12 bolt truck rear

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Any opinions here of selecting a late 60's truck 12 bolt for 500 ft lbs for use in hot rod projects? I have had really good luck over the years with all things 12 bolt and I do know there are differences from car to truck. My problem is its very easy to find 60" truck housings and nearly impossible to find any narrow car stuff around here. And the biggest deciding factor is that the cost is about half to completely go through a 12 bolt versus buying an aftermarket 9". Thoughts please?
 
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The C-Clips are the weakest link, Just like a car 12 Bolt. Requiring custom axles & ends (Big Ford 9") to be welded on.....Same price as having a axle narrowed. Truck 12 Bolts have a relatively small diameter pinion diameter, Smaller than the Car 12 Bolt & the 8.5" 10 Bolt. Though I have successfully put 500-600 ft lbs through a Truck 12-bolt using drag radials (Welded tubes) in a 1969 CST-10, But it was still traction limited being a truck & all. I needed to feather the throttle through the first 40-70 feet depending on the surface. With good weight transfer/traction off the line.....I would have broke it! The driver/left main cap is a weakness on ALL GM corporate differentials when you start hookin'.
 
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So for cruising around and the ocational mashing of the go pedal you probably wouldn't hurt it? I think this truck weighs around 1800 lbs wet. Any complaints about using the Oldsmobile type tube ends?
 
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Originally Posted by P10crew
So for cruising around and the ocational mashing of the go pedal you probably wouldn't hurt it? I think this truck weighs around 1800 lbs wet. Any complaints about using the Oldsmobile type tube ends?
You'll be fine! The aftermarket has spoken....And Big Ford Ends won a long time ago! Nothing wrong with BOP Housing ends if wanting to keep GM Drum Backing Plates?
 
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Originally Posted by Chris142
I spent my youth tearing up 12 bolt rear ends. Make sure that your foot is off the clutch before you stomp on it.
Automatics are a lot easier on differentials grin
 
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The reason I ask about the olds ends is the rear disc conversion that I make is dialed in for the gm pattern. Wouldnt take much to convert the water jet drawings to ferd though.
 
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Originally Posted by clinebarger
Originally Posted by Chris142
I spent my youth tearing up 12 bolt rear ends. Make sure that your foot is off the clutch before you stomp on it.
Automatics are a lot easier on differentials grin
I scattered them with a 350/th350 combo too smile
 
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Originally Posted by clinebarger
12 Bolt Passenger Car Differentials were only installed behind Big Blocks in factory trim.
Incorrect. 68-72 gm chevelle/ elcamino with a 4 bbl got them. Even the 350/300hp Usually with 2.73 gears.
 
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OP, what kind of vehicle is it for? You can upgrade a GM 8.5 differential with an Eaton posi, upgraded 30 spline axles and an inspection cover with the bearing cap braces...weld the axles tubes to the housing and handle 600+HP at the rear wheels all day long. It will be stronger than most stock GM 12 bolts and Ford 9" rears.
 
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Ok then let's switch the question to this. Is there a good substitute for a 58"-60" 12 bolt that can be had at a salvage yard? Fully updating the internals is no problem. For what I'm doing and with the good service 12 bolts have given me I just can't see spending 2000-3000 on a 9" or a strange. It's getting nearly impossible to find 12 bolt car donor housings but truck housings are still around. I have narrowed and set up several drag race 12 bolts way back in the day but I no longer have the 2.5" ground drill rod and donuts but I'm sure I can locate one if I need to narrow a housing and if aftermarket axles are available. 500 hp and 500 fp is the target area that I will be in. These will be in hot rod vintage retros. [Linked Image] [Linked Image] [Linked Image] [Linked Image] Like this this and this lol. What were these 8.5.s in I'll go to one of the yards and have a look see.
 
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Originally Posted by Chris142
Originally Posted by clinebarger
12 Bolt Passenger Car Differentials were only installed behind Big Blocks in factory trim.
Incorrect. 68-72 gm chevelle/ elcamino with a 4 bbl got them. Even the 350/300hp Usually with 2.73 gears.
Not the first time I've heard that, While first gen Camaro Z28's & 4 speed SS350's had 12 bolts, I've never seen a small block Chevelle have a 12 bolt....They had a 8.2" 10 bolts. Buy just glancing at them.....They look very similar. Now....It may have been a optional thing? Without build sheets to confirm these things....We are both guessing! I once had a 1969 Elcamino SS396 with a Saginaw 3 speed on the floor, It was only 100% proved by the build sheet that was luckily still in the seat springs.
 

wtd

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Originally Posted by clinebarger
12 Bolt Passenger Car Differentials were only installed behind Big Blocks in factory trim.
Not true. I have a 70 Monte Carlo that originally came with a 400 small block and a TH350 and it has the 12 bolt rear end. I've had several other first generation Monte Carlo's that were small blocks that had 12 bolt rears in them. In these cars if they came with a 350 4 barrel or bigger, they usually had a 12 bolt in them.
 
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