I am going to have the rear end of the car taken into the shop, but would like any opinions first on what it might be. With the rear of the car jacked up, spinning one wheel will make the other turn opposite but only for a couple revolutions, then it stops turning on the other side. Gear problem?

As long as the pinion is not turning the other axle will turn. If the pinion starts turning then the other axle might stop or slow down. Watch the pinion when the other axle stops turning.

It hasn't been taken apart yet. So nothing to actually look at. What does it mean if it is or isn't turning with the pinion.

Examples of the clunk:

Yesterday when loading up the car on a flatbed, I pulled out of the driveway in reverse, did a turn to line up with the truck, and when I stopped in reverse, I heard a very loud bang from the rear.

Last week, while turning on to my street, I would always hear a loud pop/clunk noise as if I had run over something that shot out from under my tire.

The pinion, or drive shaft. The drive shaft is connected to the yoke, which is connected to the pinion gear. Did you have it in park when you were turning the wheel?

If it's poping when you turn then it might be the differential. You may have the Auburn unit and it might need the oil changed. Is the rear end leakig anywhere?

When I was turning the wheel it was in drive. I was either pulling out of the driveway, or turning a corner.

It could be as simple as oil? It sounds horrible when it bangs. I haven't noticed any leaks in the rear.

Many times a popping rear end can be fixed by changing the oil and using the limited slip oil additive. You might need 2 bottles of the additive if you have the Auburn differential.

No such luck this time. My mech took off the diff cover and saw some metal on the magnets, and a broken spring/coil thing. It is an eaton posi. I was told this shouldn't happen. So now, I am faced with a (about) $600 bill to fix it. Should I start looking for bigger and badder, or is it worth fixing? It is the stock 10 bolt housing. (forgive me if I get any names of parts wrong, I'm going off memory here)

Thanks for the input BGH!

It's probably an Auburn. They have 5 springs in them. I wouldn't put another Auburn in it. I'd put an Eaton Posi in it. This is a much better unit than the Auburn. It might cost a little bit more, but it's well worth it.

There isn't much available that's stronger at a low cost. The Moser 12 bolt is probably the best deal for the money, but they start at $2200 with the Eaton Posi. The 9 bolt is a little stronger than the 10 bot, but not a lot.

It is an Eaton. I'm thinking it might have been a used unit though. When I had the rear rebuilt a few years ago, they didnt have the stock carrier, and threw in the eaton posi. It was only $800 with a new axle and the labor to drop it out. Now it's 900 just for the center rebuild.

I'd like to see some pictures of the damage. The Eaton can be rebuilt and parts are not that expensive. What exactly is broke?

I don't have any pics of it, but it's a spring or something in the carrier.

The Eaton Posi has 4 springs and 2 preload plates between the axle gears. These springs almost never cause any problems. I'd like to know what happened to make this spring get out of place. Something else must have happened to the rear end to cause this.

It seems that it wasn't properly adjusted when it was built the first time. A worm gear? or something was broken.

Eaton and Auburn don't have worm gears. It must be a Torsen, but I don't think they have spirngs.

My mechanic asures me it's an eaton. I just can't be sure of what it actually was. I know it wasn't aligned correctly though. (shims)

You might have an Eaton Gov-Loc type posi in there. Those are way common and highly prone to breakage. If it is a Gov-Loc, I wouldn't spend a dime on repairing it, they're weak as hell. As Big Gear Head said already, the Eaton clutch style posi unit is quite strong and very reliable. If you don't want to spend the money for one of those, you could pick up a used Torsen posi carrier out of a 98-02, 4th gen f-body. You can get them pretty cheap on ebay, usually $150 or less, and they use gears for the posi action, so there's no clutches to wear out. Here's a pic of a Gov-Loc unit. Btw, if you decide to pick up a Torsen, make sure to get the right series for your gear ratio. They come in 2 and 3 series. 2 series is 2.73-3.08, 3 series is 3.23-3.73.