Danspeed1

Although this topic appears to be heavily covered on this site, I cannot seem to find the information I am looking for. Apparently many of you swap your old stock third gen rears for forth gen ones. Only issue is that I would like to retain use of my stock IROC rims on my 87 and I do not like how far the stock rims stick out on the car. My question is, what rears are interchangeable besides the fourth gen rears. I am looking for three things specifically. Either 3.42 or 3.73 gears, Posi, and disc brakes. The is never going to make more than 350hp tops... so I am not concerned about bulletproofing. I just want something that will swap in that's the same size and offers what I am looking for. The original offset is important. I was under the misconception that all 10 bolts were the same size. Apparently from the threads on this site, 10 bolt is more of a style rather than a specific rear. Then there is the "9 bolt" i have never heard of but comes in our cars. What I am getting at is could I swap a GM 8.5 out of a caprice and install it on my camaro. Sounds like a dumb question I know, but I am making a reference because I need to be pointed in the right direction. If anyone can clarify this It would be greatly appreciated.

Thanks,

Dan

Drew

iTrader: (58)

-deleted

JamesC

iTrader: (5)

More info about thirdgen 10-bolts below:

https://www.thirdgen.org/forums/tran...-10-bolts.html

For added info, the following link discusses thirdgen 9-bolts in detail:

https://www.thirdgen.org/forums/faq-...now-about.html

JamesC

big gear head

You could get a 4th gen rear end and swap the parts into a 3rd gen housing. You would need to start with a '90 to '92 rear end so that you would have the 28 spline axles. You can modify the housing ends so that the disc brakes will fit. This would take some work, but would be much easier than making some other rear end fit.

Danspeed1

I was thinking of swapping out the gears and posi on my stock unit originally and leaving the brakes alone, but then I realized that it would run me nearly $500 in just parts, and although I am mechanically inclined I have never done gears before. Then I realized for half that price I could just pick up a whole rear.

So basically I need to look for a rear with gears already swapped out of a later third gen or fire bird correct?

DG

big gear head

You can probably find a good 3rd gen rear end with 3.42 gear and a Auburn differential. I don't care for the Auburn, but you might find one that still works. The Torsen from the '98 and later cars is better. Your '87 will have the small 26 spline axles, so I recommend finding a '90 or later rear end to get the larger 28 spline axles.

camaromike222

If you didn't already know, Danspeed1, the 4th gen rears are ~2" longer on either side, so if you're concerned about your wheels sticking out, just know that they will stick out further. I did a drum to LS1 swap last year and it was quite easy. Now you're just left with the gear and posi issue.

supr_fly03

iTrader: (2)

You can find another 3rd gen rear with what you want, scour the wrecking yards and piece together what you want like I did, or buy it all new.

You can find 3.42 gears in a lot of the V-6 cars. I found a auburn posi and 3.23 gears in a 96 V-6 firebird (I wanted 3.23 gears). All 95 - 02 F-bodies will have 28 spl carriers in them so find one of those in an auburn or as big gear head said find the torsen which is much better.

You can also find low gears in the S-10's and blazers with the 7.5/7.6 rear. You can find everything from a 3.42 to 4.10's in those.

Get a pair of axles from a 90-92 camaro (28 spl) that are good. Check the axle bearing spot for pitting.

You can also take the rear disk brakes from a 98 - 02 F-body for 12.1" rotors (all engines go them) or 94 - 97 F-body for 11.6" rotors (only Z28/SS got them), or any 2wd S-10/blazer rear for 11.6" brakes, correct bolt pattern on the rotors, and a drum parking brake. The blazer brake do have the old style 45* flare on them as to where the F-body stuff will have the ISO bubble flare (easier to adapt the brake lines). Modification to a drum brake axle is easy. You just need a hacksaw and a good drill bit.

If you want to know how to do gears, check out my 10 bolt axle build thread and it will walk you through the process and tell you what tools you will need.

Danspeed1

That's the issue. I know it will add an extra 2 inches to each side. I may put set of wheels on it in the future but I still want my IROC's to fit properly. Not to mention, I think the suspension geometry would change with the stock wheels correct? Any handing issues with the iroc's on?

DG

Danspeed1

I saw your axle build tread before posting. Looks quite intense to be honest. As I mentioned in my post my goal is to keep my IROC rims on the car thus any additional axle length is not going to work for me.

I will look into 90-92 rears,

Thanks for the help guys,

This site is very informative,

DG

supr_fly03

iTrader: (2)

As far as suspension geometry, you are not going to notice any real difference in going to a wider rear axle. Changing stuff in the front is different of course.

As far as I know, the bolt pattern is different on 94 and up F-bodies so I dont think your IROC rims will bolt up.

Stephen

iTrader: (12)

The bolt pattern is NOT different. Only the backspacing/offset is different due to the wider axle.
93-97 LT1 rear ends are 2" wider. 98-02 rear ends are 1.75" wider & have bigger & better disc brakes, so go for a 98-02 LS1 rear end.

Yes the rear ends are wider, but using stock 16" 3rd gen rear wheels, the tires still fit under the fenders, as shown by this blue RS with stock wheels & a 4th gen rear axle (i do not know if he has a LT1 or LS1 rear end).

siduramaxde

This is exactly what I did for my 86 Berlinetta. Only I just bought 28 spline Moser axles for my 86 rear end. Not too hard to do if you have the proper tools.

Danspeed1

Seeing as how there are 10,000 threads on here with people doing this swap, and I haven't read about any adverse effects, I wouldn't image handling dramatically changes after this swap. I don't mean to insult anyone who has done it but in my opinion the rear wheels look ridiculous that extra distance out; as something I would have to live with I have to think long and hard about doing this.... option B of course, finding a 9bolt that someone put 3.42's or 3.73's into... which will probably take quite sometime. Thanks for the input guys...

DG

JamesC

iTrader: (5)

Just an FYI: 3.42 and 3.73 are 10-bolt gears.

JamesC

Stephen

iTrader: (12)

I don't think what "looks ridiculous" is them setting out further. Just the FWD-style look of 4th gen wheels not having any kind of dish to them, is what does.

The outer edge of my rear wheels set about the same distance out, due to their offset/backspacing. But due to still being on a 3rd gen rear end, they get some dish to them. I actually wanted to widen the rears to the outside to create an even deeper dish, but widening wheels to the outside is MUCH more labor intensive due to having to having to perfectly finish the welded seam since it is seen.