Im Looking at a 9 bolt from an 88 formula from a member on here. Its sat for awhile so I'm planning in putting some fresh gear lube in it but I can't decide if I want to go with high performance gear lube or synthetic gear lube? Any suggestions. Which is better or has better benefits? Its a posi and both show they're for limited slip differentials. Also the 9 bolt has a broken wheel stud on it, whats the best way to replace the studs on the 9 bolt?

 

I used standard stuff with no additives and it seems to work just fine.

 

Make sure you check the windows on the posi unit to see how much life is left in it. I only got my 9-bolt because it was healthy and because it had the PBR discs on it. If yours is an 88 and has disc brakes it will have the pretty crappy 82-88 discs on it...



You should be able to see that just by taking the cover off.

Read here how to rebuild the posi and get an idea of the costs involved. Compare to the cost and durability of a 9 inch. If it doesnt have good gears add in the cost of replacing/installing gears.

https://www.thirdgen.org/forums/tran...hese-posi.html

9-bolts are good rear ends, but the costs involved with rebuilding/replacing/upgrading anything on them make upgrading to a 9inch a lot more appealing. At least with a 10-bolt if you blow one up you can find replacement parts almost everywhere. 9-bolts are a little harder to replace and while the design is much stronger than a 10-bolt, that's not really saying much. It's still not something I'd put more than 350-400hp into with slicks, and even that is probably borrowed time with them.

Another quirk of the design is that as the cones bottom out it causes the backlash on the internal gears to get out of spec and a lot of guys who blow up 9-bolts are actually destroying the spider gears inside it because the cones are worn, at least that's my understanding of it. So it's sort of a double whammy if the cones are worn. If the cones aren't bottoming out in that window, then it's a fine rear axle.

As far as replacing the stud. You'll need to pull the axle out (It's a breeze with a 9-bolt because they have nice bolt in axles, none of that c-clip nonsense 10-bolts have) and press a new stud into it.

There are different schools of thought on the posi additive. Ive decided for me that it's bad for 9-bolts. They're developed for clutch type posis that chatter and make noise, they help the clutches slip more smoothly. With a 9-bolt I think it just leads to more wear of the cones. So I would recommend NO posi additive. Synthetic gear lube is far superior to conventional.

 

There are great write ups on rebuilding the posi part. The killer is if you need new cones. The existing cones can be machined but you also have to machine the raised part inside each carrier half. A friend did all mine for free otherwise it could be expensive to have done. Plus the cost of shims etc. etc. Depends on what you want it for and how much time, effort and money you want to put into it. I'm super happy with mine (added PBR brakes). It took me a long to learn what was needed but it didn't cost me a lot.

 

Its from an 88 formula, its 3.23 or 3.27 posi and disk brakes, it sat for almost 11 years but that's because it originally spun a bearing in the motor so it sat for all that time. I planned on pulling the cover and looking at the cones but he's asking $130 for it. Its, fully loaded from caliper to caliper and comes with a prop valve for disk brakes so I think its a decent choice. I'm going to run 80-90 valvoline synthetic which is for limited slip differentials. But I'm running just a stock 350 vortex with fhr possibility of a bigger cam in the future so I'm not pushing a lot of power or toque. Obviously my open 3.42s are holding up alright.

 

I had a 9-bolt with 3.27 gears that I picked up for $75, good clearance on the cones, blew it up behind my 300hp vortec 350 (took out the pinion bearing)

ended up rebuilding it with all new bearings; axle, carrier, and pinion bearings as well as a new 3.70 gearset to the tune of $550 ($200 for gearset, $350 for bearings, axle bearings were about $75 each alone) doing 100% of the labor myself. Took a total of about 5-6hrs for removal, rebuild, gear setup, and reinstall. At $75/hr that would be another $400 or so to pay for a rebuild.

in short, the 9-bolt is a great rear, but if you blow it up a rebuild is gonna cost you, and if you dont have the knowledge or tools required (floor press, micrometer, dial indicator, ect...) and need to pay for a rebuild it is gonna cost even more.

I also run 85-140 full synthetic with the friction modifier added, some say the friction modifier is unnecessary with full synthetic but I run it anyway.

 

But how long did it last behind the vortec? It would cost me around the same to rebuild a 9 as it would to make my 10 bolt a posi with a locker. I'd rather have the posi already and the disk brakes. How hard is it to swap the proo valves?

 

It only lasted about 4 months, im not sure how many miles were on it when I got it, I assumed it had lower miles as the cones were still good but there are too many variables to know, could have been run low on fluid, beat on, or anything leading to the failure I experienced.

Valve swap is easy, I just swapped the front spring out of a disk/disk prop valve into my old disk/drum valve. Or you can swap the whole valve, in my experience it has the same effect.

 

The 82-88 rear discs arent really worth the trouble. Dont get it for those, especially not for those.

My 9-bolt has a 300hp vortec 350 and a T56 and it's held up for 4~5 years now. Granted, I've never done any clutch dumps on slicks, but there's a reason I dont plan on doing that.... I dont want to have to pay to rebuild the 9-bolt or pay to get a 9 inch.

 

The disk is just an added accessory for me, not that big of a deal since I'm mainly chasing a posi. I'm not running slicks or taking it down a track any time soon, its basicly an in town car

 

Also where in the hell can I get brake pads for these rear ends? I work at zone and i can't get them through work so I'm guessing hawks?

 

I found them at advanced autoparts or autozone, dont remember which, order the pads for something like an 88 camaro with rear disks, non-performance package

Raybestos part # PGD202M is what I used