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WestyJ69chevelle Feb 22nd, 05, 1:47 PM I am looking at a m21 a guy I work with is selling, could someone interpret these #'s for me? GM 3884985 3851325 3088336 P0217.. thanks a million for your help... BillK Feb 22nd, 05, 8:56 PM Westy, You need to put this in the transmission forum. Here is a link to Wally's web site that has most of the numbers on it www.muncie4speed.com (http://www.muncie4speed.com) DZAUTO Feb 22nd, 05, 10:25 PM Wes The 3851325 is the casting number of a 64-65 Muncie main case. The P0217 is a date of Feb 17. The year will be included in the VIN-----------------if it is stamped somewhere on the main case. The 3088336 is the Patent number for a Muncie, that is of no value. Now, my question to you. How do you know this is an M21 and not an M20? WestyJ69chevelle Feb 23rd, 05, 7:22 AM DZ...well I did get that far noticing that it was a 64-65 case, but as you asked, I don't know whether its an M20 or an M21.. was hoping these #'s would help me decipher that..is there any way to tell outside or inside whether it is one or the other? TIA!! Rodeo73 Feb 23rd, 05, 1:16 PM Look for the rings in the input shaft. Looks like a little groove. But to be sure, open the case by removing the side cover and count the teeth on the input shaft inside the case. Year 1963-1974 Type: M21 Rings: One Ratio: 2.20 / 1.64 / 1.28 / 1.00 / 2.27 Year 1963-1965 Type: M20 Rings: None Ratio: 2.56 / 1.91 / 1.48 / 1.00 / 3.16 Some input shafts produced by the aftermarket and General Motors have no identifying rings on them Input Shaft Tooth and Spline Count Related to Year Year 1963-1965 Type: M20 Rings: None Spline: 10 Tooth Count: 24 Year 1963-1970 Type: M21 Rings: One Spline: 10 Tooth Count: 26 | ||