ACCESS:
Remove the screws securing the plastic cover (flap attached) located under the front edge of the pelvic cushion.
IF LOCK LEVER HAS PLAY SIDE-TO-SIDE:
Tightening this bolt will reduce the space between the plates which reduces the play in the locking lever. Be sure the lever is not bound so that it cannot move.
IF TEETH ARE NOT ENGAGED FULLY:
Use two 1/2" wrenches to tighten this bolt to increase the pressure of the lock lever against the rotation casting.
This will assure that the teeth are fully engaged.