MUNCIE 4-speed QUESTION (???)

Maybe a stupid question, but... how can I know if my Muncie is a M20 or a M21? The number on the Maincase is 3851325... which means it's a 63-65 M20 OR M21... but I can't find the way of knowing if it's the M20 or the M21!
Your help will be appreciated!

 

The only way to be certain is to look inside and count teeth.

 

Thank you!
Anyway, the rebuild kits (bearings, gaskets, etc...) are the same for both M20 and M21...

 

You could also count turns, put it in 1st, see how many turns of the input shaft to get the output shaft to go around exactly one turn

 

IIRC ,check the dia. of the countergear shaft M-20=7/8" M-21= 1"

dave

 

I thought the countershaft diameter has to do with how old it is, not what ratio.

 

I think that both M20 and M21 are 7/8" if they are 63-65... and 1" if both are post 65...

 

Look at the date code on the case.... but only if it's the orginal case. You need to do all the checks to see if it is what the date code is.

· Fine Spline input shaft with 2 grooves
· Check the gear teeth angle
and the ones they've listed above.

 

The gear teeth angle is the same on the M20 and M21 (it is different on the M22).
And about the input shaft is: 1 groove on the M21 and none on the M20 (63-65)..... if I'm not wrong....

But in any case, I have to open it...

 

http://www.5speeds.com/muncie2.htm

^this helps a lot.

Funny you should post this, I was just looking it up myself to decipher which muncie I have sitting around myself to sell.

 

The input shaft on a M20-21 has 2 grooves out near the tip. Least all three I have do.

 

some have been rebuilt so many times the best way is to open it up

 

I'm just amazed at how difficult this is.....either the input shaft turns 2.5 turns (M20) or 2.2 turns (M21) when the output shaft turns once, in 1st gear.

 

It's a time zone thing.

 

What if there isn't a yoke in it squirrel? then what?

 

put a dab of paint on a spline....at the junkyard, we had a little bottle with yellow paint in it, very handy

 

still need to open it up that m21 could be a m22

5speeds.com is a good reference but isn't 100% on all years

 

Think M22's got the same output shaft spines as a turbo 400. Not much mistaking one for an M21.

 

M-22's have 26 spline input and a large TH 400 size output.

M-20 and M-21 have a 10 spline input and either 1 or 2 grooves on the input shaft.

 

I was always told that it's the number of grooves on the input shaft.

M-20= 2 grooves
M-21= 1 groove
M-22= 0 grooves

I have an M-22 out of a Ls6 Chevelle and there are no grooves.

Two people, whose opinions I value, told me this seperately. The idea behind it was the more desirable the less grooves, to stop counterfiets.

 

Just saying, so disrespect here. From what I've researched in the past about the grooves is that they can be missleading. Thru the production years and manufacturing, grooves sometimes where never put on the shafts. Also thru the years of possible rebuilds and parts swapping the grooves don't mean a thing.

 

Nope early M22had the same splines & outpu tsplines as the m20 21 Later M22 had the fine input spline & the big output.
You shouldn't go by the grooves either they could have been changed over the years