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Old 11-05-2002, 05:13 PM   #1
Ki m Le
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Default Muncie M20 vs M21?

What are the adv/disadvantages between the two Muncie trans?

Thanks

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Old 11-05-2002, 05:56 PM   #2
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Default Re: Muncie M20 vs M21? (Ki m Le)

One has close ratios the other has wide ratios.

M-20 M-21
1st 2.52 2.20
2nd 1.88 1.64
3rd 1.46 1.28
4th direct direct

I love my M-21. The gear spacing is tight, the revs are always up. Lots 'o fun. Gear selection all depends on the power curve the engine puts out.



[Modified by burners, 2:57 PM 11/5/2002]
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Old 11-05-2002, 06:04 PM   #3
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Default Re: Muncie M20 vs M21? (burners)

Waht burners said. The M-20 is more of drag race tranny while the M-21 is more of a road racing tranny.
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Old 11-05-2002, 07:04 PM   #4
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Default Re: Muncie M20 vs M21? (Fevre)

Unless you have a BB :D Then it just doesn't matter.... M-20 in mine.

Hans
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Old 11-05-2002, 07:51 PM   #5
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Default Re: Muncie M20 vs M21? (Ki m Le)

My dad always liked having the M20 in his '64 because it gave him a lower first gear to just get the car barely rolling.
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Old 11-05-2002, 07:58 PM   #6
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Default Re: Muncie M20 vs M21? (Ki m Le)

They were installed in cars with different differential gear ratios. 3:70 and numerically higher were given the M-21, 3:55 and lower were given the M-20. The lower first gear in the M-20 got the highway geared cars off the line better.
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Old 11-05-2002, 08:01 PM   #7
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Default Re: Muncie M20 vs M21? (74vetteman)

Also, the higher gear reduction of the M-20 will probably make it slightly weaker due to more torque multiplication. However, mine is living behind almost 500 ft/lbs, and plenty of drag racing. Good thing I am running street radials though!!
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Old 11-05-2002, 09:00 PM   #8
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Default Re: Muncie M20 vs M21? (74vetteman)

Quote:
They were installed in cars with different differential gear ratios. 3:70 and numerically higher were given the M-21, 3:55 and lower were given the M-20. The lower first gear in the M-20 got the highway geared cars off the line better.
not nescessarily true, there was a standard gear ratio with an M-20 or 21 but there were also optional gear ratios and this depended on year, my 73 was originally a 3.36 with an M-21, now it's a 3.55 and a much better combination in my oppinion with the M-21.

:cheers:
Pat Kunz
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Old 11-06-2002, 12:17 AM   #9
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Default Re: Muncie M20 vs M21? (73 LS-4)

[QUOTE]They were installed in cars with different differential gear ratios. 3:70 and numerically higher were given the M-21, 3:55 and lower were given the M-20. The lower first gear in the M-20 got the highway geared cars off the line better.

not nescessarily true, there was a standard gear ratio with an M-20 or 21 but there were also optional gear ratios and this depended on year, my 73 was originally a 3.36 with an M-21, now it's a 3.55 and a much better combination in my oppinion with the M-21.

My bad! Well, take what I said as a rule of thumb, not necessarily in every case. :cheers:
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Old 11-06-2002, 01:32 AM   #10
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Default Re: Muncie M20 vs M21? (74vetteman)

Quote:
Also, the higher gear reduction of the M-20 will probably make it slightly weaker due to more torque multiplication. However, mine is living behind almost 500 ft/lbs, and plenty of drag racing. Good thing I am running street radials though!!
I dunno, my dad didn't have any trouble with his M20. 5.87's in the rear, 550hp out of a 302, 10k launches. He ground off every other synchro tooth so it slipped into gear better. That's about it.
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Old 11-06-2002, 09:19 AM   #11
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Default Re: Muncie M20 vs M21? (Schmucker)

Thank you all for replied. I have the 427, L36 motor, M20 and M21 ) Muncie just over hauled them myself with all the part for conversion to manual from Auto. The car is 69 vert # matching with 350, 300HP, TH400 and 3:36 rear. All of # matching stuffs will be stored away for originality. With your inputs, I have to make a decision which Muncie to put in the car. BTW, It's going to be street driven car and occasionally, racing against the guy at work with a 64 GTO with 389, M20.and 3:55 rear. I don't want to be defeated again!

