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Trans.: Interchangable?



I just finished assembling my restored '72 w/the 385 Fastburn
crate engine (it's been 18 mo.s) and I have a question about
which trans. I have.
Can anyone tell me what the shafts look like on all 3 Muncie models and is it possible to interchange the cases and shafts?
I'm looking @ a box that the owner thinks is an M-22 (which I want to upgrade to); it has a "fine" output shaft w/2 plugs on the
side of the case. Any ideas? would be appreciated.
PS - I'll post pics when I get them.
Hi Mark,
Here's the basics:
M-20: two grooves on the input shaft
M-21: one groove on the input shaft
M-22: no grooves on input shaft
In the mid sixties only M-22 had drainplugs
By the late sixties all muncies had drain plugs
One of the best ways to be sure is to get the code off the trans. It will be on the right side, on the center support plate, reading bottom to top. The only sure way is to pull the side cover and check the angle of the gears. M-20 and M-21 use approx. 45 degree angle, M-22 uses approx. 22 degree angle.
Any gears can be put into any muncie case so pulling the side cover is the only way to be sure.
M-20 has a 2.52 first gear ratio
M-21 and M-22 have a 2.20 first gear ratio
Also M-20 and M-21 replacement input shafts did not have any grooves, only the originals from the factory.
Hope this helps
P.S. make sure you are looking at a muncie and not a borg-warner. Muncie has seven bolts in the side cover, borg-warner has nine.
Interchangeable trans. parts

Yo Mike,
I started collecting manuals, catalogues, resto. books and other stuff to help assemble my '72, but nowhere have I been able to find the info. you supplied!
This helps alot - thanks!!! Mark
You're welcome!
Try to get me the stamped code and I'll try to decipher it for you.
Also get me the numbers off the main case and tailshaft housing, these will help also.

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