I am trying to decide on the right gearbox for my car. I have chevy 350 nothing special pretty stock. I am installing 3.70 gears in a ford nine inch. I have heard some say the M20 is junk but like the M22. Most people I have spoken with have 500+ HP and think the M20 crack and basically destroy themselves. From what I know (which is not much) the M20 is wide ration and the M21 is a close ratio don't know what the M22 is. I am not road racing or drag racing, just having some some fun on back roads. The car is a Kellison J6 so its not a very heavy car. Any ideas or suggestions are appreciated.
Cool car, though the search function is your friend: https://www.jalopyjournal.com/forum/threads/muncie-4-speed-m21-m22-rock-crusher.275038/ https://www.jalopyjournal.com/forum/threads/muncie-m21-vs-m22.353917/ https://www.jalopyjournal.com/forum/threads/need-real-muncie-identification-no-really.979494/ https://www.jalopyjournal.com/forum/threads/4-speed-transmission.1015085/ https://www.jalopyjournal.com/forum/threads/muncie-4spd-inherent-problems-weaknesses.94812/ Cheers, Harv
3.70 gears you could use any of them. The 20 is wide, 21 and 22 are close, 22 is stronger. Most of the used ones are wore out at this time, be sure to get someone knowledgeable to check it out before buying.
You will be fine with a M20. M22 is a close ratio as the M21 . M22 were good for road racing back in the day , good strength and has that air plane wine but you do not have to pay a premium price for an M22 . You can buy M22 internals and retrofit a M20/M21 case. If you want a stronger transmission, there are Super T10 and some aftermarket transmissions that are even stronger. Transmission internal gear ratios play a role when detailing out overall driving experience.
Also , you need to look at what year transmission you buy if a Muncie regarding input shaft diameter and spline count, output spline count to yoke spline and if buying shifter arm levers up to 1968 and some early arms used nut and washer and later used a bolt. Levers have a round cutout to fit the bolt .
The biggest issue with the Muncie is they are getting old and finding a good candidate is an issue. The M20 and the M21 are basically the same transmission, but what GM did was gear the whole counter-shaft ratio down to get a wider gap between 3rd and 4th gears. The only difference between them is the counter-shaft and the input shaft [the input drive ratio] 1st ,2nd ,and 3rd gears are interchangeable. Also the hubs and sliders etc. M20 and M21 were just the RPO option numbers. If the car had a 3.08 rear you usually got RPO M20 If it had a 3.70 rear you got RPO M21. The M22 is a H/D version of the M21 having 22 degree helix on the gears vs 45 degree on the M21 [so the M22 is noisier] and a higher nickel content. This reduces front/rear thrust when torque is applied but required high radial load bearings.[more rollers] All Muncies and later Borg Warner Super T10's have an external shifter on the drivers side of the tail-shaft. So if you want a central shift lever in the tunnel you would need a "dogleg" shift lever. Now for a lightweight Toy with under 400hp , Use a Borg Warner T5 from a 3rd gen Camaro. But you would need the matching bell-housing for the transmission. GM tilted the trans so the shifter [with the Bell-housing and Tail-housing]was offset to the drivers side in the Camaro. So if this shifter position is suitable, you would end up with a cheaper option [and better] The T5 shifts like butter ,has better ratios, and a 5th gear overdrive. You can bolt a Camaro T5 with a normal Chevy bell-housing for a central shift lever position, but the rear mount will be at an angle [a tail-housing swap remedies this , or a custom cross-member] Camaro T5's are cheap
What hooks best when you set the line? https://www.jalopyjournal.com/forum/threads/muncie-20-or-21.1249720/#post-14298282
The M-20 is NOT junk. It was the standard offering. In the beginning, (late 63 to 65) you couldn't specify what trans you wanted and usually cars with a 3-series rear gear got the M-20 and cars with a 4-series gear got the M-21. In 1966, when the M-22 became widely avaliable, it was mostly used behind the high horsepower big-blocks. M-21's & M-22's are both close ratio, M-20 is wide. Even though the M-20 has a lower first gear than an M-21, the main difference you'll really notice while driving, is the RPM drop between 3rd and 4th gear. The M-21's and M-22's don't have as much of an RPM drop between 3rd and 4th gear as an M-20 does. (And M22's are noisy as hell!) Early Muncie's get a bad rap because of the smaller countershaft than the 66 and later models, but for your application, any of them would work just fine. As far as the M20's disentigrating behind high HP and Torque engine's, yeah... they're not designed for that. Close ratio boxes have a higher torque capacity, M22's being the strongest of the 3.
If you don't have a trans, take a look at the AutoGear Muncie transmissions. https://www.autogear.net/motorsports/
In stock form? Well down the list #1 - A-833 #2 - TopLoader big input, #2.5 small input #3 - Iron Case Super T-10 #3 - Muncie M-22 #6 - Alum case Super T-10 #7 - Muncie M21, Muncie M-20, Early iron case T-10 #8 - any V-8 B-W T-5, unless built for racing. AutoGear has everything to make a stout aftermarket Mnncie.
For brute force the A-833 is strongest, then the Top-Loader. Muncie is the weakest. Racing transmissions like the Jerico were toploader based. The Tex T101 is based on the BW Super T10 [muncie-ish] Here is an M22 that was built for Road Racing and regularly got 650 ft/lbs pumped through it It has a custom gearset with square cut gears [noisy]fully rollerized, and a dogbox conversion. look closely and it has a steel midplate a steel girdle in the front of the alloy case. It would've been cheaper to use a jerico, but It needed factory numbers on the casing/ tail-housing for FIA regulations. For a stock[ish] 350 he could save a ton of money by using a stock T5 or T56 from a 3rd or 4th Gen Camaro/Firebird If he really wants a 4 speed ,a Borg-Warner Super T10 has better ratios than a M20 and is a newer transmission [Richmond T10 is the same box] Muncies M20's biggest ratio "mistake" was widening the ratio between 3-4 [here it needs to be closer] BW did this at the lower end
He has options but doesn’t need anything more than Muncie . If he doesn’t do continuous spirited driving he can grab a good ratio Saginaw. Interested in what his budget is.
I’ve had better luck with Saginaws holding up to abuse than Muncies. The only thing I have against a Saginaw is in a over 5000 rpm clutch dump from a stop it will strip the splines or twist off the input shaft.
I like my M20, I had it gone over after a missed 2-3 shift at 5000 RPMs. I have about $1400 total into it with a Auto Gear side plate, the rebuild and original purchase price. Auto Gear runs specials now and then. Midwest Muncie is another top quality vendor. https://midwestmuncie.com/ If I were in the market I'd check Summit as well. If I had to do it all over, I'd have gone with a T10 and spend my $$ only once.
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