Repair Services, Diagnostic Information, Application Guides, and More!
For over three years now I have been servicing cruise control amplifiers and actuators that were installed on various European brand cars. These systems were found in Mercedes, BMW, Porsche, and Rolls Royce during the 1970s, 1980s and early 1990s. These two systems were both designed and built by VDO.
The first type--vacuum actuated cruise control---was seen starting around 1975 in Mercedes Benz products and around 1978 in Porsche products. This first type uses a 10-pin amplifier to control a vacuum powered actuator. This actuator, using the vacuum generated by the engine, will pull on a throttle cable and adjust the vehicle's speed. It relies on a stalk on the steering column for control signals, a hall effect sensor (usually located in the rear of the instrument cluster) and the brake light switch on the brake pedal. Around 1981 Mercedes moved to the second type. Porsche made this change later in 1989.
The second type---servo actuated cruise control---was seen starting around 1981 in Mercedes-Benz products and around 1989 in Porsche products. This type uses a 14-pin amplifier to control a servo type actuator. This actuator differs from its predecessor in the fact that it is driven by an electric motor (rather than engine vacuum) and contains a feedback circuit. Like its predecessor the 14-pin servo actuator cruise system relies on the stalk on the steering column, a sensor (either in the transmission or instrument cluster), and the brake light disengage circuit. These units were seen in Mercedes up until around 1995. These units were phased out on certain models around 1993 when Mercedes moved to newer engines with integrated idle/throttle control computers (LH). These units were seen in Porsche from 1989 to about 1999.
Using the various electronic parts catalog and other information sources I have put together an application guide that should help you identify which amplifier your car might be equipped. There were various changes during production so there might be different amplifier models for the same car. If you have any questions please feel free to contact me with your VIN and I will do my best to get your questions answered.
If you are unfamiliar with the car, often times one of them most difficult things to do is locate the cruise control components. I have assembled a collection of amplifier and actuator location photos as well as some tips on how to remove the components. Some are easier than others, some can be a complete pain!