- Wheeling Avenue, Muncie, IN 47304 765-284-1211 1-800-884-5088. Site By: Red Elephant Digital Media. Close this module. Transmission prevention,.
- Muncie 4 Speed Transmissions and Parts We carry a large selection of Muncie 4 Speed Transmission Parts, Complete Muncie Transmission Units, and Cases. We also offer Transmission Rebuild Service and Case Repair. If you don't see what you need, call us toll-free at 1-877-614-4327.
- If you have an automatic transmission the transmission dipstick which is generally easily visible in the engine bay, is a constant reminder of regular automatic transmission maintenance. Muncie and Borg-Warner T-10 and Super T-10 4-speed manual transmissions sit underneath the car hidden away like a groundhog burrowed deep in a ground hole.
Casting | Year(s) | Ratio | ||
3831704 | 1963 Only | M20 2.56 1st | M21 2.20 1st | |
3851325 (1) | 1964 - 1965 | M20 2.56 1st | M21 2.20 1st | |
3885010 | 1966 - 1967 | M20 2.52 1st | M21 2.20 1st | M22 2.20 1st |
3925660 | 1968 - 1969 | M20 2.52 1st | M21 2.20 1st | M22 2.20 1st |
3925661 | 1970 - 1974 | M20 2.52 1st | M21 2.20 1st | M22 2.20 1st |
(1) The M22 case casting is unknown at this time | ||||
Years | Type | Ring(s) | Ratio | Reverse |
1963 - 1965 | M20 | None | 2.56 / 1.91 / 1.48 / 1.00 | 2.64 |
1966 - 1975 | M20 | Two | 2.52 / 1.88 / 1.46 / 1.00 | 2.59 |
1964 - 1975 | M21 | One | 2.20 / 1.64 / 1.28 / 1.00 | 2.26 |
1967 - 1972(2) | M22 | None | 2.20 / 1.64 / 1.28 / 1.00 | 2.26 |
Saginaw M20 | ||||
M20 | One | 2.54 / 1.80 / 1.44 / 1.00 | ||
Ratio of drop between gears | ||||||||
Transmission | 1st | 2nd | % Reduction | 3rd | % Reduction | 4th | % Reduction | Reverse |
M20 (63-65) | 2.56 | 1.91 | 25.39% | 1.48 | 22.51% | 1.00 | 32.43% | 2.64 |
M20 (66>) | 2.52 | 1.88 | 25.40% | 1.46 | 22.34% | 1.00 | 31.51% | 2.59 |
M21/M22 | 2.20 | 1.64 | 25.45% | 1.28 | 21.95% | 1.00 | 21.88% | 2.26 |
Years | Type | Ring(s)/Groove(s) | Input Splines | Output Splines |
1963 - 1965 | M20 | None | 10 | 27 |
1966 - 1970 | M20 | Two | 10 | 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(1) | M22 | None | 10 | 27 |
1970 - 1972(2) | M22 | None | 26 | 32 |
(1) All M22 applications except454 engine.
(2) 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 ratiotransmissions are designated M21 or M22 depending on the gear set. From1963 to 1965 the close ratio M21 was ordered under the M20 RPO code and thefactory decided whether to install a wide ratio M20 or close ratio M21depending on the rear axle ratio specified. From 1966 on, the customer coulddecide the transmission selection.
The M20 and M21 have the same cut to the gears, theM22 is a straighter cut resulting in a greater strength. Since the M20 and M21look the same one way to tell them apart (aside from the grooves on the inputshaft) is the tooth count on the cluster gear.
1963-1965:
M21 tooth count - 27, 22, 19, 17
M20 tooth count - 29, 22, 19, 17
The letter M was used to ID the Muncie plant for the Muncie 3 speed, so P was the next logical letter. The letter O would add confusion since it resembles zero. The serial number is a date code the transmission was built for a particular year. Serial numbers from 1963 to 1966 included only the month and day. Muncie Transmission is back! General Motors stopped installing 'Muncie' 4 speeds in 1974. Complete units were able to be purchased from GM until the late 1970's. Parts trickled out.
1966-1974:
M21 tooth count - 27, 22, 19, 17
M20 tooth count - 25, 22, 19, 17
Muncie Transmission Parts
There are 7 different input shaft possibilities on a Muncie. All 26 splineinputs came with 32 spline output shafts and all 10 spline inputs came with 27spline output shafts. It is commonly mistaken that all 'fine spline'26 spline input shafts are M22 transmissions. The M22 transmission has a 20degree helix angle on the gear set as opposed to a 45 degree angle found on theM20 and M21 and were made with a higher nickel alloy. The straighter angle wasdesigned to produce less end loading of the gear train and less heat butcreated more noise, thus the nickname 'Rock Crusher' was born.Another misconception is if you have a drain plug you have a M22. This was onlytrue when the first M22 boxes were created; all 3925661 castings (1970-1974)had drain plugs.
Partial or 'concealed/confidential' VIN Stamping
Most transmissions since 1962 will also have a CON VIN (concealed orconfidential VIN, whichever term one likes) stamped in the case generally alongthe top ridge or even on a mounting surface such as the flange mounting thetail shaft to the main case noting the original car it was installed in. Thestamped CON VIN is the same that is stamped on the engine pad in all 1968 andlater Chevelles, and generally 1966 & 1967 SS396
Most plants stamped the CON VIN on the top whilesome stamped it on the side near the date code. Characteristics of the VINstamp, including the location, type size of the stamp, and the method(individual or 'gang' stamped) was chosen by the individual assembly plant.
Muncie Transmission Parts
1963 through 1966
Date codes from 1963 to 1966 included only the month & day; such asP0110 indicates January (01) 10th day (10).
1967 and 1968
In 1967 and 1968, the date code got a year designator and a letterdesignator for the month such as P8A01, meaning 1968 (8), January (A) 1st (01).Note that a Muncie dated with a September to December build date was actuallybuilt the prior calendar year. An example would be the date code P8T13, meaning1968 (8), December (T), 13th. The transmission was assembled December 13, 1967for the 1968 model year. Likewise a P8S28 stamp means 1968 (8), September (S),28th of the calendar year 1967 for a 1968 Chevelle.See second example below.
1969 through 1974
The 1969 to 1974 Muncie got a ratio designating letter at the end of thedate code. An example would be P2C25B. This decodes to 1972 (2), March (C),25th, M21 (B).
Note: The ratio designation letter didn't appear until around October 1,1968 for the 1969 model year so any Muncie in a 1969 Chevelledated August (M) or September (P) would probably not have the A, B, or Cdesignation.
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
Main Case
Muncie Transmission Seal
3831704 | 1963 Only small 6207NR Front Bearing ,Pat. Pending, 7/8' Bore |
3839606 | 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 (3) | 1968 - 1969 1' Bore Patent Number |
3925661 | 1970 - 1974 (some early 1975 cars) 1' Bore Patent Number |
(3) Colvin's 'by the numbers' book notes that Muncie data shows 1968 and 1969 M22 transmissions received main case #3925661. All documented M22 transmissions have the #3925660 main case. It is unclear why there is the discrepancy. | |
Muncie Transmission Gear Ratio Chart
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 & Oldsmobile Long Tail Driver Speedo 27 Spline |
3857584 | 1966 - 1970 Passenger side speedometer, 27 spline (all except Chevelle) |
3978764 | 1970 - 1974 passenger speedometer, 32 spline output (Chevelle only) |
Side Cover
Muncie Transmission Wiki
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 boss bolt on type w/ TCS switch on 3-4 (not verified) |
3952648 | 1970-74 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. |