This is a more subtle question that you might think.

My 9-bolt posi sometimes works. Sometimes it doesn't. Thinking mechanically for a moment, it seems to make sense that when the cones start to wear out, the more pronounced the requirement for the limited-slip effect, the more likely it won't work as the cones wear out, right?

Then riddle me this?

I just did two passes in the company parking lot. I pointed the car in an uphill direction, applied pressure to the brake and proceeded to do a burnout (while allowing the car to move) for about 50 feet. Two black stripes. I repeated the process with the same results. Great - the posi works. Over the winter, I did this a few times and I only got one stripe.

In addition, I have noticed that it doesn't seem to work on medium-speed corner exits on road racing courses. As i feed the throttle from the middle of the turn to the exit, it is clear that when the tires (no tire) breaks traction, it s only one tire.

The only variables that I see are:
1) Temperature
2) Speed

What don't I understand here?

Thanks for reading this far.

 

Even theories would be interesting. Anyone?

 

I've noticed in my Mustang and IROC that once the posi spins hard enuf it gets hot and then it'll grab. The trac-lok in the Mustang works every now and then, especially if you are putting alot power to it and it slips. You can hear it growling, then it stops and both tires hook up.

That's probably not a good thing but it's already fked anyway.

 

Ahhh... Sounds like temperature in your case. I am beginning to believe that temperature can have an impact. Thanks for the response...

 

Well I've rebuilt the trak lok system in my stang...and all the friction disks have steel disks on each side.....
about 4 of each per side I think.....
keep them cool and they stay one size.....
heat em up....they shall grow

also just an idea....the more worn the friction disks are....the thinner they get.........and then the steel would have to grow more to take up that extra space now...... only an edjucated guess on my part....

 

Mine sort of does the same thing but a little different. Maybe its because its not a 9 bolt, just a 3.23 10 bolt. If I jsut power brake at about 1500-2000 rpm and do a burnout, 2 balck marks, even if i start moving. But if I am at a dead stop and just hammer the gas and let it rev, alot of times it wil only leave one really dark tire mark. Beats me...

 

Some of our cars really don't have a true posi unit in them . We have a limited slip option. Whan the car feels one slipping it puts a pin in the dif and m,akes the other tire spin too. Sometimes it works sometimes it doesn't. You can wear out the pin so it will only work on occasions, and under high stress. I would say get areal posi put in and you will notice a difference

 

Hmmm... limited slip and posi are not the same? Hmmm...

I suppose if you want to say that a locker is the only real limited slip, then OK.

However, my understanding of the cone-based posi unit in third-gens is the following:

A properly installed 9-bolt posi will distribute power to to both wheels when the differential force between the two wheels exceeds 50 ft-lbs. This means that one wheel will slip up to 50 ft-lbs of power. The is the "limit" of the "slip"...

 

I been having a lot of problems with my 9-bolt lately. It makes a really nasty and fairly loud noise. The best I can discribe it is "metallic" metal sliding across metal. While doing burnouts and launching off the line it gets posi but if I punch it around corners it will only spin 1 wheel. It seems that my passenger side tire will spin like three times as fast as my drivers side tire sometimes. The whining noise also sounds louder when its cold

 

Posi is just limited slip. No such thing as 'true' limited slip. Locker isn't limited slip--it's either locked or not locked. As posi wears it becomes less effective or not work at all. With a non-posi rear, you can still do a 2 wheeled burnout if traction is equal on both tires. Temp can alter how well the posi works.