To tighten the box you must turn counter-clockwise. The box is not supposed to be adjusted on the car as the torque necessary to turn is to be measured as the adjustment is made. With that said the consequence to to much tightening is a car that goes where its pointed and has to be constantly corrected - the natural road following tendencies are overcome by the stiffness.
If you grab the coupling, at the box, with one hand from above and gently rotate back and forth one can "feel" the play. If you tighten the screw slowly you can feel this play go away. On this car its pretty easy and can easily be corrected if gone too far.
BTW what you are actually doing with this adjustment is raising the pitman shaft. The input shaft has the recipricating ball cylinder threading its way up and down the input shaft. It has a ball attached to the bottom which fits into a cup at the end of the internal pitman shaft arm. Raising and lowering the shaft engages the ball into the socket. When there is play the ball is loose in the socket. When its tight the arm drives the ball upward driving ball cylinder against its threads locking up the mechanism.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician