John McGraw

Maybe on of you mid year guys can help me on this one. I bought a trailer load of parts posing as a 59, and in the parts is a muncie transmission that I need to identify. My knowledge of any parts beyond 62 is very limited. The front case is part # 3851325, the tailshaft case is 3857584, and the case is stamped P0804. Can someone tell me which transmission this is and and what year cars it was used in? Thanks :seeya

Ron D

From what my books show the rear case should be 3787066 55-62 8cyl and the main case is a no show, sorry

JmpnJckFlsh

John, Ron is correct; neither part is a Corvette part number.

From the date stamp, it sounds like the main case is from a 70 vehicle, but the date stamp format typically has an alpha character for the month. For example, I would expect P0B04A for a wide ratio Muncie build February 4, 1970. Are you sure the "8" isn't a "B". Perhaps other GM passenger cars used different build date formats, but I would be surprised.

John McGraw

Thanks Chuck, I will look at the stamp, you are probably right that the character is a B. Is this a M20, M21, or M22? :seeya

JmpnJckFlsh

This is another difference from 70 era Corvette transmission build date stamps. Typically they have an alpha suffix identifying the type transmission; A=wide ratio, B=close ratio, C=M22. Your build date stamp doesn't have the alpha suffix. :confused:

Some of the guys here can probably tell you how to identify the type transmission by counting the input gear teeth, but I have never committed that to memory. I believe the input shaft on the wide ratio should have two grooves, the close ratio has one groove, and the M22 has no grooves, but I am groping in the dark with a bad memory. :D


[Modified by Chuck Sangerhausen, 9:10 AM 10/9/2001]

JohnZ

Your Muncie has a '64-'65 main case (7/8" countershaft) and a '66-'70 tail housing. The P0804 code indicates an August 4th build date, most likely in '65 (Muncies didn't get a year code until '67, and didn't get the ratio code as the last digit until '69).

There were seven different input shafts, and only the original Muncie production shafts had "groove" identification - most of the GM service parts and aftermarket parts had no "grooves" at all. Generally speaking, all input shafts prior to 1970 were 10-spline, and had 27-spline outputs; 1970 and later had 26-spline inputs and 32-spline outputs. '63-'65 M20's had 24 teeth on the input with no "grooves", and later M20's had 21 teeth and two "grooves". All M21's had 26 teeth and one "groove". Original M22's had no grooves, 26 teeth, and a 20-degree helix angle on the gears instead of 45 degrees.

Unless it was a service replacement, it should also have a 9-digit VIN derivative stamped adjacent to the Muncie code which will identify its model year, what it was originally installed in, and at which assembly plant.

John McGraw

John, There is a vin derivative stamp at the top flange where it mounts to the bellhousing but is only 5 numbers 48498. also scratched into the mold by hand was 6-4 followed by a large R and then a roman numeral 3. they were obviously done by hand and I would guess that it would indicate date and shift but who knows. Just planing on selling the transmission but wanted to know what it is if asked. It is a 10 spline no groove input but I guess I will have to open it to find out what it is. :seeya