1fastrock

im looking into swapping a 4th gen rear end into my 89 iroc. it has a 383 stroker putting out around 500 horse. is the forth gen rear end any stronger than the stock third gen rear end and will it be able to handle this kind of horse power without breaking?

Stephen

iTrader: (12)

Yes it is stronger. As for WILL it break? Sure. Everything braeks. Just a matter of how much it takes to break things.

Chances are though, your tires will slip before the axle breaks, at 500hp. Launches are what breaks things, not overall power.

DJP87Z28

The 4th gen rear are the same 10-bolt design and are the same as the 3rd gen 10-bolts. No changes except some may have a different limited slip.. Also note: they are 4" wider overall in width then 3rd gen rears.

Stephen

iTrader: (12)

While they are both 10 bolt covers, that's where the similarity ends.

4th gens have bigger ring gears, better limited slip units...besides the width.

DJP87Z28

jk

Better check your facts. The RING GEAR is the SAME 7.625 Dia as the 3rd gen. Also, I did mention that some have a different LS.

Stephen

iTrader: (12)

If the rears are the same, why do 3rd gen owners put 4th gen rears in? Because the 4th gens are stronger. If it was just the LS difference, we'd just swap the in.

Why don't the 4th gen owners put 3rd gen axles in, to fit wider wheels & tires? Because ours are weaker.

92RS702

Every thread that I have read says, that the 4th rears are just as weak as the 3rd rears,I have a 4th rear on my car but the reason is,better brakes and also I got fairly cheap.

DJP87Z28

For your input the 3rd gen rears will not fit under the wider 4th gen bodies. Do sone reseach

WIll36

iTrader: (12)

So if I had a 4th gen and wanted to put wider wheels and tires on it I should put a narrower rear end under it so that the stock wheels couldn't even be bolted up to the car?

Also these axles are not much stronger then stock 3rd gen rears

Air_Adam

4thegn rear ends are the same internally - only the axle and housing length is different, as well as the brake mounting brackets in some cases. The center section and its internals are the same. Some used a different posi, but thats it. They aren't any stronger than a 1990+ 28 spline 3rdgen rear end.

The only real benefit of installing an LT1/LS1 rear end is that it probably has less miles on it, and a better rear brake setup. Thats it.

AFTERMIDNIGHT

I thought the the major difference is the third gen used 26 spline axles and the 4th gen used 28 spline axles. The 4th gen is a few inches wider but it will fit. I have a 02 SS rear in my 89. Just run a different offset wheel in the rear to accomidate the wider rear-end.

1fastrock

i appreciate all the responces but would you guys go for the forth gen rear end swap or not? and if not what is an affordable rear end that i can put in that will handle the power?

Stephen

iTrader: (12)

Now with the name calling.... What's your age? 12?

They are a direct bolt-in, I never said mini-tubbing wouldn't be needed, but that's what people do to fit wider tires.

Orr89RocZ

iTrader: (20)

they have run shorter rears in a 4th gen before and i am willing to bet a thirdgen rear would work under a 4th gen car but would need some custom sized wheels to run it.. deep dish

later 4th gen rears are cheap, lower mileage and have better brakes than our 3rd gens, except the later PBR 10 bolts and 9 bolts. They ahve the same brakes as the 93-97 fbody rears

the 98 up has the good 12inch brakes, ls1 brakes they are called

internals are about the same strength as the later model 3rd gen 10 bolts. There was a time where GM used 7.5" ring gears and went to the 7.625 so in that sense that extra 1/8 inch may make it stronger but its still a weak rear end. you can beef them up but they still weak. Also the axle splines were updated from 26 i believe to a 28 in the later years starting around 90 i believe but i could be wrong. all 4th gens tho have the higher splined axles. So if you have a drum or wimpy disk old 10 bolt, you can easily swap in a 4th gen low mileage throw out for 300 bucks or cheaper. much cheaper than upgrading your current posi, brakes and axles

later 98 up cars also got a torsen differential thats nice. different than auburn clutch type units that wear out.


but sticky tires and hard launches will hurt these rears... its only a matter of time. My buddy ran a stout 406 on his auto car 10 bolt rear just fine for 3 years. then went to a stick shift and still ran fine. only eventually broke but thats a stout piece to last that many years behind a 10 second motor

i plan to run my 500 hp 383 on my 4th gen 10 bolt till it breaks or i have enough money for a 12 bolt, which ever comes first

Darkshot

iTrader: (4)

Sorry but misinformation. Any 4th gen rear is just as strong as a later 3rd gen rear, which is only barely stronger than a 89 and earlier rear end.

