Question: GM 12-bolt rear ends

Tom

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Question: GM 12-bolt rear ends
« on: May 27, 2018, 06:36:31 PM »
I know that the Ford 9" is 'king', but what about the 12-bolt ?  I have a chance to get one real cheap compaired to the 9" that I find.

DavyJ

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Re: Question: GM 12-bolt rear ends
« Reply #1 on: May 27, 2018, 06:38:58 PM »
the 12 bolt is a good stout rear end and can be adapted to disc brakes easily.  but if you need to narrow it is more costly as the axles are tapered after the splines and cannot be machined like Ford axles....   so if the width is ok,  no reason not to...
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jaded iconoclast

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Re: Question: GM 12-bolt rear ends
« Reply #2 on: May 27, 2018, 07:42:55 PM »
My experience (10.20s in a 4200lb street car) is that they are extremely stout. Unless you are building a truly APESHIT car, like maybe a heavy 3500lbs +, 9 second stick car with really big tires, I wouldn't think twice. Unless you are just narrowing an axle for looks, I would be hesitant to use re-splined oem axles in anything. Put it this way, anything strong enough to tear up a well set up 12 bolt will laugh at a re-splined oem axle, so its a moot point.
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Tom

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Re: Question: GM 12-bolt rear ends
« Reply #3 on: May 27, 2018, 09:22:13 PM »
Thanks guys.  Looks like I need to check the width.

jaded iconoclast

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Re: Question: GM 12-bolt rear ends
« Reply #4 on: May 28, 2018, 09:59:45 AM »
I think the 9" is over-rated. Yes, a 9" with a nodular carrier, big pinion support, Detroit locker and 31 spline axles is a stout piece. but with the typical run of the mill WAR or 2 rib carrier, a trac-loc, standard bearing support and 28 spline axles, like you will usually find in a typical auto wrecker 9" out of a galaxie or f100, its not as strong as an 8 3/4 Mopar or 12 bolt, and all the time, I see guys replace 12 bolts with a 9" like I just described thinking its an upgrade. And they would have had a stouter rear-end just by adding c-clip eliminators (or better yet, new housing ends and aftermarket axles) to the 12 bolt. I wouldn't even RUN the single rib 9" carrier, unless it was a cruiser that was never going to have slicks on it, or a very light car with an automatic.
I witnessed a friend of a friend tear the entire nose and pinion gear right out of a WAR carrier, and the car was not what I would call a stout piece at all, it was a low 12 second daily driver Fairlane with a small block and a 4 speed and skinny slicks. And I mean he tore it out, the bearing support, the pinion gear, and a big chunk of the front of the casting were laying on the track, still attached to the driveshaft.
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TS3X65MPH

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Re: Question: GM 12-bolt rear ends
« Reply #5 on: May 28, 2018, 11:30:45 AM »
I know that the Ford 9" is 'king', but what about the 12-bolt ?  I have a chance to get one real cheap compaired to the 9" that I find.
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jaded iconoclast

