Predecessor 4WD System
Before xDrive, BMW offered 4WD as an option in the 1980s for the 3 series and the 5 series. The system had a planetary center differential with a permanent 38-62 (front-back) torque split. Both the center and rear differential had a viscous lock which would engage automatically if slippage occurred (one shaft rotated at a significantly different speed compared to the other). The front differential had no lock of any kind.
4WD was again offered for the X5 and the 2001 3 series. The system was similar to the earlier system except without any of the locks. Instead, slipping wheels would be braked with the DSC system, helping transfer power to the wheels with traction.
Read more about this topic: BMW X Drive
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