dozer

The optional hi-end transfer case in '95 ZJ's (grand cherokee) used a viscous center-diff. One big problem with that case: it didn't lock up in LO either! Which was kind of a drag off-road. Didn't start sending power to front until there was already a 5 or 15 (?) rpm difference between the driveshafts...which was usually too late <g> If you have one, and stand on the brake to smoke the rear tires, you'll burn up the viscous coupler. They're not meant to have an rpm difference across them for any length of time. It also prevents you from limping home on the front only...i.e. if you break a rear shaft, then drop the rear driveshaft to limp home. You can do that with a good ol' "locked" type t-case, but not with a viscous coupler. They tended to get burnt up by being towed too...until the tow-truck drivers all learned about it. I think you'd smoke the Subaru clutch-pack diff too, with sustained rpm-delta (slip) across it. Not enough heat-dissipation capacity... These center-diffs are basically meant only to slip for brief periods. To prevent 'windup' in the driveline on hard surfaces.