How to tell M20, M21, M22 Muncie trans apart?
05-22-2008, 12:06 PM
#1
How to tell M20, M21, M22 Muncie trans apart? Hey everyone, a friend of mine has three Muncie trans from late 60s early 70s muscle cars. All are in great shape and im making a deal with him for one with a 68 date code for my 68 Firbird 400.
He doesnt know if any are the M20(Wide Ratio), M21(Close Ratio) or M22 (Close Ratio Rock Crusher). Is there a way to tell them apart? I know I can count gears but does anyone know off hand what ratio would be which?
I really appreciate the help...also if anyone has a clutch fork for one of these trans that will be the last thing I need for it so I can put my car back to the original 4 speed.
Thanks again.
He doesnt know if any are the M20(Wide Ratio), M21(Close Ratio) or M22 (Close Ratio Rock Crusher). Is there a way to tell them apart? I know I can count gears but does anyone know off hand what ratio would be which?
I really appreciate the help...also if anyone has a clutch fork for one of these trans that will be the last thing I need for it so I can put my car back to the original 4 speed.
Thanks again.
05-22-2008, 02:18 PM
#2
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try these
http://www.nastyz28.com/faq/trans.htm
http://www3.sympatico.ca/atkinsom/history.html
for parts try here http://www.5speeds.com/newm22.html
http://www.nastyz28.com/faq/trans.htm
http://www3.sympatico.ca/atkinsom/history.html
for parts try here http://www.5speeds.com/newm22.html
05-23-2008, 09:43 PM
#3
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Ok pal here you go (since I grew up with them, thrashed and broke em' plenty)...
1) Early small pin Muncies thru 1966 and on some 67's, (small pin type = you'll notice on the front of the case just below the input shaft, it looks like a silver disc).
Actually it's a cluster pin running thru the main case to hold the cluster gear that spins on it inside the tranny. if it's (pin) is a 'lil bit smaller thanthe size of a quarter (.25 cent piece), it's an early Muncie. (also has a smaller output yoke).
If it has a coarse (larger) spline input shaft with 1 groove around the input splines, it's an early M-21 Close Ratio 2.20 1st gear ratio tranny. Usually found in factory Big Block cars.
Same as above with 2 grooves running around the splines = 2.56(very early) or 2.54 1st gear Wide Ratio tranny. (Usually found from factory small block cars).
On later '67's and up, the silver disc (cluster pin) is larger .(size of a quarter head (.25 cent piece) output shaft is bigger as well. 1 goove around input shaft = 2.20 1st gear ratio, while 2 grooves = 2.52 1st gear "wide" ratio tranny. (steeper 1st,2nd and 3rd gear ratios than close ratio tranny's.)
On tranny's that looked like this, and have no grooves around the splines deserve a look inside for the gears that are almost straight (very little angle to them compared to other muncies) These are 2.20 1st gear Muncie M-22 trannies. (Also known as the Rock Crusher due to the whining sound these trannies make while upshifting 1st thru 3rd gears due to those "helical cut" straight gears.
By 1970 the output was larger ( like a Turbo 400 yoke) and had the fine spline (26) input shafts. two grooves = 2.52 wide ratio tranny while NO GROOVES = 2.20 1st gear ratio. This is known as the "Rock Crusher M-22" and Grand Daddy of the Muncies. It's more rare, has the "helical cut" straighter gears, and were an extra cost option on the Badder Big Blocks of the day.
Hope this helps you out.
Btw, use a lighter flywheel on a street car if you plan on pounding these things with anything hovering around 400 ft lbs of torque, and over 325 rear wheel horsepower. Not only do thay break the cluster drive gear, but on high H.P. cars, will break the ears off the aluminum cases (wher the four bolt attach the trans. to the bellhousing).
And By all means have the tranny dialed into the bellhousing for less problematic "6,000+ RPM Big Block Powershifts"....lol
1) Early small pin Muncies thru 1966 and on some 67's, (small pin type = you'll notice on the front of the case just below the input shaft, it looks like a silver disc).
Actually it's a cluster pin running thru the main case to hold the cluster gear that spins on it inside the tranny. if it's (pin) is a 'lil bit smaller thanthe size of a quarter (.25 cent piece), it's an early Muncie. (also has a smaller output yoke).
