I just bought a 99Z w/150,000 on the clock. The option codes come up as posi and 3:42. It does run 1500 rpm in 6th with stock tires at 70mph. So that does calculate to 3:42. However I noticed when changing the tires. Both tires don't spin the same direction when you turn one tire. Also I counted the driveshaft revolutions when turning the tire 1 revolution. It goes 1.75 turns to 1 tire revolution. To add to the confusion, if I hammer it both tires spin? Whats the deal is this normal? I used to have a 94 then a and 95. I read alot about the rear ends are weak. But, I read a book the other day that said in 98 or 99 they improved the rear ends to a stronger type. Whats the scoop?

 

While I am no expert on what came with the newer cars, normally with a posi if the car is in neutral and both rear wheels off the ground they will spin in the same direction if one is turned...unless you have a gov lock type posi which will lock the rear when one wheel starts spinning. I dont know if that is the type you have, but if they both spin when you take off the posi is working ok. Spin test is only going to work with both wheels turning the same direction and speed so ignore your 1.75 count.

 

What you are describing is normal for a torsen limited slip. I believe the later year Z28's came with the torsen instead of a clutch type limited slip.

 

Normal. You can verify operation of the LSD by doing a burnout. Should leave two approximately equal stripes.

Rich