take a Muncie with a similar grapheme after the appointment, tin can go a photograph of it and KNOW whether it'southward an M20, M21, or M22, delight pass it along.
1968
1968 Muncie transmission tag #3924706. Date stamped P8P27 for Muncie, September 27, 1967 and partial VIN of 18K116891. Reported to be M21 merely cannot observe tag number to verify.
1968 Muncie coded P8S28 for Nov 28, 1967.
1968 Muncie coded P8S15 for Nov 15, 1967
Same transmission above with partial VIN stamping.
1968 Muncie coded P8C07 for March 27, 1968.
Same manual in a higher place with partial VIN stamping.
1969
Notation early 1969 Muncie (September four, 1968) stamping without the type (A, B, or C) designation. The ratio designation letter didn't appear until around October 1, 1968 for the 1969 model twelvemonth.
1969 Muncie P9S11 ~ November 11, 1968 - M20
1969 Muncie P9T04A ~ December 4, 1968 - M20
1969 Muncie P9A31C ~January 31, 1969 - M22 with partial VIN of 19K405888.
1969 Muncie P9C15A ~ March 15, 1969 - M20
1970
P0R23A ~ M20 dated October 23, 1969
P0R29A ~ M20 dated October 29, 1969. Partial VIN for Oshawa, ON Chevelle.
P0T30C ~ M22 dated December thirty, 1969.
P0A21A ~ M20 dated January 21, 1970.
P0B02C ~ M22 dated February 2, 1970.
P0B24B ~ M21 dated Feb 24, 1970.
P0C17A ~ M20 dated March 17, 1970
P0H18B ~ M21 dated June eighteen, 1970
WO stamp establish on a 1970 Flint LS6 M22.
Warranty transmission. Note CT0 (Chevrolet, Transmission, 1970) and 42862 serial number.
1972
P2P28A ~ M20 dated September 28, 1971.
P2E15C ~ M22 dated May 15, 1972
Manual Identification
1964 to 1968 Muncie 4-speed transmissions can be identified from subsequently models by the mode the manual arms attach. Early Muncie side covers had a stud and the shift arm attached with a nut on the stud while the 1969 and afterwards model side covers had a pigsty and the shift arms attached with a bolt.
Those installing a 1969 or later Muncie into 1964-1968 Chevelle and using a Hurst Contest Plus shifter must get the proper shifter tower assembly for the 1964-1968 Chevelle and the installation kit for the 1969-1972 Muncie due to the shift arms bolting onto the transmission differently. The same is true if y'all are going to install a 1964-1967 Muncie transmission into a 1968-1972 Chevelle. The Hurst Contest Plus Shifter fits both with and without console.
| Year Chevelle | Muncie Type | Shifter Number | Installation Kit Number |
| 1964-1967 | Muncie (451) | 3917308 | 3733163 |
| 1968 | Muncie (451) | 3918014 | 3733163 |
| 1969-1972 | Muncie (452/453) | 3918014 | 3737834 |
| 1973-1974 | Muncie (453) | 3916848 | 3737897 |
If using a Hurst Super Shifter on a Muncie at that place is only ane shifter and one installation kit. The shifter is #3917535 and the installation kit is #3738616. This shifter is NOT vehicle specific so they will non fit a panel, and probably not a bench seat due to their location, and floor pan modifications are generally required.
The Saginaw iv-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 example instead of the tail housing.
The proper Hurst Competition Plus system for a 1966-1967 Saginaw is shifter #3917307 and installation kit #3734297.
Early (64-68) side plate. Note the shift arms are held in place by a stud/nut arrangement.
Late (69 >) side plate. Notation the shift arms are held in place past bolts.
Part Number Tags
Some of these tag numbers/codes may apply to other Chevrolet models (not just Chevelles) in these years.
Those listed in accept sample images.
Those listed in accept been found simply numbers do not appear in whatsoever Chevelle Associates Manual.
