Muncie 4 speed....M21, M22, Rock Crusher?

I was just wondering how many different variations there are of the Muncie 4 speed and which ones are best and for what reason(s). I currently have an M22 Rock crusher in my '56 Chevy pickup, and have another M22 that was rebuilt about 6 years ago by my father but never used. I also have what I believe is an M21, but I'm not certain. The M22's are both close ratio and the M21 is a wide ratio...again from what I was told years ago. I know that the M22 was supposedly stronger than the M21 and that the close ratio rock crusher was supposed to the the beefiest, but not sure why or if this is even true. Anyone have any input?

 

M20 = wide ratio
M21 = close ratio
M22 = stronger close ratio

 

Look on the right side of the case and you'll find a number sequence, like "P0139A" The last letter ID's the trans A M20 B M21 C M22.
If you have two M22s, you should buy a lottery ticket

 

I think he already won the lottery with 2 of 'em ..

 

So an M21 cannot be a wide ratio. I'm pretty sure the extra one is an M22 also but I'll check to make sure... I know the one in the truck is an M22 for sure.

 

the m-22 has a stright cut first gear set and that makes it stronger for those 6grand side-step starts

 

See, now I'm almost positive that they're both M22's... I recall my pops saying he couldn't believe how much harder it was to find the straight cut gear set as opposed to the standard set when he was rebuilding it.

 

Actually, they are not completely straight.. Close, but not completely..
That's where the 'whine' come's from with those transmission's..
Also, there's companies out there that are making new gear set's for Muncie's as well..not just stock replacement stuff either.
You can outfit an M20 or M21 with Rock Crusher type gears, OR actually make a 3 speed O/D out of a 4 speed case. Forth being the overdrive obviously..
Kinda nice if you want the Muncie look and an overdrive..

 

Google "muncie transmissions" and a "gearzone" website will come up. Go to it and click on "identification" and that page will tell you everything you need to know about muncie transmissions. You will be able to tell when yours was made and what kind of car it was in.

 

Info
http://www.5speeds.com/muncie2.htm

 

Also, all '71 and newer Muncies had the 26 spline input, Turbo 400 size output, and drain plug that the M22s had, so don't be fooled into paying M22 prices for a non M22 transmission. Honestly, if I had a pair of M22s these days (and not the cars that they came in), I'd sell at least one of them and put the $$$ into something I needed for my build.

 

http://autogear.net/muncieproducts.htm

I got one here with OD. It's cool.

 

the new autogear super case muncies are REALLY nice!

 

when i was looking to see if my muncie was a 21 or 22 i noticed that the 21 had say 6 holes to mount a shifter plate to where as the 22 only has 3-4.

 

OK, I ran the numbers. It turns out that only the one in my truck is an M22, the other two are M21's. I pulled the plate off the each of the two spares and compared them and the rebuilt one does have the straight cut gears. Basically a faked M22 in an M21 case. Thanks for the help guys...

Dang, I was going to head up to Vegas too...sheesh.

 

I'm trying to feel bad for ya that you have 2 M21s. **** the 21s are bringing jumbo $$$ too. Not as jumbo as a 22 but pretty high based on my shopping experiences. Like I said, I'm trying to feel bad for ya...really...nope, not happenin

 

As far as I know the M20 + 21 are the same xmsn and are both wide ratio. Only the M22 is close ratio.

 

The M21 and M22 ratios are the same:

http://www.5speeds.com/muncie2.htm

Oh, I'm not looking for sympathy...just was hoping that I had a spare M22. Funny thing is, my dad collected this stuff like it was baseball cards..its crazy the stuff he had stored away in the garage.

 

good thread

Im in the muncie market

looking to back a mild 354 hemi up with one

alot of info to weed through with these trans

all info helps

 

""You can outfit an M20 or M21 with Rock Crusher type gears, OR actually make a 3 speed O/D out of a 4 speed case. Forth being the overdrive obviously..
Kinda nice if you want the Muncie look and an overdrive""

Actually the 3rd gear station becomes the OD and the 4th gear station becomes 3rd,so the shift pattern is a little weird,1-2-4-3.

