Actually the quaife does use gears, not clutches. It uses a gearing system that basically drives the gears into the housing of the diff to "lock" the differential. The housing is made out of billet steel to give longevity and assure that it will not "grenade".
Here is a pic of how the Quaife works:
More info on the Quaife can be found on their homepage:
Quaife
