[Tim Corcoran]

I appreciate your very detailed history on GM differentials but I am having difficulty sorting through your dissertation to find my answer.

In my car I have a 10 bolt Pontiac rear end from a 65 GTO. I purchased a 12 bolt Chevy rear to handle more torque for my new combo. I would like to use the backing plates, wheel cylinders, brakes and drums from the Pontiac 10 bolt on the Chevy 12 bolt. Will this work? Thanks for your advice.

['ol Pinion head]

The backing plates off the original '65 8.2 Pontiac rear will bolt on the 12 bolt chevy rear as the spacing between the bolt holes on each rears axle flange is the same. Same diam & width of brake shoes used on the backing plates. Conversely, to install the 12 bolts backing plates on the GTO's original rear would require a lot of time with a die grinder to the center of each backing plate. Not a big fan of stock 12 bolts as an "upgrade".

Throwing the torque of an upgraded engine to a stock 12 bolt posi rear, it's a good measure to upgrade the pathetic stock axles & the weak 10/18 spider gear/side gear combo in the OEM Eaton posi. Also fit a steel LH bearing cap. Currently have three 12 bolt housings in the racks, with broken LH caps/need to be fitted with steel caps in order to be built up. The lower the gear ratio & the harder these rears were "popped" was reason each rear was heavily damaged. Pulled 4.56 & 4.88 pinions out of each rear. Stock (junk) axles with leaking c-clip elims out of one.

[Half-Inch Stud]

Post 2 nailed your question: use every bit of the 10-Bolt Brake setup onto the 12- Bolt.

Throw the 12- Bolt brake setup in the creek ( or try selling em ).

[Tom Vaught]

Thanks for refreshing my memory on the 10 to 12 and 12 to 10 swaps, ol pinion head.

I remembered one being a royal PIA. (12 bolt's backing plates on the GTO's original 10 bolt's rear would require a lot of time with a die grinder to the center of each backing plate.)

Tom V.

[Tim Corcoran]

Thanks for the simplified answer, it was the answer I was hoping for because the new 12 bolt has no brakes or drums and backing plates are in sad shape. As for the 12 bolt upgrade it has new steel axles installed and a new after market posi unit with new 3.08 gears. I am installing it in my 67 LeMans street machine. I believe the 12 bolt Chevy is a strong unit, certainly strong enough for my needs. Many years ago I found a 12 bolt in a wrecking yard, I pulled the 12 bolt rear out of a 65 or 66 Chevelle that had a small block in it and it was a four door car. I installed Moser axles, c-clip eliminators and a spool with 3.73's and stuck it in my 65 LeMans. Drove it on the street for several years started out a low 12 second street car then it evolved into a low 10 second bracket car. The car has hundreds of 12 second, 11 second and 10 second 1/4 mile passes 60' times 1.39 to 1.45 depending on conditions and still runs strong never even changed the oil been running it since 1995 and still racing it. Did some street racing with the car years ago in California too but just couldn't get it to hook up on the street. The only problem I ever had with that 12 bolt was c-clip eliminators would leak oil until I figured out how to remedy that and they haven't leaked in over 20 years.

[bob prichard]

Not meaning to hijack this thread, but wondering what size the stock 65 GTO 8.2 uses for the u-joint attachment flange? 1330? 1350? I’m changing my 8.2 to Chevelle 12 bolt and need to buy a pinion yoke. Thank you.

[400 Lemans]

65 GTO uses a 3r u-joint from the factory and most 12 bolts have a 1310 pinion flange. You can save some money and get the conversion u-joint.https://www.amazon.com/Moog-372-Univ.../dp/B009HQJGVW

[bob prichard]

Originally Posted by 400 Lemans

65 GTO uses a 3r u-joint from the factory and most 12 bolts have a 1310 pinion flange. You can save some money and get the conversion u-joint.https://www.amazon.com/Moog-372-Univ.../dp/B009HQJGVW

I was planning to use a 1350 yoke, is there a conversion u-joint for that swap? I have heard that conversion joints are weak. Also read here in another forum that a yoke from a big Pontiac will work with GTO u-joint, but don’t see how it would work on a Chevy 12 bolt. Thanks for responding.

[400 Lemans]

Originally Posted by bob prichard

I was planning to use a 1350 yoke, is there a conversion u-joint for that swap? I have heard that conversion joints are weak. Also read here in another forum that a yoke from a big Pontiac will work with GTO u-joint, but don’t see how it would work on a Chevy 12 bolt. Thanks for responding.

https://www.dennysdriveshaft.com/c14...556_insid.html

[bob prichard]

Originally Posted by 400 Lemans

https://www.dennysdriveshaft.com/c14...556_insid.html

Thank you for the link. I saw their conversion joints are grease able, meaning they are hollow. I emailed them to see if they have the non grease able available.

