Alright,

I know that the easiest way to determine if my 9 Bolt rear end is a posi or not is to take off the cover and look. I dont have the time to do that right now so please bear with me, here's what I have noticed and learned so far...

When I had completely bald tires, my back left tire would not spin at all in a straight line, no matter what I did, I had no such thing as straight line traction. The only time the back left tire would spin would be during a left turn while doing a donut on pavement.

Now that I have brand new tires, I can now leave 2 burnout marks on the pavement. I thought this was weird so I went to an empty park to look at it.

Sitting still and holding the brake, I tried a burnout. Both my tires would spin! It would NEVER do this when I had completely bald tires. it would always just spin the back right tire.

The one thing I noticed is that if I jabbed the gas too quickly the back left tire wouldn't spin but rather "twitch" like it was wanting to go forward but couldn't. If I halfway eased into the gas the back left tire would break loose and spin just fine.

Could I have a posi unit and it just be really worn out?

Could the extra grip of the new tires be causing the posi to halfway engage?

 

the easy way to find out is to jack up the rear end and spin the tires by hand and if they both spin the same way its posi but if they spin opp... its not! T

 

All that time spent in that empty parking lot, you could have had the rear cover off and known for sure

 

I did this in both PARK and in DRIVE, in park with the rear end up, I spun the back left tire forward, the back left one turns backwards. In drive, I turned the back left one forward, and the back right one went forward as well. (probably supposed to do this anyway, just never tried it myself)I have read posts on here before that some posi rear ends will spin opposite even though they are a posi, is there any truth to this?If it's not a posi rear end, then why do both of my tires spin?

 

Open can drive both tires, but the moment one tire has less traction, it gets all the power. If both have the same, then both will spin. In posi, you get a ratio of power put on the wheel with more traction from the wheel with less traction. This works until you get to 0 traction on one tire, because we dont use electronic differentials, we're stuck with a static multiplier for mechanical force.

This means, an open can at times, look and work like a posi.
Limited slip diffs will usually be loose enough to work like an open for things like turning (so you dont get wheel hop like a locked diff), and such things, but over a certain torque, it will work as you'd expect a limited slip to.

Your diff's friction cones are probably worn or you are too loose, which would be why with your "slicks" it didn't work right, but with new street tires (less traction) it does.

That would be my guess.

 

So I more then likely have a worn open end?

 

no, probably a worn limited slip (posi). 9 bolts are noted (due to age) for having worn cones or the diff has too much play for the cones to catch good.

Take 10-20 min and some rear oil and open it up, look and see, take pictures if you cant tell the difference. It may just be a matter of tightening it up, or it could mean that you need to have it rebuilt if you want the limited slip to work again.

 

I think I have found the answer lol.

Today when I went out, I got to looking at the rear end, and I noticed a metal tag connected to one of the bolts, the tag said:

-------------------------------------
l SPIN RESISTANT DIFF l
l Use only approved lubricant only l
-------------------------------------

I tell you what that absolutely made my day right there. There was also another tag on one of the other bolts that told me i had 3.27 gears.

I took the cover off the rear end, drained out the 20 yr old oil, and put some new fully synthetic oil in it along with the factory posi-additive from the dealer.

Jesus christ that stuff was nasty, and smelled nice too lol, I have never seen a blacker liquid come out of my car before, it had to be the original stuff.....

I am letting the tube gasket "cure" before I drive it. If I don't see a seat of the pants difference, then I will at least know I did a good thing by getting that old crap out of there lol

 

i may be mistaken, but posi additive was for 10bolt posi units, not BW 9 bolts. Not sure if it's detrimental, but i think i remember reading from someone who knew what they were talking about that the BW friction cones do just fine without the additive and may get damaged from it. Dont quote me though. maybe someone else can chime in, i haven't read about it since i put mine in back when i got the my car.