[Mister Pontiac]

Recently I swapped the rear end in my 67 Tempest Wagon to get more highway friendly gears. After sourcing a correct 67 vintage 8.2" with a 2.56 Posi, I set to work swapping the rear out.

After pulling the 10 bolt in the car, I decided to swap covers as I wanted the old chrome cover on the replacement rear as well. Only then did I realize I had something different. The bolt holes on the cover didn't line up. As I stared at things for a minute, it finally dawned on me... I had pulled an 8.5" and was installing an 8.2". With my trusty tape measure, I confirmed my suspicion.

This was a pleasant surprise, as you might imagine, and now I have a spare 8.5" with a 3.23 Posi that works well. I have a feeling it will find its way under my 72 LeMans GT pretty soon.

But here's where I get to my question(s)... I had actually pulled this 8.5" from a 71 LeMans about 20+ years ago, and installed it in my wagon about 18 years back. At the time, I didn't know the difference between the two sizes, and simply installed it as a "10 bolt 3.23 Posi." Who knew.

So tell me... did Pontiac ever put an 8.5" in one of our beloved A-bodies? I have been under the impression these were found only in Buick's or Old's, not Pontiac's. Is this correct? If so, the LeMans I sourced it from back in the 90's had pirated it sometime before that from something else. Interesting!

Second, I know the 8.5" is stronger than the 8.2", but compared to a 12 bolt, are we talking about a step in between 'strength wise,' or are we comparable to the 12 bolt?

[PontiacJim1959]

Yes, the 8.5 found its way under 1971-72 Pontiac A-bodies.

It can be as strong as a 12-bolt and many drag racers use them. More plentiful and cheaper than a 12-bolt.

[4zpeed]

I have a 72 323 nodular 8.5 posi rear end from a 72 Lemans in my 68 GTO, which is stronger than the standard 8.5.

Yours could also be the nodular, check the case for a big N on the drivers side, if so you have a nice rear there.


Frank

['ol Pinion head]

Originally Posted by 4zpeed

I have a 72 323 nodular 8.5 posi rear end from a 72 Lemans in my 68 GTO, which is stronger than the standard 8.5.

Yours could also be the nodular, check the case for a big N on the drivers side, if so you have a nice rear there.


Frank

Have any pics of that particular housing, Frank?
Would like to see pics of the casting number on center housing.

[Mister Pontiac]

Thanks for the input, Gents. I'm happy to hear these did come in Pontiac A-bodies as well.

I'll take a peek next week to see if I have an "N" casting. I'll report back.

[David Jones]

I thought the “N” rears were 8.2’s?

[4zpeed]

I just looked and I don't have any that show the casting numbers, I should have taken a couple.

I'll try to get a few and post them up, any particular reason why OPH, just wondering.


Frank

['ol Pinion head]

Originally Posted by 4zpeed

I just looked and I don't have any that show the casting numbers, I should have taken a couple.

I'll try to get a few and post them up, any particular reason why OPH, just wondering.


Frank

Frank, I'm one of the 4 originators of the 8.5 A-body rear buildup & swap. Have built up over 330 8.5 A-body rears since the early 90's. Nearly every one of those rears was built off a core housing which came from a single track rear. Have pulled 8.5 A-body housings & core rears in over a dozen states, I still pick one or two up each year.

Beginning in the mid 80's, my main attention Pontiac wise, has been sourcing parts for & restoring higher performance factory '70-72 Pontiac A-bodys, esp '71 & 72 455 HO cars. Have also hauled in three '72 400 3spd & 400 4spd cars, each of which had a factory Safe-T-Track 8.2 rear. That noted, have never ran across a 8.5 A-body rear factory installed in a '71 or '72 Pontiac A-body. I believe what you may remember as an N is actually a raised A. In the early 90's that raised A along with a few casting numbers, on that particular housing, is something I used to hit with the angle grinder. There was a several year run in the early to mid 90's where when I was setting up at swappers with fresh built 8.5 A-body rears, we were not trying to educate our next competitor. That competition came later.

[Mister Pontiac]

Originally Posted by 'ol Pinion head

...have never ran across a 8.5 A-body rear factory installed in a '71 or '72 Pontiac A-body...

Very interesting OPH. This was my understanding too.

So what exactly did the 8.5's come under?

['ol Pinion head]

Pontiac installed LATE PONTIAC 8.2 10 bolts in nearly all of its 71 & 72 A-body's & GP's.

'70 GP's w 400's & manual transmissions, as well as all '70-72 factory installed 455 Pontiac A-body's & GP's received 12 bolt McKinnon built rears. The McKinnon built rears have numerous detail differences from a "normal 12 bolt" Malibu-Chevelle-Elco rear.

