Volvo Forum + Help for Owners
We get many questions in the MVS Volvo Forums regarding Volvo’s AWD system. Longtime forum contributor Jimmy manages to write almost everything an owner (looking for an AWD system overview) would want to know. Jimmy’s explanations cover the first three Haldex generations specifically. . Here are his words, edited and formed into a summary.
There are a few different systems.
Gen 1 that is the 850 platform is the delicate one.
Gen 2 2001-2002 XC70 is less so but still needs care.
All others since then are very low in problems other than a pressure/temp sensor that has been updated.
The front drive connection to rear drive is via wavy discs splined alternately to input and output with a silicone gel, viscous coupling, VC.
There is also a one way clutch in the VC that is overridden up to approx 30 mph so you can have power to rear wheels in reverse.