I have looked and looked but can't seem to find if I can do a simple swap or do I have to add/ remove things? If so what do I need to do? The rear end is a '86 disc brake iroc posi and I have a '91 rs v8. My plan was to just disconnect the drive shaft, shocks ect. And put in the complete axle of the '86.

 

The thing will bolt right in. It's exactly the same save for the brakes, you might have to fiddle with the lines, but you'll definitely need a different proportioning valve.

 

The '86 brakes are not that good, but the rear end will bolt in. If it's a 9 bolt then it's fine, but if it's a 7.5 10 bolt then you are downgrading. The axles are smaller and the posi is an Auburn, which probably will not last long, if it's not already worn out.

 

Ok now I found an "Australian" 9 bolt posi. It says 82-92 z28/iroc, is an Australian different in anyway?

 

The 9 and 10 bolts are different but both are exact fits. The 9 bolt was manufactured in Australia hence the name. The 9 bolt uses a different kind of "posi", the parts can be harder to find and be more expensive but it's billed as slightly stronger. If the posi is worn the rebuild could be expensive if you can't do most of it your self. 10 bolts are much more common and parts are easier to get. Depends on how much you want to do. There are many threads on both axles.

 

The Borg Warner limited slip differential (posi) in the 9 bolt Austrailian rear end can be reconditiond at least one time, unlike the Auburn in the 10 bolt, which is scrap metal when it wears out. You must do a little machine work on the Borg Warner unit to get it to work again, but it's not too difficult. I just did one a few weeks ago. The 9 bolt is a stronger rear end, especially when compared to the '82 to '89 10 bolt.

If you get the 9 bolt be sure that you get one with at least a 3.27 gear. If you get one with the 2.77 then you will have to replace the differential if you want to use 3.27 to 4.11 gears in it. That gets real expensive.

 

Speedo will be off and you will need to change proportioning valve under master cylinder but besides that its a straight forward swap as long as the donor rear is complete with calipers and emergency brake cables. Like other's have mentioned the borg warner 9 bolt is super strong and definitely better then the average 10 bolt but its also more in demand and harder to get ahold of atleast in my opinion.

 

There should be a tag on the axle that states the ratio but the only sure thing is to take the cover off and see what is stamped on the gears. Also, you can see if anything looks bad and check the wear on the cones. If it's original it almost certainly will need to be rebuilt. The machining can be the hard/expensive part if you can't do it your self or know someone who can do it. Again, lots of threads on how it's all done.