Campag front mech slipping under load: any ideas?

When out of the saddle sprinting my front mech slips inwards from the big ring - it's not enough to derail the chain but it starts rubbing. Shifters are 1994 Record, front mech is a 2003 Centaur triple.

The frame (1994 Litespeed Catalyst) probably isn't the stiffest around. I tried replacing the ratchet g-springs and the ratchets themselves are in good order.

Any other ideas to stop this happening?

Sometimes it's worth taking a close look at the spring mount ring (EC-RE112), they can crack through, though it's not that common on LH - happens on RH much more often, I guess as the number of shifts is far higher.

The damage isn't always easy to see but you can open it out with your fingers if it is cracked.

The heels of the springs will also waer little depressions in the mount ring so it's usually worth changing it for that alone, as the depressions prevent the spring from holding the ratchet as tight as it might otherwise do.

When we do a lever service, we replace the mount rings along with the springs as a matter of course, for just this reason.

Frame flex *might* do it, but I'd be surprised. You'd likely hear it, too, as the lever would be forced to "snap back" a notch ...

Thanks, that's really helpful!

It's also worth checking your set up - if the FD is coming up against the high limit screw part way between clicks, then the cable will be held under a fraction more tension as you push the lever across to acheive the click & the FD doesn't move any further.

A pull or sometimes a jolt will then cause the ratchet to slip back a notch. This is the downside of a non-gated ratchet ... the upside is that you can conveniently service it

In theory this particular problem should not happen as the FD should overshoot the final resting place of the FD cage, which should come up against the high limit screw only momentarily on that last click, in order to push the chain fractionally beyond the big ring before nudging it down onto the teeth of the big chainring. There is a small amount of "slop" built into the clicks to allow this to happen.

This can be a problem with initial set up, or it can occur with cables settling in with use - what was a good set up initially can "gain" a click or a part-click as ferrules are pulled fully onto the outer, or pulled hard into the locations on the frame - this all gets worse if some cheaper, lower-quality outers are used, ditto plastic ferrules, ditto in-line adjusters of poor design ...

A good tip which I will have a look out for with the limit screw. The cables and outers are all Campag ones, so should be OK.

Last one to look at - levers fully tight on the bar? If the lever can move (likely out of the saddle on full gas) you might get phantom shifting but I think you'd notice the displacement of the lever ...

Yep, if all Campag cable you should be OK on that score. Not so many of the 3rd party alternatives ...

The lever is definitely tight. I can hold the mech over when out of the saddle by holding the paddle across a little, so I suspect that your suggestion of a cracked spring mount ring is right. It looked OK, and the holes did not appear worn as it was a bit of a fiddle to get the G-springs to fit in the holes, but I can't say I looked specifically for a crack.

I'd guessed at first that one of the two G-springs was broken and was really surprised to find both intact. When one snapped on the rear/right shifter the shifting was fine but with soggy lever action. I'll also check if the front mech has an adjustable spring tension. I can't remember whether it's Campag or the 'fishing tackle people' but I know somebody's does.

Re:

Nothing I know of in Campag-land with variable FD sping tension

Definitely sounds like spring mount ring issues ...

Finally fixed it! The spring carrier indeed was the problem, although it wasn't cracked. Putting the replacement (thank you Hewitt Cycles) next to the old one it was clear that the old was ovalised and therefore the ratchet springs were pushing less hard. New carrier and bingo: the shifters are a bit more clicky and heavy to use, but the ghost shifts are gone.

Many thanks gfk_velo on where to look for the problem.