When I bought my car, I paid very little attention to the rear end other than to note that it was indeed a 12 bolt. I later learned that what I have is a mini-spooled 4.11, with Hotchkis boxed lower control arms, Hotchkis frame stiffeners, inner spring air bags, and an aluminum rear cover marked T/A. (What does that mean?) Obviously this rearend was designed to make the car go in a straight line under considerable power. However, while I have no intent to drive the car hard enough to merit all that beef, I don't want to replace it either. (It's not a numbers matching car anyway.) At a point, I will change to a posi with a more streetable ratio. I am curious though, about the upper control arms. They are the stock GM parts. Since the previous owner changed everything else under there, should not the upper arms also have been upgraded? Do the stock upper arms render the rest of the upgrades less effective? As I said, I 'll probably keep everything pretty much as is except for the gears, just trying to get a better understanding for this whole rearend geometry thing. Anyone with insight to share is greatly appreciated.
Patrick

I'd think the condition of the bushings both in the upper arms and the rearend may be of more concern than the upper arms themselves. I've got Edelbrock adjustable uppers, but I don't plan on adjusting them unless necessary--thus keeping stock length/geometery. I replaced all bushings too. The factory stuff may be sturdy enough for moderate power levels (whatever that means ;) ). If you'll drive that car on the street I'd lose the spool real fast for an Eaton posi or you'll be in trouble on those turns.