Here's why the rear might feel like an open differential in 4WD:
* Part-time 4WD System: Part-time 4WD systems are not designed for use on dry pavement. When engaged on dry pavement, the tires may spin at different speeds. The front and rear axles rotate at different speeds during turns because of the different turning radii. This difference in rotational speed is what makes the rear differential *seem* like it's open. The system isn't designed to handle this constant speed differential under these conditions. One axle can overpower the other, resulting in a loss of traction and the sensation that the rear is disengaging.
* No Automatic Locking Differential: Your truck likely doesn't have an automatic locking rear differential. This means there's no mechanism to automatically lock the axles together when one wheel loses traction. On dry pavement, this isn't a problem in 2WD, but in 4WD, the varying speeds can create binding and cause one wheel to spin while the other does not.
* Transfer Case Operation: The transfer case distributes power to both axles. On hard surfaces, the different speeds between the front and rear axles lead to binding, torque distribution issues, and the feeling that the rear is acting like an open differential which is allowing only one wheel to spin.
In short, the behavior you're describing is typical of a part-time 4WD system used on dry pavement. It's designed for off-road use where all four wheels need equal traction. Using it on dry pavement can cause premature wear and damage. Always use 4WD only when necessary, such as in mud, snow, or ice, and disengage it once traction is no longer needed.
