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Old 03-13-2010, 09:51 PM
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gm 12 bolt

i have a 79 trans am with olds 403 that will be hopefully. putting down numbers close to 500 hp. I have a 700r4 trans built for 650 hp. I was originally going to rebuild the stock 8.5 10 bolt i have and install 3.73 gears. i recently came across a 12 bolt that came out of a 79 Camaro. it has 4:10 gears and it doesnt have that many miles on it. He wants $550 for the rear end. It has no brakes with it. I know the 12 bolt would be better but is that a good price? What can i sell my 10 bolt for?
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Old 03-13-2010, 11:56 PM
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10 bolt value.

A good resource for checking out what the street value of parts is craigslist.com. I paid $1200 at a local reputable shop to have my 10 bolt upgraded from 2:56 to 3:42 with heavy duty axles in my Suburban. I will probably do the same for Firebird unless I find a good 12 bolt. I sometimes determine what something is worth by what it would cost to replace or rebuild it. Market value is always determined by supply and demand. craigslist on the low side, ebay on the high side. Hope this helps.
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Old 03-14-2010, 12:19 AM
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If good parts were used in the 12-bolt that is a real good price, but if it doesn't have aftermarket axles and c-clip eliminators in it you might be better off to just build what you already have. Not a very big difference in strength between the two once you start using aftermarket parts, especially the axles.

The brakes from your 10-bolt will transfer over.

Value of your 10-bolt depends on what gears are in it and what posi, a 2 series gear and posi unit is worth less than a three series gear and posi.

Complete good factory stock 3 series with 3.23 or better gears might pull $300-500 in my area, 2 series 1/2 that or less.

I take it this is a swapped in 12-bolt Car rear in this 79 Camaro, as it wasn't stock.

If that is a 12-bolt Truck swapped into that Camaro forget it, not worth it at all, keep what you have and build it up.
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Old 03-14-2010, 02:46 PM
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What did the 12 bolt come from? Does it have an Eaton Posi or something else? The '70 Z28 and SS Camaro are the only second gen F bodies that had a 12 bolt, so this could be a '70 rear end. $550 for one of these is a pretty good deal. If it's a modified Chevelle rear end then it wouldn't be worth as much. If it has a spool or c clip eliminators in it then I would pass unless you only plan on drag racing the car.
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Old 03-16-2010, 08:33 PM
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the guy who is selling the 12 bolt said there are no weld marks or anything that he can see. it was put into a 79 camaro and then pulled when he took the car apart. would it be obvious that its a chevelle rear end? What should i look for to make sure its the right one?
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Old 03-17-2010, 06:45 AM
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Check the casting numbers and the code stamped into the right axle tube.
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Old 03-17-2010, 07:00 AM
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Quote:
Originally Posted by dman0712
would it be obvious that its a chevelle rear end?
Yes.

If it came from a coil sprung car like a Chevelle or Impala, there will be large lugs cast into the center section that would have located the control arms. The lugs will extend out from the center section and will be hollow now, since you are using leafs (there may possibly still be the bushings inside the lugs).

A leaf spring rear end's center section will not have these lugs.
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Old 03-17-2010, 07:35 AM
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That is usually true, but I know of several people who cut these off to make it look more like an F body rear end.
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Old 03-17-2010, 08:24 AM
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OK, a leaf spring rear end's center section will not have these lugs.

Or evidence of these lugs having once been there, if they've been removed.

Better?
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Old 03-17-2010, 11:00 AM
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Old 03-19-2010, 03:47 PM
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If that is a 12-bolt Truck swapped into that Camaro forget it, not worth it at all, keep what you have and build it up.[/QUOTE]

Can someone explain why the truck 12 bolt is not worth it? thanks
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Old 03-19-2010, 03:53 PM
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Quote:
Originally Posted by Custom10
Can someone explain why the truck 12 bolt is not worth it? thanks
HERE is a thread on the subject.
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Old 03-19-2010, 03:55 PM
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The only real difference between the truck and car 12 bolt is the pinion shaft diameter and size of the inner pinion bearing. The truck has a smaller pinion shaft and smaller inner pinion beairng. Everything else can be changed or fixed. The truck 12 bolt is not a bad rear end. The pinion shaft in the truck 12 bolt is larger than the pinion shaft in a 9 inch Ford, and nobody complains about them. I've never heard of anybody breaking a pinion shaft in a truck 12 bolt.
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Old 03-19-2010, 03:57 PM
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The pinion of a 9" Ford is supported on both ends.
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Old 03-19-2010, 04:34 PM
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OK well I have the 12 bolt in my 72 C-10 with factory 3.73. Have no plans on changing it out however a posi would be in order since it will soon be behind a stout 383 so really what choice do I have, I need a posi and with this non leaf truck swapping to a car style would just be a expensive pain. Not planning on racing this truck or anything just wanting posi for extra traction when yarding my boat out of the launch etc. ARE there any proven posi units for these truck 12 bolts that anyone can recommend or have used themselves?

thanks for the link cobalt, interesting thread.
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