Porsche 928 GT1991, Owner'S Manual

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Porsche limited-slip differential
(PSD)
The PSD is an electronically controlled diffe-
rential lock which switches on automatically
without intervention from the driver.
It is an aid to driving off on road surfaces
with varying degrees of traction and serves
to improve driving stability when cornering
with high lateral acceleration.
In spite of this it still remains the responsibil-
ity of the driver to adapt his style of driving
to the prevailing road and weather condi-
tions, as well as to the current traffic condi-
tions. The higher degree of safety af-
forded by this system must not be re-
garded as justification for taking greater
risks.
Aid for driving off
The PSD cuts in whenever a speed differ-
ence (slip) of more than 2 km/h occurs in the
drive wheels and the speed of the vehicle is
no higher than 30 km/h (19 mph). The extent
of the differential locking effect is deter-
mined by the slip of the drive wheels. How-
ever, some skidding of both drive wheels
cannot be avoided if acceleration is too se-
vere.
Acceleration out of corners
The PSD cuts in over the entire speed range
whenever the control unit receives a high lat-
eral acceleration signal when accelerating
out of corners and the inside wheel shows
signs of slipping.
The lock transmits the non-transferable driv-
ing force of the inside wheel to the outside
wheel.
The lock is opend for safety reasons if both
wheels slip.
Deceleration in corners
If the control unit receives a high lateral ac-
celeration signal at speeds of over 60 km/h
(37 mph), a limited-slip torque is also built up
when decelerating in corners to counteract
any slewing of the vehicle.
Note
A solenoid valve regulates the gentle built-
up and reduction of the limited-slip torque.
The acoustic timing noise indicates that PSD
regulation is occuring.
Should the control unit detect a fault in the
limited-slip differential, the PSD is switched
off for safety reasons and the following fault
display appears in the information system:
You should then have your PSD tested at an
Official PORSCHE Centre as soon as possi-
ble! The switching-off of your PSD changes
the driving characteristics of the vehicle.
The switching-off of the ABS System always
results in the PSD being switched off.
The PSD indicator light in the instrument
cluster lights up when the limited-slip diffe-
rential is activated or if both drive wheels
slip.
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