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Any can fit and all are externally the same.

M-20 is a wide ratio, M-21 is a close ratio and M-22 is a H-D close ratio.

M-20 and M-21 have a coarse spline clutch gear or input shaft.

Both have a small driveshaft yoke, same as a PG, T-350 or Saginaw.

M-22 has a fine spline clutch gear and large T-400 driveshaft yoke.

Thanks
Randy
 

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"Which one" largely depends on your budget, what you have available to you, and how the car is going to be used. This is a good article to read:
www.motortrend.com/how-to/guide-muncie-m20-m21-m22-four-speed-transmissions/

For a street car, a wide ratio M20 is what I would consider "the best" due to having a more user-friendly first gear ratio (~2.56:1, like a TH350). The close-ratio M21/M22's are great if you like to keep the ratios close, but the first gear is steep (2.20:1) and often less enjoyable on the street.

My BEST advice would be to call up Autogear in Syracuse NY and let them guide you. They build brand new Muncie transmissions and offer updated, improved versions that are superior to used stuff. I seriously considered one of their "M23Z's" for my car before going LS.
 

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I believe that anything after 1970 has the turbo 400 driveshaft yoke, not just the M22. I have an M20 with fine spline input shaft and t400 output that is from a 1971 vehicle. The M20 has a lower first gear as well which is nice if you are running a lower numerical differential gear. Are you replacing a Saginaw gear box, or starting from scratch and installing a 4 speed in a car that was an automatic? If your starting from scratch, you have more options. If you are replacing a Saginaw box, and not replacing the clutch or yoke and you want the floor shifter in the right spot, you'll need to make sure the Muncie trans that you buy is a direct replacement.
I also second calling Autogear. Especially if your car has a very low numerical gear in the rear, like a 3.00 or 2.73. Autogear has 3.0 first gears which really help, plus you'll have a brand new trans. You might also want to consider a Tremic TKX.
 

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Have a Saginaw now car has 4:11 gears in the rear. Just want something stronger and don't want any problems with the shifter hitting the bench. seat. Buddy of mine has an M21 so of course leaning towards that one.
Muncie should swap right in without much issue, just make sure your shifter is equipped with the correct shifter extension for the seat you have. Yoke may be an issue (if it's not a 27 spline), may not and I would likely change your clutch and throwout bearing though for a fresh start (depending on whether you find a 10 or a 26 spline Muncie).

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Borg-Warner T-10 out of a early 80’s Camaro/Vette had a 2.88 low gear, this works great with higher rearend gearing. And probably are cheaper than a fragile Muncie. That’s doesn’t matter in your case, but it would help someone with higher rear gears.
 

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1969 Nova . . 2dr . . Chino Valley,Az USA
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Hi Dom - how it's going. Did you ever find that front bench seat ? (I still have my spare - and, a quick trip to Chino Valley ; and we can load 'her up) .

Talk about 'steep first gears' = my T 5's first gear is - 3.97 , with my stock 3.08 rear. But I like it real well behind my L 6 . . get up & go .

Here's my question - you don't want an O D trans ? The TKX , seems to be the hot ticket , and would be really great.
But I know you like to keep that original car , more original looking. I get that .

Here's one listed in Prescott Craigslist - I never could find one local, when I was looking ; so I bought another Saginaw . . then, changed again , when I found my T 5 .




.


just info .

Please Be Safe - out there .

jim
 

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Discussion Starter · #11 ·
Thanks Jim didn't find a bench seat yet, mine is still good just wanted something with stiffer springs. I do like to keep the car original as much as I can. ( The original 350 is still in the garage with the original 3.42 gears) I'm old school always wanted a Muncie. I would like to take the car to the track sometime and since the Saginaw is original to the car I would hate to blow It apart at the track.lol. Thanks for the info brother!👍
 

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1971 Nova 350 SS 4 speed bench seat Classic Copper
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Any can fit and all are externally the same.

M-20 is a wide ratio, M-21 is a close ratio and M-22 is a H-D close ratio.

M-20 and M-21 have a coarse spline clutch gear or input shaft.

Both have a small driveshaft yoke, same as a PG, T-350 or Saginaw.

M-22 has a fine spline clutch gear and large T-400 driveshaft yoke.

Thanks
Randy
Too much misinformation here to list
 

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Agreed, you are correct, I was trying to give the basics, not every variation.

I guess GM was preparing for the B-W ST-10 changeover.

Thanks
Randy

I believe that anything after 1970 has the turbo 400 driveshaft yoke, not just the M22. I have an M20 with fine spline input shaft and t400 output that is from a 1971 vehicle.
 

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I'll vouch for the 2.20 first being not as streetable. The close ratio Muncies can be driven on the street, of course. But those ratios are a little slower out of the box, especially with more street friendly gearing (say, 3.55 and down). With 4.11s you won't feel that as much from a stop with the 2.20 first gear, but then again that's a tough car to go down the freeway with at 75+ on a long trip with that gearing. Overall street use will be better with the wider ratio trans. My experience is about 4 months with a '66 that had a close ratio Muncie and 4.11s in the rear, and over 90K miles in a '65 with wide ratio muncie and 3.31 rear. Either Muncie a great trans.
 

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With 4.11s you won't feel that as much from a stop with the 2.20 first gear, but then again that's a tough car to go down the freeway with at 75+ on a long trip with that gearing.
But with the right engine and traction, not too many lost light to lights... And $20 dollar bill test, I still have all my $20's.. LOL
 

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M21/4.11s/SBC is a classic Chevy launch. If it never sees the highway, then I understand it.
And an M22/4.11/SBC is a classic Chevy Lunch!! :p
 
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