Need to ID my 10 Bolt rear end
 

I am trying to ID my 10 Bolt in my 72 Lemans. The gear tag is missing and I don't know if it is the original rear. By jacking up the car and rotating the drive shaft, I know that it is an open diff and somewhere around 2.73 gears.

Is there any way to tell what kind of 10 bolt I have from looking at the housing? ( 8.2, 8.5, 7.5 ) I want to order a Powertrax Lock-Right and need to know which to order. Thanks.

the axles on the B O P type rear bolt into brake flange

8.2" rear used U-bolts to retain the U-joint. 8.5" used the straps and separate bolts to retain U-joint. Both had bolt-in axles. I had a '72 LeMans parts car. It had the later style 8.2". Its a 8.2", but different from the early 8.2s" and not an 8.5".

From the factory, a 72 Lemans would have a 8.2 BOP 10 bolt, 27 spline pinion stem, 28 spline non-cclip axles, 7/16 LH ring gear bolts. Chevelle and Monte Carlo El Camino had 8.2 10 bolt Chevy, c-clip axles, 25 spline pinion stem through 72. 71-72 Buick and Olds had 8.5 10 bolts 30 spline pinion without c-clips, known originally as the B and O axle, later to become the corporate GM 10 bolt 8.5. The rear end cover on a 71-72 Buick or Olds 8.5 10 bolt looks the same with the crecent notches left and right on the rear end cover as the BOP 8.2 does. Although, the 8.5 has large 'squared lugs' sticking out of the left and right of the rear end housing. I believe the Chevy 8.2 will have the oil groove stamped into the cover for lubricating the carrier bearings. The chevy 'c-clip' will neck down on the axle tube right before the backing plate. The backing plates will be held by nuts and bolts. The axle tubes on the 8.2 BOP and 8.5 71 72 B and O will neck up just before the backing plate and oval headed studs will be visible retaining the backing plates.

Wow, thanks for all the great info. I will see if I can get under the car tonight and id the rear.