curt86iroc

Most of the data I've gathered for the 1990 3rd gen model year states that IROCs with the L98 G92 package received a 10 bolt rear with 3.23 gears. However, my car came from the factory with a BW 9 bolt 3.27 gears (I know its a factory rear because I have the original sales order for my car and all service records).

Am I correct in assuming that my car is most likely an early build and received a left over rear end from the '89 model year?

Does anyone else own a 1990 L98 G92 with a factory 9 bolt?

Any info for be appreciated. Thanks!

92purplehaze

iTrader: (8)

i believe the early 90s which are actually 89s built to oct. recieved them. mine is a september build with a 9 bolt.. hope this helps

tpi-hearse

iTrader: (27)

ALL 1990 Irocs were built in 1989 due to the license for the name I.r.o.c. expiring on 12\31\89..

92purplehaze

iTrader: (8)

i confirmed i have a 10 bolt (rpo shows 3.23s) was the info i recieved about some cars getting a 9 bolt in the 89/90 year false?

f1ls1

iTrader: (2)

The first Iroc's with the 5.7 Got the 9 bolt axle until GM ran out of them After that it was the 10 bolt. Mine was built in September 89 and it has the 9 bolt.

pinky93

iTrader: (2)

Isn't the 9-bolt supposed to be stronger? Austrailan built, right?

f1ls1

iTrader: (2)

Yes, that's why they put them behind the 5.7.

pinky93

iTrader: (2)

Well, GM uses the term "Stronger rear end" a little loosely. I love the General's cars, but as soon as you get a sticky tire, those rearends seem to break. I had good luck with my 02' SS with the 10-bolt and drag radials, by using one of those TA differential covers that actually preload the bearings to prevent distortion. I actually fried the clutch before I ever hurt the rearend.

With the ProCharger coming, I will likely do a 12 bolt (at least) or maybe even a 9 inch Ford..... I was looking earlier today and Moser has some nice 12 bolts that are a direct fit. Hmmmmm....I need to do some more research.

85 T/A WS6

There is documentation of a 9 that has survived the abuse of a 500hp/500+ lb/ft Big Block for a few years now.

4 pinion design adds beef

Uses a shorter distance between bearing caps than the 10 bolt giving it added strength.

All 9 bolt rears for f-bodies use 28 spline axles.

Pressed on tapered axle bearings; allows the axles to be bolted in instead of using C-clips

TTA 1387

It's plenty strong. Mine was completely stock and ran 1.6x short times all day long. 121mph in the 1/4. Try doing that with a 10 bolt.

And you were lucky with the 10 bolt. My 10 bolt lasted for 50K miles before giving it up. 1.7x short times with a M6 will do that.

pinky93

iTrader: (2)

85TAWS6 and TTA1387, I definitely appreciate the feedback! I will give the 9 bolt a shot then. I will order one of the TA differential covers, in hopes that will lengthen the life of this rearend.
Again, thanks for the input. I guess I had given up on that 9 bolt before it gave in on me!

Drew

iTrader: (58)

There is no shortage of blown up 9-bolts out there either. The gears themselves like to break.

pinky93

iTrader: (2)

You are right, but I am going to give it a shot. Like we noted above, I got lucky with the 10 bolt in my 4th gen. We will see how that luck holds out on this 3rd gen. I really am not worried until I actually start hooking up. I suppose that is when I will be looking for a built 700R4 too.....

customblackbird

iTrader: (15)

yea i just found out that my 87 formula 350 came wit a 9 bolt.i have the build sheet from the factory for my car i found it under the driver seat when i replaced the carpet and it says 3.23 gears...but i thought they came with 3.27... does it still have the 28 spline axels etc, i want to beef this thing up for a 500hp 383. so im gona use moser axles, support girdle and a raytech instillation kit, and a posi but idk what one to use? i dont want to go to a 12 bolt etc bc they eat up way to much power.

i was pretty upset when counted the bolts bc i kno how hard it is to find parts for these.
but if they are stronger then i will give it a try.

pinky93

iTrader: (2)

Well, the most certain thing is that it will hold up until it breaks!!

TTA 1387

9 bolt did come with 3.27 gears and not 3.23.

The 12 bolt won't loose that much power. The 10 bolt takes less power and I replaced that with a 12 bolt in my 96 WS6. The ET and MPH were exactly the same as pre swap. The 9 bolt will take the abuse but eventually will fail. If you're going to sink all that money into the rear, why not get one that is proven stronger?

I really liked my 9 bolt. Heck, the GTO is just an updated version but in IRS. It was still a Borg Warner until DANA bought them out. Although they still have problems, they have shown they can still take a lot of power. But if the 12 bolt wasn't a $4K option, I'd go for that.

Your call, but you won't loose much in terms of power. But gain piece of mind in the long run. IMHO, of course

beltran89

How much power will a 1990 iroc 3.23 10 bolt handle decrntly before things dtart to break? can it handle 350 ?