I did a LS1 rear end swap. I bought it for $260 and it had 80,000 miles on it. For that price I went from 2.73 open diff w/ drum brakes to a 3.42 Zexel Torsen posi w/ 12" disk brakes. Enough said. Swapping internals requires setting up the gears again, which requires skill and special tools or paying somebody $$$ to do it for you (more than what you would pay for a complete low mile 4th gen rear) and in the end you still don't have the upgraded brakes.

To the original poster: With that power I wouldn't waste my time putting in another 10 bolt that isn't going to be any stronger. You could spend a grand beefing it up but even then you still have a weak base and you're almost half way to a bullet proof rear end which you may end up needing anyway when you break your "beefed up" 10 bolt. Sure some people have taken 10 bolts low 11s, but a lot haven't. Risk you want to take spending money on a 10 bolt?

PhantomFE3

if the 4th gens have a higher spline count, thats means there are more contact points on the axle which means the amount of pressure per contact point is reduced so you have less of a chance of stripping the teeth on the axle, but thats really not a huge worry with these rears because there is plenty of other things that will break way before any of that happens

Darkshot

iTrader: (4)

Later 3rd gen rears (90+) also had that higher spline count. It's not just a 4th gen thing.

Aaron91RS

iTrader: (2)

Good grief 4th gen rears have been covered a million times.
The 1st post should have been do a search lazy.
Instead we have 16 replies going in circles.

BTW Spline count is pretty irrevelant since that's not where a 10-bolt will first break.

Screw a 10-bolt. Mine broke years ago.
Get a 9-bolt for cheap and be done with it.

Orr89RocZ

iTrader: (20)

9 bolts arent cheap no new parts available that i know of so its hard to find a low mileage good condition 9 bolt with good gears

Aaron91RS

iTrader: (2)

I pull them out of the junkyard for $150 all day and bolt them up as-is.
Worst case is I have to replace a seized caliper or something.
Thinking you have to automatically rebuild it is a myth.
The current one in my car has been in it 6+ years AFTER coming out of a junkyarded mid 80's fbody and still never been touched internally other then new diff fluid.
That's 20+ years of use with no problems.
Did my friends 9-bolt the same way no problems.
Got a spare 9-bolt in my shed and know where I can go pull another 9-bolt out of the junkyard tomorrow if I want.

Orr89RocZ

iTrader: (20)

must be nice..i got a 3.27 ring and pinion and 3 series carrier used and threw it in my car, 1 year 6 months later it blew up

Hard to find a carrier around here or anywhere for that matter. Considering how few cars got the 9 bolt. Ppl on here charge an arm and a leg for good carriers... i said screw that for the same price i can get a like new 4th gen rear takeout. 30K miles, 3.42 gears, 12 inch disk brakes for 300

69442DREAMCAR

What cars will have the 9 bolt? How will I be able to distinguish the 9 bolt from the regular rear ends in the junkyard. Do you have to remove the backing plate or is there another way? One last thing, I have a 89 RS with the 2:78 single track. I found a 4th. gen with 3:23 posi. If I go with the 4th. gen. can I use my wheels? If not what backspacing do I need?

Stephen

iTrader: (12)

Only the 3rd gens got 9-bolts. GTAs were standard with them (and TTAs). Some other Firebirds & I've heard of some Camaros getting them, but I dunno the "guideline" for what did & didn't.

Identifying a 9-bolt is as simple as the name implies.....Look at the rearend cover...10 bolts = a 10-bolt rear, 9 bolts=a 9-bolt rear. Simple as that. But not all 9-bolts are created equal. If you get one, get a 89+. Before 89, they had smaller & "weaker" brakes.

And yes.....Despite some beliefs, you CAN use your stock rear wheels. They'll line up almost perfectly with the fender lip. Gives your car a nice, wide stance too.

jersyboyy

iTrader: (8)

I just had to mention how im selling a COMPLETE 9 bolt WITH brakes sway bar lca's and all 3.27 posi 9 bolt for 200 dollars with almot new rotors and pads...but NO ONE has even shown interest in it other than 1 guy. Funny when people are sayin everyones charging an arm and a leg.
Its obvious people just DONT use the search feature on this site for info or parts they just complain about crap and ask why over and over.

confucius101

i have a 91 stock fire bird with factory wheels I think the are 15"
will my wheels fit a 98/99ss rear ?

Stephen

iTrader: (12)

Nope. The 15" wheels won't clear the 98+ brakes. Good excuse to get 16" wheels, but even then, you might need to clearance the calipers, depending in the whee. Or just get 17"+!

confucius101

Frigging Ricking Racking........

Thanks i've been trying to locate a posi disk rear all week and only came across one and it wont fit LOL

no room in the budget for new wheels just yet