 

Well now, THAT i didn't know...Just it could be done and talked with a guy that did it....never even asked him where od was...
That is a bit weird..still cool though.
Thank you for the info

 

You could also run the deeper first gear M20 wide ratio with a higher rear gear. To some extent an overdriven close ratio is just widening out the ratios

 

You can sink a grand into a rebuild very easily. I never want to ever, ever think about it agian, so It was worth the $1800 for a new unit. Word has it, the AutoGear is way stronger than the M-22 ever was back in the day. From the looks of mine, I believe it.

 

Yeah the 4th gear station is hooked up directly to the input so there is no way to OD in that station and since 3rd gear rotates around the main it is the one that has to be used to turn the output faster than the input.
However having said that,the OD set up like that is prolly not particularly durable as 3rd gear in a normal 4spd is under driven and is prone to sieze on the main shaft(no bearing,just a cushion of gear grease) I would imagine that being over driven in 3rd would exacerbate the situation.

 

M20's and M21's can be close or wide ratio, different gear sets for different years, different applications. The number of rings or lack of rings on the input shaft splines is the indicator. I don't remember all the details now, I'm sure the aforementioned websites must list 'em.

M20's and (I think) early M21's had a smaller 7/8" diameter cluster shaft, later boxes all had 1" shaft.

Re the in-box overdrive: Yes, original forth becomes third, overdrive goes in the original third gear position in the box, you flip the 3-4 shift lever on the side of the trans so it points down instead of up and your shift pattern remains the same.

 

I don't believe that this is how AutoGear achieves OD in 4th. The shift levers install as usual. They have ahuge line of parts for these things.

 

So here's the deal guys...I'm going to let go of the rebuilt M21. It's never been installed since rebuild. There is some surface rust on the output shaft and the yolk because right after my father p***ed someone left it outside for a few months. It was UNDER an overhang so never go drenched or even very wet, but rust still did begin to take on the external steel parts.

Here's the catch, as usual. If you really want it it's yours, but I'm in a situation where the first guy to come up with the do-re-mi gets it as I simply need some fundage. I'd be fine with a check, cashiers check, MO, etc... as long as it clears. I'm guessing shipping at around $125 or so in the continental US (to be calculated by zip code), so you'll need to add that to the total once I know your location. Do I hate getting rid of it? What do you think, but hard times require hard decisions...heck, I'm still KICKING myself for selling my '69 Charger!!

Hey mods, if this is a no-no, I truly apologize...I just figured it was a good place since I asked this question 2 years ago.

Here are the actual numbers on the case:

Cast into case: 3853125
on the cover: 3884685
Pat No: 3088336
stamped on bellhousing end: 0124610 (date code maybe?)

As far as I was told by my father, he built this to M22 specs.

I've seen the M22's go for $1,500 to $2,200 but seeing as this is an M21 I'm figuring less.

Asking: $1,200 obo...if you don't think this is fair, make an offer. Talk to you all later...

Bill

 

HI. your fake M-22 is more than likely an M-22 that the ears on the case where broken off of or worse and someone switches all the stuff over the a good case. if you want to sell it let me know. TC

 

DOES IT have a PO****x number on the case?

 

I also had a 56 Chevy Pickup with an M22 that I put in. Not a good match; even with the stock 3.90 rear ratio the truck was difficult to get going in first gear. Really hard on the clutch. The large rear tires probably contributed.

I replaced the M22 with the wide-ratio M20 Muncie, which made the truck much more driveable. The M22 is now in my 37 Ford. It is a far better match to a lighter vehicle with a 4.11 Ford rear and smaller diameter rear tires. I love the cl***ic howl of the near straight-cut gears.