Sirs

I've perused the forums for answers to my questions but can't quite get this figured out. I have a 70 Cutlass S with a 2.56 open rear end. Of course like everyone else I want a "posi" rear with better gearing for around town driving. I've been back and forth with spending money to convert my differential with internal changes, although expensive.

I've now been offered what has been described as a posi differential out of a 1969 GTO with 3.23 gears. A co-worker has it and states that it's ready to go, he has installed new brake parts and such. I initially wanted 3.42 but I think the 3.23 would be fine, plus a bit better on the highways. He's offered it to me for 600 bucks.

My questions: will this install exactly in place of my current rear? I plan on adding boxed lower control arms with a sway bar, I'm under the assumption that the "A" bodies share many suspension similarities through these years. I desire as direct of a fit as possible.

Should my driveshaft still be the correct length with the Pontiac diff? If I need to start sourcing new parts then the deal gets more expensive.

Finally, are the 69 GTO rears hard to get parts for? If I would like to go with 3.42s someday, are the parts readily available?

Thanks for any ideas or opinions. I'm open to all.

 

It's a good price, but not sure about the driveshaft. Everything else is a bolt in though.

 

Back when these cars were relatively new, I swapped parts from one brand to another to make whole cars. I used to repair both fire and recovered theft cars, and it was not unusual for me to put an Olds engine into a Chevelle that originally had a 396 that was stolen, or for that matter any other combination. I don't specifically remember the drive shafts being a problem, but I know that we rarely had to have a drive shaft modified. Usually they were bent, and that was the repair that was needed. Even if you have to have a new yoke added to the rear of your existing drive shaft, it isn't a big deal to have done.
I know of a 1964 Olds Vista Cruiser that was converted into an ambulance, and it was shipped to the conversion company with a Buick rear in it. I don't know the reason behind the swap at the assembly plant. How it was learned that it was a Buick rear, was when they needed to replace the rear axle seal, and the Oldsmobile seal was different. It took some investigation, and that is how they determined that it was from a Buick. Oldsmobile, Buick, and Pontiac cars were assembled in the same line in the Linden NJ plant.

 

The driveshaft would need shortened 1/2"-3/4"
The 69 rear is a direct bolt-in,as far as all of the mounting points go. If that rear is going into a mild street cruiser it should be fine.The posi unit in those rears is the cone style,and don't fair well with today's modern power,plus it is 43yrs old. As far as the gearing goes,I would leave the 3:23's in there.If you drive it with the 3:23's,then switch to 3:42's,you really won't notice any difference between the two.

 

Ok thanks guys for the opinions. I'm buying the rearend, I figure if it doesn't work out I can always get my money back out of it fairly easily.

One last question though, will the standard Olds u-joint work to mate my Olds drive shaft to the Pontiac rear? Or do I need to use a "special" u-joint for this application?