70sgeek

I'm building a BOP 10 bolt 8.5 corporate rear for the ragtop with a nicer '72 housing than the original unit. The original has an embossed O on the carrier body and apparently doesn't take the scalloped cover.


The code I've been able to make out on it is SA O 132.


Is this an earlier "O" style rear that I've been reading about, or is it just another 8.5 corporate that simply takes a fully round cover?


I'm presuming this rear was original to the car but the guy building my new rear suspects the gears may have been changed due to painted setup marks on the gears and the ring gear part number pad area having been ground off.


Had been planning to clean the housing up and store it for a spare but would hate to think it wouldn't use the same parts as the unit going onto the car.


thanks

Fun71

The O on the center section is the same as the 8.5" corporate 10 bolt in my 71 convertible. It's not an O-Type as those have a 12 bolt cover.

70sgeek

appreciate the reply


I wasn't sure since it appears to take a fully round cover instead of the scalloped one that came on the other 10-bolt that's going in the car. My other unit has an embossed 'A' on top of the center section - other than having 2 welded weights on each side of the cover surface instead of 1 @ side, they are essentially the same design.


The original has open holes at 3 and 9:00 positions on the cover surface that the scalloped cover leaves exposed. Other unit doesn't have those.


Maybe just an early/late production version variation? I'm presuming the SA O 132 code translates to 2.73 ratio, Olds manufacture, 132nd day (May 11 1972) - that date if accurate would be approx 1 month after the frame date code of 4/12/72


thanks

Rocketbrian

There were 3 or 4 divisions of GM that made the corporate 10 bolt rear end. The O is for Oldsmobile and the covers weren't scalloped. The B is for Buick and those covers were scalloped. I have that rear in my 71 SX. I believe Pontiac and McKinnon made them as well. I've only ever seen the Oldsmobile and Buick rears.

Inline

There you go:

70sgeek

Makes perfect sense now - the unit going into the car now is a Buick manufacture (had an SA B code stamped on the axle tube) but it came from another '72 cutlass whose owner was installing a 12 bolt for race use.


So basically the old W27 cover that was on my original replaced a factory round cover.


just curious - did the 2 extra open holes actually serve a purpose?


Thanks for the info!

techg8

The 2 open holes at 3 and 9 o clock were used as locating/tool points for case spreading tools used for differential install.

I also think the 3 o'clock hole was used by a diff cover with the oil ledge to feed oil to the carrier bearing. The oil ledge directs oil to the hole.

monzaz

They were used on the c-clip rears that needed oil on the axle bearing to by pass the carrier bearings and the reason the chevy 10 bolt 8.2 and the 12 bolt 8.875 c-clip chevy rears had the cover with the bends in them. THAT bend was like a trough that guided the OILED through the holes and into the axle tube.

BOP early rears never needed the tough cover or the holes because they were sealed bearing systems which never got differential oil.

After a while it just did not matter as the oil was thin enough after a 5 minutes of driving they found out it really did not make any difference it oiled just fine.

LOL. ... just left over casting stuff ....that did not make a hill of beans difference, BUT I am sure some ENGINEER got paid for it !!!

Jim J D

monzaz

That is a 10 bolt 8.5 corp rear.... will take the same parts as all 1971-1987 cars with 8.5 10 bolt rears. Jim