Got a question for you. I currently have 2 muncie transmissions. One is a 1" M-20 (based on case code) and the other is a 7/8" M-21. The M-21 has the better of the internals. Can I take the M-21 gears and put into the M-20 case just by changing out the counter shaft gear? From what I understand, this is all that is needed but I want to check with you two, or anyone else familiar with muncie trans, before tearing into this project.

Also, this is going in a 69 Chevelle with 3:55 gears, so will the trans gearing have any appreciable effect on driving? I know I would probably be better of with the M-20 first gear ratio but the M-21 has the better gears.

As always, thanks for the help!
Durand

Cluster gear is specific to the 7/8" or the 1" - not interchangable.
http://www.muncie4speed.com/munciecat.pdf
Might overbore the hole to 1" to fit.
Post your case #'s to verify your findings.

Mike:

I realize the cluster gear is specific, but was wondering if I could buy the cluster gear for the one inch case and then swap the guts over. I was thinking since the gears, sliders, etc were good in the old 7/8", I could buy the cluster and use the 1" case.

Appreciate the response!
Durand

Got a question for you. I currently have 2 muncie transmissions. One is a 1" M-20 (based on case code) and the other is a 7/8" M-21. The M-21 has the better of the internals. Can I take the M-21 gears and put into the M-20 case just by changing out the counter shaft gear? From what I understand, this is all that is needed but I want to check with you two, or anyone else familiar with muncie trans, before tearing into this project.

Also, this is going in a 69 Chevelle with 3:55 gears, so will the trans gearing have any appreciable effect on driving? I know I would probably be better of with the M-20 first gear ratio but the M-21 has the better gears.

As always, thanks for the help!
Durand

Durand,
Based on my understanding of your question, YES, you can put ALLLLLLLLLLLLLLL of the M21 (close ratio with the 2.20:1 first gear) guts into the later case with the 1in cluster gear shaft EXCEPT the cluster gear itself. You WILL need to get an M21 cluster gear for a 1in shaft.
The 63-70 M21 input gears will all interchange. BUT the 63-65 and 66-70 M20 input gears are different and thus will ONLY MATE with a 63-65 and 66-74 M20 cluster gear respectively.
Now, while we're on the subject of swapping Muncie internals, take a look at the tail shafts. Specifically, look at the surface where the speedometer DRIVE gear is pressed onto the shaft. The early tail shafts had a short surface (just wide enough for the gear to be positioned in ONE location). Whereas the later tail shafts have a wider surface which will permit the speedo drive gear to be positioned in one of two different locations. If upon examination of the shafts, you discover that one shaft has the short surface and the other shaft has the long surface----------------YOU NEED THE SHAFT WITH THE LONG SURFACE TO LINE UP WITH THE SPEEDO HOLE OF A TAIL HOUSING WHICH HAS THE HOLE ON THE PASSENGER SIDE!!!!!!!!! If you're going to use a tail housing with the speedo hole on the driver side, it won't matter which tail shaft you use.
If you need pictures to clarify this, I can post them tonight when I get home.

Tom:

I think I saw a picture of the shafts posted last week. You answered my question. If I get my act together and work on my car like I should, I would like to meet you at CB 09 and personally thank you!

Durand

Here are the 2 different main (tail) shafts. They are 100%, TOTALLY interchangeable. The ONLY difference is the length of the surface for the speedo drive gear.
The early has the short surface, the later has the longer surface. The shaft with the longer surface can be used with EITHER driver or passenger side speedo hole. The shaft with the short surface can ONLY be used with a tail housing that has the speedo hole on the DRIVER SIDE.
http://i65.photobucket.com/albums/h219/DZAUTO/Driveline/100_0214.jpg


Notice the tail housing with the passenger side speedo hole (left housing) has the hole further back. This is why a tail shaft with the longer surface is required when used with a tail housing that has the speedo hole on the passenger side. :thumbsup:
http://i65.photobucket.com/albums/h219/DZAUTO/Driveline/100_1769.jpg
http://i65.photobucket.com/albums/h219/DZAUTO/Driveline/100_1769.jpg

Tom:

Much appreciated!

Thanks,
Durand

Hey Durand,
Did the cluster shaft arrive yet?

Tom:

Yes! I sent you an e-mail. Again, many thanks for all your help! BTW, when you commented about the countershaft hole being elongated, you were correct. I thought since the shaft fell out as if nothing was holding it, the wrong shaft was used. Error in "thinking" on my part. But on a positive note, the internals are good and I am going to find a machine shop to open the 7/8" bore to a 1" and use the shaft you sent along with a new countershaft gear for the M-21. I will verify it is an M-21 though since the previous owner had no real clue about the trans and was told it was an M 21.

Durand

Durand, DO NOT locate a machine shop that can open a 7/8 case to 1in!!!!!!!!!!!!
It is imperative that you locate/use a source that has MUCH EXPERIENCE at doing this process! Larry Fischer of D and L Transmission http://www.dandltransmission.com/ is the ONLY place I use for having this done! This process requires critical accuracy, AND, the front and rear holes are different sizes (check each end of the shaft and you'll see what I mean). But I'm sure there are others, probably Cajun John in TX does it.

Tom:

I may just use the 1" case and get the cs gear for the M-21 set-up and just swap over. This sure is a learning process for me. Thanks for the schooling and keeping me from screwing up even more!

Durand