Sab

Is the LSD option standard in the newer '90 and up cars?
How does one find out which options a car has? VIN?

Thanks,
Sab.

rixter

rear hatch area under the carpet is a tag with the option codes on it

928Quest

I think PSD is standard on 90 and up

Sab

Thanks, so a '90 or '91 S4 would not show option 220 on the option codes but still have it?

Nicole

PSD is not LSD. And since it was standard, there should be no option code for PSD.

Vilhuer

And if there is anyway, code for PSD is 221

Sab

So 221 should show as an option?

MikeN

If its a '90 or above.....S4/GT/GTS it will have PSD standard whether it shows on the option codes or not.

Sab

Thanks for the info, I really wanted to make sure, since I am shopping for a newer car and I would not want a 928 without LSD / PSD.
So I guess my '87 S4 having LSD makes it more desireable.
regards,
Sab.

morganabowen

Can someone explain the difference between LSD and PSD
I know that my mechanic explained it to me, but after sooo many years of LSD, it slipped my mind

Jim bailey - 928 International

LSD is a simple mechanical system with clutches inside the differential carrier which when one wheel spins do to poor traction it can transfer some of the power to the other wheel. The later limited slips only move about 40 % ,early slips can do as much as 80 %. The PSD system is a computer controlled system with a hydraulic pump in the left rear 1/4 and a slave cylinder mounted to the differential housing and it pushes on a clutch arm. This allows it to have infinitely variable transfer of power between the rear wheels. It works with the ABS sensors / as well as lateral motion sensors to do things like engage the differential clutch somewhat in high speed sweepers to add stability by "dragging" the inside rear wheel. So the PSD is much more that just a simple mechanical limited slip.

MikeN

LSD is a totally mechanical device with a set % amount for how much the LSD will lock up when it sees one wheel spinning faster than the other. PSD is mechanical in nature but uses electronic controls and sensors to vary the % of lock deemed needed for the situation. There are pros and cons to both.......but I see the PSD as a definite step up from the LSD. And yes, LSD in a pre '90 928 is a good thing to have but is not necessary under most driving conditions.

morganabowen

Jeez, I thought it came in a sugar cube

PorKen

The clutch style limited slip diff also has different ratios between accelerating and braking. It depends on the shape of the ramps of the teeth that rotate when one wheel has a different torque level, and push against the clutch pack.

It may be 40% on accel and some higher number, like 80%, on braking.

What ratio does PSD have, and is it programmable?

Vilhuer

I think traditional acceleration/deceleration locking ratio do not apply in PSD. Computer deside on both cases how much lock is correct based on inputs. It can be anything between 0 and 100%. What % exactly is used in different situations is known only to Porsche and Bosch.