Muncie History

HISTORY and IDENTIFICATION

The Muncie 4-speed transmission was used with many different GM models and engine combinations from 1963-1974. The basic design and operation theory of the gearbox changed little during that time, though several design upgrades and modifications were made during the total production run.

The Muncie was used with most performance engines and is not to be confused with the Saginaw or Borg-Warner 4-speeds. The Muncie is distinguished from the Saginaw in that the reverse lever on the Muncie is mounted in the extension housing, where the Saginaw reverse lever is mounted in the side cover. The main difference between the Muncie and the Borg-Warner is that the Muncie has a 7 bolt side cover and the Borg-Warner has a 9 bolt side cover.

MUNCIE DATE CODING

Many Muncie 4-speed maincases, extension housings, and sidecovers have a casting date code. On maincases, the code is usually found on the passenger side of the case below the casting number. The extension housing code is usually within a few inches of the casting number also on the passenger side. Muncie casting date codes are very different from other transmission manufacturers. The code consists of two circles, both 1/2-inch in diameter and divided in half. One circle is called the date marker, the other the status marker.

The date marker has a month designator for when the part was cast or manufactured. This is represented by the numbers 1 through 12(Jan - Dec.). The opposite side of the date marker has between one and five dots, representing the week of the month. The easiest way to discern the proper date mark circle is to look for the week designator spots. Always check to see that the date marked precedes the final assembly stamp code. The status marker has the latest blueprint change number on one side of the circle, and a deviation notice letter on the other side if the part change letter is active. This information was only useful to the Muncie plant by allowing the tracking of problem parts. This circle is usually blank.

MUNCIE PARTS IDENTIFICATION

Muncie main drive gear and countergear parts are easily identified when the transmission is apart. The following table outlines the differences between the Muncie models.

MUNCIE MODEL/YEAR	MAIN DRIVE GEAR (TEETH)	MUNCIE MODEL/YEAR	COUNTERGEAR (TEETH)
M20 1963-65 Wide Ratio	24	M20 1963-65 Wide Ratio	17 19 22 29
M20 1966-70 Wide Ratio	21	M20 1966-74 Wide Ratio	17 19 22 25
M21 1963-70 Close Ratio	26	M21 1963-74 Close Ratio	17 19 22 27
M22 1965-70	26	M22 1965-72	17 19 22 27

MUNCIE 4-SPEED ALUMINUM
COMPONENT CASTING NUMBERS

YEAR	APPLICATION	MAINCASE CASTING#	EXTENSION HOUSING CASTING#	SIDECOVER CASTING#	FRONT BEARING RETAINER CASTING #
1965	Passenger Corvette Chevy II Chevelle	3851325	3846429* (to 2/65) 3857584 (after 2/65)	3831707	3851326
1966, 1967	Passenger Corvette Chevy II Chevelle Camaro(1967)	3885010	3857584	3884685	3851326
1968, 1969	Passenger Corvette Chevy II Chevelle Camaro	3925660**	3857584	3884685(1968) 3950306(1969)	3915020

*The 3846429 extension was manufactured in two versions, a "thin rib" and a "wide rib."
**Muncie data shows 1968 and 1969 M22 received maincase #3925661. All documented M22 transmissions have the #3925660 maincase. It's unclear as to why this discrepancy exists.

How can you tell if the transmission in your car is the one the car was originally built with? All original Muncie transmissions have ring grooves on the input shaft and counter gear. These grooves were put on for the Muncie assembly line workers to readily identify which input shaft to install and therefore shouldn't be used for positive identification of tranmsissions since many of these shafts have been replaced. Also several Muncie parts -primarily the maincase- were found to have documented "oddball" casting numbers on production vehicles. None of these maincases are shown on the original build records from the Muncie plant and should also not be used for identification purposes.
Many transmissions over the years have been rebuilt or replaced, upgraded from a 3-speed to a 4-speed etc. which can make identification somewhat difficult at times.
Shown below are some diagrams that will describe where the serial number is stamped on all transmission cases. The 9-digit code will tell you which division, year, model, assembly plant, and car the transmission was pulled from. The first digit tells what division the transmission is built for (Oldsmobile's number is 3). The second digit is the last digit of he model year (7=1967, 9=1969 etc.). The third digit is the code for the assembly plant the car was built in. The last six digits should match the last six digits of your V.I.N. (generally found on the door hinge of 1964-1967 models and on the left top side dash of 1968-72 models). If the numbers don't match, your transmission has been changed, though remember that even an original tranmission may have had parts swapped for repair work at some time through its life.

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