Technical Muncie 4 speed identification

I'm sorry i'm sure this has been asked before, but i am looking for some verification about this muncie 4 speed i bought for my car. The case number is 3885010, it is a 10 spline input shaft with 1 ring on it. I have some other numbers i will include in the pictures. From what i have looked up i believe its a 66-67 m21 but id like if anyone has any input to what it is for sure. Thank you for any input. I paid 300 bucks for this transmission a couple years ago and plan to replace a blown up saginaw 4 speed in my car.

 

I am no expert on Muncies but that looks exactly like my M20. 62ish Impala

 

Casing # 3885010 = 1965 – 1967 1-inch cluster [or countershaft pin]
One groove on the input = M21

Edit: for the street, give it a bearing and synchro "rebuild" and add "hook sliders" . This prevents jumping out of gear in 2nd & 3rd on deceleration [the most used gears on the street]

Muncies are childs play to rebuild, but be warned........it is 53 years old

 

At this point in time , the trans may or may not be what the numbers rings on the input would suggest it is . For example the Muncie m-20 in my car is parts of ,at least, 5 different transmissions . The way most were beat on in the muscle cars and cars since , there's very little chance that you have a virgin. Really doesn't matter functionally if it does what you want ..

 

Thank you!

 

With an M21 and M20 the main differences are the Input and Countershaft [the countershaft is geared lower on a M20 widening the ratio between 3rd and 4th]
All the other gears , hubs etc are interchangeable between these two.
The countershaft drive gear must match the input gear!
so if you build a "Bitsa" with a M21 input, it will need a M21 countershaft making it a M21 Trans.

They are simple transmissions, but there is 2 different tooth count M20's [with 7/8" countershaft pins]
But ^^^ is an M21

 

Single groove ten spline denotes M21 Close ratio with large input bearing, #3885010= one inch bore 1965 to 1967 build date. 07 march.
I'm pretty sure but until you pull it apart and check the insides , I hope this helps

 

Great transmissions, lots of part and rebuild kits available. My shop out here will rebuild with new synchros, bearings, updated sliders, etc. for $500 cash. When he's done, I can shift through all the gears with one finger.

 

The one I sold for $400 had a factory installed drain plug and first gear wined out like a GMC 6-71 blower.... It came out of a "very rusty" '69 Camaro SS big block car....

 

The one that was in my uncle's 1969 Z/28 always made that noise; I think it was a loose/worn mainshaft from years of being beat on when it was a drag car. He had it rebuilt by a guy who was pretty good with them, and he did a good job with his, although I remember when we brought it to his house, he was busy smoking marijuana and telling us, "I can rebuild these things with my eyes closed!" to which we pleaded that we would prefer he do it with his eyes open. That was around 1982 or so... where did the time go?

 

That was about the time I sold mine... M-22 Rock Crushers have gone up boocoo bucks since then.. Yeah, where did that time go???.

 

Bought a supposedly rebuilt M21 off of Craigslist for $500 from a sketchy guy...of course no paperwork to prove the rebuild, so you know it hasn't been done. Took it to my transmission guy to check it out and, yep, no rebuild. But the really great news was that it was actually a M22 Rockcrusher that the guy could have gotten $2k for. Payback gods were good.

 

Thanks for all the responses! I pulled the side cover off and counted gear teeth to confirm its an M21.

 

your answer hereMuncie 4-Speed Identification Guide - Chevy DIY