How does a variable torque split diff work. In the cossie its 66.666 rear 33.333 front. How can you control the amount of torque going to one diff but not induce slip at the same time?

If it was like a viscous coupling would you not just induce slip? I have never really sat down and thought how that works and would be interested to know. I expect that from the answer to this question I will be able to work out how an evo works when it varies the torque front to rear and side to side in the later models.

Any info would be appreciated

Thanks Steven RW