[Tim Corcoran]

Wonder if that Dana Spicer P/N 5-3205X (Neapco) U-Joint is forged or cast. Doesn't say on their website and they don't answer the phone anyone know? I have the same concern not too happy about using a U-joint drilled for grease fitting. Wonder if anyone has a non-greaseable 1350 to GM 3R U-joint.

[bob prichard]

Originally Posted by Tim Corcoran

Wonder if that Dana Spicer P/N 5-3205X (Neapco) U-Joint is forged or cast. Doesn't say on their website and they don't answer the phone anyone know? I have the same concern not too happy about using a U-joint drilled for grease fitting. Wonder if anyone has a non-greaseable 1350 to GM 3R U-joint.

I tried a quick internet search and could not find any.

[Tim Corcoran]

Bob

Denny's Driveshaft's website says they have them in stock

https://www.dennysdriveshaft.com/c14...556_insid.html

[Half-Inch Stud]

Fact: i have removed a 65-70s Big Car rear's Yoke and slide it onto a Chevy 12-Bolt pinion shaft input, finished the install and drove without failure nor leak. Did it again on every 12-Bolt thereafter. Go forth and enjoy.

Generally you could say Chevelles dropped driveshafts and GTOs chunked their differentials. But i happen to observe 2 GTOs drop their driveshafts at the rear yoke. I've been at the 1350 U-joint system since. And rims attached with Half-Inch Studs

Ueless Side note: The chevy Kingswood Estate Wagon 12-Bolt Posi rear is of amazing strength and parts sizes, and would come close to Dana60 dimensions. But i never got the Yoke.

[Schurkey]

Originally Posted by Tim Corcoran

In my car I have a 10 bolt Pontiac rear end from a 65 GTO. I purchased a 12 bolt Chevy rear to handle more torque for my new combo. I would like to use the backing plates, wheel cylinders, brakes and drums from the Pontiac 10 bolt on the Chevy 12 bolt. Will this work? Thanks for your advice.

You're asking the wrong question.

Why would you use brakes from a '65 GTO (9.5" diameter) when you could inexpensively upgrade to ~11" brakes from a B-body? Enormously more stopping power, dirt cheap at the Treasure Yard. One-tenth the hassle of a rear disc "upgrade" that probably isn't an "upgrade" at all.

[bob prichard]

Originally Posted by Tim Corcoran

Bob

Denny's Driveshaft's website says they have them in stock

https://www.dennysdriveshaft.com/c14...556_insid.html

Solid 1350 x 3R conversions? Thanks.

[bob prichard]

Originally Posted by bob prichard

Solid 1350 x 3R conversions? Thanks.

I looked again at Denny’s and don’t see any solid non grease able 3R to 1350 conversion u-joints.

[Tim Corcoran]

Originally Posted by Schurkey

You're asking the wrong question.

Why would you use brakes from a '65 GTO (9.5" diameter) when you could inexpensively upgrade to ~11" brakes from a B-body? Enormously more stopping power, dirt cheap at the Treasure Yard. One-tenth the hassle of a rear disc "upgrade" that probably isn't an "upgrade" at all.

I appreciate the info. I was not aware of that possible upgrade. What year B-bodies would have these brakes? So I would need the backing plates, drums, the shoes and all the goodies? You know it's getting pretty hard to find any of these older vehicles at the salvage yards these days almost all of them have been scrapped long ago.

Might be a dumb question but what model vehicles are the B-bodies? Thanks

[Schurkey]

Originally Posted by Tim Corcoran

Might be a dumb question but what model vehicles are the B-bodies?

Chevy B-body would be Biscayne, Bel Air, Impala, Caprice. I'd expect anything from '65--70 would work, perhaps older or newer. That's what I'd be looking for in the Treasure Yard, since you have a Chevy axle.

I'm thinking all full-size Pontiacs are B-bodies.

Olds had a mix of B and C bodies, as did Buick. But C-body brakes might work for this swap also.

I don't know how the backing plates from Pontiac, Olds, Buick and potentially Cadillac might bolt up to the Chevy axle. Knowing GM, they're likely a direct swap in the '65--'70 model year range; but I know that GM had lots of axle assemblies. Perhaps not everything interchanges.

For the record, I grabbed an axle from a mid-'70s A-body that had 11" drums with the intention of putting them on my '68 'Camino with a 12-bolt; but never finished that project. I'd expect certain A-body brakes could work for you, too.

[Tim Corcoran]

Schurkey,
Thank for the info much appreciated, but now the quest to find a B-Body in the salvage yards, like I said now days most of what they have left is late model stuff cars made in the 70's are all mostly crushed a long time ago.