[sbc500hpchevelle]

I know the M22's had straight cut gears and were very loud. The guy I just purchased my 68 chevelle from told me its an M22 and was just wondering If the #'s on the side could tell me that or if I have to pull the cover to see if they are straight cut gears. I found #3925661 and #3978764GM1 It definetly sounds like an M22 when you drive it.

 

[Mike]

FYI , the M-22 didn't have straight cut gears ,more accurate is that they had straighter cut gears.
M-22's had a 20° helix angle ,and the M-20/21 had 30° helix angles.
All 3925661 castings had drain plugs so you can't go by that.
Good luck.

 

[LS7]

Link to CRG> http://www.camaros.org/trans.shtml

 

[Bill Pritchard]

Casting numbers aren't going to tell you anything. If you have knowledge that the transmission has never been apart, you may be able to tell from the stamped numbers on the main case, but on a ~40 year old transmission, the odds are that it's been messed with some time over the years. The easiest thing to do is just pull the side cover and look at the gears.

 

[L7870_cortez]

It might be a M-22, but not original to a 68. A 661 Case is a Midyear 70 Muncie.
Mike

 

[DougA]

Could be a little earlier,too.My 661 M-22 was built Dec.19,69.(POT19C)

 

[straightaxle]

Link to CRG> http://www.camaros.org/trans.shtml

Isn't there a distinguishing feature that the M22 output shaft diameter somewhat larger than the M20 & M21 ?

 

[Redmanf1]

Duane, In short no. Some of the later close ratios had a fine spine with a larger output shaft. Another thing to look for on the case is the lower drain plug.

 

[Mike]

Drain plugs common on all the 661 cases regardless of use.
661 case use is 70-74.

 

[sbc500hpchevelle]

It has the lower drain plug. But that doesnt mean its a M22? Does that mean anything? Thanks for all the info guys.

 

[huffhuff]

1963-65 M20 2.56 ratio 10-spline 7/8-in. shaft - no grooves- 27-spline output shaft
1966-70 M20 2.52 ratio 10-spline 1-in. shaft - 2 grooves - 27-spline output shaft
1971-74 M20 2.52 ratio 26-spline 1-in. shaft - 2 grooves - 32-spline output shaft
1963-65 M21 2.20 ratio 10-spline 7/8-in. shaft - 1 groove - 27-spline output shaft
1966-70 M21 2.20 ratio 10-spline 1-in. shaft - 1 groove - 27-spline output shaft
1971-74 M21 2.20 ratio 26-spline 1-in. shaft - 1 groove - 32-spline output shaft
1965-70 M22 2.20 ratio 10-spline 1-in. shaft - no groove - 27-spline output shaft
1971-74 M22 2.20 ratio 26-spline 1-in. shaft - no groove - 32-spline output shaft

 

[1966_L78]

1963-65 M20 2.56 ratio 10-spline 7/8-in. shaft - no grooves- 27-spline output shaft
1966-70 M20 2.52 ratio 10-spline 1-in. shaft - 2 grooves - 27-spline output shaft
1971-74 M20 2.52 ratio 26-spline 1-in. shaft - 2 grooves - 32-spline output shaft
1963-65 M21 2.20 ratio 10-spline 7/8-in. shaft - 1 groove - 27-spline output shaft
1966-70 M21 2.20 ratio 10-spline 1-in. shaft - 1 groove - 27-spline output shaft
1971-74 M21 2.20 ratio 26-spline 1-in. shaft - 1 groove - 32-spline output shaft
1965-70 M22 2.20 ratio 10-spline 1-in. shaft - no groove - 27-spline output shaft
1971-74 M22 2.20 ratio 26-spline 1-in. shaft - no groove - 32-spline output shaft

BUT, THE "GROOVES" ARE ONLY USEFUL IF IT HAS THE ORIGINAL gm INPUT (oops, sorry about the caps lock)...

most replacement inputs (M20/M21) don't have grooves either...

the ONLY way to determine M22 or not is by taking off the side cover and looking at the gears...

 

[Mike]

Keep in mind that any case (w/correct shaft hole) could be used as a replacement.
With this in mind ,you can check the gear helix ,but still doesn't validate an actual REAL M-22.
So it might be an original or not -no real way to determine.

 

[DougA]

1963-65 M20 2.56 ratio 10-spline 7/8-in. shaft - no grooves- 27-spline output shaft
1966-70 M20 2.52 ratio 10-spline 1-in. shaft - 2 grooves - 27-spline output shaft
1971-74 M20 2.52 ratio 26-spline 1-in. shaft - 2 grooves - 32-spline output shaft
1963-65 M21 2.20 ratio 10-spline 7/8-in. shaft - 1 groove - 27-spline output shaft
1966-70 M21 2.20 ratio 10-spline 1-in. shaft - 1 groove - 27-spline output shaft
1971-74 M21 2.20 ratio 26-spline 1-in. shaft - 1 groove - 32-spline output shaft
1965-70 M22 2.20 ratio 10-spline 1-in. shaft - no groove - 27-spline output shaft
1971-74 M22 2.20 ratio 26-spline 1-in. shaft - no groove - 32-spline output shaft

Almost correct,my Dec. 69 built,model year 70,M-22,is 661 with 26 spline input,32 output.Orignal to car,never been opened,verified by all previous owners,+vin stamp.

 

[Mike]

Don't think he has that option.
'70+ case in '68 car ,all word of mouth at this point.