I think the power for the rear wheels comes off of the front differential. On the Civic Wagons there is a viscous coupling on the drive shaft that allows the front wheels to power the car normally until they begin to lose traction. When there is a difference in speed (about 3%) between the front and rear axles, the viscous coupling will send power to the rear wheels. The CRV has a more complicated system that I've heard doesn't work any better.