I just picked up an 87 Iroc that has disc rear with posi. Not sure on the gear ratio as I couldn't find the identifier on the axle tube where I have read it is located. I am going to look further this weekend to see if I can determine it. I did find the "slip resistant" tag bolt to the rear end and jacked it up and spun one wheel and the other spun with it equally so it appears to be working.

So one of my questions is if somebody knows how to determine the gear ratio other than jacking it up and spinning the wheels or taking the cover off. No bid deal since I will figure it out this weekend.
Edit- I discovered it is the G92 3.45 rear end.

My bigger more important question comes with brake replacements. I don't want to swap in a 4th gen rear, and I want to keep this rear end. That being said, everything I have read about these delco moraine calipers makes it sound like they are not reliable at all. I am going to be replacing everything except the booster since this car has been sitting for years and everything is rusty or clogged up. So, do the newer PBR calipers fit on these rear ends without modification? Simply put, can I purchase the newer calipers for 89 and newer disc rear ends and just hook them up to this rear end? If not, what modification is necessary? I figured since I am already going to replacing everything, I might as well do this the first time rather than buy new delco moraine style and then swap later. From what I have read on here I think in 89 the part number changed for the master and prop valve, so I don't know if that means fittings changed as well as everything else. Essentially, I want to go with the newer 3rd gen rear disc stuff with as little to no modification as possible.

 

While the Delco-Moraines have a bad rep on TGO, but my experience with them was good. Working calipers and rotors, new pads and lines, along with fluid and you might be well satisfied. That said, here's a link to the PBR replacement:

https://www.thirdgen.org/forums/faq-...iscs-89-a.html

BTW, if the rear end was original to the 87, it's probably a 9-bolt.

JamesC

 

I was hoping to literally just be able to put the bigger rotors on and then the newer calipers and be good. So I will probably stick to ones that are designed for this rear end for now. I might just get slightly better than the cheap ones at part stores. I always used the cheapest calipers on any vehicle I owned from O'Reillys and never had any issues until the 88 Camaro I bought. I went through 7 of them before I figured out the problem I had was the hardline. But 3 of the calipers seized on me while trying to bleed it. Never had the issue before. I ended up getting them from Napa and they were way better finish and they were painted.

And it is the G92 9 bolt rear end that originally came in the car.

 

The PBR system will bolt right onto your existing housing. All you need, is the correct backing plates for your rear (9- vs 10-bolt), "abutment" brackets, calipers, and rotors. Remove calipers & rotors, pop the axles out, remove 4 bolts; installation is reverse of removal.

Finding all the parts is a different matter. Not sure if any of the 4th gen versions bolt directly up to our rears, but I would guess the LT1 version would be more likely to than the LS1 one.

 

 

So is the rear you have to pop the axle out because you have to remove the bolts for the backing plate? Sounds simple enough based on your breakdown. I plan on replacing the rotors, calipers, pads and lines anyways and figured this would be a good time to upgrade. It is a 9 bolt G92 from 87 so as long as the 89 9 bolt backing plates work I should be able to make the swap correct?

I believe the LT1 would be because the rear end is supposed to be almost a straight swap. The LS1 was different from what I have read on here.

 

Yup, 89 9-bolt PBRs would be a direct swap onto that rear. Only 9-bolt ones will do; 10-bolt won't fit.

Popping the axles out of a 9-bolt isn't quite as trivial as a 10-bolt but still easy enough to do. The reason of course is that the hole in the center of the backing plate won't fit over the axle flange.

Both the LS1 and LT1 rears are about equivalent swaps, as a whole. LS1 ones however use a "drum in hat" parking brake whereas the LT1 used the same type of system as 89-92.