There are lots of options on posi units, OE and aftermarket. Some use multi-disc clutches, others have cone clutches, and one called a Detroit Locker actually mechanically locks the two axle gears together when one wheel starts to spin. That one ratchets over itself in a low-speed turn and makes all sorts of clicking noises- - - -no way to quiet it down. It's possible someone installed a limited slip carrier sometime in the truck's past. Positraction, Trac-Loc, No-Spin, and a bunch of other names have been given to traction-equalizing rear ends by various manufacturers. All of them allow the axle speeds to differentiate in a low speed power-off turn, but lock up if a wheel slips excessively.
Jerry
