I have an external Apple floppy drive, model M0130. It doesn't take any disks I try to feed into it. Any given disk will only go so far.

Here's a picture of its internals: http://i.imgur.com/3lKgwaD.jpg

As you can see from the top middle part of the photo, the disk goes in as far as it can. No other mechanisms are triggered, nothing happens. It just sits loose in there.