72 Chevelle Malibu. Bulid sheet says 10 bolt posi w/2.56.

Upon inspection 2.56 open with no c-clips. Cover is circular with 'indent' towards center at 9 & 3 o'clock position.

Axle tube pass side R2B0951. Carrier number are 1235197. Gears are 1234476. Tooth count is 41/16.

Hunch is a BOP rear.

Yes BOP rear. Do you have some pictures of the cover area with a bit of the outer cast area. I can tell you if it is a 8.2 or a 8.5. Did you get a date code off the webbing? Jim
is the u-joint held onto the rear end yoke with u-bolts and nuts or straps with 4 bolts? Jim

I'll try to get a pic and th other info. The pinion nut is 1 1/4, not 1 1/8 like in a standard 8.2. Almost make me think this could be a corporate.

Check the info here: http://www.oldsmobility.com/10bolt-tech.htm

It does not have the casting like the first pic, simmilar to the 8.5 3/4 way down the page, but not the same as that either.

I show R2 was used by Oldsmobile for 2.56 ratio various years.
Your date format is 70+.
R2=2.56 non posi
B=Buick
095=Day of year assembled
1=work shift
Try to find the cast date on one of the support webs to verify year.
Found this posting on Olds site where this code and housing number
common to early 70's Olds. Might be helpful
http://www.oldspower.com/vb/showthread.php?t=1714

U-Joint has straps with 4 bolts. Here is a pic below. The casting below the cover is whats confusing me. Dosn't look like the BOP photos I found on-line. Also the 1 1/4 pinion nut indicates an 8.5 not 8.2.

Every site I go to has conlicting info:clonk:

This is photo from an E-bay car 72 Buick Skylark rear
Looks like yours...
http://i4.ebayimg.com/05/i/08/1a/e6/b9_12.JPG
Big Gear Head may be able to tell you if there were 8.5 corporate gears
used in these 70's Buick rears.....

This is photo from an E-bay car 72 Buick Skylark rear
Looks like yours...


You nailed it, thanks shooter

That is the early 8.5 10 bolt. They had bolt in axles with no c clips. All of the regular 8.5 parts will fit it except the axles. This is the better 8.5 to have because you don't have to worry about the axle bearings wearing the axles, and you don't have to worry about an axle coming out if you break it. Put a set of gears and a new Eaton posi in there and you have a great rear end.

ditto. I build alot of these rears and make super 10 bolts out of them with moser 30 spline axles eaton 30 spline 8.5 posi. great rears. right up there witht he 12's. Jim

Thanks for all the great Info, Maybe we'll keep it after all. I'll have to check the junkyards for some swap parts.