GrumpyGel
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Sounds like the Haldex used in F2 and many other SUVs. Not so sure it is without problems though, there's plenty of F2s that have had their diffs chewed up by Haldexes that few (inc professionals) know how to maintain - just like the VCU!This is all interesting. The Freelander replaces a Nissan X-Trail and they have a completely different 4WD system. There's a multi-plate clutch in the nose of the rear diff which is electrically actuated, so you can have a switch on the dash for 2WD, "Auto" and "Lock". I thought that was a better system than the viscous one that LR use, and true enough, it was one of the few parts of the X-Trail that never gave us a minute's bother in the whole time we had the car
The Haldex setup looks to have cornered the market nowadays. I think the 'best' system was probably that employed on the RR and Subarus which have a center diff, so you do get a real distribution of torque, but with a VCU in there to limit slip so you have immediate locking when needed. The Subaru one was probably a better design because the VCU is engaged electronically, so you can pull a fuse and it is disabled - eg if you're running mismatched tyres, have a slow puncture or the VCU has gone tight etc.