Okay, guys (and gals), I'm at a loss here...

Car is a 1965 Starfire convertible. It's body-off and the chassis is nearing completion. At this stage I was replacing the pinion seal of the rear-end prior to bolting the back-end of the chassis back together. Rear-end cover is 10-bolt.

The problem started with me not reading the CSM until the pinion bolt was off, and not marking as instructed in step 1. My bad.. Searching some threads I learned that a new crush sleeve was in order, so I went digging to find out what it was I should be looking for.

Then I figure while I'm tearing it all down, why not take a look at upgrading to limited-slip. This was planned as a future maybe, but worth a closer look now. When I removed the carrier, I was surprised that the ring gear is 12-bolt. Web searches came up empty, except for reference to "O" type, which I understand as 12-bolt case and 10-bolt ring gear. Searches here at CO ignore the numeric 10 and 12, so no luck there (if this has been addressed prior, I apologize for the repeat). I managed to catch somebody on quickperformance.com online chat, but he was at a loss without measurements... These are the measurements he asked for:

Axle spline count: 31
Pinion spline count: 28
Pinion nut size: 1.24" as the wrench would sit, 0.80" ID
Ring gear diameter 8.875"

I've also collected:
Crush sleeve ID: 1.315"
Ring gear stamp: 42 13 GM 664SL
Carrier numbers: 8363-123 (6 is hard to read, could be an 8)
Stamp on the axle sleeve: OG

Any direction from the experts? Is this an original configuration? What are my options? I think I'm fine with the 3.23 ratio, and the pinion and ring gears are in good shape (translated I'd rather not spend the extra to replace them). I don't know if that's even an option. I assume I would rebuild with all 10-bolt components. Do they fit in this bizarre 10/12-bolt bastard of a diff?

Maybe I should just search out the dang crush sleeve, set the preload, and get back to reassembly...

Thanks for any feeback. Sorry for the long post.

 

Also, it does have the cutouts in the cover like the other BOPs... I'm wondering if this could be it:

http://www.gmbbodyforum.com/t172-gm-8-75-10-12-bolt

I'll try to take a more careful ring gear measurement, and double-count the splines tomorrow.... I give up for now.

 

If nobody replies with the answer you might contact monzaz. Jim is one of the resident experts with differentials and his business of JR Racing sells parts for many of the differentials used under Oldsmobiles.

John

 

And another...
http://purplesagetradingpost.com/sum...208%203-4.html

Pretty sure this is it at this point.

 

LOL BAstard rear. That rear was the most popular Full size car rear ever. 1965-1976 came in ratios of 2.29-4.33 31 spline axles Bolt in and c-clip There are MANY many versions of it all the way to 1985 even.....

In the beginning Gm created the integral Pontiac rear 1965
1st gen 1965-1970
specs-
1.875 pinion shaft diameter
28 spline pinion
M3R / Saginaw u-joint
10 bolt cover
12 bolt ring gear
ring gear bolts can be right hand early or left hand late 7/16" x 20
ratios were 2.56-4.33
Axles were all 31 spline bolt in and 60 degree spline
11" x 2 drum brakes
2nd gen 1971-1976
1.875 pinion shaft diameter
30 spline pinion
M3R / Saginaw u-joint and 4 bolt flange constant velocity joint
10 bolt cover
12 bolt ring gear
ring gear bolts are left hand 7/16" x 20
Ratios were 2.29 - 3.42
Axles were all 31 spline bolt in and 45 degree spline
11" x 2 drum brakes
3rd gen 1977-1985
1.625 pinion shaft diameter
30 spline pinion
M3R / Saginaw u-joint and 4 bolt flange constant velocity joint
10 bolt cover (cover will have a fill plug in the back)
12 bolt ring gear
ring gear bolts are left hand 7/16" x 20
Ratios were 2.29 - 3.42
Axles were all 28 spline c-clip axles 45 degree spline some wagons may have had 31 spline 77 78 79 80 ish
11" x 2 drum brakes

A-Body 1973-1977 version is the same as the B Body 1977-1985 version

I have rebuilt kits crush sleeves cover gaskets bearings etc for these rears
DO NOT HAVE ANY NEW RING AND PINIONS. very few used and usually not good ratios.

keep your 3.23 gears they will be great. all you need is a posi and you are all set.
Jim
JD

 

Thanks a ton for the reply @monzaz, I was considering contacting you based on 2blu442's suggestion. I'm still not getting it, though. If this is the Pontiac 12-bolt, then I still cannot find any resources that match my situation. My searches for Pontiac/GM/BOP 12-bolt all take me to either the "O" type or the Chevy 12-bolt with the 12-bolt cover that looks nothing like mine.

My cover looks like the 8.2 BOP (which all seem to be 10-bolt/10-bolt) in the attachment. All the comparisons I find look like the one directly below it.

The exception seems to be this 8.75. Same as the links listed above.

Can you send me some links to help clarify? I'd be very happy at this point to learn that I have a more common setup, with parts available...

Thanks again!