So tomorrow might I'm going to check out a new rear end for my car. Been looking to get a posi and I finally found one. It's out of an 87 GTA has posi, disc brakes and is supposed to be the Australian one with a 3:42 gear . First off good or bad rear end and second if I do to check this rear end out how do I check to make sure it's not junk. Thanks for any help

Won't have 3.42 if it's the "Aussie" (9-bolt) rear; that rear doesn't come in that ratio. Might be 3.45 though. Count the teeth while inspecting it.

Unfortunately if it actually came in the 87 car, it'll have the terrible cast-iron Saginaw disc brakes. Arguably worse than drums; I'd bet that 95% or more of them remaining on the road today are nothing but unsprung dead weight. But it is what it is; if you get the rear, learn all you can about them, so you'll know what to do to make them at least do something besides consume gasoline by weighing down the car.

The 9-bolt uses cones as its posi clutch elements. They, and the carrier inside surface they rub against, wear down; and as they do, the cones sink farther and farther into the carrier toward the outside. There's a slot in the bottom of their place that you can look in and see how much clearance they have left: if the clutch looks bottomed out, it's no good. Oftentimes they can be machined to renew them but not always. Not sure if you can actually get new ones; I've heard some people say that the ones for GTO will almost fit, can be used as raw material to make what is needed, but I've never done it so don't take my word for it.

Beyond that, look at the gears for signs of scoring or other wear; make sure all the bearings run smooth; check the fluid carefully for metal chips, metal dust, or other signs of worn parts. Look for leaking seals at the axles and the pinion.

So the stock calipers arent good is what you are saying?

The old iron calipers are not very good. The later aluminum PBR calipers are good. I think the switch was in '89.

Did any 9 bolts come with a 3:42 gear?

3.42 is a 10 bolt gear. The 9 bolt gear was a 3.45.

if its still in the car, isnt there some way of jacking up one side, and using a torque wrench to see how much torque it takes to break the posi loose? thought i heard something like that before somewhere?

Remove the cover, take a dial indicator with you and measure the tolerance in the gears, I'm not sure what it is. You can also take indicator paint, not sure what the real name for it is. Paint several teeth, rotate the tires back and forth several times on it to see where the meshing points of the gears are, center is usually the best, but the gears may have a natural outside or inside indicator pattern. Consult a local shop that builds differentials and ask them what are some key points to look for.

Bought the rear end last night. It had been sitting in a storage unit for about a year.

Not completely worn out, but very close.

Yup... in fact the driver's side may be gone, hard to tell for sure on that one but it looks like you can see a burr of metal thrown up where it's been bottoming out and spinning. Pass side, not all the way dead but definitely not much left.

I read something about being able to machine the cones down. Not really sure what it accomplishes. Can any explain it and tell me if I have that option

Best explanation you will find:

I've rebuilt a few of the Borg Warner units. It's not a big deal if you have a lathe and shims.

Machining the cones consists of knocking a few .001"s of metal off the bottom of the cones, so that the bottom of the cone no longer hits the bottom of the space in the carrier. That allows the cone part of it to contact the carrier like it's supposed to. Then stack shims on top of the cone so it's the right height again.

Problem sometimes is, the inside of the carrier where the cone contacts it, can be damaged too. In which case the carrier is no good, and fixing the cones won't make it all work right again. No way to know that as far as I'm aware, without tearing it down and examining. Fortunately they're usually OK it seems, from people who've done a bunch of them, odds are usually good.

There are some good informations on www.9bolt.com Technical Page.

The also sell all the parts needed for 9 bolts rear axles, but they are located in Australia. Ordered a remanufactured carrier and a used pinion/ring set from them, and everything came fast and in very good shape.

Concerning the posi cones, as far as I know, you can still find them pretty easily in the US on the Internet by searching a little bit.

I have heard that if you buy new cones the carrier's will need to be machined due to a difference between stock cones and the remanufacturered cones. If this is true it seems alot more cost effective to just machine the cones I already have. Is there a reason that buying new cones is better?