newsboy

I was speaking with someone who did allot of instructing in Canada when the C4's came out. He told me that when you removed the cover in the center tunnel,
there was wiring there for a switch that would disconnect the traction control system, thus keeping the front/rear power at 37/63. These were ROW cars. He said that many of the drivers utilized this. I looked in the ROW section of the PET and couldn't find anything. Is anyone familiar with this modification? Would be great to have a C4 that could handle like a C2 at the flick of a switch.

newsboy

Just to clarify, the power to the front/rear on the C4 is 31%/69% (my mistake), without the traction control
sensing any wheel slip. The switch he was referring to would keep it at this value.

964rh

Didn't see any spare plugs or wires when I had my console out last year, it was fairly busy behind it though cause of the alarm system so I may have missed it.

Wouldn't mind giving it a go it you have any luck finding it.

Rob

rob964.c4

I dont think it is possible because it is mechanical 4w heel drive here is some info.


robert



All wheel drive (AWD) is exclusive to the Carrera 4. This system is purely
mechanical. Under normal driving conditions on dry roads, the drive torque is
distributed 31% to the front axle and 69% to the rear axle.
An electronically controlled, hydraulic-mechanically activated traction control system
called PDAS (Porsche Dynamische Allrad Steurung, German for Porsche Dynamic
All-wheel Control) works with the AWD mechanical components to enhance traction
in adverse driving conditions and to overcome the ferreria effect “over steer leading
to a spin”.
Principles of operation
The AWD gearbox is fundamentally the same as the rear wheel drive version with
many common components, especially in the gearbox section.. Engine torque is
transmitted to the gearbox via the flywheel and clutch assembly. The main difference
is the addition of the drive assembly to the front wheels and the addition of the
center differential (Power Transfer Unit). The gearbox drive is connected to the hollow shaft.
The hollow shaft is connected to the power transfer unit. It is here that the drive is distributed
31% to the front and 69% to the rear. The rear drive is provided by the pinion shaft which runs
from the PTU back to the rear differential. The front drive is provided by a purpose built
flexible drive shaft mounted inside a static torque tube. This drive shaft is connected to
the front final drive unit (front differential). Drive is transferred to all wheels via half shafts.
Note; Failure of a rear half shaft requires the differential locks to be engaged to move.
WARNING —
The all wheel drive system is permanently engaged and can-not
be switched off. Do not allow a Carrera 4 to be tested on
a 2-wheel dynamometer. This applies equally to an officially
sanctioned emission inspection station or a performance
shop.
CAUTION —
Do not tow a Carrera 4 with two wheels on the ground. The
safest technique is to transport the vehicle on a flatbed truck
or trailer.

Computamedic

The original question was regarding the PDAS, not the AWD. Whilst the AWD system is (a) mechanical and (b) permanent, the PDAS system is purely electronic in it's origination even though it activates hydraulic/mechanical clutches to engage the diff locks. It seems perfectly sensible that the electronic actuation could be disabled to prevent the diff locks being engaged.

How that might interact with the rest of the system is another, entirely different question and might be worth some further investigation.

Regards

Dave

meek

I thought the PDAS system already had a switch; the brake pedal. According to the manual, tapping it will disengage the sytem. Never tried it, so don't ask what the actual effect is. I think it is discussed in the Wringing Out article.

Computamedic

Adam,

That's not quite the same thing though is it?? Using the brake to "turn it off" implies that it's only going to turn off the PDAS once it activates. The purpose of the original question was to prevent it activating in the first place.

In my (admittedly, limited) experience, PDAS only seems to activate for literally microseconds at any one time so the chances of using the brake pedal to deactivate it would be miniscule to say the least. Switching the system on manually via the rotary switch is an entirely different matter - and for an entirely different purpose.

Regards

Dave

meek

Indeed Dave, not the same thing as switching it off full time. I am just not sure how long the system turns-of for when the pedal it touched? I assume it must be momentary as the main point of the system is to help in the corners. Not much point braking hard into a corner, for the sytem to then stay off for a few seconds in the turn when you may actually need it.

In agressive road driving, it rarely seems to activate anyway and I would think disengaging it would make little difference to the way it handles i.e. still 4 wheel drive and not 2. I guess track work would bring the PDAS to the fore.

