I recomend that you go to the eaton web page and learn all about it first hand. they have a movie of how a locker works from the inside ( cool solid modeling)
from the page:
>Posi? Locker? What's up with that? Seems you'd expect an >Eaton Posi system to provide positive traction under any >conditions, right?
>And a locker? Seems a locker should be a differential with >the axles locked together all the time… Makes sense, right?
>Obviously, you can't have the rear axles locked together >all the time. That would make turning a corner pretty >tricky. And Eaton Posi? Well, keep in mind that's our >trade name for the finest "limited slip" differential >available on the planet.
>Basically, the difference between the two is this: A >limited slip differential sends power to the non-drive >wheel based on input torque; that is, power coming to the >axle from the engine.
>So, when high torque comes to the differential and both >wheels are on a high traction surface, like a drag strip >or country road, and high torque is delivered to the axle, >the clutch pack clamps the gears to the differential case. >This clamping action is in proportion to the torque >delivered. The higher the torque, the higher the clamping >load.
>The idea here is to prevent wheel slip -- at either wheel -- in the first place. If one wheel starts slipping before >the other, the clamping force drops in proportion to the >torque delivered to the slipping wheel.
>The whole point of the torque sensing limited slip >differential is to reduce the likelihood of wheel slip.
>The locking rear differential locks the drive and non->drive wheels together based on wheel slip at the drive >wheel, regardless of engine power input.
>Want some details on that? To take a quick look at the >difference between these two and figure out what's best >for you click Mechanical Locking Differential or Limited->Slip Differential.