The drawers on many older cabinets and wall units ride on wooden runners, not metal slides. This low-tech system works well, but there's no mechanism for stopping the drawer. If it's pulled out too far, it crashes to the floor. The solution is install a stop block at the rear of the drawer.
Cut a small hardwood block about ½ X ¾ X 2 inches long. After boring an off-center hole through the block ¾ inch from one end, screw it to the rear of the drawer.
Turn the block horizontally and slide the drawer partially into the cabinet (above). Then, turn the block vertically and push the drawer all the way in. Now when you pull the drawer out, the block will hit against the cabinet face frame and stop the drawer. If you ever need to remove the drawer, just turn the block 90 degrees to clear the face frame.