Because I put my take on the AWD 4404 in some post that might get lost, I am copying it here.
The AWD a differential permanetly engaged. It will lock ONLY when the difference in speeds between front/rear AXLES is high for a certain time - like when your front or rear wheels are on snow). In that case, the
Viscous Coupling fluid will become hot and change from a thin liquid a very thick solid-like fluid, locking the inner part to the outside part of the VC.
Otherwise is a 35/65 split between torque/power of the front/rear axles (in normal driving).
First, some 101 about epicyclical differentials:
http://en.wikipedia.org/wiki/Differential_gear#Epicyclic_differential
The rear shaft is connected to part #225, that in turn is connected inside the annulus (#322). The front shaft is connected via the #83, #18, chain #90 and gear #63 to the INSIDE part of the VC (#64). The outside of VC is connected inside the annulus (#322), therfore directly to the rear shaft.
So, when the liquid inside VC is thin - the shafts spin independently via the differential and chain. If liquid spins faster inside VC (because of difference in axles speeds) it will heat up and thicken. Now the front and rear shaft are semi-solid connected thru this semi-solid/thick liquid (the chain ratio is 1:1 and the epicyclic ratio give the final ratio beween the shafts torque/power). The power will go on the axle that is not rotating, but the friction transfer via liquit will heat it (the liquid) up. A lot.
Input shaft (#107) slides, without connection, thru the VC and goes inside the sun part (#65) of differential.
Chanses are, once you remove the front shaft and the VC runns hot for moths in row, the VC is fried. You cannot put another front shaft back in, probably will bind on ondulations in highway and eat the tires or worse.
If the VC doesn't fry from running hot prolonged periods of time, then it is a great pice of engineering.