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post #1 of 31 (permalink) Old Jun 6th, 00, 07:38 AM Thread Starter
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I have a 69 396 SS that had a auto transmission and I want to switch to a 4 speed. I have been told that I need a M-20 by one person and a M-21 by another. What is the difference between the two? What is a resonable price for a rebuilt one?

Thanks
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post #2 of 31 (permalink) Old Jun 6th, 00, 08:02 AM
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I've got a Muncie 4 speed in mine, it's alot of fun, but it gets old after awhile, especially in traffic! Sometimes I wish I had an automatic, but don't think I'd want to go through all the hassle of the conversion, although yours will be more difficult, going from auto to 4 speed. I've seen them selling for as low as 300 (needs rebuilt) all the way up to 1500 (rebuilt.) Anywhere around 500.00 for one that is in good condition would be a pretty good price, if you can find one. I'm not sure about the differences between the M20's, M21's and M22's (rockcrusher), but I think they will all fit in a 1st generation Camaro, with different modifications. KZ
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post #3 of 31 (permalink) Old Jun 6th, 00, 08:10 AM
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A M-20 has a lower first gear ratio than the others. You can run a more friendly gear, and still have a good bottom end feel. The M-21 and M-22 both have a high first gear, and need to have atleast a 3.73 rear end ratio or lower to work well. The M-22 has straighter cut gears, and the transmission actually has a whine, hence the name "Rockcrusher", 'cause it sounds like an old crusher mill. a rebuilt one should run you somewhere in the neighborhood of $600 for a M-20, add $100 for a M-21, and a M-22 about $1300 +.

[This message has been edited by Doug Garland (edited 03-02-2001).]
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post #4 of 31 (permalink) Old Jun 11th, 00, 08:31 PM
 
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the M-21 and 22 have closer gears also.
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post #5 of 31 (permalink) Old Jun 13th, 00, 12:08 PM
 
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I got an idea, I have thought about selling my M-22 (RockCrusher). I have it in my 68 camaro...I bought the car with it in it. I adore automatics... I've heard anywhere from $1,500.00 to $2,000.00 so I'm not sure what a good price would be. But I am looking for a T-400 trans. anyhow.. I'm in Ga also... close to Carrollton if you have ever heard of that....
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post #6 of 31 (permalink) Old Jun 13th, 00, 12:10 PM
 
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by the way, I have 3.73 gears and I run 67 mph at 3000 RPM.... and take of like you wouldn't believe. it's capable of around any where from 20-60 in second... up to around 90 in third gear...so on...
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post #7 of 31 (permalink) Old Jun 13th, 00, 12:12 PM
 
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Oops... sorry for not saying... it is in a 68 camaro with a built 396.. so on..
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post #8 of 31 (permalink) Old Jun 13th, 00, 01:28 PM
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I'd stick with the automatic. Probably faster than the four speed with normal shifting and a lot more consistant. Hard to beat the setup you have now. Of course if you want the four speed, nothing else will do the trick usually.
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post #9 of 31 (permalink) Old Jun 13th, 00, 05:41 PM
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The wide ratio M20 was not offered in big block cars as it did not have the torque capacity to handle a big block.
The solution was to use the M21 close ratio. The close ratio has a 2.20 ratio first gear which limits the torque multiplication applied to the rest of the gears of the transmission.
In other words, the lower the first gear ratio the more the engines torque is multiplied by the gears, placing more strain on the rest of the trans.
Also a big block having more torque does not need as low a first gear anyway.
David

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post #10 of 31 (permalink) Old Jun 13th, 00, 09:08 PM
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go to www.gearzone.com alot of info
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post #11 of 31 (permalink) Old Jun 14th, 00, 04:01 PM
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I disagree with David on this. The M-20 was offered as a base tranny on L-34& L35 big block cars, and small block cars. The M-21 was the hi-po option on these cars, and std. on L-78 cars, and the M-22 was the H.D. hi-po option on some cars. You could basically order what tranny you wanted back then if you knew what box to check.

Fireman: Call me, I find turbo 400's all the time. My email bit the dust today, so it might be a couple of days before it's up and running. My # is 706-253-3513.

[This message has been edited by Doug Garland (edited 06-14-2000).]
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post #12 of 31 (permalink) Old Jun 16th, 00, 02:10 AM
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I have an ALL ORIGINAL 1968 SS396 Chevelle with the original window sticker that list M20 - Wide Ratio 4 Speed Transmission. It also has the last 8 digits of the VIN stamped in the transmission case. There is NO durability difference between the M20 & M21. The M22 is more durable because of the straighter cut on the gears. I just had my local Muncie expert convert a M21 to M20 for street use. IMHO, the M20 is much better for the street. I can't recall the ratios off hand, but there is only 1000 RPM drop between the 2-3 upshifts. Really keeps the engine in the powerband.
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post #13 of 31 (permalink) Old Jun 22nd, 00, 07:44 AM
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I thought the choice of rear gear ratio determined whether you got a 20 or 21. Lower numerical (less than 3.31?) got M20's. Any thoughts?
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post #14 of 31 (permalink) Old Jun 22nd, 00, 10:30 AM
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Guess I was wrong in stating no bigblocks came with the M20. Thanks for correcting me. I'm learning a lot here too.

The main point I was trying to convey is there is a greater risk of breaking an M20 compared to a M21.

I've read where the really high output bigblocks were paired with the M21 only, not the M20 because of the added torque multiplication of the lower first gear of the M20.I don't recall exactly but maybe it refered to the 454 engines, not the smaller 396 bigblocks used in the first gen camaros.

I'll take your word for it that firstgen Camaros were equiped with the wide ratio trans. I'm certanly no expert.

The M20 and M21 trannys are the same inside except for tooth count.
But the lower first gear of the wide ratio trans multiplies the torque and lowers the manufacturers max torque rating of the trans.

Example of a 454 making 450 ft lbs of torque:
450ft lbs X 2.20=990ft lbs.
450ft lbs X 2.56=1152ft lbs.

Big block engines are harder on manual transmissions because they make more torque and they have a heavier rotating assembly. The crank, rods , pistons, flywheel, and damper all weigh a lot more than a small block and when you get all that mass spinning and dump the clutch, that's a big load.
That shock load can be several times the rated torque of the engine.
Multiply that times the first gear ratio and you have a huge loading compared to a small block.

My Richmond 5 speed catalog lists three first gear versions of the SAME transmission.
ratio-mfr torque rating.
3.27=450ft lbs
4.06=400ft lbs
4.41=375ft lbs

It looks to me that they are de rating the trans because the lower first gear ratios apply more torque to the rest of the trans, so they have to lower the input torque rating to keep output torque within design limits.

So using my reasioning, a wide ratio trans would be slightly weaker (15% to 20%) than a close ratio trans, WHILE IN FIRST GEAR.

If you don't have much traction, then that becomes the torque limiter on the drive train. But if your car really hooks up then at least in theory, the wide ratio would go BANG before the close ratio tranny.

I had the wide ratio in my 67 and I liked the low first gear but in the 3rd to 4th shift the revs really dropped.
David

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[This message has been edited by davidpozzi (edited 06-22-2000).]
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post #15 of 31 (permalink) Old Jun 22nd, 00, 10:50 AM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by CORNHOLIO:
go to www.gearzone.com alot of info<HR></BLOCKQUOTE>

Is this a joke?
Wrong kind of gear!

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