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-   -   m20 to be installed! (

pixelmonkey 04-23-2010 09:37 AM

m20 to be installed!
well... life took a few twist and turns. have my project almost ready to be resurrected.

recently purchased a m20 from 68-69. no shaft play, all gears clean without chips or missing teeth and just a tiny bit of wear on the forks.

i'm looking at the transmission and wondering if it should be rebuilt before even considering installing. from visual inspection, are there key wear points that should flag it as needing rebuilt before running?

couldnt find an exact answer, but how much fluid will the transmission need? last check, 40 oz. is this correct?


cobalt327 04-23-2010 11:09 AM

My M20 took about a quart and a half. Buy 2 quarts and use what you need.

You want to fill it after it's installed so all the moving, tipping, etc. that's done during the install doesn't create a mess from leaks from the ends. In my case, filling was easiest to do through the shifter boot from inside the car- but be sure you do not drip any on the carpet! Use a big old towel, etc. to keep things clean- the smell lingers.

The correct fill level is similar to a diff- fill to the bottom of the plug- or slightly less (you just want to be able to wet a pinky finger when inserted).

Amsoil's 75w-90 GL4 MTG lube is what I've used. I had no experience w/synthetic lube like this before using it, but there have been no issues since using it and the tranny ran and shifted fine.

BTW, GL-5 spec lube is said to be hard on brass- don't use it unless it specifically says OK for use w/brass tranny components. Some synthetic GL-5 lube is said to be compatible w/the Muncie's guts- but check first! Or, just use GL-4 and don't worry about it. lol

Good luck.

eloc431962 04-23-2010 03:54 PM

This needs to be in the transmission-rearend section.


AutoGear 06-09-2010 02:13 PM

muncie spec
Saw this post from days gone by. I work for Auto Gear in Syracuse and we produce and sell muncie parts. Heres the deal; the case will hold a quart and a half. My SuperCase will too. If you add a quart and a half, the trans will run hotter and eventually the oil will work its way out the front drain hole and if it doesnt drip on the ground as GM designed it; it will end up on the clutch...bad news

We; and most of the builders reccomend a quart.
Additionally; we ONLY reccomend NON synthetic NON blended 85w90 or the like WITH the GL-4 designation or GL-5 with the MT1 listing. These are safe for the old school synchros. The brand we recommend is Valvoline in the white bottle 85w90 or whatever it is. The blue bottle is a blend and has caused problems in the past. Synthetics are TOO slippery for the synchros to use as a friction brake and they end up clashing...

This isnt a advertisement for my company; Im trying to save you guys on parts, although if you have a gearbox question, just ask

a1supersport 06-09-2010 04:08 PM

Would you know who would have the best deal on M22-close ratio gearsets? I know where there's an old M21-wide for dirt cheap. Was thinking of making my own rockcrusher. :D Trying to buy an original is kinda pricey. :(

AutoGear 06-10-2010 07:38 AM

Thanks for the interest in keeping 4speeds alive. I don't want the mods to annihilate me for posting info; but you can verify this outside of me.

Replacement gears come in 2 flavors. Italian (Masiero and Euroicambi) and everybody else (asia and india etc.)
The italian stuff is more expensive, but better quality than the offshore or OEM gearsets. Notice I didnt say the offshore stuff is no good. Its plenty serviceable for a street car, as long as your visual inspection is top notch before assembly.

That being said, my italian vendor moved across town and to set up tooling takes time. I wont be importing any M22 italian stuff until late july.

So, for a hawaiian customer I would suggest Erickson's Gear in Seattle WA as he might have existing stock. If you want to go with offshore stuff, I cant recommend one way or the other because I don't deal with them.

However; If you don't really NEED an M22 and want that ratio made by italians, (we have several muncie ratios), I have plenty of M21 stuff, and so should Erickson's. Just make sure your case is in good shape, or buy an aftermarket one.

Hope this Helps, and if I overstepped my bounds, please let me know

pixelmonkey 12-06-2010 07:06 PM

thank you for posting info on the weight and quantity of oil needed for this transmission.

here are a few photos of the saginaw being removed and muncie taking it's place

Now to the next part.

It looks like the best option for a clutch release is going to be a hydraulic throw-out bearing. McLeod racing list a part number on summit for a M21 and M22.

Parts I have include:
- 12 lbs. Hayes aluminum flywheel
- mid 90's camaro stock clutch
- cast aluminum bell housing from late 60's corvette

Master is currently a stock Chevy S-10 from 1987. *several years are the same up to 1994*

From searching around on Summit, I find "McLeod RACING 13005" will work with the M21 & M22

Checked the case numbers on the transmission and it's 3925660 for the main housing, which would make it a M-22

If I need to order a new master and have braided lines built for the correct length, I'm 100% fine going about it this way. If I can use the current master and have the McLeod slave, while again having new lines made, I'm 100% fine doing it this way.

I dont want to have to buy parts multiple times.

Open for suggestions and part numbers, as the McLeod Industries site appears to be down.


TimoFinn 12-07-2010 12:34 AM

that case number can be m20/m21 too,and your gears are m20 or m21,not m22,count teeth to be sure which one you have :)

TimoFinn 12-07-2010 01:33 AM


Originally Posted by TimoFinn
that case number can be m20/m21 too,and your gears are m20 or m21,not m22,count teeth to be sure which one you have :)

I guess you have counted because you posted m20 installation... :rolleyes:

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