MY CHEVELLE HAS TRANS TAIL# IS 3978764 CASE COVER IS 3950306 AND MAIN CASE IS 3925661 NO DATE CODE OR VIN STAMP BUT DOES HAVE THIS # CCO-43639 WHERE VIN USALLY IS, DOES ANYONE KNOW THAT CODE THANKS JIM

Jim,

The CC0 43639 is an over the counter replacement case:
C = Chevrolet
C = Case
0 = Year - could be 1970, 1980 or 1990 etc.
43639 is the sequence number (starting at 40000)

The 3950306 side cover is a 1969 only piece I believe as all 1970 and later Muncies had the TCS switch boss on the 3-4 shift shaft. The 3978764 extension housing is 1970 M22 or 1971-74 M20/M21/M22 piece. If I were a betting person, I would bet that your transmission quite probably was pieced together and without knowing the history there is no way to tell.

So, there is no way to tell whether it is an M20, M21, or M22 without removing the side cover to check the helix angle of the gears.

As David said, the gear helix angle will tell if its an M22 or an M20/M21...

A quick check of the first gear ratio will determine if its an M20 (wide ratio, usually 2.52 :1 first gear) or an M21/M22 (close ratio, 2.20:1 first gear)... iF it is the close ratio, then you have to pull the cover... Pup the trans into first gear and spin the input shaft while counting how many times the output shaft spins...

TOOK SIDE CASE OFF HAS STRAIGHT CUT GEARS LIKE 22 WOULD HAVE, IS THE BIG TAIL SHAFT CORRECT FOR A MAY 70 MODEL CAR OR IS IT SUPPOSE TO HAVE THE SMALLER OUTPUT THANKS

The large output shaft would be correct for a May 1970 vehicle.

Does any know what the going price on a NOS 69 M22? Like never been run.

A friend just got a like new 72 for a grand.