And the debate is ON!!!!
The 4WD vehicles were simpler. The output shaft from the transmission went into a transfer case where the engine power was split between front and rear driveshafts. In 2WD, the rear driveshaft turned a pinion inside the rear differential, spinning a ring gear that turned the right and left axle shafts, eventually turning each wheel. With the transfer case lever engaged in 4High or 4Low, a fork would engage a chain drive, turning the front driveshaft and pinion (at the same speed as the rear driveshaft) in the front axle's differential, also turning the ring gear and right and left front axle shafts, then the wheels. This is also referred to as a "part-time" 4WD system because the 4WD had to be manually engaged, and without a center differential it could be used only on low-grip terrain or driving surfaces.
AWDAccording to the Society of Automotive Engineers, an all-wheel-drive vehicle is one with an on-demand feature that occasionally or intermittently sends power to the non-primary powered wheels. The most basic systems often begin with a front-drive platform with some kind of power-splitting differential housed inside the transmission in or in a separate box. AWD is able to send rotational power through a prop shaft to a rear differential where power is directed to each of the rear wheels.In some cases, a certain percentage of engine power is sent to the rear wheels, until the computer sensor detects front wheelslip and redirects more power. Many crossovers or small SUVs were originally developed from passenger car platforms, so the AWD systems were adapted to work for the platform, rather than being designed specifically for that vehicle. Although this type of system doesn't offer an extra low-range gear, it does provide a good amount of traction in snow, rain, or icy conditions when the computer system can detect small and large amounts of wheelslip between front and rear wheels. Just as 4WD systems have benefitted from the advancement of added computer power, so have AWD systems
