Technical Muncie M20 for dummies

Hey guys so I just bought a Muncie 4 speed M20. I don’t have a clue about these things. The guy I bought it from said it came off a Pontiac and that’s all he knows. I have a 3 speed column shift manual 1963 impala that had a Saginaw in it. I know enough about that tranny since I removed it and opened the inspection cover. So now that I’ve got this 4 speed M20 muncie sitting and waiting to be installed what do I need to do to get acquainted with it? The previous owner did open the inspection cover to take photos of the inside however it was reinstalled with the shift forks in the correct positions.
So I’m the dummy . How do I know if this tranny is good to go? What should I do next? I plan on putting this in my ‘63 impala in the next couple weeks when I get all the stuff to properly install it.
Thanks

 

I would talk to the guys at Medtronic’s and get a bearing and syncro kit for it and do those and a good inspection at a minimum.

 

First question, did it come with a decent shifter? A new Hurst competition plus and linkage and correct shift handle won't leave much for a beer and a burger out of 800 bucks if you can get it for that.

 

Learn from the master. Check out gearboxvideo on YouTube. You might be some time! Buy Paul's books too.

Chris

 

If you believe the pictures you were given, fill it with gear lube and install it. If it doesn't shift for shit, pops out of gear, growl's or howl's like a banshee, it's time for a rebuild. At the minimum, I'd reseal the speedo bullet and replace the rear seal, just incase it is good. Then you can see if the counter shaft is leaking in the front of the case.

 

The all important tailshaft bushing is inexpensive and keeps your driveshaft from wobbling and tearing up the seal. Got any pics of the inside when it was open?

 

I bought an M20 here. The pictures looked good. Opened it up when I got it home. Innards looked fresh. New synchros, etc.

So I put it in my car. I already had a shifter for it. It shifted well. I glossed over the fact that yhe countershaft pin was recessed quite a bit and it leaked.

Ultimately I broke it and I had a good manual guy go through it. It needed some new parts and it was modified for a 1" pin and a 2.52 1st gear. The builder said it was garbaged together and was surprised I said it shifted so well.

Lesson learned about used Muncies. I would buy a new one before another "good" used one. While yours is out, it should be gone through. All told I am into mine for around $1400.

 

Haven't done it for a while , but I made good side money starting in the late 60's " Frankensteining" muncies together out of used parts , bushing cases , mixing & matching parts, welding ears back on , at the rate guys broke them back then , it was a good gig . With a little effort , even factory shifters could be " tuned up" to work really well , I gotta admit ,I always had a thing for the reverse lock out finger hooks shifters . With the quality Italian gears available now , muncies can be rebuilt reasonably , there was a time when parts were scarce ,now they're pretty easy to source .

 

Early 4 speeds are not to be feared, however I would dissemble and thoroughly inspect and replace warn parts. The cluster shaft can be worn along with the thrust washer. The synchro teeth on the first through fourth gears can be worn badly or missing and even with new brass blocker rings, will not work well.
Definitely find a good Hurst shifter. They also can be disassembled, cleaned and re-lubed . The shift rods kit with correct trans levers is important and new lever bronze bushings are required.

 

It has a hurst shifter and linkage minus the knob. That’s part of the reason why I got it. If I remove the cover without it being in neutral how do I get it closed back up?

 

Slide everything back into the neutral position and put the cover back on.

 

You will need a short dummy shaft to put the transmission back together. I had one made out of steel , by a friend. But you can use a wooden one . Makes assembly way easier. Other than this putting that transmission back together is fairly easy.





Bones

 

Paul Cangialosi has a great book on Muncie 4 speeds and how to rebuild them, if you are interested? Book is really detailed.
Auto Gear in NY has hooked me up in the past with the Italian gear sets and locking sliders.
Had to use one of their cases on a rebuild a few years ago to replace a cracked original one.

 

Yep, and great YouTube vids, as Gearboxvideo, mentioned above.

Chris

 

I put a Muncie M20 or 21 in '62 Impala, 3 on the tree, some years ago. I remember shortening the driveshaft by an inch or two. Just a heads up...

 

I don't think you should have had to shorten the drive shaft, same length overall (???)

 

The regular 3 speed in the 58-64 chevy full size cars was a short version of the muncie 318. So it would make sense if he had to shorten the driveshaft. If the OP has a Muncie 319 (overdrive) it is about the same length as a muncie m20 or m21 4speed.
FWIW, the chevy 1/2 ton trucks up to around 1965 used the same short muncie 318.

 

Muncie 4 speeds have to be in second gear before the side cover can be removed or installed.

 

Yeah I saw Paul’s book on Amazon and I’ve glanced at some of his videos. Seems kind of daunting the way he rebuilds them. Aren’t muncies supposed to be the best trannies? How can someone wreck one? A dumbass not having oil in it?

 

A833 cast iron case Chrysler was the best 4 speed. Muncies, not so much.

 

Anybody ever fix the leaking countershaft themselves? My understanding is you need to disassemble, and have a steel bushing installed in the case?

 

Only if it is wallowed out of round do you need the case bored and a sleeve pressed in.

 

That is the only way I know to properly fix the leak. I've never seen a steel bushing used (I guess it would work fine) I've seen bronze bushings used many times. You also need to put a bushing in the mid plate also when putting one in the main case.

 

Is there another reason it would leak? Truth be told I have one that was leaking, so I replaced it and it’s sitting under my bench. I just never got around to inspecting it further

 

any concerns with doing this by hand, or is it best sent to a machine shop

 

The countershaft location is kinda' critical, I think I'd leave it for a machine shop.

 

Agreed 100%
The counter gear pin needs to be parallel to the main shaft so the cluster gears are running on the main gears for normal wear. That is why the mid plate needs to have a bushing in it also. I would take the case and mid plate with the counter gear pin to a machine shop.

 

Muncie 4 speeds are great transmissions, but you have to remember they are around 55-60 years old now. Most, if not all have been rebuilt with other used parts.. So most of the time they have been patched together.
If you properly rebuild one with quality parts and the driver doesn't abuse it, they are usually very reliable.

 

Mine had the 7/8" pin. It walked backwards and it spun, dug up the mid plate like a giant lathe bit.

So the builder I used went with new Italian gears, bored the case for the 1" pin. My old one was perfect somehow. He also used some good used parts like the mid plate, yhe reverse idler, etc. I had already replaced the side cover with one from Auto Gear.

 

Find me a vintage Muncie 4- speed case that's not wallowed out !