rob964.c4

you are absolutly wright, sorry

perhaps this is the right info
The traction control system is described as Porsche Dynamic Allrad Steurung
(PDAS) in German language documents and Porsche Dynamic Four-Wheel Drive
(PDFD) in English language documents. This form of traction control system
exclusive to the 964 Carrera 4 series among the 911 Carrera series.
Note: A similar system was developed in tandem by Porsche engineering for the
Porsche 928 series from model year 1990. This system was called PSD and only
acted on the rear wheels. PSD (928) and PDAS (964) control units are not
interchangeable.
The PDAS is a non-integral electronically controlled, hydraulically activated,
mechanical locking system. This system utilises the AWD G64 transmission and the
differential locks are installed into the transmission. However system failure has no
affect on the normal operation of the permanent AWD. The PDAS is activated and
de-activated only when required to assist in retaining traction or grip.
The system was developed from the mechanically variable differential drive control
system used in the Porsche 959 with its Paris-Dakar transmission. The Paris-Dakar
transmission was also installed into the 20 964 Carrera C4RSs assembled at the
Porsche motor sports department at Weissach Germany.
System purpose
The primary purpose of the traction control system is to enhance the advantages
provided by the permanent AWD system. The traction control system is used to
positively enhance the C4s handling using the already superior traction provided by
the AWD. The traction control system has two differential locks.
The longitudinal (inter-axle) which provides a variable lock between the front axle and
the rear axle and
The lateral (transverse lock) which provides a variable lock between the two rear
wheels.
The lateral lock is applied to reduce the danger of over steer from the ferraria effect
while driving the C4 in curves. “Anti-spin control”. This function works very well, but it
is not infallible. It is still possible to spin a Carrera 4 if the limits
of the system are exceeded.
The longitudinal lock is used to stabilise the C4 when it is accelerated out of a curve.
If for example one axle of the C4 is on ice and the other is on a dry surface, the
wheels on ice could spin during acceleration. To counter this the longitudinal lock will
be activated and it will send more drive or torque to the slower turning axle (the one
of the dry surface). The lock will remain engaged until equal wheel speeds are
restored. The drive ratio when the longitudinal differential lock is activated can be
changed infinitely from 0 to 100% or 100 to 0% in fractions of a second.
Note: If the brake pedal is depressed, the traction control system will automatically
disengage, regardless of conditions.
Warning When either or both of the differential locks are activated, massive under
steer will occur. It is possible to deactivate the system when these conditions
are unwanted, by just tapping the brake pedal. This procedure requires practice and
should not be utilised without some training in controlled conditions.
System components
Electronic control unit (shared with the ABS) located in the front right of the luggage
compartment.
Note: The part number of the model year 1989 and 1990 PDAS/ABS control
unit is 964 618 126 00. For model year 1991 and up the control unit part number was
changed to 964 618 126 01. The –00 versions can be exchanged for a -01, but not
vice versa.
4 wheel speed sensors (shared with the ABS).
Wheel speed sensor with combination plug (noise suppressor) photo by Tom Sharpes
Differential lock dual solenoid valve located behind the control unit.
Slave cylinder or differential lock actuator, one externally mounted in the power
transfer unit and the other externally mounted in the rear of the G64 transmission.
Mechanical actuation lever internally installed in the power transfer unit and the other
internally installed in the rear differential.
Longitudinal differential lock integrated into the power transfer unit assembly.
Lateral differential lock integrated into the rear differential.
Lateral (transverse) accelerometer mounted in the centre tunnel forward of the gear
stick.
Longitudinal accelerometer mounted in the centre tunnel forward of the gear stick.
Used for the ABS system of the Carrera 4 only.
Note: Access to accelerometers is via a small panel on the right side of the tunnel.
This panel is held in place by two self-tapping screws.
Traction control program activation **** located on the centre console.
Note: On model year 1989 C4s, the traction control activation **** is alone in the
centre console. On model year 1990 C4s and up, the traction control **** is joined
by the rear spoiler manual operation control ****. The traction control **** is the
**** on the left.
Traction control activation indication system which consists of a yellow led mounted
in the center console.
Warning system.
Under and Over voltage protection system.
Power interlock circuit (shared with the ABS)
Plumbing.
Wiring harness.
Component locations from left to right: PDAS/ABS control unit, differential lock dual solenoid valve,
brake hydraulic boost pressure accumulator, ABS hydraulic unit.
Component operation
Electronic control unit:
The electronic control unit is a small, multi-channel electronic computer. It is able to
calculate from the signals received from the wheel speed sensors, speed of wheels,
acceleration of wheels, speed of axles (mean value of wheel speeds) and the speed
difference between axles.
The control unit contains a safety circuit which will detect erroneous signals in the
electronic control unit as well as defects in wire harness and plug connections. The
safety circuit also monitors battery voltage. If battery voltage drops below the
specified value, the PDAS will be inhibited until battery voltage again reaches the
specified value. In addition to the monitoring function, safety circuit also has an active
section, the test cycle, also known as “BITE” (Built in test equipment). The test Cycle
is an integrated test program that checks the control unit and the dual solenoid valve
when the ignition is switched on (see beginning of this chapter to see how long the
PDAS and ABS warn lamps may remain on for after engine start. A further test
program is initiated at a road wheel speed of 7 kph which checks the wheel speed
sensor inputs.
Wheel speed sensors:
The rotary motion of wheels is picked up by inductive sensors and sent to the
electronic control unit in form of electric signals.
Speed sensors consist basically of a magnetic core and a coil. The pole piece is
surrounded by a magnetic field. As the road wheel turns the teeth of pulse gears
move through this magnetic field. This changes the magnetic flux and induces
alternating voltage in the coil. This alternating voltage changes its frequency
according to the wheel speed and consequently can be used to measure the road
wheel speed.
Dual differential lock solenoid valve
This unit contains two separate solenoids. One is connected to the longitudinal lock
slave cylinder and the other to the lateral lock slave cylinder. The control unit will
open and close the respective solenoids to pressurise the hydraulic system to
activate the locks as required.
Slave cylinder
Hydraulic force for the operation of the multiple clutch plate assemblies of each
differential locks is provided by a slave cylinder.
Longitudinal (inter-axle) differential lock
Is installed into the power transfer unit. The differential lock consists of a multi clutch
and friction plate assembly. The plate assembly is actuated by a lever mechanism
which itself is operated by the slave cylinder. Pressure being supplied to the slave
cylinder is controlled which makes the clutch application variable. One set of plates is
effectively connected by a gear arrangement to the input shaft to the power transfer
unit (rear axle drive) and the other set are effectively connected by another gear
arrangement to the output shaft of the power transfer unit (front axle drive). When the
lock is activated and the clutch and friction plates come together the rear axle and
front axle are directly connected together. How much torque or drive transferred is
dependent upon the hydraulic pressure being applied to the slave cylinder. Initial
pressure starts at 40 bar.
Lateral (transverse) differential lock
Is installed into the rear differential assembly and is very similar in operation to the
longitudinal differential lock, except the multi-plate clutch assembly is effectively
connected to each rear axle.
Note: The contact pressure of both the differential locks multiple plate stacks could
be so great in an extreme case, that the locking torque would exceed 1000 Nm.
Note: Differential lock clutch or multi-plate stacks
Both differential locks use the same clutch inner plates. These clutch plates had
Gylon friction liner on both sides until replaced by Valeo as described in Porsche
technical service bulletin 39306 issued September 1993.
The friction-lined plates or the outer clutch plates are also the same. However
because they have a spiral groove for oil supply they must installed correctly because
of the different direction of rotation between the longitudinal and lateral locks.
Lateral (transverse) accelerometer
The accelerometer is a simple moving mass device which provides an output of
between 0-5VDC to the control unit. The accelerometer is axis is mounted at 90
degrees to normal driving line. The signal provided to the control unit provides the
sideways acceleration of the C4 in a curve or the tendency to start to spin.
Longitudinal accelerometer
Is the same construction as the lateral unit but is mounted with its axis along the
normal driving line of the C4. It provides acceleration and deceleration data to the
ABS section of the control unit. This data is used by the ABS section of the control
unit to determine if ABS or PDAS is to be used. PDAS can only be used when the C4
is accelerating and ABS can only be used when the C4 is decelerating.
Note: Whilst this accelerometer is used by the ABS section of the control unit it is
included in this section because only the C4 is fitted with such an accelerometer. It is
not installed on all other versions of the 964 with ABS only.

