The all wheel drive doesnt work only the front tires spin in the snow

The 08 Vues AWD system is very different than from previous models. The new Vues system is more like the technology on the Outlook. I' don't know detail on the hardware, but from a function standpoint there are two big differences:

1)The system is PREDICTIVE, not reactive. It does not wait for wheel-slip to make it engage. The system monitors throttle position, steering angle ect. and re-directs torque before wheel spin occurs.

2) The old system sent extra torque to the wheels that were slipping to boost traction. The new system sends power to the wheels that are gripping.

The result is a better, smoother system that will do a better job of keeping the Vue from getting stuck.

The old system was a single gerotor type AWD system. Essentially, a gerotor AWD system uses differences in rotating speed to spin a pump and apply pressure to clutchs. The single gerotor system used in the Vue essentially engaged and disengaged the rear axle when a differences in rotating speed occurred between the drive shaft and rear differential (indicating the front wheels were spinning faster the rears). From here on out, power goes into an open differential and was distributed accordingly (i.e. not very well).

GM also uses a twin gerotor system in the form of Versatrak. This operation in much the same manner, using a difference in rotating speed to spin up a pump and apply pressure to clutches, except the Versatrak system has a pump for each output axle. This allows the rear differential to act of each rear axle much in the way a limited slip differential does, better managing torque distribution.

The new system used in the Vue (as well as the Outlook, Acadia, and Enclave) is controlled by a microprocessor and operates by means of an electromagnetic clutch. It is very similar to the Haldex system marketed by Haldex Traction AB. The main difference being that Haldex still uses hydraulic pressure to apply the clutches, while the electromagnetic system used by GM (which I believe is developed by Borg Warner) uses electromagnetic force to apply the clutches. The operating principles are the same though. The new GM system is well integrated with stability control, traction control, and ABS. The system actively monitors vehicle dynamics and driver input to determine when to being engaging AWD before it is actually needed. With the ability to manipulate power delivery using AWD and stability control (by selectively applying brakes at each individual corner), the new Vue is very robust in terms of torque management. For all you folks in the snow belt, it should be dynamite in slippery conditions!

Hope this helps answer your question. Good luck and be safe on the snow.