Generally Speaking,
SL: I have a Muncie four-speed with the numbers P8D15 and 3025660. What year and model is it?KT: It is not always true, but generally the splined part of the input shaft of the M20 has two angular grooves and the M21 has one. The M22 has none.
BT: You can't always rely on the input shaft grooves. If it is out of the car put the trans in first gear and rotate the input shaft 1 revolution. Count the number of times the output shaft turns; this will tell you if it is a M20 wide ratio or M21, M22 close ratioes.
TT: I believe the casting number you have could be 3925660. This would be for a 1968- 69 Muncie box.
The other code you supplied is P8D15. I believe this is a build date:
P=Muncie, 8=year1968, D15=April 15.
You can compare this build date with the build date on the car and the motor to see if the Muncie is correct for the your car. There should also be six holes in the tailpiece and casting numbers on the side cover and tailpiece.
On transmissions which have been rebuilt, however, you will also see the differing years of the parts which were used in the rebuild.
Archivist: Tom Wilson
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