AWD uses a Viscous Clutch to transmit power to the rear wheels. On some, like the RAV4, it is controlled by a magnetic clutch in the rear, the front PTO is locked to the transmission so when the front wheels turn, so does the driveshaft. Power distribution is controlled in the rear.
I did a little looking around and the Ford system is similar with the Viscous clutch, which is a dry clutch in later models, similar to the Toyota with a magnetic coupling, attached to the rear diff. The PTU, which is what Ford calls it is connected to the passenger side CV axle, so it should NOT move when in park with the tires on the ground. It will move with them in the air and the rears on the floor in park due to the differential in the transmission when in park, same an any differential with the wheels rotating opposite of each other.
The PTU contains 3 gears and a ring and pinion. The input connects to the transmission where the passenger axle goes on 2WD, which is now a driven gear, the CV connects to the other side of it, there is a idler gear and the output gear that connects to the ring, the pinion then connects to the driveshaft.
Now this setup has me wonder. If the drivers wheel is spinning, then no power transmits to the other 3 wheels due to the differential inside the transmission. Seems like an odd setup, and without ABS it would not function at all with one wheel spinning.
I did a little looking around and the Ford system is similar with the Viscous clutch, which is a dry clutch in later models, similar to the Toyota with a magnetic coupling, attached to the rear diff. The PTU, which is what Ford calls it is connected to the passenger side CV axle, so it should NOT move when in park with the tires on the ground. It will move with them in the air and the rears on the floor in park due to the differential in the transmission when in park, same an any differential with the wheels rotating opposite of each other.
The PTU contains 3 gears and a ring and pinion. The input connects to the transmission where the passenger axle goes on 2WD, which is now a driven gear, the CV connects to the other side of it, there is a idler gear and the output gear that connects to the ring, the pinion then connects to the driveshaft.
Now this setup has me wonder. If the drivers wheel is spinning, then no power transmits to the other 3 wheels due to the differential inside the transmission. Seems like an odd setup, and without ABS it would not function at all with one wheel spinning.