I've got a 09 Specialized Tricross Sport which came set up like so:
- 50/39/30 JIS (square taper) crankset
- 68x103 JIS bottom bracket
- Tiagra triple front derailleur
- 11-34 cassette
- Deore LX long cage rear derailleur
I changed the crankset and cassette so that it is set up like so:
- 46/34/24 Stronglight Impact JIS crankset
- 68x110mm JIS bottom bracket (Stronglight recommends a 110mm-width bb)
- (original) Tiagra triple front derailleur
- Sram 12-26 cassette
- (original) Deore LX long cage rear derailleur
I installed the bottom bracket and crank arms per the instructions on bicycletutor.com, including tightening the bb's drive side to 300-350 in lbs and torquing both crank arms to 420 in lbs. I used a Park TW-2 torque wrench.
I adjusted the front derailleur per the Tiagra triple derailleur instructions, setting height 1-2mm above the big ring, setting the rotation parallel to the rings, setting the stops correctly and setting the tension to allow me to trim in the middle ring.
The set-up allowed me to shift into all cogs from the middle ring and shift easily into the big or small ring, without dropping the chain off of the big or small ring. I test rode it shifting into any combination I could think of and it worked great.
Then, early into my ride the other day, I shifted from my middle to my small ring at the base of a hill, crested the hill and shifted back into my middle, and at the beginning of the next hill, when I shifted my derailleur to my small ring position, the chain just wouldn't derail onto my small ring; it would just rub against the front derailleur but not shift.
I tried adjusting my low stop but it's let out all the way and when I manually place the chain onto the small ring, with the derailleur in the small ring position, the chain is perfectly centered between the sides of the derailleur cage.
I tried adjusting my cable tension but that produced no effect.
My front derailleur's height looks great, 1-2mm above the big ring when shifted into the big ring.
I can still shift between the big and middle rings and trim the middle ring.
Again, it was working and then it spontaneously decided to stop working. I'm all ears, or eyes, I guess.