Thanks





[Modified by Ki m Le, 7:20 AM 11/6/2002]
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Old 11-06-2002, 11:27 AM   #12
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Default Re: Muncie M20 vs M21? (Ki m Le)

My L36 '68 is currently running a stock trans and rear, an M21 and 3.55. I don't like this combo one bit, and the day I rebuild the transmission is the day it becomes an M20! I plan to run a 3.36 axle with the M20. This combo would give both a better launch and lower highway revs than my current combo. The L36 makes plenty of torque, so the M21/3.55 is a major mismatch. I honestly can't think of one senario where I would want to run my current combo on the street. Torquey big block, high strung small block, no way.

The M21's 2.20 first gear is way to low for a good launch. Just look at all the aftermarket transmissions today, their first gears are usually 3.00+.

Have you guys seen the new M22 gears that are available with the M20 gear ratios? M22s usually have the M21 ratios. I want one!
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Old 11-06-2002, 08:49 PM   #13
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Default Re: Muncie M20 vs M21? (Flareside)

why is it sometimes called the "rock crusher" thats what i wanna know :cheers:
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Old 11-07-2002, 12:48 AM   #14
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Default Re: Muncie M20 vs M21? (OatBoy)

Quote:
why is it sometimes called the "rock crusher" thats what i wanna know :cheers:
I figure it is because if you put rocks in it, it would be strong enough to crush them. It is a heavy duty trans. I doubt it would crush the rocks.
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Old 11-07-2002, 01:58 AM   #15
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Default Re: Muncie M20 vs M21? (Flareside)

Switching from a M21 to a M20 wont change you highway cruse RPM's at all. Fourth gear is 1 to 1 in m20, M21 and M22. You can only lower your highway RPM by increasing your tire diameter, lowering your rear gear ratio or putting in a overdrive unit or transmission.
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Old 11-07-2002, 08:44 AM   #16
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Default Re: Muncie M20 vs M21? (OatBoy)

sounds torquey!
Quote:
why is it sometimes called the "rock crusher" thats what i wanna know :cheers:
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Old 11-07-2002, 10:28 AM   #17
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Default Re: Muncie M20 vs M21? (OatBoy)

Quote:
why is it sometimes called the "rock crusher" thats what i wanna know :cheers:
If you had driven in an M22 car, you would know why they call it the rock crusher. Some think it sounds like it is crushing rocks inside :)
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Old 11-07-2002, 01:00 PM   #18
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Default Re: Muncie M20 vs M21? (OatBoy)

Only the M22 trans is called "The rock crusher". From what I understood, it was because of the sound the gears made while driving. They aren't exactly known for "silent running" ;)

Dep
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Old 11-07-2002, 01:51 PM   #19
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Default Re: Muncie M20 vs M21? (Dep)

M22 is a rock crusher because of the gear noise. to reduce gear noise in a normal car, engineers put in a helical cut gear at 44 deg( I believe). THis provides a quite comfortable ride but at the cost of strength and the additional side loading on the tranny case caused by the gear tryto get pushed into the case. THe M22 has 22deg helical cut gears, increasing strength and reducing loading on the case but they are as noisy as all hell.
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Old 11-07-2002, 02:01 PM   #20
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Default Re: Muncie M20 vs M21? (Dep)

My 76 has an M22 w/a 3.73 rear... gets me in trouble with the law quite a bit around town :D
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Old 11-07-2002, 02:01 PM
 
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