[pontiacs-r-us]

Were their any true 12 bolt BOP rears made?I have one from under 66 GTO.It has bolt in axles,12bolt cover,but has 8.2 carrier(10 bolts used to mount ring gear)Its correct length for my 66.I have a 68-72 chevy 12 bolt that has big ring gear with c-clip axles,but has 1/2in. longer axle tubes.I wanted to use bolt-in axles,so wouldnt have to install c-clip elim.Are their any advantages to the BOP 12bolt over the stock 8.2 10bolt? Thanks for your help,Kenny

[GStage1]

Olds 12 bolt has a circular cover and a 10 bolt ring gear. Sounds like that is your rear axle. Chevy 12 has an oval cover and 12 bolt ring gear.

Olds 12 bolts are not worth your time, effort and $$$ to set-up. You are better off with the corporate 8.5" from a 71-2 Skylark/Cutlass...much better parts selection and cheaper prices since the center section, 8.5" ran thru 87 with 28 spline axles.

[pontiacs-r-us]

Thanks GStage1 for the info.So there were no BOP 12 bolts w/big ring gears?Were the 68-72 Buick-Olds-Pontiacs cars with 12bolts a chevy type rear(c-clip)?Again thanks,Kenny

[GStage1]

Full size BOP cars had 9 3/8 ring gears....think they were the largest for a pass car....but you need an A-body rear....biggest is the Chevy 12 bolt with a 8 7/8 ring gear. For a street car, you can use the corporate 8.5

[performerrpm]

i have the olds 12/10 bolt rear and they are definateley a pain to get parts for easiest thing to get was axle bearings. when it breaks i will be doing the chevy type. it is nice being able to unbolt the axles but your definateley limeted on parts. i think iam stuck with the 411 gear" which right now iam having alot of fun with" but will wanna go taller later possibly

[GonicGM]

From 1966(late?) to 1970, Oldsmobile had their own 12 bolt rear in the A body. It had a smooth rear cover as mentioned above. It had 10 ring gear bolts. I believe ring gear diameter is about 8.5". They had bolt in axles. I believe most common was 28 spline but I think there was a heavy duty version with 31 spline axles. I think Richmond is now offering aftermarket gears for this rear end. The Chevrolet 12 bolts, known as the "C" axle, were also used in Buick, Oldsmobile and Pontiac. 1968 to 1970 on Canadian made Buicks, 1970-1972 on 455 powered Pontiac A and G body, not sure on years on Olds. These rears had the BOP u-joint yoke with internal c-clips.

[pontiacs-r-us]

Thanks Guys for your help.I think I would be better-off with my Chevy 12-bolt and use c-clip elims.As for these Olds 12-bolts, Im not sure why parts would be so hard to find?They are standard 8.2 ring-n- pinions ,and carriers?aint they?Thanks again,Kenny

[GonicGM]

Originally Posted by pontiacs-r-us

As for these Olds 12-bolts, Im not sure why parts would be so hard to find?They are standard 8.2 ring-n- pinions ,and carriers?aint they?Thanks again,Kenny

Kenny,

NO

Did you completely miss my post in this thread, #6?

[n2ogpsj462]

my 71 grand prix has the stock 12 bolt. it has the 12 bolt ring gear but like gonic said it has the bop u-joint. which i believe is larger and uses the inside clips. can you use the moroso joint girdles with these u-joints? because just by looking at them id say no since the cap itself sticks slightly farther out than the yoke

[pontiacs-r-us]

GonicGM,I did read your post,and thank you for your imput.You said in your post that you though that they are 8.5 ringgears,Best I remember no one had 8.5 ringgear 10bolts untill around 71-72,so must be 8.2?right?The 8.2 carrier looks like it would drop right in,is the pinion different?Im not sure what you thought I missed.Kenny

[GonicGM]

Originally Posted by pontiacs-r-us

Best I remember no one had 8.5 ringgear 10bolts untill around 71-72,so must be 8.2?right?

The Oldsmobile is a 12 bolt (cover) not a 10 bolt (cover), ring gear is 8.5". No other gears interchange in rear.

Originally Posted by pontiacs-r-us

Best I remember no one had 8.5 ringgear 10bolts untill around 71-72

68-70 Buick 10 bolt Special Skylark Gran Sport Stage 1 and LeSabre had a 8.5 inch ring gear.

['ol Pinion head]

HMMMM...

Let's see if can straighten out some of the above inacurracys.

First, there really is no such thing as as a "BOP 12 bolt" that factory fits in '64-72 GM A-body.
Over the years, folks have referred to several GM rears as a "BOP 12 bolt", but none fit the true "BOP 12 bolt" moniker.

There are:
-Type "O" (Oldsmobile) 10 bolts
Identified by 12 bolt smooth cover, had 10 bolt 8.3-8.4" ring gear & either 28 or 31 spline bolt-in axles.
Stock in VAST majority of mid '67-70 OLDS A-Bodys, B-bodys, & C-bodys. Only the Olds guys call them "12 bolts"... the only thing 12 bolt about them is the smooth rear cover with 12 attaching bolts.

