It has now been several years since I last opened up a 400K drive, so my memory is foggy on certain details. But I can say with certainty that two things make direct contact with the floppy media. The head is one (of course), and the other is a piece of felt on a post (?) that pushes on the other side of the disk to ensure intimate contact of the media with the head. If the felt has been worn away or ripped off, then the disk will not make reliable contact with the head.