There are a few fallacies being propogated above. First, check out a couple articles I wrote on this subject probably ten years ago. While a little wordy, they seem to be effective on explaining the differences between lockers & LSDs.
What? Why do I need a locker? I thought I had 4X4! -
4x4 & Torque answers -
Essentially, a LSD increases the torque delivered to both tires in low traction situations, and it does so in the usual 50:50 split. It increases torque by coupling the tires on an axle together so the tire with the most traction can create more resistance for the engine to work into. The engine can only deliver as much torque as it takes to get one tire spinning.
Automatic lockers don't lock when they sense poor traction, their normal mode is 100% locked. What they do automatically do is un
lock (!) when the outside tire in a turn is trying to rotate faster than the inside tire, as it must do. When the tires are again turning at the same rpm, an automatic locker locks back up. An automatic locker is always locked unless you're turning left or right.
Where a LSD is concerned, which is true for both the Jeep Tracloc and the Detroit Truetrac, is that when one tire is in the air with no traction available to it, it does not "lock up". All it does is help couple the resistance of the tire still on the ground to the tire in the air so the engine sees more resistance so it can deliver more torque to both tires on the LSD-equipped axle.
An engine can develop very little torque when it is not working into a resistance. So to some extent, a LSD slightly increases the amount of resistance the engine sees so the engine can then deliver slightly more torque to both tires... equally. A LSD doesn't ever "transfer torque" to the side with more traction, it simply slightly increases the amount of torque delivered to both sides.
Where a locker is concerned, it totally locks the spinning tire to the tire with good traction so it dramatically
increases the amount of torque delivered to both sides.
To my way of thinking, LSDs are not good in terrain where both tires on an axle are not usually firmly in contact with the ground, at least they are not nearly as good as a true locker is in those situations. I consider a LSD's primary benefit to be on the street where all four tires are in contact with the surface. Off-road, much less so.
So for paved road use, a LSD is best. But in my strongest possible personal opinion, a locker is by far the best traction enhancing device for offroad use..
I wish I had known this 16 years ago when I installed front/rear Detroit Truetrac LSDs into my previous TJ. In the very uneven terrain I prefer wheeling in, the Truetracs were not very effective at all. Within a couple years I replaced them both with true lockers and the offroad benefits of the lockers was nothing less than dramatic/startling/grin-producing... day and night differences.