On Sat, 26 Dec 2009 16:19:28 -0800 (PST), Jo Ann
wrote:

Hello all,

I am a newbie to the group, relatively new homeowner of a relatively
old home (late 1800s). I'm not an especially skilled DIY'er, but not
a complete idiot, either. Needless to say, with an old house to
maintain, I learn more every day!

My current issue is a bifold single door that will only open about
halfway. It's not off the track and doesn't visually appear to have
anything wrong, but when I try to fold it open more than about
halfway, it resists and feels sort of "sprung." I can force it back
all the way by pushing on it really hard, but it won't stay. It
doesn't drag or stick, opens smoothly to about halfway. It happened
suddenly -- opened it once and it worked fine, opened it the next time
and it wouldn't open all the way. It feels as if there is something
caught behind it keeping it from opening all the way, but there's
nothing there. It's the kind that hangs from a plastic/nylon roller
in the top track and pivots on the lower corner (no track on the
bottom). I've had a lot of bifold doors before and thought I knew
every way they could go wrong, but this is a new one on me. Any
ideas?

Thanks in advance,
Jo Ann

I would check the roller and see if it's damaged. The "plastic/nylon
roller" can have a piece (think flat tire) broken off and not roll
correctly in the track. Also check that the track is secure and not
moving about, flexing or such.

Perhaps the hole for the roller (drilled in top of the door?) is
"wobbled" out and flexes the roller during movement.

Perhaps a screw holding the track has broken, causing the track to
flex a bit.