Guys I need some help. I have an 88 formula but I have disk brakes in the rear? And sometimes she slides nice like its posi/lsd, and sometimes it'll sound like its only spinning one tire and won't drift? I haven't jacked it up (will on sat). Any idea's?

Any ideas about what?

My bad... That was a little less clear than I meant it too be. I want help on what kind of rear end? I didn't think my car came with disk brakes? And why will it slide well sometimes and not others?

No reason for a '88 to not have discs. My 87 GTA came with discs stock on the 9-bolt. Is it a 9-bolt or 10-bolt?

Your Limited-Slip could be slipping more than it should when it was new, due to wear inside.

How can I tell 9 bolt vs 10 bolt? And you think the G80 LSD is just going?

Look at the rear end cover.

9 bolt heads = a 9-bolt. 10 bolt heads = a 10-bolt.

Do you have the SPID sticker showing G80? Or are you just assuming G80? Because G80 won't apply to the type of differential inside, between the 2 rear axles.

Whats an SPID sticker? And where can I find it? I check and according to the rear of the pumpkin its a 9-bolt. Its the 350TPI formula. I thought this car came factory with an lsd or posi?

Both the 9 bolt and 10 bolt have cone type limited slip differentilas in them. When these wear out they will no longer spin both tires. The 9 bolt Borg Warner differential can be reconditioned at least once to make it work again. The 10 bolt uses the Auburn, which is scrap metal when it wears out. If you have the 10 bolt then get ready to buy a new differential. I recommend getting the Eaton Posi instead of another Auburn. The Eaton is a much better differential. If you have the 9 bolt then there is a thread on here somewhere that explains how to recondition it.

Stephen, I appreciate you helping me out. I'm trying to figure this car out. Its my first muscle type car. Every day I find out I got lucky. It has all the suspension bushings replaced, a borla exhaust, some yellow struts (koni yellows?) WS6 wheels... But I like to slide and now I'm getting issues... What do you think cost to recondition the lsd?

thanks big gear head too. I'm going to see if I can find the thread for recon

Info in the following link will answer many of your current and/or future questions:

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

JamesC

[quote=big gear head;4441106]The 10 bolt uses the Auburn, which is scrap metal when it wears out. If you have the 10 bolt then get ready to buy a new differential.

Is a whole new diff necessary? Or can't a new limited slip unit be put in?

a whole new rear end is NOT necessary. I could put an lsd in but I'm also wondering about upgrading the rear to something stronger. (I have a 9-bolt thus looking for a 10-bolt)

Before you buy anything you may want to think about future goals for car.

Stock 9 bolts are actually a little stronger than 10 bolts. There are parts available to beef them up but both are relatively weak. 400 hp is around upper limit of a well built unit. Aftermarket rear ends that bolt in and can handle any power will cost $2,500.

A new posi unit will be a few hundred so it may not be worth it if you have other plans. On the other hand if you need posi to function now for a few years, cost won't be to big of a hit.

You could look to see if there are any 4th gen rear ends for sale in your area. They bolt up to your car and come with disc breaks and posi. I sometimes see them for sale on craigslist for a few hundred.

Did you look at rear breaks to see what kind they are?

ok. cool. I wanted to eventually upgrade my 305 to a mild 350 with 290hp. Then put headers and exhaust getting it closer to 330+/-. I was under the impression that the 9 and 10 bolts and the 700r4 would be too weak for that but it sounds like I was wrong.

A friend told me there were limited slips that were decent for $100. Is there such a thing?

No. Check what big gear head says above, then search Summit or Jeg's for prices.

JamesC

Got it. Eaton it is. thanks.

With that power level in mind a 9 bolt and 700r will hold up. There are things you can do to help them survive longer. A transmission cooler would be a good idea if you don't have one and some rear end upgrades (rear end cover, better cross pin, etc). You may start breaking things if you race it with drag slicks at the track. I think the posi unit will be around $500 on summit.

Check out this post too. 9 bolts are very similar to 10 bolts however 9 bolt parts are harder to find.
https://www.thirdgen.org/forums/tran...-upgrades.html

I have no idea what breaks are on the back, but they are disk. It sounds like the 9 bolt will be fine up too 350-400hp with a good lsd? And what does the 700r4 need to withstand a little beating? Like drifting but not much more power adders...

Early 9-bolts had the iron calipers. Later years had the aluminum PBR calipers. I believe '89 was the crossover year.

There is only one LSD for the 9 bolt, and that is the Borg Warner unit. This is a cone type with 4 pinion gears. It's a strong differential.