Is it possible to simply swap gearsets out of a M20 to a 21 or must you buy the complete tranny? I have a good 21 and I'm curious if there are gearsets available that'll give me the wide ratio and 2.52 ( or better) 1st gear, i.e. convert my 21 to a 20 during a rebuild.

[This message has been edited by Gene Chas (edited 08-02-99).]

Anyone, is this possible to do? I'll even use Italian gears!

Gene,

A guy I know who restores Chevelles for a living says the guy who does his trannys can convert them from M21 to M22.My guess is you could go the other way. It would probably cheaper though to buy a refurbed M20. I don't have time this week verify the above info. I am out the door in about a half hour to to go to Reno for Hot August Nights and I won't be back until Monday. I will check when I get back to see if it is possible to do the swap.

------------------
Jeff ACES#841 TCG#158
68 SS396(454)
68 L78 Project
87 MC SS

Jeff, you're a lucky dog I'm jealous. Thnx a bunch .

Gene,
All you need is a matching input shaft/cluster gear. ALL, I MEAN ALL other internals are the same.
Do you have the 63-65 with the 7/8in cluster shaft or the 66-74 1in cluster shaft?
For the M-20 (wide ratio, 2.56 for 63-5 and 2.52 for 66-74), the small shaft cluster will only mate with the 63-65 input and the big shaft cluster will only mate with the 66-74 input.
ALL M-21 (close ratio, 2.20) inputs will mate with 63-74 clusters.
If I understand you correctly, you have a M-21 and want to convert it to a M-20, right? You just need a wide ratio input and cluster for this conversion. If this is what you want to do, a set of gears should not be too difficult to find. Let me know if I can help.

------------------

DZ, thnx. I actually asked the question for a friend of mine, Mike, who has the most cherry 66 ( complete resto ) I've ever seen. His problem is the 4.11's and the close ratio. We haven't found a Muncie "expert" here in western NY that we'd feel comfortable to do the work. Mike either wants to simply swap, or to have his 21 completely redone with the 20 gears.

If your friend has 4.10 gears and wants to put in an M20, his first gear will be really low. I put the M20 in my '66 and ended up putting in 3.42 in place of 4.10s. With the 4.10, first was useless, tire went up in smoke, and second gear was pretty much the same. $th is still 1:1, so no change on the freeway.
Although most parts are the same, I think ALL the gears need to be swapped, not just the cluster and input. Fourth is 1:1, but ALL the other ratios are different between the M20 and M21. Therefore, even the gears on the mainshaft need to be changed, but if they are within the design years someone else mentioned, they should swap easily.
I have done this swap, but many years ago.

If your friend has 4.10 gears and wants to put in an M20, his first gear will be really low. I put the M20 in my '66 and ended up putting in 3.42 in place of 4.10s. With the 4.10, first was useless, tire went up in smoke, and second gear was pretty much the same. 4th is still 1:1, so no change on the freeway.
Although most parts are the same, I think ALL the gears need to be swapped, not just the cluster and input. Fourth is 1:1, but ALL the other ratios are different between the M20 and M21. Therefore, even the gears on the mainshaft need to be changed, but if they are within the design years someone else mentioned, they should swap easily.
I have done this swap, but many years ago.

I didn't mention it, but the 4.11s are on their way out too.

DZ is correct. The only difference between the M-20 and M-21 is the cluster gear and the input shaft. The mainshaft gears are the same. Incidentally, i'm currently using an M-20 with 4.56s. Launches are good and hard, and it pull likes hell.

Like Larry said, ALL the gears in a Muncie are the same (even M22 rockcrusher gears are the same except that the teeth are cut at a different angle which precludes their use with M20 or 21 gears). What makes the 2nd and 3rd gear ratios different between an M20 and M21 is the difference between the M20 and M21 input/cluster ratio. Trust me, for example, if you take let's say, a 1968 M20 and M21, and remove the input and cluster from each and swap only those gears and put the 2 trannys back together-----------EVERYTHING interchanges. Honest!

While we are on the subject of Muncies, let me throw in one other tidbit. Many years ago(and I mean a bunch)when I first started building Muncies, I noticed that the 1-2 and 3-4 syncronizers in the Chev parts book had different part numbers. I NEVER could determine the difference, but I knew there was something different about them. Finally one day I asked an old timer what the difference was. He said "listen very carefully,--------------- the syncro slider is turned around the opposite direction on the hubs". Boy did I feel like an idiot!
So if any of you who have noticed 2 different part numbers in the book for syncros, they are the same. One just has the slider going the other direction on the hub.
------------------


[This message has been edited by DZAUTO (edited 08-04-99).]

DZ I've said it before and I'll say it again "You Da Man". BTW, Mike's decided he's gonna get rid of those 11's before he does the tranny, which makes perfect sense to me. Anyone have a 3.31 gearset for a 66 10 bolt?GM?

Learned some on Muncies. Even with my 3.73s I could stand a bit more 1st gear and I mean just for driving around town. During the next engine tear down, I might just use the info you guys posted. But maybe I'm misunderstanding you guys. If I swap out a similar ( my M21 is definitely a 69 and later) input/cluster from a 20, I get the 20's ratios? Or is it just the spread between ratios?

Larry, while I was in "dream" mode I pictured a richmond and 3.31's which would've given me a 1st very close to your 2.56/4.56. Yeah, it's gotta pull like hell!

Thanks all for your help!!

[This message has been edited by Gene Chas (edited 08-04-99).]

[This message has been edited by Gene Chas (edited 08-04-99).]

If you swap out the input/cluster for an M20, then you get the regular M20 gear ratios: 2.52, 1.88, 1.46, 1:1 (66-74).
Just for the record, 63-65 M20: 2.56, 1.91, 1.48, 1:1. And M21/22 ALL yrs: 2.20, 1.64, 1.28, 1:1.

------------------

DZ, thanks again. I think that going to be my own plan during the next rebuild. I'll call your boys in LI at that time to get the parts. And I'll let my friend Mike know as well. It certainly make the "swapo" ( that's a HRM term) real simple.

Thnx.

[This message has been edited by Gene Chas (edited 08-05-99).]