hi all. mid 90s columbus sl frame. campy cranks and 10spd 53/42 rings. 10 speed campy 11-28 cassette. campy 10spd chain. chorus 10spd shift/brake levers. it all works flawlessly - 99% of the time. every once and a while, mid ride, i can't seem to shift from the small ring to the big ring. it happened again just this morning. i only had about 9 miles left so I just rode it home on the small ring. when I got home, i immediately put the bike on the stand and it shifted from the small ring to the big one like it is supposed to. I then rode down the street and everything works!?!?! this scenario is about the fourth or fifth time this has happened since the spring. I currently have two other bikes one with 2x11 105 and one with 2x10 ultegra that have never had this issue. I have had other Campy bikes in the past that never had this issue as well. does anyone have any idea what is going on? thanks in advance

Don’t have a definitive answer, but would first try changing your front derailleur cable. I have the same setup on my early-80s Bianchi and when shifting was compromised, I did that first.

You might try tightening the shift cable juuuust a little tiny bit. Stretching over time may mean your full pull isn't moving the derailleur cage as far as it did previously.

When something's funky about shifting the FD, I always go back to the fundamentals.

1. height of derailleur cage
2. angle of derailleur cage
3. stop screw settings
4. cable tension

After all of that is correct, if I have some trouble shifting up, I'll ease up the top stop screw a bit, so the cable can give it a little extra "oomph" before settling into the correct position. This is precisely what the Di2 derailleur does--it pushes the cage a little "beyond" for an instant, then settles back down.

Thanks rsbob, Fahrenheit531, and terrymorse - all great tips! I'm confident that everything is adjusted properly. a new cable couldn't hurt.

also in addition to what Terrymorse has listed, it's good to give the outer stop on the FD just a bit more leeway to allow the FD to go a hair past the shift point.
Not enough to drop the chain, but enough to let the FD bring the chain over and have the ring catch the chain, even under a load.
On a bikestand, or easy riding, the shift will happen cleanly - have the chain under a real load and the shift may not happen...
I gave my Chorus gruppo away quite some years ago, when 10 spd became 'it'.
Ride On
Yuri

I would start with slightly backing off the limit screw. That is one of the most likely, and certainly the easiest fix. Another is making sure the cable is secured properly at the cable anchor bolt, including the angle of the cable exit. Some derailleurs are finicky at that attachment. I guess it messes up the amount of cable pull on the dr if not correct.

Thank you all for the replies