SACHS useful tip: Replacing CDC dampers.
Early in 2012, the twelve millionth CDC damper for passenger cars since the start of production in 1994 left the line at ZF Friedrichshafen AG’s Schweinfurt location.
Ride comfort and dynamics
More and more automotive manufacturers opt for the continuously variable damping system called Continuous Damping Control (CDC) in their vehicles. It permanently monitors influencing factors, such as the road condition, load, vehicle body acceleration, and driver’s actions. The vehicle sensors register all changes. From this, the control unit determines the optimal damping requirements. The proportional valve adapts the damping force in milliseconds for every single wheel.This means better ride comfort and dynamics, less rolling and pitching motion, and a shorter braking distance due to better road contact. Advantages that are increasingly also used in buses, coaches, trucks, and agricultural machinery.
1 Body sensor, front right
2 Sensor, suspension strut right (wheel acceleration)
3 CDC control unit
4 Body sensor, front left (body acceleration)
5 Body sensor, rear (body acceleration)
6 CDC damper, rear
7 Sensor, suspension strut left (wheel acceleration)
8 CDC suspension struts, front
If there is an electrical or mechanical fault, the CDC damper must be checked just like a conventional damper and replaced if necessary. Gerhard Endriß, a service engineer with ZF Aftermarket, dispels possible concerns among mechanics: “Even when you have to replace CDC dampers, no additional work on the electrics is required. In order to remove the CDC dampers, you only have to disconnect the plug from the wiring harness of the proportional damper valve and reconnect it during installation.”
The CDC system is capable of performing a self-diagnosis but it only recognizes electrical faults, not mechanical malfunctions. In the case of a fault, the CDC control lamp on the dashboard lights up. To narrow down the problem, a diagnosis unit (for example, the Bosch KTS) is required. It can be used to read out and delete the error memory. Depending on the vehicle, it is also possible to compare the target/actual values in order to check the sensors of the CDC system.
Replacement in pairs
Gerhard Endriß expressly points out that CDC dampers must always be replaced in pairs. To guarantee full functionality, the add-on parts – impact stops, protection tubes, and suspension strut mounts – must also be checked for wear before assembling the dampers. Every time the dampers are replaced, the service kit consisting of protection tube and impact stop must also be exchanged.
The service engineer explains: “Tension or strain on the dampers can be avoided by tightening the lower fastening screws only when the vehicle is standing on its wheels. After that, the wheel geometry is measured and readjusted if necessary.” After every CDC damper change which is carried out per axle, the system functions need to be checked. When the ignition is switched on, the CDC control lamp must go out after approximately ten seconds. That’s all: Your CDC damper system is ready for use again.