Automatic limited slip differential

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Automatic locking differential (ASD), SA Code 211 , English: Automatic limited slip differential was a limited slip differential system, which was applied in vehicles from Mercedes-Benz. The system was replaced by the electronic traction control system ASR in the 1990s .

The ASD is an electro-hydraulic operating system which serves as a start and during spinning of the wheels differential completely blocked. Better traction is thus achieved. A disadvantage of the ASD compared to comparable systems is the higher susceptibility to malfunctions and defects due to the higher number of components.


The system has the following assemblies:

Mode of action

The control unit uses the wheel sensors to determine the speed of the driven and non-driven wheels, at that time at Mercedes generally rear-wheel drive . If one or both drive wheels turn 2 km / h faster than the non-driven wheels, the ASD is activated up to 35 km / h. The ASD hydraulic unit is activated and a pressure of around 30  bar acts on the ring cylinders of the axle shafts. The drive bevel gears are pulled outwards and lock the differential. Intervention is indicated to the driver by the function display. At speeds above 40 km / h, in coasting mode and when braking, the lock is not activated or it is released so that the vehicle does not tend to skid. In these driving conditions, the multi-plate clutches act like a self-locking differential with a fixed locking value. A diagnostic program integrated in the control unit monitors the ASD system and switches it off in the event of defects. The driver is informed about this via the fault display.


  • Workshop information service (WIS): Mercedes-Benz S-Class
  • Europa-Lehrmittel, Fachkunde Automotive Engineering , Edition 2001, page 428, ISBN 3-8085-2067-1