Hi everyone! I'm fairly new to 3rd gens and especially the differences in rear ends. I have a 88 Iroc 5.7 auto car that is only a street driven cruiser. The car is all original but high mileage. I would like to rebuild my 9 bolt rear and keep the car numbers matching. It is a posi 2.77 gear ratio with disc brakes. The rear has a lot of slop and clunks very loudly when going in gear. I would like to rebuild and upgrade to a 3.23 gear ratio. For parts will I just need to get a new series 3 posi unit, gears and install kit? Is my 9 bolt considered a 7.5 or 7.625 in unit? I know I'll have easily $1500 into it but all the rears like Moser, Quick Performance, Hawks etc that I priced will run at least $3500 plus having to figure what to do for brakes since mine won't transfer over. Any help would be greatly appreciated. Thanks!

 

3.23 isn't an option for 9-bolts, you'll have to go 3.27s. It'll be pricey no matter how you cut it. I would replace your U-joints before diving into the rear though. A clunk when going in gear is tell-tale for bad U-joints.

In terms of your parts listed, yes, that about covers it. You could consider doing 3.45s though since you're already in there, I don't know what your transmission situation is like. I have the 3.27 posi behind an SBC crate motor with a stock T-5 and it's about perfect for a cruiser.

 

Thanks for your response. I may look into the 3.45. If I buy from Summit, is there a brand that is better than most like Yukon, Motive, etc? If I go with all the stuff listed will I still use the factory posi cones? Also, I remember reading something about a crush sleeve eliminator?

 

I haven't bought gears so I couldn't speak to what brand is better that the others. Also no clue on crush sleeve eliminators, might try a search on here.

 

If I go with a new series 3 posi carrier say from Yukon will I still use the factory posi cones or are those specific to the factory 9 bolt posi unit only? Thanks for all your help.

 

I imagine you'd have to go aftermarket, but that's just a guess. You should reach out to the folks over at 9bolt.com They sell all the stuff for these.

 

the 9 bolt rear was made by Borg Warner Australia and is different design from the 10 bolt axle 7.75 ring gear.Seems there is a gear type posi similar to the Torsen posi found in 1998-02 4th gen 10 bolt axles.That type of posi ,along with 3.27 or 3.45 grears would be ideal Look around past threads and you will find imformation about the Torsen type posi carrier for the 9-bolt.

 

Since you have a 9-bolt, your options are somewhat limited.

Your play is probably the pinion bearings. So yeah, it's rebuild time, for sure.

The 9-bolt ring gear size is 7.75". 7.5" and 7.625" are the same thing, for all practical purposes, and are the numbers for the 10-bolt that also came in these cars. Nothing that fits inside the 10-bolt will fit your 9-bolt.

7.75" is NOT a 10-bolt size.

Since you have 2.77 gears now, that means you have a 2 series carrier. You can't put 3 series on it. The highest ratio you can use is 3.08, without replacing the carrier. AFAIK there are no "special" "thick" "adapter" gears available for the 9-bolt.

There are no "numbers" on your rear axle to "match". That's monkey-spank.

The same crush sleeve eliminator fits the 9-bolt that also fits something else. 8½" 10-bolt maybe, I forget. Butt it's available at least.

No, 9-bolt cones will not fit in a Yukon carrier. (if Yukon even makes one for the 9-bolt; not sure) You wouldn't need them in any case, since any posi carrier you buy, from whomever, comes with all its own internals. None of those interchange among mfrs except for the cross pin in some cases and the little bolt that holds that in.

Your 88 rear has the super crappy Delco-Moraine discs that never work. Yours probably don't either: if you don't believe me, put your rear up on jack stands under the axle tubes - under the axle tubes ONLY, NOT under the pumpkin, NOT under the frame, NOT NOT NOT NOT - then start the engine, put it in Drive, and see if you can stop the wheels with the brakes. I'm betting, not. There is NO SENSE WHATSOEVER in spending gigabucks "rebuilding" and "upgrading" a rear, and leaving that CRAP on there. The 89-up system is SO MUCH BETTER it's hard to believe; it will bolt right up to your rear, but you'll have to have THE WHOLE system, from backing plates outwards, which can be rather difficult to come up with. I would STRONGLY urge you to obtain that full system BEFORE tearing into your rear, lest you $$$$pend on gears and carriers and whatnot, and then discover your rear brakes STILL don't do anything at all.

Another issue frequently reported about that rear involves axle seals. For whyever, the 2 sides are different, and there is more than one version of them, I have no idea what the exact details of that are, like year models or whatever, on how to identify which version you have. One side of one version (the right side I think) is almost impossible to find. Make double damn sure you have THE RIGHT seals for YOUR rear BEFORE you tear it down, like maybe have BOTH versions on hand so that whichever you have you're prepared, otherwise you may find your car disabled for a REALLY long time, or that you just have to resign yourself to an axle seal that leaks.

 

I had mine rebuilt a decade ago, and from what I remember I had to order the parts from Australia. Probably even harder to get now. Mine had a whine when under load, which would go away when I took my foot off the gas.

 

Between doing this and upgrading to 89-92 disc, you have a super nice rearend

https://www.thirdgen.org/forums/tran...sen-style.html

 

Thanks so much for the reply and help. I also have a 92 G42 rear that will need rebuilt. Am I better offer getting this one rebuilt over my 88 rear?

 

No idea what "G42" is.

 

Sorry. I meant G92.

 

Yes, I would rebuild the 92' rear end, especially if its a disc brake rear. The 92' would be a 7.625" GM 10-bolt and will be much easier and less expensive to get parts than the Borg Warner 9-Bolt. Plus, as sofa mentioned, the 89-92 rear disc brake setup is far better than the 82'-88'.

The 9-bolt is a very good rear end and I rebuilt mine on my 89', but parts were hard to come by and expensive. I sourced most of the parts from Australia. Not sure I would go down that same path again.