Muncie 4-Speed Identification Guide - Chevy DIY.How to Identify a Muncie Four Speed: Build Date Codes, VINs, and Input Shaft
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Chevy 4 speed manual transmission identification. Manual Trans Reference GM 3, 4, 5 and 6 speeds V24
The next two digits are the day of the month, the 23rd, while the "B" in the last positions designates the Muncie M21, with "A" for the M20 and "C" for the M Identify Muncie to transmissions. These Muncies have the same serial number format, minus the gear ratio designation, so a spline and gear tooth count must be done. According to Nasty Z Both the M 21 and M 22 have 10 splines and 26 input gear teeth, however, the M 22 has "straight cut" gears, which are not as pointed as M 21 gears.
A native of New Haven, Conn. After working as a reporter in Oregon, he is now based back home in New Haven. Step 1 Inspect the transmission. Step 2 Locate the serial number to differentiate and up Muncie transmissions.
Step 3 Decode the serial number. Step 4 Identify Muncie to transmissions. Tips The input shaft runs from the transmission to the engine and is part of the transmission. The splines are on the shaft going into the engine and the input gear goes into the transmission. This is illustrated at the top of the Year One Tech page, while the input gears are illustrated at the bottom see Reference 2.
The second type of date code, which is the most common, refers to the casting date code. This type of date coding is used on engine blocks, heads, transmission main case, transmission tailhousing, transmission side cover, etc. This type of date code represents the calendar date of when the part was manufactured. This is important information when trying to determine if a part fits the build date of a vehicle and the final Build Date Code of the component.
Most of the Muncie four-speed transmissions will have a casting date code on the main case, extension housings, and side cover. The main case date code is usually found on the passenger side of the case just below the casting number. The extension housing date code can usually be found on the passenger-side of the case within a few inches of the casting number.
The side cover date code is usually found near the casting number. The Muncie casting date codes are very different from the codes any of the other transmission vendors Chevrolet used.
These codes can be difficult to read on some units and are comprised of two circles that are divided into two halves. One circle is the Date Marker and the other circle is referred to as the Status Marker. One half of the Date Marker circle will have a month designator for when the part was cast.
The month is determined by numbers 1 through 12, which correlate with the months of the year. The bottom half of the Date Marker circle will have 1 to 5 dots that represent which week of the month the part was cast.
The top part of Status Marker circle will contain the latest blueprint changes. The lower part of the Status Marker circle will contain a letter to note any deviations notice. It can be acceptable for the Status Marker circle to be blank. The Status Marker information was used by the Muncie plant to help track a problem part. Remember, all of these casting codes should precede the final production code of the transmission.
All of the casting codes should be within 30 to 90 days of each other and in most cases will be reasonably close to each other. Another way to confirm that the transmission is original to your car is most Muncie four-speed transmissions will have a Vehicle Identification Number VIN number stamped on the main case.
The engine and transmission were stamped at the same time by the final assembly plant. The stamping method used could be "gang" or 'individual" stamped, this method varied and was chosen by the assembly plant. The location of the VIN stamp can vary but it can usually be found on the top leading edge of the main case or on a mounting surface near the Build Date Code. The number of characters in the VIN stamp varied from plant to plant. However, the Corvette assembly plant in St.
Louis from was relatively consistent. The first character was the last digit of the model year. The following six digits were the last six digits of the VIN. For and newer Corvettes the first character was the letter "S," which was the designation for the St. Louis assembly plant. Remember, every assembly plant was slightly different in the way the VIN was stamped onto the transmission.
There is another way to quickly identify Muncie transmissions. All Muncie transmissions have a ring groove on the input shaft and counter gear.
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