Most new bi-fold doors hang from the top only. The reason for the track on the bottom is to help align the doors when closed and provide a little additional stability. You might consider a by-pass set of doors for the replacement.

You can replace the old hardware with bifold door hardware that doesn't require a bottom track. You can find the hardware a your local home center. If you want to order online:

http://www.johnsonhardware.com/fdindex.htm

Model 1700 is sufficient for most bifold doors.

Mike

I haven't seen mirrored bi-fold doors, but it makes sense that they would have a bottom track as they would be quite heavy. Hollow-core wood bi-folds only need a top track and a bracket at the bottom corners. The hardware usually comes with the doors.

Should be fairly easy to remove. Most have a spring-loaded rollers. Just push down, and slip the door out of the track.

David