(Wiki)The viscous type is generally simpler, and relies on the properties of a dilatant fluid - that is, one which thickens when subject to shear. Silicone-based oils are often used. Here, a cylindrical chamber of fluid filled with a stack of perforated discs rotates with the normal motion of the output shafts. The inside surface of the chamber is coupled to one of the driveshafts, and the outside coupled to the differential carrier. Half of the discs are connected to the inner, the other half to the outer, they alternate inner/outer in the stack. Differential motion forces the interlocked (though untouching) discs to move through the fluid against each other. The greater the relative speed of the discs, the more resistance the fluid will put up to oppose this motion. In contrast to the mechanical type, the limiting action is much softer and more proportional to the slip, so for the average driver is easier to cope with.

Viscous LSDs are less efficient than mechanical types, that is, they "lose" some power. They do not stand up well to abuse, particularly any sustained load which overheats the silicone results in sudden permanent loss of the LSD effect.[4] They do have the virtue of failing gracefully, reverting to semi-open differential behaviour, without the graunching of metal particles / fragmented clutches. Typically a visco-differential that has covered 60,000 miles or more will be functioning largely as an open differential; this is a known weakness of the original Eunos Roadster sports car. The silicone oil is factory sealed in a separate chamber from the gear oil surrounding the rest of the differential. This is not serviceable and when the diff's behaviour deteriorates, the VLSD centre is replaced.