The 8.5 A-body rear was factory installed under '71 & 72 Buick & Oldsmobile A-body's. Have never ran across a factory installation in a 71 or 72 Pontiac A-body & I've been under tons of them. The axles in the 71 & 72 configurations of 8.5 A-body rear are stronger than the garden variety 12 bolt c-clip axle. Original axles of a 12 bolt taper down, then flare up where the splines begin, this is a trouble spot. The 8.5 S spring posi unit & the factory installed Eaton 12 bolt carriers, are both of a 2 pinion design. The small spider gears in the GM installed Eaton 12 bolt carriers are a trouble spot, and at the least need to be replaced as a 4 piece set.

Chevrolet's '69 COPO Chevelle was equipped with what has to be the high water mark in factory 12 bolt A-body rears. Most on this site will most likely never run across one, only a few were built. Special heat treated axles, ring & pinion, as well as a special 4 series carrier with special side gear & spider gears. In my differential building experience, the only factory 12 bolt that had an edge in strength over a blueprinted '71 8.5 A-body rear. Aftermarket axles & 30 spline Eaton (& Eaton clone) posi carriers are available as an upgrade to the 8.5 A-body rear. If inclined to go 30 spline axles, make sure to note whether the housing accepts A9 or A10 axle bearings, there are 3 different center housing/axle tube combinations.

[4zpeed]

My apologies to Mister Pontiac if I've misled him in any way.

OK OPH, now you've really got me wondering, I'll try to get some pics of the casting numbers as well as the letter on the housing.

Meanwhile here are some pics I took, just wondering if you can tell anything at all from these, I hate giving someone bad information.

I pulled this rear from a 72 Lemans I owned that came factory with a 4spd, and had assumed the rear end was original to the car.

As in many cases, in trying to answer a question, I've come up with a few of my own, I'm always willing to learn and appreciate any help.










Frank

['ol Pinion head]

From looking at the pics, the rear is a Pontiac 8.2 10 bolt. The shape of the lower webbing of the center housing is the telltale. I can tell the posi carrier is an original carrier. If this rear has 3.23 gears & a N housing, I would ck the dates inscribed on the gears & the factory code stamping on the housing tube. Either one of two things is possible, a set of 3.23 gears have at some time been set up in an original '72 3.55 STT coded rear's original housing. This would require installing a mid ratio 8.2 STT carrier. Either that situation, or 3.23's were factory installed in one of the remaining '70-72 Pontiac 8.2 cast Nodular housings. Have never seen or heard of that before, but with axle production winding down of the '72 style 8.2 Pontiac rears (73's would take a totally different geometry 8.5 A-body rear) there remains a possibility that Pontiac's axle plant built such a deal just to use up an excess N housing. Would be interested in pics of the stamped axle tube among other pertinent pics. Can relay '72 coded N 8.2 Pontiac rears are few & far between.

[mrennie]

Originally Posted by Mister Pontiac

I know the 8.5" is stronger than the 8.2", but compared to a 12 bolt, are we talking about a step in between 'strength wise,' or are we comparable to the 12 bolt?

A few numbers of interest:

-8.2 BOP uses a 1.438" pinion shaft with 27 splines, while the Chev 8.2" is 1.438" with 25 spline. Compare to the 8.5 and 12 bolt which use a 1.625" shaft and 30 splines. I believe this is a big part of increased strength.

-8.5 axles meet the side gears using 28 splines. 12 bolt is 30 spline, but factory axles (as OPH mentions) are tapered and a weak spot.

I looked for quite a while up here for a 71-72 A body 8.5" to build up as I wanted the bolt in axles, but could not find one. Ended up using a 1968 12 bolt housing that was original to a Canadian Buick, fitted with new Eaton posi, upgraded carrier bearing cap and bolts, and Tom's axles.

If I lived closer to OPH I would buy a 71-72 8.5 housing for a future build .

[Mister Pontiac]

Great intel here, Gents. I love these "deep dives," especially when I realize how much I don't know! We all continue to learn, and I appreciate all the wisdom on this site. Thanks for all the detailed breakdown(s). I will have a more critical and discerning eye going forward.

I'm happy to know I have an 8.5" on the shelf now. Really making the case for sliding it under the GT as she's currently a one-legger.

[Rugratman]

Was there not a "Corporate" rear 8.5"?
10 bolt with bolt in axels.

Supposed to be stronger yet. It has been awhile since I had all this info in front of me.
If I remember - there was no 3.55 ratio option. 3.42 or 3.73 options.

['ol Pinion head]

"Corporate 8.5" is just a later day description for all the 8.5 differential, not nearly as bad as the foolhardy connotation of a "BOP" 8.2 10 bolt.

GM divisions had a lot of autonomy in differential mfg up into the early 70's when more divisions began to share more specific rear ends. It wasn't that way in the '60's, just compare the rear suspension designs & rear ends under each divisions big cars.

The 8.5 rear design was introduced for 71 model GM passenger cars. GM 1/2 ton pickups would have to wait til '77 model year.

1971 GM 8.5 uses:
A-body: Buick & Olds both mfg 8.5 bolt in tapered bearing axle rears for the A-body.
Little over a million were installed in two production years.

