'98 Z28 with the T56.

Now ive only had her about a month so i dont know everything about her. When im going in a straight line and peel out, etc the posi kicks in fine. But if I'm turning and the weight is even slightly uneven between the two rear tires when i try to kick the rear out it often will only spin the inside tire? Now I thought that was the whole point of limited slip compared to an open differential? The car itself runs fine, shifts fine, nothing to suggest that it has been worn out. Whats going on?

 

Its a stock rear end right? I know the LT1 diff requires a limited slip additive probably the same for the LS rear. Has the diff fluid been changed out and was that additive...well... added?

 

yah stock rear. I have no idea if it's fluid has been changed or added. How do you go about adding limited slip additive? and where do you get it?

 

you can get it at any auto parts store

It should be added to the diff fluid at the time of the fluid change. I've never seen what happens when its not added but maybe the clutch disks inside the diff are still ok? Maybe not. If I where you I would change out the fluid in the rear and add the limited slip additive.

I haven't crawled under the car to see but Im pretty sure there is no drain plug just a fill plug so you would have to take the diff cover off to drain out the inside. clean it out really well then replace the cover with a fresh gasket then put in the recomended amount of additive first then the diff fluid. Fill it till it over flows out of the fill hole then replace the plug.

If your lucky the posi will start acting normal again after a while of driving.

 

ive heard that it may help to drive around in a bunch of tight turn circles to both sides. that it may help distribute the fluid and fix things up?

 

well...you do know the point of a posi is to allow for both wheels to be locked together when load is equal....straight line

and when in a corner, due to the outer wheel having to to cover more ground, the posi unit unlocks and allows each axle to spin independantly.

theoretically you should be able to get them both spinning in a corner...but depending on exactly how you are executing your turn...it sounds like the posi is doing it's job.

are you saying in a turn you can smoke one tire and the other does nothing??

 

The limited slip diff has 1 job... to increase traction. The only time a posi unit slips bad enough to only spin 1 tire is when its worn out or broken in some way. If the posi unit is working correctly both wheels will spin all day no matter what you do.

A clutch style posi unit will not unlock it will slip an internal clutch. The internal clutch is what needs the additive.

My 94 will kick out the rear end on command just blip the throttle with the clutch out.

 

Yes. Although it seems more likely to only smoke one tire when im turning right then when I turn left.

 

and that will be because of how torque is applied to the rear from the spinning drive shaft.
One side has a tendancy to lift more than the other.

 

BINGO...i had the same question when i got my 02 Z with 75k miles a couple months ago. then i realized after just driving it more, going to the dragstrip/autox courses, and talkin to a couple tech guys, thats just how our limited slip works, and a lot of times, only one tire will spin through the corner

 

The mechanism for engaging the posi clutches is a difference in rear wheel speeds, and modified by load... doesn't matter if its going in a straight line or in a curved path. When one wheel turns at a different speed than the other, the clutches MAY lock up depending on the load applied to the wheels. If you take the turn under "normal" power, the clutches should continue to slip and allow differnt wheel speeds. If you apply power in the turn, the clutches will begin to lock up, and one wheel has to lose traction.

Moving to "Drivetrain".

 

It seems the LS1s operate differently than the LT1 rears lol. I'm not sure of the exact specific differences but I've seen alot of LS1s doing exactly what you describe (zexel-torsion rear ends). The LT1s I've owned and my friends own have no problems at all sliding the rear end (auburn posi) around in any situation.

 

My 94 did exactly the same thing before I replaced the rear.

What you've got is a worn out Posi. I beleive the LT1 cars and the LSx cars have the same posi except for the SS cars. The reason for the aditive is to keep the posi quiet. Otherwise a strong clutch pack will creak and pop going around corners (found this out with my new Eaton), adding an additive will not make it grip better.

 

If the car won't spin both tires in a turn (under hard acceleration), then the posi-unit is wore out. The crappy thing about the Auburn style posi-unit is that the clutches bite into the unit itself. There is no way to repair/rebuild the unit. Get yourself a new posi-unit. I replaced mine with one out of an SS (Zexel-Torsion) and I love it. Haven't had a problem with 300 ft long single tire black marks since.

 

ive got a eaton posi for sale, has about 1000 miles on it, if your interested let me know