12 Bolt Posi Questions

[SpicedIcePirate]

My '72 is currently an open diff, I have a 12 bolt with trailing arms, I was just wanting to know what my options for making it a posi rearend, whether that's just changing the guts or swapping the whole unit. Can I do a junkyard swap with the guts out of any 12 bolt?

[demian5]

No, a truck is a truck 12-bolt and a car is a car 12-bolt.

If this helps, I did buy a used carrier, ring and pinion from a 1980 truck and put it in my 1970 truck diff.

[Shaky]

I re-did a 12-bolt truck rear with new everything, including an Eaton cone-clutch posi. Setting the pinion depth is the biggest challenge and usually requires special tools.

So - if you are re-using your gears and bearings, you could gamble that leaving your pinion and bearings alone doesn't affect the pinion depth, and bolt your old ring gear to the new posi carrier. Checking the gear patterns tells the final story. If you don't get a good pattern, you can try shimming the carrier side-to-side to bring it back in.

Having time and patience would be a good thing...

[SpicedIcePirate]

Originally Posted by demian5

No, a truck is a truck 12-bolt and a car is a car 12-bolt.

If this helps, I did buy a used carrier, ring and pinion from a 1980 truck and put it in my 1970 truck diff.

I did mean to say I was aware of the car vs. truck rule and that they aren't interchangable in any way. But it is good to know that the internals of a newer truck 12 bolt can be swapped. This has answered probably as much as I need.

[SpicedIcePirate]

Originally Posted by Shaky

I re-did a 12-bolt truck rear with new everything, including an Eaton cone-clutch posi. Setting the pinion depth is the biggest challenge and usually requires special tools.

So - if you are re-using your gears and bearings, you could gamble that leaving your pinion and bearings alone doesn't affect the pinion depth, and bolt your old ring gear to the new posi carrier. Checking the gear patterns tells the final story. If you don't get a good pattern, you can try shimming the carrier side-to-side to bring it back in.

Having time and patience would be a good thing...

I hear a lot of good things about the Eaton Posi units. I know my dad has swapped other C10 12 bolts to posi with new stuff (along eith other makes and models), so I would have an experienced hand that could help me out. I just am trying to avoid that new price if I can.