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Old 06-01-2013, 09:53 AM
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12 bolt rear end for g body

I found a 1970 cutlass 12 bolt rear end for sale i no chevelle 12 bolts work good in g bodys i just wasnt sure about 12 bolt out of 70 cutlass thanks for any info

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Old 06-01-2013, 10:48 AM
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The Cutlass 12 bolt from '68 to '70 is not the same as the Chevy 12 bolt. This is known as the O axle and is not actually a 12 bolt on the inside. The O axle has a 8.5 inch ring gear and the axles do not have c clips. There are not a lot of after market parts available for this rear end and the parts are more expensive than the Chevy parts. It's not a bad rear end, just don't take it for the Chevy 12 bolt.
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Old 06-01-2013, 11:04 AM
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stronger than the 7.5 in the g bodys
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Old 06-01-2013, 11:32 AM
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Originally Posted by gamedawg03 View Post
I found a 1970 cutlass 12 bolt rear end for sale i no chevelle 12 bolts work good in g bodys i just wasnt sure about 12 bolt out of 70 cutlass thanks for any info
Besides the whole "Type O" axle issue noted above, I'm not sure any A-body axle "works good" in a G-body. You need expensive upper control arms with ball-type rod ends to make up for the different rear suspension geometry, and even after you spend that money, you still have an axle that is several inches wider than stock. Can you make it work? Sure, many have. Is it your best choice? Probably not.

I'm also surprised when people claim they have cheap A-body axles to use in G-body cars. Here in the mid-Atlantic area, A-body axles go for stupid money. If that Type O axle is cheap, it's because the seller also bought it thinking it was a Chevy 12 bolt and now is trying to dump it.

For a mild street-driven car, a properly built 7.5 will be fine. If you are making serious HP and have traction to use it, spend the money and get one of the 9" housings made to bolt into a G-body.
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Old 06-01-2013, 11:52 AM
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Besides the whole "Type O" axle issue noted above, I'm not sure any A-body axle "works good" in a G-body. You need expensive upper control arms with ball-type rod ends to make up for the different rear suspension geometry, and even after you spend that money, you still have an axle that is several inches wider than stock. Can you make it work? Sure, many have. Is it your best choice? Probably not.

I'm also surprised when people claim they have cheap A-body axles to use in G-body cars. Here in the mid-Atlantic area, A-body axles go for stupid money. If that Type O axle is cheap, it's because the seller also bought it thinking it was a Chevy 12 bolt and now is trying to dump it.

For a mild street-driven car, a properly built 7.5 will be fine. If you are making serious HP and have traction to use it, spend the money and get one of the 9" housings made to bolt into a G-body.
moser makes a 12 bolt all new, thats about the same cost as the 9",
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Old 06-01-2013, 12:23 PM
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The O axle is going to be 3 inches wider than the G body rear end. The G body rear end is 58 inches wide and the O axle is 61 inches wide. The angle of the upper eyes on the G body and A body rear ends is different, so the control arms must be custom. You can also get custom lower control arms to work with the A body lower brackets, or you can cut the lower brackets off of the G body rear end and weld them on the A body rear end in the correct location and use G body lower arms.

The Moser 12 bolt is a bolt in with stock G body arms. The Moser 12 bolt is also much stronger than any Chevy 12 bolt and lighter and cheaper than a good 9 inch.
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Old 06-01-2013, 01:33 PM
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Thanks for all the info its a strip and street monte carlo ss i have a built 7.5 but have broke it twice and my new motor is 421 stroker with nitrous so i no im gonna have to get a better rear end
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Old 06-02-2013, 07:15 PM
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I had a guy give me a 12 bolt out of 66 impala i have tried to find info on how to make it work i only can for a body rear end for g body. I no i will have to get it shortened and modified but will it work thanks
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Old 06-02-2013, 08:10 PM
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The only way you are going to make that work is if you use ladder bars or a 4 link. You can not make it work with the original suspension.
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Old 06-03-2013, 09:02 AM
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Yep, the Imp rr won't work...in one sense you can divide Chevy rr end types by those that have cast-in "ears" on the top of the diff for upper control link bushings, and those that don't which may be for leaf springs or links that use brackets welded to the axle tubes. The Impala does not have ears, your G-body needs them. That can be a welded mod onto a 9" with it's sheetmetal housing, but not a cast-center 12-bolt. So...no Impala rear. (Save it for something else, though...)
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Old 06-03-2013, 12:54 PM
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That can be a welded mod onto a 9" with it's sheetmetal housing, but not a cast-center 12-bolt. So...no Impala rear. (Save it for something else, though...)
Not necessarily true. Many cast center sections are cast STEEL, not cast iron. Cast steel can be welded just fine. The real issue is taking care not to distort the bearing races when welding.

Again, though, by the time you narrow the axle, get custom shafts, weld on the appropriate ears, get custom control arms, etc, etc, you're money ahead to buy one of the Moser units described above.
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Old 06-03-2013, 02:05 PM
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The Chevy 12 bolt center is cast iron. I don't recommend trying to weld highly stressed critical parts to it. I don't know of any of them that are cast steel. Some are nodular iron and some are regular gray iron.
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Old 06-05-2013, 04:26 PM
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Yeah i sold the rear end and got a 9in coming already done for a g body hurt my pocket but i no its gonna hold up. My next question what shocks would u recomend for front and back thanks
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Old 06-05-2013, 07:57 PM
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Probably need to start a new thread for that.
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