Front derailleur problem?

Jason Spaceman wrote in message ...
I have a 2004 Trek 5200 with a double chainring and Ultegra derailleurs,
brakes,
crank, etc.

Every so often, when I am climbing, I will attempt to shift from the large
chainring
to the small ring. Instead of the chain shifting to the small ring it will
fall off
onto the bottom bracket frame shell. I then have to stop, get off the bike,
and
move the chain back onto the small ring.

I'm wondering what the problem could be. Does the front derailleur or
shifter need
adjusting? This only happens when I am climbing, and even then only once
every so
often; but it can be a pain in the ass.



Chainring diff. too great. Loose BB. Loose crank. loose chainring. Gap
in fork of shifter too great. Rear wheel/chainstays out of alignment. BB
shell out of alignment. Cain tension insufficient. Overshift by mech..
Chainrings too close to each other.
All the above. I like half step.
TJ