7691

I read somewhere that effective Oct. 21 1968 a suffix letter was added to the plant build date code to aid in identification of transmission ratios.
P----A = M-20 P----B =M-21 P----C =M-22

My question, is there a way to identify any M-22 transmissions with out taking it apart.(pre 68 or newer)
Trans in question is not in a car. Thanks, CG

Tampa Jerry

I think the M-22 has two rings on the pilot shaft. I has been a long time since I have seen one. Jerry

Nowhere Man

If the trans is out of the car then just pull the side cover off and look for your self. Chances are it's a M20. They made a hell of a lot more of them for all other GM cars.

JohnZ

If you know for sure that the transmission is all-original and hasn't been rebuilt or molested, the input shaft will have smooth splines, with no rings, and it will have a drain plug (all Muncies had a drain plug from 1970-up). It will also have a steel tag on a side cover bolt with 3879987 embossed on it.

The only way to tell for sure is to remove the side cover and look at the helix angle of the gear teeth - the M20/21 teeth are at a 45* angle, and the M22 teeth are about 20* angle from horizontal.

Everybody seems to think they have an M22, but the reality is that they're as rare as chicken lips and hardly anybody really has one.

plaidside

As usual John is dead on. I wish I had a dollar for everyone over the years that told me they had an M-22 in their car because they do not have any grooves on the input.
I have installed many aftermarket inputs and they ALL come without the grooves, whether it is an M-20, M-21 or an M-22.
Joe

Here is comparison of an M-20/21 on the left and an M-22 on the right:
[IMG][/IMG]

midstyle

Here's a comparison of the input (clutch) gears; the M22 is on the left; the M21 on the right. shows the angle difference that John mentions.



c

7691

Awsome info from everyone, Thank you,Thank you

DZAUTO

In addition to John's observation about people claiming to have an M22 (when they don't), is that MANY, MANY, MANY, MANY people are (for some unknown reason) under the assumption that the 71-74 Muncies are ALLLLLLLL an M22 because of the fine spline (26 splines) input and the larger 32 spline tail shaft. THAT ABSOLUTELY AND POSITIVLY IS NOT CORRECT!!!! ALLLLLLLLLLLL 71-74 Muncies have the 26 spline input/32 spline tail shaft and VERY, VERY, VERY few of them were an M22!

redvetracr

incorrect information

69z28&ss396

I've got a C stamp 660 case M22 in my Z/28. That is what I wanted because the original, probably 21, was long gone when I got the car. Either way JohnZ and DZ are correct in both the fact that very few were made, AND all 71-74 were M22.. But if you do want to talk rarity of an M22 try finding a 1965 M22 7/8 pin tranny. Supposedly, according to GM data, they exist but I have never seen one. Stories though?? Heard a bunch!!

tjstarduster

All the M22s I've seen have no grooves on the input shaft. I installed one in my '66 BB. I believe M21s have 1 groove and M20s have 2 grooves.

tjstarduster

Original M22s are rare, however a good transmission shop rebuilt my M21 with M22 gears. The shifting is a little stiffer but I love the whine! Sounds like an old John Deere tractor!

flared66

Is the the plant build date code I.D. the o.p. is speaking of with the C suffix.my trans has a drain plug and I was always told it was an M22 but have never researched it.thanks dan

JohnZ

That's a correct stamp for a '71 model year M22, built April 19, 1971.

flared66

Sorry just realized picture posted upside down

flared66

Thanks john z.as tstarduster said "it shifts stiff and whines like a john deer tractor"cheers:

65 fi

What would the 65 M22 7/8 pin transmission look like?

DZAUTO

From the information which has surfaced so far (and it's reliable) about the tiny handful (57 units??????) of 1965 M22 trannys, the cases were bored to accept a 1in cluster gear shaft. Also, since these were 1965 model Muncies, the ONLY main case at the time was the 325 case. That case was used and modified (the casting number was machined off) for assembly of the few 65 M22 trannys.
John mentioned above that regular M22 trannys were are scarce as chicken lips. WELL, the 1965 M22 trannys are even more scarce than that!!! To date, the BEST information about the 65 M22s is that all of them were installed in 396 cars only.
Most likely, John has better information as to what the determining factor was for installation of an M22 in a 1965 396 car vs an M21.

Thus, a 1965 M22 would look EXACTLY like any other 1965 Muncie, but with the casting number removed and a drain plug.

And now, with the mention of a drain plug on Muncie cases:
As mentioned, UP THROUGH 1969, MUNCIES DID NOT GET A DRAIN PLUG--------------EXCEPT THE M22!!!! Then, beginning with the 1970 models, ALLLLLLLLLLLLLLLLLLLL Muncies got a drain plug.
Now, here is where I'm going with all of this. For over 45yrs, I've been rebuilding Muncies. MOST, and I mean MOST of them got a (magnetic) drain plug installed----------------AND, the magnetic donut inside was removed!!! Also, MANY other tranny rebuilders have installed drain plugs in Muncies. Thus, there are a bunch of NON-M22 Muncies out there with drain plugs which have been installed by those of us who rebuild them. ALL the Muncies in my cars (5) have had drain plugs installed, plus the 7 Muncies under my workbench. I have no clue how many customers' Muncies I've installed drain plugs in, but it is a bunch.
Finally, my whole point with all of this, is if you see a Muncke with a drain plug-----------------THAT NO LONGER MEANS IT IS AN M22!!!! Again, the ONLY, ONLY, ONLY, ONLY way to know for sure if a Muncie is an M22, is to remove the side cover to observe the angle of the gear teeth. Oh ya, and just because the date code on a Muncie case is followed with a C, that DOES NOT assure that it has M22 gears inside of it. Soooooooooooo, that takes us right back to the statement that the ONLY way to know if a Muncie has M22 gears, is to remove the side cover.