Is there any difference between the M20 and M21 transmissions as far as strength goes? I can get a M20 with main case changed to 660 case with 1 inch counter shaft. Would this be about the same as a M21? Other than gear ratio. Thanks in advance for any help I can get.

The M-22 about 475 to 500(?) or so............

The M-21 will go 450 t isn't it guys??

And the M-20, 425 t or so??

They say the new supercase with the italian gear set and steel mid-plate is good for 600+ t...

Pricey tho, imho....

pdq67

No difference in strength between the M20 and M21 but if I were going to put a lot of power to one I would consider a steel mid plate. They are available at most of the rebuilders.

By the way the new Italian gears are not so new! They have been the original suppliers of Muncie gears for years. (Antonio Maserio sp.)

Jim,

The diff. between the M-20's, 2.52 or 2.56 first gear ratio and the M-21's 2.20 will up the M-21's torque capacity a schosh.

Same thing with the flatter angle cut of the gear teeth between the M-22 and the steeper M-20/21 so the M-22 is stronger..

And all this said, I figure that the Italian gear SETS are made out of a stronger/tougher alloy steel and when coupled with the steel or ductile-iron mid plate is a bunch stronger imho!!

Thus the hoped for above 600 t capacity!!!!!!!!!!!!!!!

pdq67

The less the gear multiplication the stronger the gearset is that is a physical fact. In a Muncie thats not really the problem. The case is.

The only difference between the M20 and M21 is the number of teeth on the input and counter gears. All M21’s have 26 teeth on the input gear while the M20’s (with a 1 inch counter gear pin) have 21 teeth.

The counter gear tooth count is as follows:

M21 = 27-22-19-17
M20 = 25-22-19-17

Notice that only the front (driven) gear on the counter gear has a different tooth count (to engage the different input gears). The counter gears that engage 1st, 2nd, and 3rd gear have the same tooth count in both transmissions.

First, second, and third mainshaft gears have the same tooth count in both the M20 and M21. In fact the exact same gears are used in both transmissions.

1st gear = 36 teeth
2nd gear = 30 teeth
3rd gear = 27 teeth

With nothing more than changing the input and counter gear you can change an M20 into an M21 or visa versa.

I believe the difference in strength is negligible between the two transmissions.

I think it has something to do with the two gear drive centerline's spreading a schosh b/c of the aluminum case is all

So that is why the iron mid-plate helps.................

I thought about creating a front iron plate too for more support................

pdq67