Like the title says, Upgrading from 8.2 to 8.5 rear in a 1971 Skylark. Is it a straight swap? If not what's needed?? driveshaft? etc......
Like Jim said, your 71 would have come with the 8.5. Still lots of parts get changed out in a 40+ year old car. As long as the donor rear came out of a 71-72 Skylark/GS, or Olds Cutlass, it will bolt right in. If you are truly going from an 8.2 to 8.5, the drive shaft needs to be shortened a bit. That's about it. The swap gets even easier if you pull both axles on the donor and existing rear, unbolt the backing plates, and then swap the rears, and re install the axles. That way, you don't have to mess with the brakes at all. Both rears are bolt in axle rears.
The best way I found to tell the difference is look to see if you have U bolts or straps and bolts for the yoke.