If it has a coarse (larger) spline input shaft with 1 groove around the input splines, it's an early M-21 Close Ratio 2.20 1st gear ratio tranny. Usually found in factory Big Block cars.
Same as above with 2 grooves running around the splines = 2.56(very early) or 2.54 1st gear Wide Ratio tranny. (Usually found from factory small block cars).
On later '67's and up, the silver disc (cluster pin) is larger .(size of a quarter head (.25 cent piece) output shaft is bigger as well. 1 goove around input shaft = 2.20 1st gear ratio, while 2 grooves = 2.52 1st gear "wide" ratio tranny. (steeper 1st,2nd and 3rd gear ratios than close ratio tranny's.)
On tranny's that looked like this, and have no grooves around the splines deserve a look inside for the gears that are almost straight (very little angle to them compared to other muncies) These are 2.20 1st gear Muncie M-22 trannies. (Also known as the Rock Crusher due to the whining sound these trannies make while upshifting 1st thru 3rd gears due to those "helical cut" straight gears.
By 1970 the output was larger ( like a Turbo 400 yoke) and had the fine spline (26) input shafts. two grooves = 2.52 wide ratio tranny while NO GROOVES = 2.20 1st gear ratio. This is known as the "Rock Crusher M-22" and Grand Daddy of the Muncies. It's more rare, has the "helical cut" straighter gears, and were an extra cost option on the Badder Big Blocks of the day.
Hope this helps you out.
Btw, use a lighter flywheel on a street car if you plan on pounding these things with anything hovering around 400 ft lbs of torque, and over 325 rear wheel horsepower. Not only do thay break the cluster drive gear, but on high H.P. cars, will break the ears off the aluminum cases (wher the four bolt attach the trans. to the bellhousing).
And By all means have the tranny dialed into the bellhousing for less problematic "6,000+ RPM Big Block Powershifts"....lol
Last edited by RapidRick; 05-23-2008 at 09:50 PM.
05-23-2008, 10:35 PM
#4
Thanks 02hawkta for the link, ill have to save it and read through it.
Also Thanks RapidRick, you seem as if you have had a few
All of my muscle cars so far have been TH350s, im looking forward to having a factory 4 speed.
Thanks again guys!
Also Thanks RapidRick, you seem as if you have had a few
All of my muscle cars so far have been TH350s, im looking forward to having a factory 4 speed.
Thanks again guys!
05-24-2008, 03:56 PM
#5
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Yea, quite a few of 'em & you are most welcome sir.
Btw, Clutch should grab about 1/3 to almost 1/2 off the floor for a clean powershift w/Diaphragm clutch setup on a street car.(even if you streetrace it) tho not legal in all 50 states...lol
I like the Ram single disc w/about 2600# pressure plate holding power, if your not doing the more expensive dual clutch CenterForce or Spec route setups.
Also as on all older stick cars, especially Muncies & for less driveline breakage, when you go to launch it, holeshot, etc. follow this suggestion:
Before you dump the clutch, let out the clutch pedal just enough to put tension on the driveline (preload it as in powerbraking an auto trans. that's why Auto's break less parts than high power stick cars)
This way the driveline will be "loaded", then push the clutch in ever so slightly as to be able to get your revs up to where you'd like. Then off your foot and then beat it like it owed you money!
Btw, Clutch should grab about 1/3 to almost 1/2 off the floor for a clean powershift w/Diaphragm clutch setup on a street car.(even if you streetrace it) tho not legal in all 50 states...lol
I like the Ram single disc w/about 2600# pressure plate holding power, if your not doing the more expensive dual clutch CenterForce or Spec route setups.
Also as on all older stick cars, especially Muncies & for less driveline breakage, when you go to launch it, holeshot, etc. follow this suggestion:
Before you dump the clutch, let out the clutch pedal just enough to put tension on the driveline (preload it as in powerbraking an auto trans. that's why Auto's break less parts than high power stick cars)
This way the driveline will be "loaded", then push the clutch in ever so slightly as to be able to get your revs up to where you'd like. Then off your foot and then beat it like it owed you money!
