A transfer case for a motor vehicle. An input is rotatable about an axis to receive torque, an output is rotatable about the axis to transmit torque, and a planetary gear set is rotatable about the axis and operatively coupled between the input and the output. A shift sleeve circumscribes and is axially slidably carried along the axis, and a shift sleeve lock is automatically engageable with the shift sleeve responsive to the transfer case exceeding a predetermined rotational speed, to prevent axial movement of the shift sleeve above that speed. A related method is also provided.