Technical 4 Speed transmission

Can you guys tell me what these transmission are?

 

Muncie
Casting: 3885010 Years: 1965 - 1967 Ratios: M20 2.52 1st , M21 2.20 1st, M22 2.20 1st

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

 

So is Casting: 3885010 a M20 or M21?

 

Check the Web Page. Input shaft rings will tell what it was originally. Parts may have been changed.

 

Ending in 903. Borg Warner Super T-10. Hard to see how many grooves are on the input shaft. 6 grooves? 3.42 first gear? Go to PontiacPower.Org/BW.htm for the full rundown. I am Butch/56sedandelivery.

 

The input shaft is 26 splines on 3885010

 

The 903 case is 26 splines as well

 

Fine spline makes it an M22, speedo outlet on the passenger side makes it about '66 or newer. There are 2 transmissions there, other one looks like a T10.

 

Anyone else have info?

 

The Muncie could be a Frankentrans. That fine spline input is a 1970 or later transmission. The 1969 and earlier ones were coarse spline inputs. Two radial rings on the input was a wide ratio 2.52 low. one ring was a 2.20 low and no rings was the "rockcrusher" trans. If the shift shafts on the side had a stud protruding for the lever mounting that was a 1968 or earlier transmission lever. 1969 and later had a hole drilled in it. IIRC the rectangle for the shift lever was the same size at least through 1970. Memory is getting dim but IIRC 1971 and later all used a large output shaft spline that was the same as TH400's. But I also think that you could use a fine spline input in an earlier transmission but I could be wrong as when I used to blow up Muncies on a regular basis in my OT Big Pontiac I searched out the 69 and earlier ones because I had to change out the output shaft as it was 6 and a half inches longer than the regular transmissions used. The curse of the big Buick Oldsmobile and Pontiacs with a four speed.

 

If a Muncie case has "Patent Pending" cast on it that is a 3/4" cluster shaft, 63-64 and early (?) 65. Very undesireable unless a restoration. All Muncies Achille's Heel is the cluster shaft bores. They can wallow out after a lot of abuse. I've had the cases crack in that area, it seems that the case will almost stretch between the input and the cluster gear. I also have had them to the point that the cluster shaft will fall out of the main case without pressing them. That scraps the case out obviously. I have had Muncies in a lot of cars since 1968 and have sent a lot of them to "Muncie Valhalla" over the years. They will take a lot of abuse to a point...........

 

I wish I could post the photo here of one that I exploded in 1970. I literally broke it into several pieces. It locked up at about 75 MPH in 4th gear. Broke the extension housing cleanly in two, blew out the side of the main case at the bellhousing side and split the aluminum bellhousing in two pieces. Best that we could figure out from the carnage we could find is that a gear on the mainshaft fractured and jammed it up. Well at least from the broken gear pieces inside that were left over. I still have the mainshaft at home, the output splines are twisted but I think that was from the holeshots I used to pull with it......still kind of a cool memento.

 

M-22 rock crushers have the drain plug like this picture you included (quick visual ID)


Never seen a M-21 with one...except for the ones I drilled out to make look like M-22's that is. Rock crushers have square cut gears so it easy upon inspection. Like the guys have said, usually course splines input and turbo 400 style output shaft (also found on the M-21 HD close-ratio corvette box in LT-1 cars from early 70's from what I have seen).

 

Still at work so I grabbed a early parts catalog. Looks like 70 standard duty uses the same input gear back to 1965. So that would be a coarse input shaft. Heavy duty 1970 is the same as 71 and later Muncie and that should be the fine spline input shaft. Could not remember the break point on 1970's, sorry about that. This information came from the last printed parts catalog for Chevrolets thru 1975, dated April 1983.

 

And IIRC all service Muncie cases also had the drain plug like the M-22's. I'm using a Rockcrusher case in my OT Pontiac with wide ratio gears in it.

 

M-20 has 7/8" countershaft , m-21-22 have 1" countershaft , fine spline input can be m-21 or22, m-22 gears are less helical cut [less angled] than m20-21, after 50 years you're liable to find most anything in most any case , worn countershaft case bores are easily fixed w/a bushing...
dave

 

Beg to differ on that. 64-65 case part number is 3851324, 66-74 case part number was 3925659 with no difference for M20-21-22 option. So GM was using the M22 case with drain as service replacements.
I was wrong on the cluster gear shaft size, it was 7/8 from 1963 to 1965 not 3/4"
1" was used 66 to 74.

 

Shovelheadrider has some good info. I'll add that the 3885010 case is 1966 and 1967...and has a 1" pin. The earlier Muncie with case ending in 1325 was 1964 and 1965 with the 7/8" pin. No rings on the input can mean M22 but can also be a replacement input. 1966 and 1967 cased Muncies in M22 form are SUPER RARE. So doubtful it's one of those...there were many M21s though back then it seems....and as mentioned the fine spline input being a signal of an M22 didn't start till 1970...so it might simply be a replacement input shaft...

 

You do know this photo is of a BW Super T-10, and is not a Muncie. The site I posted will have everything to decode a BW T-10, PontiacPower.Org/BW.htm. I am Butch/56sedandelivery.

 

Shoverheadrider....those part numbers you cite aren't casting numbers...they're different. It's a GM part number oftentimes the casting number is a near number...in this case...the early case you mentioned is casting number 3851325...and the later one is 3925660....sometimes they have no correlation at all...

The 3925660 cased Muncie was factory equipped in 1968 and 1969 cars...they show it as a replacement from 1966 to 1974 because itll work....but as far as what specific year it actually was used in production is what I included above.

 

Not true....in 1963 to 1965 all Muncies had 7/8" cluster pin..regardless of gearing. 1966 to 1974 Muncies had 1" pin regardless of gearing...the ratios inside had no bearing on the cluster shaft pin size...

Also fine spline input can be M20...as after 1971 or so...they were all fine spline

Rest of your info is good...

 

thanks for the correction....
dave

 

So after ready all of this the 3885010 is more than likely a M21-M22 and the other one I posted is a super T-10. now for the next question which one would you take if could only choose one.

 

Black Panther, Sorry, I should have said casting number or part number. I've been dealing with GM part numbers since that fateful day in 1970 that I said "sure, I'd love to work in a parts department".......and I just assume everybody knows what I'm saying.

 

Hot Rod Ron, I think the Borg has a stronger case. Other than that I cannot remember the differences. Also the fine spline input on the Muncie was supposed to be a tighter fit to the disc. I did have one or two M20/21's coarse spline inputs with cracks on them also. I never saved any of those "trophies" though.

 

HotRodRon....the Muncie is likely a M20 wide ratio..with a chance it's a M21 close ratio. Not very likely it's a M22.

 

Thank you all for the info on this. I am going to choose the 3885010 and tear into it too see what have.

 

Why would you take a Muncie over a super T-10?

 

FWIW I would probably go with the Borg-Warner..

 

There are pics of two different transmissions. One is a Muncie, and one is a Borg Warner Super T-10. Do you have any photos of the other side of the trans, with the side cover and shift arms?