Originally Posted by pauld73
Select Trac has special differential gears that can slip when the front and rear tires are turning at a different speed.
Not exactly for the KK (2008 and newer), but close. The select tract does not have a differential like the older cases. It has a locking system to lock in the front driveshaft similar to the command trac except that the locking mechanism contains a clutch pack that allows slip. The amount of lock is variable and controlled by the computer. When the computer senses wheel spin, it will engage the clutch with more force. So in normal everyday driving in 2WD mode, there is not any difference between the two cases operation (some say the command trac may be stronger but I dunno). The select trac in automatic 4WD mode will engae a bit of the clutch, so you do feel it on turns and it does put more wear ant tear on the front end. The select trac will completely lock in 4WD low.
The select trac is by far the best case for the street, especially for those that want to set and forget. Run it all year round. Yes it is true 4x4 case and yes if the other drivers in the family forget to switch out of 4WD there will be no damage to the vehicle. That is one of the biggest advantage.
The traction control works the same on either system, uses brakes to slow down a spinning wheel. The optional system available on the grand cherokee and commander adds computer controlled locking difs, but those are not available on the KK.
If you are off roading in low range there is no difference in the KK case capability. In high range, either one will pull you through when only one wheel has traction. Get the selectrac if you can find one.