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Re: Question: GM 12-bolt rear ends
« Reply #6 on: May 28, 2018, 04:22:29 PM »
Tom, what is this going in? To be honest, if I were starting from ground zero, and it wasn't a sub 11 second stick car with slicks and lots of track time, I would put an 8 3/4 mopar in it over either the 12 bolt or the 9". I have run lots of them in the past, and have one in my S-10 now with a Detroit locker, 4.56s and Moser axles, it launches wheels up and runs 1.57 shorts@3430 lbs, nary a whimper, and LOTS of abuse on street too. They aren't very expensive to buy, no c-clips, you can cut down the stock axles if its not going to see a lot of track time with slicks, and its stronger than a 9" with a two rib or WAR carrier. The 8 3/4 is my first choice down to around 10.70s with an auto, or high 11's with a stick and slicks. If you go to a nodular carrier, big pinion support and 31 spline axles, THEN the 9" is stronger, but not many of those laying around the wreckers anymore. I would take the 12 bolt over a 9" that doesn't have the good stuff, and that's based on lots of street racing and track experience with all three rears. The 12 bolt is ultimately somewhat stronger than the 8 3/4, but how much beef do you really need? Is this is a fast, heavy street race car that is going to have slicks on it all the time, or is it a street rod with some power?
If its something that's really going to kill a good 8 3/4 or 12 bolt, I would skip right over the 9" with a grands worth of aftermarket parts thrown at it, and go straight to a Dana 60. Don't get me wrong, I have 9" stacked up like cordwood here, I am putting one in my T-bucket (mostly because I have a '57 housing, and they are so damned pretty) and I have a mustang dimple back for my '65 falcon, another one in my '67, so I have plenty of first-hand experience with 9"s, and some experience makin' them spew their guts out as well. The dana is cheaper and easier to find in the wreckers than the 9", and stronger than all of the above, without any fancy carriers or anything. You buy one out of a 3/4 ton truck, because you are going to cut the housing ends off anyway, and put whatever ends you need to suit your brakes when you narrow the housing. Those things are common as dirt, they were put in a shitload of duallies and 3/4 tons over the years, and if you find an older one, it will have a dana spicer clutch type sure-grip in it. If you can break THAT shit in a street/strip car, then you are a braver man than me.
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jaded iconoclast

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Re: Question: GM 12-bolt rear ends
« Reply #7 on: May 28, 2018, 04:31:09 PM »
Heres the 8 3/4 in my truck. The drain plug isn't stock, but I hate gear lube in my face. I've got buddies that run low tens on these rears with an auto.
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Tom

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Re: Question: GM 12-bolt rear ends
« Reply #8 on: June 02, 2018, 08:10:09 AM »
Perhaps I should explain why I was asking.  I had a chance to buy a '32 3-w coupe locally and reasonably priced to boot.  But the engine was weak, trans was suspect, and it had a 12-bolt rear.  There were other things wrong with it - suspect bodywork mainly, but again the price was right so I gave it some thought.

Regarding the 12-bolt - I wanted to understand if there was any reusability of components I was going to remove from the car, and thought that I might learn something in the process.  Thanks for all the info !

(BTW I did not purchase it primarily because of the bodywork.  It had a nice chop and the doors opened and shut nice, but I know enough about the shape of deuce 3-windows that I can tell when something 'just ain't right'.   The unknown amount of bodywork scared the hell out of me.)

jaded iconoclast

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Re: Question: GM 12-bolt rear ends
« Reply #9 on: June 02, 2018, 09:52:10 AM »
Perhaps I should explain why I was asking.  I had a chance to buy a '32 3-w coupe locally and reasonably priced to boot.  But the engine was weak, trans was suspect, and it had a 12-bolt rear.  There were other things wrong with it - suspect bodywork mainly, but again the price was right so I gave it some thought.

Regarding the 12-bolt - I wanted to understand if there was any reusability of components I was going to remove from the car, and thought that I might learn something in the process.  Thanks for all the info !

(BTW I did not purchase it primarily because of the bodywork.  It had a nice chop and the doors opened and shut nice, but I know enough about the shape of deuce 3-windows that I can tell when something 'just ain't right'.   The unknown amount of bodywork scared the hell out of me.)
One thing to be aware of, there are "12 bolts" and "12 bolts". The truck 12 bolts have a smaller pinion shaft, smaller axles and are harder to get aftermarket parts for, They are ok, but I avoid them for performance use. They have a differently shaped cover that isn't as "round" as the car 12 bolt, and doesn't have the oil gutter. There are also Olds 12 bolts that have the same issue with aftermarket parts support, and they are even worse than the truck rears, they actually use an 8.2 crown gear like an early ten bolt, and small axles. The Olds rear has a smooth cover with no bulge, and the axles are bolt-in, instead of c-clip. As far as I know, there are no new posi units for this rear, and NO new performance oriented ring and pinions (like 3.73, 4.11, 4.30 ect) and used olds OEM ones are a FORTUNE. Avoid this rear like the plague. To add more confusion, some late sixties Olds and Buick cars built in the Oshawa Ontario plant in Canada, used chevy 12 bolts. Just one more reason why Canada rules! We are bigger and on top... ;D
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