M-20 to M-21 swap question
 

What is involved other than just removing one & installing the other? I may want to make a change & want to know of any issues. The m-21 is out of a 68 going in a 69. Thanks

Tucker

All Muncie transmissions use the same case design, but I believe there were differences in the number of splines on the output shafts over different years.
If the M21 is from a different year than your M20 you may also have replace the slip yolk. I can't think of anything else that would be different though.

Except for the slip yoke and maybe clutch spline count, nothing much. However a short ratio doesn't work well with a lower numerical rear gear.

The 2.02 first gear is not going to be fun with a 3.08 or 3.36 or even a 3.55 rear gear

It's 2.20, but if the engine has enough torque it'll be fine.

68 and 69 should both be course spline. I think fine spline came in 71.

Ditto on M21 not best with tall rear gears unless it is a motor with plenty of low rpm torque.

If you get it one already rebuilt for any less than $1000 you should definitely buy it!! :0)

The side cover is different between 68 and 69. In 68 they used a 3/8" (fine thread) male stud to attach the shifter arms. In 69 they went to a 3.8" (course thread) female "socket".

Ed

But this is counter-intuitive. If the engine has a nice big torque curve (like almost all the engines we build today) take advantage this and use the wide ratio M-20.

I have a like new m21 that liberty built for me with a steel mid plate and bushed main shaft. I also had them build me a wide ratio with the rock crusher maserio m22 gears, i tried both transmissions with 4.11, 4.33 and 4.56 rear gears. For the track, the only choice is the wide ratio, I would not even think of using the m21 with anything smaller than a 3.70. The wide ratio and the 4.56 was a handful. Ended up with the 4.33 and wide ratio . Anybody need an m21 26 spline big output trans?

Great info guys. Thanks, I will have to do more research as I am going to pick the car up Monday or not based on my inspection. I am just trying to start my education on these cars now as I am going to be an owner soon. Thanks again

Tucker

ps Kevin nice to hear from you. Sorry my wife can't read a calender & we missed the last party. We are planning on coming down in May if the party is still on.

Tucker,
I didn't even realize that was your post I was replying to. :crazy:
Good to hear you might be getting a C3. Now you will be able to spend many fun filled hours laying on your back under a 40 year old car like I have been for the last few months. :rofl:
Send us some pics when you get it. :thumbs:

BTW, The party is still on. Should be a really good time, although I will only be there for Sunday.