Running Gear
Running gear - overview
Front axle/steering
McPherson wheel suspension with offset spring. Twin-tube gas-filled shock absorbers in standard or sports version.
In order to obtain greater stiffness with reduced intrinsic weight as compared with steel, the following components have been made from aluminum: Control arm, diagonal brace, track rod, wheel carrier and cross member / side member.
Rack-and-pinion gear (ratio = 16.9 : 1) with hydraulic assistance. Steering wheel longitudinally adjustable (40 mm).
Further improvement of steering precision and reduction in the turning circle (10.6 m) as compared with the previous 911 Carrera (993).
Rear Axle
The multi-link rear axle used in the 911 Carrera (993) served as the basis for the further development in the new 911 Carrera (996). Important considerations here were to achieve further weight reduction while preserving the familiar good vehicle dynamic properties. The longer wheel base offered additional potential for improvements in driving comfort and handling.
The wheel suspension consists of five aluminum control arms, of which the two upper control arms are aluminum florigens.
Gas-filled shock absorbers in standard or sports version.
Wheels and tyres
Brakes
Hydraulic dual-circuit brake system with front-axle / rear-axle brake-circuit distribution.
Vacuum brake booster, internally ventilated and perforated brake discs with four-piston fixed calipers at front and rear axles.
ABS 5.3 (3-channel system) standard.
ABS/TC 5.3 (4-channel system) on request.
TC = Traction Control, consisting of ASR (anti-slip control) and ABD (Automatic Brake differential).
Parking brake (handbrake):
Drum brake acting mechanically on both rear wheels.
Information on ABS 5.3 and ABS/TC 5.3
General
The Porsche 911 Carrera (996) is equipped as standard with an anti-lock brake system (ABS 5.3).
"Traction Control (TC)" is available on special request on the basis of ABS 5.3.
Traction Control (TC) is a combination of Antislip Control (ASR) and Automatic Brake Differential (ABD).
TC is a further system for increasing driving safety.
Control module, hydraulic unit
ABS 5.3 is optimized with regard to installed volume and weight compared with the ABS 5 (ABS 5 on the 993). Control module (No. 1), hydraulic unit (No. 7), pump-motor relay and valve relay (No. 2) of ABS 5.3 and ABS/TO 5.3 form a unit that is located next to the brake master cylinder.
Diagnosis and system tests on both systems are carried out with the Porsche System Tester 2.
Differences between ABS 5.3 and ABS/TC 5.3
ABS 5.3 = 3-channel system (diagram: refer to Diagram).
ABS/TO 5.3 = 4-channel system (diagram: refer to Diagram).
The essential distinguishing features between ABS and ABS/TO are:
^ Number of brake lines at intermediate piece (No. 8 in the Control Module, Hydraulic Unit illustration):
ABS 5.3 = 3 brake lines
ABS/TC 5.3 = 4 brake lines
^ TC off switch for switching driving stability control on and off is not available on vehicles with Solo ABS (ABS 5.3).
^ TC (ASR/ABD) warning light and
TC (ASR/ABD) function light
(information light) in vehicles with ABS/TC.
These lights light up when the ignition is switched on (lamp check).
In vehicles with ABS 5.3 (Solo ABS) these lights are not fitted in the instrument cluster.
A figure showing the warning lights and the function light is shown in the ABS ABS/TC Component Locations illustration.
ABS 5.3 (3-channel system) system description
ABS operation
The ABS control module receives a signal from the brake-light switch and the AC voltage signals from the four speed sensors. These signals are converted into digital wheel-speed signals independently of each other by two microprocessors. The wheel slip (approximately proportional to the computed vehicle reference speed) is formed from these wheel-speed signals.
If vehicle deceleration and excess slip at a wheel are detected, the pressure-holding phase is initiated, i.e. the inlet valve for the relevant wheel is closed to prevent a further increase in pressure. If in spite of the pressure being held constant the wheel tends to continue to lock up, the pressure in the wheel cylinder is reduced. For this purpose, the Wet valve is opened and the brake fluid is pumped back to the brake master cylinder via the return pump (pressure-reduction phase) until the wheel turns again. Then, depending on the control cycle, further appropriate cycles are initiated.
This function and the input signals are continuously monitored. If a fault is detected, the control unit switches the ABS function off, switches on the ABS warning light and stores the fault in a non-volatile memory in the control unit.
In addition, whenever a journey is begun and a speed of 6 km/h is exceeded, a test program is started. The solenoid valves and the pump motor are electrically actuated and checked. If a fault is detected, the control module switches the ABS function off, the ABS warning light is switched on and the fault is stored.
Diagram: ABS 5.3 (3-channel system)
ABS / TC 5.3 (4-channel system) system description
Note: Traction Control (TC) represents an extension of the ABS system and is a combination of anti-slip control (ASC) and Automatic Brake Differential (ABD).
TC prevents spinning of the drive wheels when moving off and accelerating. Driving stability and traction are improved over the entire speed range.
Traction Control (TC) is ready for operation when ever the engine is started.
The TC information light in the instrument panel is lit during a control process and warns that the driving style must be matched to road conditions.
Function
Driving-stability control:
If Traction Control (TC) detects that a certain speed difference between the wheels has been exceeded (wheel spin), engine power is automatically reduced.
Brake control:
In addition to reducing the engine power (driving stability control), the TC (via the ABD) brakes the drive wheel that is spinning.
Since this control requires the drive wheels to be individually controlled, the ABS/TC system is a 4-channel system.
Switching off driving stability control*
Press the "TC OFF" logo of the rocker switch. Driving-stability control cannot be switched off during a TC control process (information light on).
One-sided wheel spin on the drive axle is further prevented by brake control up to a speed of 100 km/h.
Driving stability is not monitored, since the drive wheels can spin at the same rpm (slip).
With driving stability control switched off, the TC warning light in the instrument panel and the indicator light in the rocker switch are lit.
It can be advantageous to switch off driving stability control:
^ on a loose surface and in deep snow
^ when "rocking" the vehicle free
^ when using snow chains.
Switching driving stability control back on*
Press the indicator light in the rocker switch.*
Driving stability control cannot be switched on again during a TC control process (information light on).
* Press the switch for at least 0.1 second. Then a further 0.3 second will pass until the routine is complete. Only then is driving stability control switched off or on.
Diagram: ABS/TC 5.3 (4-channel system)
ABS ABS/TC component locations