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#1
04-13-2020, 07:05 AM
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GM 12 bolt rear housing strength
I have a 12 bolt with a 2.56 open diff. I'm considering using the housing with a new posi carrier and 3.55's. I've read that the carriers of these highway gear 12 bolt rears are weak but are the housings weak as well? Are all housings equal in strength regardless of what carrier and ratio was used within?
I just broke a 10 bolt so I am looking for something stronger. |
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#2
04-13-2020, 07:20 AM
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What style 10 bolt?
The Chevy type 1971 and up 10 bolt with aftermarket internals last for years at the strip with slicks and about 600 hp or so, no less a 12 bolt fitted the same!
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#3
04-13-2020, 07:23 AM
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The rear I broke is a BOP 10 bolt from a 66 GTO. I split the driver side bearing cap.
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#4
04-13-2020, 07:40 AM
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I am surprised a Axle did not go south first or a clutch cone or spider if it was a posi?
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#5
04-13-2020, 07:58 AM
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Quote:
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#6
04-13-2020, 08:34 AM
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To me the weak point in a original 12 bolt GM setup is the carrier caps and the area in the housing the carrier bolts thread into, looking at the wall thickness there its pretty thin
Iam not saying they are failure prone but just looking at basic structure compared to other rear ends . I once had a Tom's rear ends cap kit it upgraded the cap and bolt size from 7/16 to 1/2 but if you took the housing threads out to 1/2 you dont have much material left around the threads, I didn't execute
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A man who falls for everything stands for nothing. Last edited by Formulas; 04-13-2020 at 09:34 AM. |
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#7
04-13-2020, 08:51 AM
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I use Strange billet aluminum bearing caps, they are a lot stronger than stock.
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1967 Firechicken, 499", Edl heads, 262/266@0.050" duration and 0.627"/0.643 lift SR cam, 3.90 gear, 28" tire, 3550#. 10.01@134.3 mph with a 1.45 60'. Still WAY under the rollbar rule. |
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#8
04-13-2020, 09:29 AM
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Not surprised you broke a BOP.
The stock housing 12 bolts are plenty strong for street cars if built correctly. We've had them in the 10's in near 4,000 lbs. cars without failure. Just good parts inside and proper setup. I generally like to use the bearing cap support covers if it's going to be abused to that level though. Just for a little piece of mind. For a 12 second or even an 11 second car, not much is really needed, maybe good axles if that's a concern for you. I've got a near stock 12 bolt that is original to my Chevelle and I've been throwing 600 hp at it for the last 18 or more years. It's been perfect. It never sees a stock street tire either, always has stickies on it. Just a Moroso posi, Moser non taper C-clip axles, and that's it for aftermarket parts. Nothing special. Dad's car is a stock 12 bolt, stock GM posi. The only aftermarket part in it are a set of Strange C-clip eliminator axles. That rear has been together for more than 20 years with more racing than I can count. It cuts 1.5 60 foot times and he's currently pushing 724hp/760tq to it and has been for about 5 years now. That rear hasn't flinched. I just recently put a bearing cap support cover on it last year. We seriously thought about a 9 inch upgrade 5 years ago when the engine upgrade happened, but I talked him into running it and see what happens. It's been perfect. Last edited by Formulajones; 04-13-2020 at 09:36 AM. |
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#9
04-13-2020, 09:55 AM
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Search 12 bolt here on the street forum. Lots of good info to help make a decision.
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#10
04-13-2020, 10:00 AM
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The 12 bolt rear is stronger than most think. Use a support cover and proper set-up and it should live a long time on the street. We used to run 12 bolts under Super Stock Hemi Mopars with a 4 Speed. They took less HP to turn.
__________________
66 GTO Nostalgia Super Stock/Street Legal Car 421 CID, stock block, Wenzler Intake, 2- Carter 750 AFB's, 3.90 Gears, Full Factory Interior, Full Exhaust, Stock Suspension 3750LBS 9.77@136.99 Multiple NSCA/NMCA World Champion 66 GTO 389 3x2, 4 speed, 4.33 gear, Montero Red 33K original Miles 67 GTO 2dr Post, 428, Tri Power, 3.55 Gears 80 Trans Am Black SE Y84 W72 WS6 |
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#11
04-13-2020, 03:46 PM
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Thanks everyone. I take it I should not be concerned that my 12 bolt housing started out with the 2.56. I'll just be using the housing and axles if they are good. I'll get a new carrier and gear set.
More about the 10bolt bop failure: It was not spectacular or catastrophic and I could still drive the car. It just had a real bad whine, especially in 4th on the gas. Cap is cracked through, but the bolts are intact Otherwise, I didn't dive into it too deep yet. Took the cover off, saw the cracked cap and then pretty much closed up the garage... |
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#12
04-13-2020, 03:48 PM
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I thought the weak part was the C locks, you brake an axle and your going to have some major body damage when tire comes flying out of the wheel well.
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#13
04-13-2020, 03:59 PM
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Quote:
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http://www.machdevelopment.com/album...775/527566.htm |
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#14
04-13-2020, 08:27 PM
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Make sure what year the 12 bolt is or measure it. 1" overall length difference between early and later years. Important to know if you decide on new axles. New axles and bearings are cheap insurance.
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#15
04-13-2020, 08:39 PM
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At what power level should one weld the axle tubes?
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Will Rivera '69 Firebird 400/461, 290+ E D-Ports, HR 230/236, 4l80E, 8.5 Rear, 3.55 gears '64 LeMans 400/461, #16 Heads, HR 230/236, TKO600, 9inch Rear, 3.89 gears '69 LeMans Vert, 350, #47 heads: Non-running project |
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#16
04-14-2020, 06:10 AM
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I've seen the axle tubes move on the street without sticky tires but from the combination of beating on the car with a 4 speed and shot rear end control arm bushings!
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#17
04-14-2020, 07:40 AM
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Thanks again for all the input. The 12bolt rear I hope to use is in my other 65 GTO (future project). Nevertheless I am still going to measure it and check the id numbers before I invest in new parts.
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#18
04-14-2020, 09:23 AM
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Spider gears in stock posis can blow out. Buick GS buddy brake them at an NMCA race in a low 12 second 455 car. Tom's Differentials has better spiders.
__________________
Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#19
04-14-2020, 10:20 AM
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Quote:
It is good insurance and if you have the ability or the means, I'd suggest it. The only time I've seen the tubes twist is in a leaf spring application, on a stick car, and the pinion just goes straight up and slams the floor, lol. I've never seen it happen in a coil spring application, likely because the control arms do a pretty good job of holding things in place. |
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