bi-fold hardware assistance

Hi! I have several bi fold doors that keep falling off their contact points, both the stationary and moving (on track) points. The doors are old and super heavy, and the pieces are well worn. The piece that runs on the track stays in the track, but the door unscrews itself from that piece. It also falls off the stationary side because the screw isn't long enough to keep it there. I am looking for possibly longer screw or base components so they'll stay in place? Any help would be much appreciated!