Question for the Campy experts

[glepore]

2015+ 11 spd sr rear derailleur, sram red (quarq) crank, kmc chain. On an Ottrott with a good chainline.

Very occasionally, but enough to be annoying, when "sweeping" to multiple larger cogs (lower gears, say at the base of a hill) or shifting both front and rear semi simultaneously, the chain slips off the lower jockey wheel to the inside. The only way I notice is the noise, everything continues to function normally.

Ideas? I'd just throw a jockey wheel at it, but the sr's aren't cheap.

[fmradio516]

Derailleur hanger straight?

[Tony]

Worn chain?
Should mention NOT a Campy expert.

[glepore]

Yes and yes. Newish chain and hangar is good. I know that with some Campy rd's there was talk of the actual cage "wearing" out of alignment, but if I recall that was pre 2015, but my memory might be faulty.

[ultraman6970]

Did you check if the lower jockey wheel is cracked?? maybe is not straight??

[bikinchris]

Did you check if the lower jockey wheel is cracked?? maybe is not straight??

That's would what I would try first. Worn, cracked jockey wheel. I don't know if that is a directional pulley. It could be on backwards.
If Campy jockey wheels are expensive, maybe look for BB Infinite replacements. They were less than SRAM Red for my wife's bike,

[kramnnim]

So the RD is suddenly taking up a lot of slack in the chain?

[Hindmost]

"...front and rear semi simultaneously...". Are you asking too much of the rear derailleur?

[dddd]

This might in part be an "A"-tension issue, as the cage may be contacting the largest cogs that you are sweeping toward, thus causing the cage to suddenly turn counter-clockwise, thus causing momentary loss of chain tension.

This would be most likely if the cassette is at the extreme of the largest size offered, since it's common for folks to use as much "A"-tension as possible in order to preserve shifting response toward the small end of the cassette.
Reducing the "A"-tension would help with cage contact if this can be done without hindering shifting quality over the smaller cogs, especially while in the big ring.

Look for any signs of contact between the outer cage plate and the cog teeth as an indication that the cage plate might be "snagging" momentarily on the rotating larger cogs.

Moving the paddle more slowly during sweeps toward the larger cogs will also allow more uptake of chain along the larger cogs, which will tension the chain more and thus tend to rotate the cage favorably in the CCW direction, sparing contact between cog teeth and the cage.

[rain dogs]

"...front and rear semi simultaneously...". Are you asking too much of the rear derailleur?

No way... this is one of the things that is excellent about the function of Campagnolo and has been since forever way back to the 2000's. You can drop the chain at the front and shift 3/4 cogs in the back simultaneously, no change in cadence, no a second of hesitation. You should be able to push both thumb buttons pre-climb all the way through all clicks in one motion and land in almost exactly the same gear inches, but with the range needed to then go up the climb just surfing the cassette. Not being able to means something is wrong.

Re: the OP question, if it isn't a damaged pulley then I'd think it must be with the h-screw and the clearance between the top pulley and the cassette (the job formerly done by the b-limit screw.)

However, I'm just trouble shooting/guessing as I have never ever seen or experienced the issue described.

The last thing could possibly be a stuck link on the chain or a bad quicklink but again..... that's a weird one

[oldpotatoe]

Cage been removed and reinstalled up side down?
Cage a wee bit 'bent'? Somehow.

[thwart]

No way... this is one of the things that is excellent about the function of Campagnolo and has been since forever way back to the 2000's. You can drop the chain at the front and shift 3/4 cogs in the back simultaneously, no change in cadence, no a second of hesitation. You should be able to push both thumb buttons pre-climb all the way through all clicks in one motion and land in almost exactly the same gear inches, but with the range needed to then go up the climb just surfing the cassette. Not being able to means something is wrong.

This. Do this several times every ride (both up and down, but down more frequently) and it's Campy's most obvious benefit over using Shimano or SRAM.

I'd change out the chain first, assuming the cage and jockey wheel look good and appropriately installed. And of course also assuming chain length is correct.