That's normal for part-time 4x4 systems without a center differential (like the Tacoma). Without the center diff, the front wheels and the rear wheels are both being driven at the same speed. But when you turn the front wheels to the side, physics dictates that they cannot turn at the same speed as the rear wheels.
Because of that, you get the binding problem on dry pavement. If the pavement were wet/slippery, the front wheels could slip a little bit and not cause the binding. So, it's best to only use the 4WD modes when necessary due to slick pavement conditions or off-road.
In contrast, vehicles like crossovers with AWD or some SUV's with 4WD have a center diff that mechanically allows the front wheels to turn at a slightly different speed. Then there is no binding at all, and those systems can be driven with power to all 4 wheels all the time. If the center diff can be locked, then locking the center diff would take it out of the equation and then it's just like there is no center diff.
2013 Highlander Limited
2009 Tacoma DC SB TRD Sport 4x4
Retired: 2000 Tacoma Xtra Cab V6 TRD Off Road 4x4
Last edited by toto; 11-20-2011 at 07:47 AM.