B body:
for '71, most GM divisions used a c-clip axle 8.5 B series rear in their base B series models.
LeSabres, Impallas, Catalina's w 400 engines.
Most likely Olds 88's with 350 Olds engines, can't remember stripping a '71 Delta 88 rear.

F-body, c-clip axle, often when equipped with a posi unit, that posi unit was a Warner Motive cone type posi (think a light duty Auburn style carrier).

1972:
first 8.5 X-body was installed.
'71 Novas & Ventura II' s originally had Chevy 8.2 10 bolts

Cadillac did not use an 8.5 rear till the introduction of the Seville in mid 1975.
These were nothing more than a Nova (X body rear). For '77 model year, the Seville gained rear disc brakes w 5 on 5 bolt pattern axles & rotors. The calipers & caliper brackets for '77 & early '78 model Sevilles was one style, late '78 &'79 are another. In the 90's & early 00's I stripped many dozen Sevilles of rear disc pieces as well as stripped down quire a few to bare housings, occasionally with a #9 (high ratio) posi carrier.

[Kenth]

Didn´t Buick use an 8.5" Corporate 10-bolt w/tapered wheel bearings for the 1969 Sportwagon?

['ol Pinion head]

Originally Posted by Kenth

Didn´t Buick use an 8.5" Corporate 10-bolt w/tapered wheel bearings for the 1969 Sportwagon?

Kenth, 69 Sportwagon 10 bolt is a '68-70 BUICK 8.2 rear AKA the late LATE Buick 8.2 rear.
Same style of gearsets & carriers in this rear as in '68-70 Buick GS rears
Another reason there is no such thing as the misused & erroneous "BOP 8.2" ridiculousness.

Have parted several '68 GS 400's & rebuilt a few of this style of rear. Buick Sportswagons of the mid to late 60's are tricky as to original wheel bearing usage. In the earlier years they took a wider sealed axle bearing. Clearing out the cobwebs, if remember right, the '69 Buick Sportswagon axle takes an early tapered axle bearing, I'd have look it up, I do remember its not a Set 10. Hope this helps.

[Half-Inch Stud]

Type "O" for Oldsmobile. were 8.5" rears with either 12-or 10- bolt covers. I only ran across 12- Bolt covers. Stronger than 8.2" BOPs up until you reach the axles as they were same same.

I found Type "O" in a few Stick GTOs 1970, but doesn't make it factory issue huh.

Also found Chevy 12-Bolts in 70 GTO, GP and Stick Formula Firebird, which was factory issue.

['ol Pinion head]

Originally Posted by Half-Inch Stud

Type "O" for Oldsmobile. were 8.5" rears with either 12-or 10- bolt covers. I only ran across 12- Bolt covers. Stronger than 8.2" BOPs up until you reach the axles as they were same same.

I found Type "O" in a few Stick GTOs 1970, but doesn't make it factory issue huh.

Also found Chevy 12-Bolts in 70 GTO, GP and Stick Formula Firebird, which was factory issue.

Type "O" Olds A-body rears were originally installed in '67-70 Olds A-body's. There was a B-body version as well. Many of the A-body style have ended up in Pontiac A & G's over the decades often due them being a direct bolt in, or hey i found a 3.08 or 3.42 ratio, no other reason. Have had dozens of 28 spline Type "O"s, nearly all coming in under partscars.

Physical Attributes:
-12 bolt smooth cover.... the cover bolt pattern is slightly different than 12 bolt Chevy cover.
-Slightly less than a 8.5" diameter ring gear, some call it an 8.4.
-factory Anti-Spin carriers are of the first S spring design with replaceable clutches.
-Most have sealed axle bearing axles. Similar lack of pinion support as earlier gray iron 8.2 rears.

In '67 & 68, a 31 spline axle version of the Type "O" rear was used in 3.42 & 3.91 ratio rears. Even lower ratio gear sets were available over the counter. These Low ratio '67 & 68 Type "O" rears took their own specific housing due to larger diam carrier bearings/mating caps which were required for the larger diam carrier ends & 31 spline axles. Higher ratio gear sets like 3.08's & 3.23's were used in the standard housings which received carriers with sealed axle bearing 28 spline axles. 2.56's wre very common. For the '69 models, the 28 spline axle was used for all ratios of Cutlaas/442 type "O" rears. Have a '68 3.91 Anti-Spin rear, it's the second I've had & both have had bad sealed bearing axles. To order in new axles & axle bearings & wheel studs ones knocking on $500, the replacement parts add up.

For 1970 models, Type "O" rears used a 28 spline Tapered Bearing axle. ThIs was the year the rare & highly collectible aluminum center housing Type "O" rear was offered. The '70 model Type "O"s are prob the best Type "O" reaes to pick up cheap & throw in a low budget '67-70 Olds Cutlass or 442, if one does not care about the rearend having an Anti-Spin (posi) unit. With wider tires & side loading forces being what they are, this last year of Type "O" rear is not going to go through sealed axle bearing axles like its predessors.