Okay guys. I know some of you have run into this problem and I've already did a search of the archives to see what was up. According to Tom Wilson there where 3 different series of rear-end housings for '71 chevelles. 2 series, 3 series and the 4 series. I bought a 12 bolt that supposedly came out of a '71 Monte Carlo. I know it will fit in my '71 Chevelle, but what I don't know is what series it is. On the center section, the only number I found was 3969278NF and on the tube was KDC 233 B. I have no way telling exactly what it is or where it was built. Can someone please decode this thing and tell me what I've got and if it is a series 2 rear housing, how low a gear I can put in it?

Is it a posi carrier? Not many Montes have a posi carrier, so that would be a surprise if it is. I used a 12 bolt out of a Monte in my 71 and the Monte was just a 2.73 open rearend so I replaced it with a new posi carrier. Check www.tomsdifferentials.com (http://www.tomsdifferentials.com) for the best ever prices on Eatons and such. Good stuff there.

Bill C.

BC, it's an open-end 2:73. I was wanting to put 3:73 gears in it, but some guy at Precision Gear told me over the phone that it was a series 2 housing and that I'd have to get a different housing, i.e., series 3 or 4, in order to go that low. Then he just hung up the phone. Anyway, I was hoping someone could decode this thing and tell me exactly what it is. thanks though.

you do not need to replace the whole housing, just the inner carrier needs to be a third series. they all use the same outer housing. just buy a eaton third series differential from ground up and pick the gears while your at it. tom

Sorry, I missed the whole bit about the housing and not the carrier! Like was said above, the housings are all the same, there is no difference, only in the carriers! For 3.73, you will need a new series 3 Eaton sytle posi unit and gear set. It will bolt right into the existing housing.

Bill C.

Thanks guys. That helps a bunch. I was beginning to worry about if I was gonna have to get another entire housing and all.