Hello,
I have an borg-warner 9 bolt 3.27 limited slip rear axle in a 87 formula.

-when i bought the car the limited slip worked great! if anything it would chirp the tires slightly around slow corners, and when lifted in park it was very difficult to get the tires to spin opposing directions.

-i changed the fluid using valvoline semi synthetic 80w-90 gear oil, and the trans-x limited slip addative. And ever since then it has been more or less "open" i can spin the tires in opposite directions with ease when lifted, if i try to get the car sideways at slow speeds it just spins the inside tire.

-I removed the new fluid, and put plain gear oil in place in hopes of it tightening up again... with no success.

i also have noticed with both the 9 bolt cars i ownd that their is a slight hummm at 40-60mph. anyone found a cause/solution to this???

as far as i know no work has been done to the axle.

i want to be able to do donuts again

Thanks,

~JaSoN

 

Try using a different LSD additive, i know some work well in certain LSD's and on others they do absolutley nothing!

Try a bottle of the GM stuff in there, if that doesnt smarten it up it may just be time to rebuild it or replace it.

 

I'm not sure on the 9 bolt posi's, but I've heard that synthetic gear oil wreaks havoc on the auburn units, which use cone clutches similar to the 9 bolt. As a last ditch effort, you could pull the cover off, drain all the fluid out, and use a whole can of brake parts cleaner on the carrier assembly, paying special attention to where the clutch cones are. Then blow it out good with compressed air, then put the cover back on and put regular old 90 wt. gear oil and posi additive back in. If this doesn't do the trick, you'll probably have to re-shim the clutch cones to get it to grip good again. There's a really good article on how to do this in the tech articles section of this site. Since yours just starting slipping, you could probably re-shim the cones with good results. Btw, nine bolts are notorious for the posi units going south.

 

I hate to say it, but the humming is probably the bearings telling you its time for a rebuild. With the posi slipping, its a great time, before anything is broken beyond repair, to change the bearings, seals, and service the posi, as Pat Hall said there above. I just redid my whole rear, due to brake swap/diff cover upgrade. My posi worked fine, however, I think I used synthetic, which is making the posi slightly choppy, I think I'll have to change it to dino oil soon.

I got the rebuild parts from Randy's ring and pinion for a decent price. while you are there, you should probably change the axle bearing too, but they require a press, and in my case, I needed to heat the retaining rings with a torch.