-std duty Chevrolet 12 bolt CAR rearend (c-clip axle)
Installed in millions of Malibu's, Chevelles, Monte's, Elco's from '65-72.
A few late versions were even built up in very HD form from Buffalo axle plant...think '69 COPO Chevelle rears
Most are highly overrated & need considerable ugrades to truly be "HD".

-McKinnon cast 12 bolts (c-clip axle) 12 bolts:
Stock in many '68-70 Canadian mfg Olds A-bodys & some lower horse '68-70 Buick A-bodys. Mckinnon cast 12 bolts were also used in MOST '70-72 455 equipped Pontiac A-body & G-bodys. One thing I've noticed over the years is most Pontiac 455 single track 12 bolt applications in '72 did not receive the McKinnon cast rears but similiarly assembled 12 bolts out of Buffalo axle plant.

The McKinnon plant cast 12 bolt rears were cast differently (date coded differently) & ID coded differently, had the 3R (BOP useage flange), had different c-clip axles than std Chevelle axles, & came with the BOP style backing plates. That's it, std Chevy 12 bolt gears & carriers inside.

'71+ M-P series 8 7/8" rears which were stock in many '71-76 & '77-85 GM B-bodys, '73-77 A-body wagons, & even some '73-76 Pontiac A-bodys.

AS far as '68-70 BUICK 8.2 10 bolt rears go, these did not use not use an 8.5" diam ring gear, but the '68-70 design of BUICK 8.2 rears were cast with their own housings & had their own design of gears along with their own design of BUICK 8.2 carriers.

Hope this helps,

[GonicGM]

Originally Posted by 'ol Pinion head

HMMMM...

Let's see if can straighten out some of the above inacurracys.

First, there really is no such thing as as a "BOP 12 bolt" that factory fits in '64-72 GM A-body.
Over the years, folks have referred to several GM rears as a "BOP 12 bolt", but none fit the true "BOP 12 bolt" moniker.

There are:
-Type "O" (Oldsmobile) 10 bolts
Identified by 12 bolt smooth cover, had 10 bolt 8.3-8.4" ring gear & either 28 or 31 spline bolt-in axles.
Stock in VAST majority of mid '67-70 OLDS A-Bodys, B-bodys, & C-bodys. Only the Olds guys call them "12 bolts"... the only thing 12 bolt about them is the smooth rear cover with 12 attaching bolts.

-std duty Chevrolet 12 bolt CAR rearend (c-clip axle)
Installed in millions of Malibu's, Chevelles, Monte's, Elco's from '65-72.
A few late versions were even built up in very HD form from Buffalo axle plant...think '69 COPO Chevelle rears
Most are highly overrated & need considerable ugrades to truly be "HD".

-McKinnon cast 12 bolts (c-clip axle) 12 bolts:
Stock in many '68-70 Canadian mfg Olds A-bodys & some lower horse '68-70 Buick A-bodys. Mckinnon cast 12 bolts were also used in MOST '70-72 455 equipped Pontiac A-body & G-bodys. One thing I've noticed over the years is most Pontiac 455 single track 12 bolt applications in '72 did not receive the McKinnon cast rears but similiarly assembled 12 bolts out of Buffalo axle plant.

The McKinnon plant cast 12 bolt rears were cast differently (date coded differently) & ID coded differently, had the 3R (BOP useage flange), had different c-clip axles than std Chevelle axles, & came with the BOP style backing plates. That's it, std Chevy 12 bolt gears & carriers inside.

'71+ M-P series 8 7/8" rears which were stock in many '71-76 & '77-85 GM B-bodys, '73-77 A-body wagons, & even some '73-76 Pontiac A-bodys.

AS far as '68-70 BUICK 8.2 10 bolt rears go, these did not use not use an 8.5" diam ring gear, but the '68-70 design of BUICK 8.2 rears were cast with their own housings & had their own design of gears along with their own design of BUICK 8.2 carriers.

Hope this helps,

Good information. What is the ring gear diameter of a 68-70 Buick 10 bolt, really?

[pontiacs-r-us]

Thanks for your all help guys,Kenny

[gloryrestoparts]

to add further to the great info by oph and gonicgm, the first ones appeared in 67 W-30s. It is referred to as the Type O rear end or Type O 12-bolt. the 31-spline versions are found mainly in 68 cars, ie W-30s and H/Os.

I know people who have turned down a Ford 8.8 carrier to fit the Type O.

Richmond makes a limited number of gear sets for the Type O.

Your best source for Type O parts (and info for the breakdown on carriers and gear sets) is http://www.supercarsunlimited.com/

[GStage1]

Buick Skylark rears from 68-70 are 8.2" and not worth rebuilding.

Best bet, get the 71-2 Skylark/Cutlass rear which is the corporate 8.5"

[corn goat]

this might be treasonous, but I am almost of thinking of anew 9 inch housing w/all a body brackets and axles etc all new for 700.00minus ring and pinionposi and pumpkin.or is this too extreme?

[GStage1]

You can build a complete 8.5" for $700.......ready to run.

[corn goat]

george give me an idea on a price break down please.

[GonicGM]

Originally Posted by corn goat

george give me an idea on a price break down please.

rough estimates:
gears $180
install kit $90
posi $450
handling $7
Wheel bearings and seals $75
Labor ????$
rear end core ????$