adamfogerty

Odd...mine is activated by large bumps and/or potholes in the road (when I'm not able to avoid them), so can activated be quite frequently, even under 'normal' driving. This makes sense, as I guess when driving over a pothole one wheel might momentarily lose contact with the road...especially with an agressive suspension setup.

I find it's easier to spot the yellow activation LED during night driving, when it can be seen in my peripheral vision.

Sorry for going slightly off-topic.

(the other) Adam

ValveFloat

This is interesting. I didn't realize that the C4 had an electro-hydraulic locking diff in the rear as well as the center.
I may be totally wrong here, but it sounds like the system is similar to that on a Subaru STi?
On the STi there is a **** that enables the driver to vary the amount of center diff clutch lock-up, including an "open" setting that would be no clutch engagement.
If this is true, and you could "disable" the center clutch, it probably would make the car more entertaining, I know it does on the STi.
If there isn't a hidden switch, maybe a person could split the center clutch solenoid power wire with a switch?

964rh

[QUOTE

I find it's easier to spot the yellow activation LED during night driving, when it can be seen in my peripheral vision.
[/QUOTE]

I notice it loads more since I stuck a bulb in the clock light.

It goes off when I hit potholes and bumps as well, hardly ever on track though?!?!?

newsboy

The person I was speaking with was pretty sure that this switch or wiring for the switch was on ROW c4's.
The location(center tunnel door) is where the accelerometers are located. So perhaps it had something to do with de- activating them. I'm thinking about this for Track/Auto -X only. Wonder if pulling a fuse might accomplish the same thing?

garrett376

This is not correct: it would not handle like a C2. If you've ever driven a C4 on a race track and had the PDAS stop working, you'd realize that you were driving a car that just spins its inside FRONT wheel in hard corners under power. A C2 never does that! A C2 will try to spin an inside REAR wheel in a corner under load, which is a lot harder to do than an inside FRONT wheel due to weight distribution and cornering loads. If you see pics of 911 race cars with their inside front wheel raised in the air, just imagine if the drivetrain was putting its power to this wheel (due to the way open differentials work)!! That's what happens when there is no PDAS management of the drivetrain: you go nowhere fast since you're losing a third of your power to a spinning wheel. That's one reason I installed a reset switch in my race cars in case a fault ever occurred that disabled the PDAS management.