I have a 70 cutlass I am swapping 350/350 with 455/400. I have a 12 bolt cover 10 bolt open now. would like to make it posi.
I did pick up a 12/12 rear end from i think a 69 gto with 4:56 I was thinking about swapping in, but want to know if I would be better off leaving my current one if there is a easyer cheaper way of doing this?

 

Leaving the existing rear in there is always nice,but having the 12-bolt chevy with a posi,you're almost there.Just swap the 4:56's for 3:73's.I can only assume that with the 4:56's,the posi unit is a 4-series,and they do make 3:73's for the 4-series carrier.I have a set.
If the 12-bolt Chevy came out of a Canadian car,by chance,it will have the same yoke as the 12-bolt Olds,and the driveshaft & u-joint could be left alone.Most typical 12-bolt Chevy rears use a 1310 u-joint,which will require you to use an adapter style u-joint,which has 2 different dimensions.If your original driveshaft is a 2-piece shaft,then I would have a new one made anyway.
If you decided to rebuild your existing 12-bolt Olds rear,the cost for the parts(posi unit,gears,bearings/seals) will be about $900.00,once you get them to your door,so that is also something to think about.You would still need to have everything installed.You coukld sell the 12-bolt Chevy,to help fund the project,or just keep going with that,and do a gear swap.

 

Thanks Brian, I think I am leaning towards using the 12 bolt. I'm not shure if its the original gears in there, but how would you tell what series it is? and is there a way to tell if it is a Canadian car?

 

There are casting numbers on the carrier than will tell you what series it is.
If you can send pictures of the yoke,I can identify it.

 

I cant post pics for some reason

 

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Anselmosiphonepics2170.jpgAnselmosiphonepics2011.jpg

 

I guess I just want somebody to check if this is correct. Looks like this is a 3 series carrier set according to the pics above, I found this web site to try to verify but just do not want to make a mistake buying the gears.

http://www.richmondgear.com/cfide/sc...partsearch.cfm

http://www.richmondgear.com/catalogpdf/catpg12.pdf

 

Wow.Where was that sitting?I have never seen gears with pits all over the edges like that.You do have the Canadian yoke on it,which takes the same u-joint as the O-axle,but it is too pitted to use.That whole rear will need gone through,due to the rust inside,but it can be saved.Take it completely apart,races & all,and have it hot-tanked,to remove the debris.Then have it blasted to remove any leftover rust.Now,you are ready to build it.Go through the posi unit,get the rust off it,and shim the clutches tighter,for a better-working unit.get a complete bearing/seal & install kit,and get the gear ratio of your choice.If you can find another Canadian yoke,great,if not,I would buy an aftermarket yoke for the 1350 u-joint,and do that upgrade.Check the bearing surfaces on the axle shafts,and see if they are good enough to reuse,or if you need new shafts.

 

Where would I be able to find someone to hot tank it? I cant seem to find any place here.

 

The machine shop closest to my work has a tank to fit them in.They charge me about $15.00 to tank them.Totally worth it to me.