Limited Slip vs Posi Trac - help me out here
 

For the heck of it, I jacked-up the Targa and spun the rear wheel while it was in gear (yes, the boy and I ran out of stuff to pester Mommy with!). The other rear wheel spun in the opposite direction. That means it's a limited slip differential right?

Here are some questions - what is the gearing dif between posi trac and limited slip?

What is better for track racing? I would think limited slip around courners.

Did Porsche put different transaxles on different models?

Spin it in neutral, if the other wheel spins in the same direction it is a LSD

sounds like yours is open



None, the same ring gear is bolted to the LSD. positraction is just a US name for the same type(made by Eaton Dana , etal) of LSD as the ZF units used in Porsches

Generally the ZF type w/ clutch/ friction disks is considered superior to the Quaiffe type gear driven types for track use, For A/X just the opposite would be true.

From the factory only open or ZF were offered. Later models from 964T on used an asymetrical ZF LSD which is even better, Though the normal models implementation of the clutch/friction disks was poor.

Good info Bill, the kinda stuff you like to know but never bothered to ask.

I've never heard that term Bill, can you expand on what an asymetrical ZF LSD is?

asymmetrical LSD were first available on the '91 up 965s an ROW 964 RS where they used 20% lockup on acceleration and 100% lockup on deceleration(20/100), 993s w/ LSD used a 25/65 version and 993RS used 40/65.

Paul Guard(to the best of my knowledge) now offers a version for 915 as well as the G50 and G60 series trans. the lockup factors are selectable.

In nuetral the other wheel didn't spin, in 1st it spun the opposite way. What does that mean?

It means you have an open diff. I think the behavior in neutral is caused because the ring gear is just turning the pinion shaft.
-Chris

yup it means you have a stock open diff. Youre wheels have to turn in the same direction if you have a limited slip.

Open diffs the wheels go reveresed from each other and some times the other wheel wont even turn.

Same as my 72T and 73S. I was surprised porsche didnt go the extra distance to put a limited slip even on the S.
Every Bmw Ive owned had limited slips, just makes the car way more fun and a more planted feel.
A porsche without a limited slip is a bummer.
Im looking for one right now but $1300. Damn

I have an 82 sc and i just figured out today thet i have a lsd. I had to unstick the e brake so i was messing with it and at the same time checked for lsd. Sure enough both wheels turn the same way. And jeesh is it a pain to jack up both sides at once. Anyway im wondering exactly what type of lds was offered for this year from the factory and if theres any kind of special maintinence it needs. I think it has swepco fluid in it now. Its bright red like auto tranny fluid. Im sure glad it has lsd :) it makes it harder to burnout though

Swepco is blue.

You need to change the gear oil more often than if you have an open diff. I recommend 10k miles.
You also have to ensure the oil you use contains the additive for LSDs. If not, you can fortify it with the GM LSD additive you can get from any Chevy dealer.

good to know. Ill ask my porsche mechanic what he recommends the next time im in for somthing.