I figure it out from doin some research. The following quote in from an article sent to my by Quaife engineering. The open differential spllts Torque 50/50 all the time. It doesnt however split POWER 50/50. Power as u may know is torque times rpm or wheel speed. So when one wheel starts to spin and the friction limit is met the Power is limited or Torque if u divide out the wheel speed.
This is why braking works. Applying the break increases friction so in order for the wheel to continue to spin at the same speed more torque is needed sending more torque to the other wheel.
Same as with the Transfer Case which I was wondering about. A locked rear will increase the overall demand for torque, limited by the power the locked rear can transfer to the ground, from the engine that is split 50/50. More Torque will go forwards with a real locker, however you are still limited to the Power the wheels can put to the ground.
Illustration 1A and 1B show the common open differential. The driving torque, taken from the ring gear passes through the differential housing to a crosspin, which passes the torque to the spider (or planet) gears, thence to the output, or side gear. The open differential always splits the torque 50% to each wheel. The even torque split gives the most predictable handling and is easiest to set up, tunable with just springs, swaybars and dampers and caster. Handling is consistent through a wide range of power application.
The limitation of the open differential is that the thrust available is limited to the maximum thrust (acceleration grip) of the wheel with the poorest grip. Again, with a 50-50 split of torque, both tires have exactly the same thrust, limited by the tire with weaker grip.