I just bought a Muncie 4-speed off of a guy I know. He said he wasn’t sure if it was an m20,m21,m22. But it had an aluminum case and I when I decoded what I could read of the "stamping", I found out it was a (P):4-speed Muncie, (7):made in 67, (S):assembled in November, on the (11):11th day. But I cannot read the last letter. It looks like the top-half of a 7, like the 7 was cut in half. So I don’t know, does anyone have a clue??? Can they be identified by any other means?

The 22 has a drain hole in the bottom.., L89SEDAN

Well, It has a drain plug on it. But my friend has a 21 with a plug.??

To elaborate on L89's statement, the M22 has a drain plug on the bottom of the pass. side and a fill hole on the same side, only higher in the case. However, ALL Muncies after '71, and the '70 M22 , have drain plugs. Maybe your friends' M21 is a 71-up trans?
Since it is a '67, the input shaft will be of help (providing it hasn't been changed)
The M20 has two rings on the input shaft, cut at 90 degrees to the splines. An M21 will have one ring, and generally an M22 will have no rings. The sure way to tell is to pull the sidecover off the trans and look at the gears.
The difference is in the gear ratios. An M20 has a first gear ratio of 2.52 (or 2.56 depending on year) the M21 close ratio has a first gear ratio of 2.20, and the M22 has a 2.20 low gear, and HD gears.
As a general rule, cars with 3.73 and lower rear gears used a close ratio trans, and cars with 3.55 and higher used a wide ratio M20. There were exceptions to both, like M22's in LS6 cars with 3.31 gears, and wide ratio M20's in '69 Z28's with 3.73 gears.

From 1970 on back only the M22 had a drain plug. From 70 on all muncie 4spds had drain plugs. check out sept.99 issue of Muscle Car Review, page 66 there's an article on how to identify all Muncie 4spd transmissions, there's a lot of good info there.

Jeff

I looked at the input shaft, and it has two lines on it. The ID number says it is a 67, but it does have a drain plug. My friends is from a 69Z28, and it has a drain plug also. My car has 3.73s, so IF it is an m-20 my cruise RPMs will be kinda high? Are m-20s weaker than m-21s? And could the input shaft have been changed?

Check out www.gearzone.net (http://www.gearzone.net) .It'll tell you everything you need to know about a muncie.

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John 67SS
ACES #2887
TC #127

your cruise rpm's will be the same regardless of the type of transmission since the 4th gear ratio on all of them is 1:1

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Hey KIKNSS, My M21 in a 70 has two plugs on the pass side. One about half way up and the other almost on the bottom just as it says it should in the book "Chevrolet by the numbers, pg245. Also the "B" stamped at the end of the date code is weak so I'll bet your 7 is a B.

A lot of Muncie rebuilders, including myself, install magnetic drain plugs during a rebuild. A muncie without a drain has a magnetic donut GLUED in the bottom of the case. That really scares me! I remove the donut and install a magnetic plug for 2 reasons. 1) To get rid of the donut in case it ever comes unglued. 2) There is no way to drain/change the tranny oil without pulling the tranny. I don't like that either.

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