Mystery Buick Rear End Decode

[clm69z28]

I have searched the internet high and low for the decoding of this rear end. The seller told me it was out of a 68 GTO which I believe is not true, but the only codes I can find on it- other than the casting # 1375689- is on the axle tube and it is "LA 42D". I have attached some photos (sorry about the quality) which show the #'s and the diff style. My thought was that it may be from a '66 or earlier Buick rear end series 42 with a 2.78 axle. Am I warm?? Thanks.

[monzaz]

Need more of the full center casting to get a complete ID and the axle tube and spring perch areas.

I would say you are dead on with the ratio 2.78 LA

That would be a OPEN ...Non Posi rear.

These rears WERE used in the lower powered Pontiacs...So could it have come in a GTO? Probably NOT... But A pontiac lemans/tempest Yes. Jim

[clm69z28]

Here are some more pics for your review. I had planned on replacing my 72 Chevelle 10 bolt 8.2 non posi with this one- it was advertised as 10 bolt posi with 3:36's, which I believe it has, but I think I should just rebuild my original instead. Any opinions? Thanks.

[monzaz]

The pictures you sent are still a bit iffy. I still am going with the 64 65 66 buick 10 bolt 8.2 rear. These rears were found in all the Pontiac, Buick, Olds A-body cars with bolt on springs to the rear. The width will be narrow as you need 53 1/4" backing plate to backing plate.

The only way you will find out the true ratio is to crack it open and read the ring gear stamped numbers on the edge of the ring gear (reference picture) IE 3.23 ratio 13 42 tooth count. Jim

[clm69z28]

Thanks Jim for the assistance. I will keep looking for a better application.

Chris