If your VAG Group vehicle has four wheel drive then the drive to the rear wheels is likely through a Haldex coupling (depending on your exact model). It will require regular oil and filter changes, just like your engine does.
The coupling is a submerged multi-plate, wet clutch system that engages upon slip and transfers power to the rear final drive. The Haldex Coupling is a separate component from the Rear Final Drive, but is directly attached to it. The system is computer controlled with very fine engineering tolerances. If the Haldex oil is dirty, it will damage other parts and affect performance.
Dirty oil can overheat the coupling or cause the clutches to burn out or burn our the Haldex Pump and will lead to loss of rear drive and eventual failure.
The Haldex pump pre-charges the oil inside the Haldex assembly to allow the coupling to engage faster. This part is prone to failure on higher mileage cars or if regular maintenance in not performed. If your pump is faulty, you may experience loss of engine power to the rear wheels due to the pump becoming contaminated with old fluid and no longer activating.
Haldex Final Drive Differential – This is the mechanical system which provides the drive to the two rear wheels. This uses a lubricating gear oil which according to the owner’s manual is a lifetime fluid. Many of our customers however choose to replace this oil between 50,000 and 75,000 miles as a matter of preventative maintenance.