Why do the LS1 12 Bolts break when the......
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Joined: Feb 2002
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From: Native Texan
Why do the LS1 12 Bolts break when the...... Why do the LS1 12 Bolts break when the other Cars like Chevelles, Skylarks, Old Camaros, Cutlass's etc seem to make them live just fine with the heavy duty carriers? What is so different?
Now I know that a lot of guys have made them work but why have some not been able to g make them live?
Later,
Bart
Now I know that a lot of guys have made them work but why have some not been able to g make them live?
Later,
Bart
Well, I don't think it is the type of 12 bolt, but I may be wrong. I would think that it is the sheer weight of the new f-bodies, as well as increased traction. It is usually the posi that breaks nowdays, not the housing or axles. So if I had to say, I would bet that these cars made it because they had less power and traction. And if they were made into race cars with traction, they put in a spool.
My opinion...
The people making these housings now arent as accurate with their manufacturing as GM was when they made them originally. I think that is why you see more noise problems with them also. They arent made in very large numbers, so there isnt as much R&D going into them either. The 9" 3rd member on the other hand is made in very large numbers, and the housing itself just needs to be rigid and has nothing to do with the geometry of the gear set. When you set up a gear a couple of thousandths can make a difference in gear life and noise, and I dont think the housings are made with close enough tolerances.
The people making these housings now arent as accurate with their manufacturing as GM was when they made them originally. I think that is why you see more noise problems with them also. They arent made in very large numbers, so there isnt as much R&D going into them either. The 9" 3rd member on the other hand is made in very large numbers, and the housing itself just needs to be rigid and has nothing to do with the geometry of the gear set. When you set up a gear a couple of thousandths can make a difference in gear life and noise, and I dont think the housings are made with close enough tolerances.
I agree. Tolerances and quality control. The name of the game today is: "Just get it out the door. We don't have to warranty it anyway. It's for racing".... It's that way w/almost everything we buy today--unfortunately. WJ 
shear weight of an f-body..
...i doubt the f-bodies weigh more now than they used to...and any of the cars that were made fast back then i'm sure prolly had a spool in it...i would think that the quality would be better nowadays seeing that there is new technology...
...i doubt the f-bodies weigh more now than they used to...and any of the cars that were made fast back then i'm sure prolly had a spool in it...i would think that the quality would be better nowadays seeing that there is new technology... I had problem with my stock carrier it was a POS and I swapped it for an Auburn cone type posi unit and added some moser axle shafts while I was in there. I have beat the hell out of it at times and she still is together. I guess it just depends on your luck.
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I have been building 12 bolts for many years. I have personnaly never had a problem. I have been running a transbrake for years now and launching 1.60 60' times on the street! I think there is something to be said about the "NEW" 12 bolt housings. I have never had one, but there could be some kind of issue with machining issue, or they are just not assembled properly. As far as abuse, the "old" cars abused them a little harder then the average car today would.
Take a 70' chevelle for instance, with about 450 ft/lb of torque and massive wheel hop problems that every car had, STOCK 30 sline axles(everybody today runs a bigger axle), and they weighed about 4000 lb!! Wheel hop puts more strain on a rear then side stepping the clutch. As far as the posi unit itself going, If your talking clutch pack, that has been a common problem since the begining of time. I have to rebuild my clutch pack about once every year or two. That is just normal maintance if you want a tight posi. I like how I can ajust my preload also. That is my .02
Take a 70' chevelle for instance, with about 450 ft/lb of torque and massive wheel hop problems that every car had, STOCK 30 sline axles(everybody today runs a bigger axle), and they weighed about 4000 lb!! Wheel hop puts more strain on a rear then side stepping the clutch. As far as the posi unit itself going, If your talking clutch pack, that has been a common problem since the begining of time. I have to rebuild my clutch pack about once every year or two. That is just normal maintance if you want a tight posi. I like how I can ajust my preload also. That is my .02
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I think tire technology, and suspension technology has probably advanced quite a bit in the 30+ years, and our cars on average are probably hooking a bit harder then they were back then.
Its the torque arm.... The unloading of the right tire causes a lot of stress for the differential to have to deal with. This is why most are running a 12-bolt and a spool. I am not sure about the older muscle cars suspension but I would assume they are 4-link systems, with ladder bar setups that dont see the problem of unloading one wheel.
Originally Posted by Ryan1985
They dont make **** like they used too. I have a freind with a 72 camaro stock rearend running 11.80's through a 4 speed and has never had a problem with his stock rearend.
