stickshift Posted December 17, 2013 Share Posted December 17, 2013 Hey guys, I looked on the side of my transmission and the casting # is 3925661, it also has P3T12 on it. The patent # is 3088336. I didn't see an A, B, or C beside the P3T12. Can anyone tell me which Muncie this is? Quote Link to comment Share on other sites More sharing options...
MCfan Posted December 17, 2013 Share Posted December 17, 2013 Ken, Your casting number indicates a 1970 -1974 Muncie but it could be an M20, M21 or M22. The stamping of P3T12 confirms it is a Muncie built December 12, 1972 (for the 1973 Model year) but lacking the A, B or C letter on the end, it does not indicate which model. You can easily identify an M22 by its characteristic "blower drive" whine or you can open it up to see the gear teeth. Both the M20 and M21 have teeth faces that are angled nearly 45 degrees relative to the shaft axis, the M22 teeth faces are angled much less from that axis. See comparison photo below. If the transmission is out of the car, you can check the first gear ratio by counting and comparing revolutions of the input and output shafts. An M20 is 2.52:1 while an M21 or M22 is 2.20:1. You might also check for a small stamped metal tag under one of the side cover bolts on the driver's side that will show the GM part number and tell you which model it is. Not all Muncies have that tag, however. Pictures below are of the housing stamping and metal tag from my 1970 M20. BTW, here's the link to an interesting web site on Muncie Identification if you don't already have it: Muncie Identification Quote Link to comment Share on other sites More sharing options...
Murphy Posted December 19, 2013 Share Posted December 19, 2013 It's really odd that the designator A, B, or C isn't stamped on the end of the P3T12 serial number?? Although the case number (3925661) does confirm between 1970 to 74. Quote Link to comment Share on other sites More sharing options...
stickshift Posted January 8, 2014 Author Share Posted January 8, 2014 I just purchased another M-22 Muncie for $200. I purchased it just for the main casing because mine has a hairline crack in it with one of the ears missing. The transmission that I just purchased looks good other than a couple of gears being stripped out. The casting # on it is 3885010. The patent # is 3088336. It has P7H09 on it also and it has the large shaft. Quote Link to comment Share on other sites More sharing options...
Murphy Posted January 8, 2014 Share Posted January 8, 2014 Hey Ken, sent you a PM. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.