1965 M20 3857577
1965 M20 3857578 Z16
1966 M20 3890534 L78
1966 M22 3879993 L78
1967 M20 3870357 L34, L35, L79
1967 M22 3879993 L78
1968 M20 3915079 L34, L35, L78, L79
1968 M21 3915085 L34, L35, L78, L79
1968 M22 3925626 L78
1969 M20 3950301 L48, L35
1969 M22 3950318 L78, COPO L72
1970 M21 3968012 (disc.3-eleven-lxx)
1971 M20 3974484 WN
1971 M22 3978766 WO
1972 M20 3974484 WN
1964 M20
1966 L34/L35 M20
Found on 1966 L78, M21
1967 M21
Found on 1968 L35, M20
Institute on two 1968s, reported to be M21 merely number (3924706) cannot be establish to verify
Found on 1969 L78, M21
1969 L34, L78, M20
1970 L34/LS3/L48/L78, M20
1970 L34/LS3/L48/L78, M21
1970 LS6/LS6, M22
Plant on 1972 LS3, M20
Found on 1972 LS5, M22
If you're lucky enough to notice one of these attached to your Muncie 4-speed it indicates the GM part number of the transmission assembly aiding you lot further in identifying the transmission. Exist forewarned these tags are being reproduced, see case below, so be wary of the tag'south condition before accepting the fact it is the correct transmission for your application. The WB and WO suffix in the 2 examples above besides correspond to the circulate codes on the build canvass.
Reproduction transmission tag.
M20/M21 vs. M22 gear sets & input shaft
From left to right:
No grooves - 1963-1965 M20 and 1965-1972 M22
Two grooves - 1966-1970 M20 (1971-1974 M20 has 26 splines every bit opposed to the 10 spline early unit shown here)
I groove - 1963-1970 M21 (1971-1974 M20 has 26 splines as opposed to the 10 spline early unit shown here)
The input shaft to a higher place is a 10-spline unit while the one below is a 26-spline unit. Note the much effectively splines on the one beneath.
Another ten-spline versus 26 spline comparison
Note thicker teeth on the M22 input shaft equally well as the straighter cut gears.
RPO M20/M21 gear gear up - compare the angle cutting of the gears to the M22 beneath.
RPO M22 gear gear up
Warranty Replacement
Transmissions were also field of study to replacement, be it simply the case or the entire transmission. These volition accept a stamp something similar "CC" for Chevrolet Case or "CT" for Chevrolet Transmission. The same data well-nigh fractional VINs on engine blocks besides applies to transmissions.
Muncie iv-Speed Casting Numbers
Main Case
| 3831704 | 1963 Only minor 6207NR Front Bearing ,Pat. Pending, vii/8" Bore |
| 3839606 | 1964 Regular Bearing Pat. Pending, 7/8" Bore |
| 3864_____ | 1964 Milled off last iii digits 7/8" Bore Patent Pending |
| 3851325 | 1964 - 1965 7/8" Bore Patent Pending By and large 1964 |
| 3851325 | 1964 - 1965 7/8" Bore Patent Number |
| 3885010 | 1966 - 1967 1" Bore Patent Number |
| 3925660 (three) | 1968 - 1969 1" Bore Patent Number |
| 3925661 | 1970 - 1974 (some early on 1975 cars) 1" Bore Patent Number |
| (three) Colvin's "by the numbers" volume notes that Muncie data shows 1968 and 1969 M22 transmissions received chief case #3925661. All documented M22 transmissions have the #3925660 main case. Information technology is unclear why there is the discrepancy. | |
Tail Housing
| 3831731 | 1963 "Thin Fin Tail" Driver speedometer 27 spline |
| 3846429 | 1964 - 1970 "Thin Fin Tail" Driver speedometer 27 spline |
| 9779246 | 1964 - 1968 Pontiac & OLong Tail Commuter Speedo 27 Spline |
| 3857584 | 1966 - 1970 Passenger side speedometer, 27 spline (1970 M20/M21 only) |
| 3978764 | 1970 - 1974 Passenger side speedometer, 32 spline output (1970 M22, all 1971 thru 1975) |
Side Cover
| 3831707 | 1963-1965 Early side cover stud type shift shafts |
| 3884685 | 1966-1968 Used with 3857584 tail stud type shift shafts |
| 3950306 | 1969 Short boss with bolt on type shift shafts - no switches |
| 3952642 | Long dominate bolt on type w/ TCS switch on three-4 (non verified) |
| 3952648 | 1970-74 Short boss bolt on type w/ TCS switch on 3-4 |
| 335308 | Long boss bolt on type with neutral prophylactic switch. Some have a boss for the switch that is bandage but not machined on ane-two. |
It should be noted that there are many different websites and publications with Muncie transmission information that seems to exist in conflict as to various casting numbers, input/output shaft splines, etc. I've tried to weed through equally much of this as I tin can and bring y'all the consensus of what's right. If you have some reference or documentation that contradicts anything here I'd beloved to hear from you.
Source: http://chevellestuff.net/qd/muncie.htm
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