I thought Posi Traction meant that both wheels turned at the same rate of speed/power and Limited Slip meant that the load bearing wheel would be slowed down and the un-loaded wheel would spin because the power would take the route of least resistance...?
My understanding is posi trac is GMs version of limited slip. It uses clutches and springs to apply pressure to the spider gears to in effect lock the to axles together. In extreme situations, such as going around a corner the clutches slip allowing the axles to turn at different speeds. Other types include a "rachet " type aka Detroit Locker.
An open diff still has spider gears, but no clutches or springs to "lock" the axles. A third type used in race only drag cars is the spool. It has a solid "spool" that bolts to the ring gear and splines for the axles. Not for the street !
If you jack up one side of a car with an open rear end, it would be easy to turn that wheel with the other on the ground. With posi trac it would be very difficult (if the clutches are in good shape) With a spool it would not turn at all. I think I'm close on most of that :
Just two different marketing names for the same kind of device; most use clutch packs (Eaton), some use cones (Auburn), some use ratchets (Detroit Locker). The device transfers torque from a wheel with no traction to the other wheel when one wheel is on a low-traction surface (snow, ice, etc.), and puts essentially equal torque on both rear wheels when both are on good-traction surfaces (a conventional "open" differential favors the right rear wheel at all times, and can't compensate for traction loss). The clutch packs slip to some extent to allow different wheel speeds when turning a corner, but are essentially locked up when moving straight ahead on an even-traction surface. They all do the same thing, just accomplish it differently. Lots of marketing names (Positraction, Limited-Slip, Sure-Grip, etc.), all have the same function.
Limited Slip Differential ... STP oil treatment. Remember how popular those blue & red STP oval stickers were back in those heady days of AA fuel altered dragsters?. In mid-sixties I had a sticker on my wheels (a skateboard) ... sticker looked just like the STP one ... 'cept it read LSD:eek :eek :eek