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The letter “P”, which stands for Muncie Plant, is always the beginning of the serial numbers for Muncie 4 speeds. P was chosen because it was the next logical letter, the letter M was already used to ID for the Muncie plant for the Muncie 3 speed while the letter O, resembles zero that might add confusion. The serial number is a date code the transmission was built for a particular year. 1963 to 1966 serial numbers includes only the month and day. P0101 would indicate January 1st. From 1967 to 1968 the serial number got a year designator and a letter designator for the month such as P8A01, which means January 1st 1968. A Muncie dated with a December build date, is actually built the prior year, this is one significant point to take note of. An example would be the date code P8T13. This is for a 1968 production car. The T stands for December and 13 is the day. To confirm this simply look at the VIN number. It will usually begin with a 18S101350 or a 28N12950. This means the Muncie was assembled December 13, 1967 for the 1968 model year. The VIN number will usually be a low number. 1969 to 1974 Muncies got a ratio designator at the end of the serial number. An example would be P4D23B. This equates to April 23, 1974, M21 ratio.
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Month Code Chart |
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Month |
Letter |
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January |
A |
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February |
B |
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March |
C |
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April |
D |
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May |
E |
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June |
H |
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July |
K |
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August |
M |
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September |
P |
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October |
R |
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November |
S |
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December |
T |
Ratio Code Chart Letter: A M20 Ratio Letter: B M21 Ratio Letter: C M22 Ratio
Note: Originally, the rings were corresponded with rings or grooves on the counter gear so that the assembler matched a one or two ring input with a one or two ring cluster. General Motors and the aftermarket produce some input shaft that has no identifying rings on them. GM stopped making inputs with these marks, possibly to save machining operations when manufacturing was stopped. Some come with a 1 inch counter shaft, while 3831704 and 3852325 castings come with a 7/8” counter shaft. In the years 1963 to 1966, there were some odd ball castings that were produced.
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MUNCIE Four 4 Speed TRANSMISSION Service Repair Manual is available now. |
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This is the same Muncie Transmission used on all the GM cars of the 60's & 70's era including Corvette, Camaro & Firebird very informative and illustrated with easy to follow directions. All the information you need to show you how to completely rebuild this Muncie transmission by yourself.
The manual is available in two versions:
For the printed version please click here
For the downloadable e-manual version click here
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