2003 Jeep Grand Cherokee 4-w drive

The positrack in the rear is locking up every time I turn. What can I do?

“What can I do?” You can provide a more detailed explanation. That’s what you can do.

This differential (D44A with Veri-loc) requires 75w140 synthetic lube with 4 oz of friction modifier added. Most likely whoever changed the fluid last time did not add the friction modifier.