My friend has a 12 bolt from a 69 C10 that he will give me if I want it. I'm toying around with fabbing it up for my car. I gather that the truck 12 bolt is weaker than a car rear. Is it even worth my time using this housing? I can weld/fab pretty well, and would like to save some money. Thanks!

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I would probably try and use a 8.5" 10bolt out of an '89 or later truck or Caprice, some Caprices got 7.5" rears but LT1 cars and cop cars got the 8.5" so they are very common. The '89 or later 8.5" is 12bolt equivalent upped the spline count to 30 spline and they are stout..

The cop cars and Roadmaster got a axle that was like 1.25" narrower than the civilian LT1 cars might be near the right width.

 

You need to find out more about the 12-bolt.

Does it have a limited slip differential? What gear ratio does it have? If it's not a posi and not the gear ratio you want, replacing the carrier and the gears will cost you $800 in parts.

What condition is it in? Would probably be a good idea to replace all bearings and seals - add anpther $100-125 for parts.

What is the width? If it's too wide it will have to be narrowed. Generally, you need a fixture to narrow it and weld it up. Then you'll need to buy new axles.

What is the bolt pattern on the axles?

Now start fabbing. Cut all the mounts off the 12-bolt and all the mounts off your 10-bolt. Weld all the 10-bolt brackets (shock mounts, spring mounts, panhard bar mount, LCA mounts) onto the 12-bolt, in precisely the correct positions.

Next, the real challenge - how do you fab up and attach a mount for the torque arm?

I knew a very skilled fabricator who built his own 12-bolt using a used unit from another vehicle. After he got all done, he said he wished he had never done it, and would not recommend the project.

Why would a truck rear be weaker than a car rear?

 

What he said though I think an axle jig is mandatory to keep everything plumb.

 

It has 3.73 gear, which I desire but no posi. I am still on the fence about it, and may not bite.

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With a 95 M6 3.73s are not really a great choice, 4.10s make 6th more usable.

 

I was happy with the stock 3.42s. 3.73s in my street car will be fine with me. Still on the fence about using the housing. I hear the truck pinion dia is 3/16 smaller than the car, but the gearset is stronger. Ill look into the torque arm mount fabrication.

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