Campy 12s RD anomalies

[cgolvin]

I have over 17k miles on my Chorus 12 groupset and the rear shifting has been pretty much perfect … until yesterday.

First, it suddenly started making a lot of noise, like the indexing was way off. I adjusted the cable tension and it was OK, though more noisy than before.

Second, on a steep climb I shifted down to the second largest cog and it started making noise like the upper pulley was rubbing against the cog -- which it was. Really strange since I have never touched the pulley height adjustment after initial installation.

I got it home, put it on the stand, detached and re-attached the cable and went to adjust the shifting. I had to move the pulley height adjustment quite a bit but that part seems fine. However, I cannot get the cable tension adjusted so that shifting is smooth across the cassette. If the shifting is good in the small cogs then it doesn't smoothly transition from the biggest to second biggest cog, and if the shifting is good on the large cogs then the indexing is poor on the smallest cogs -- in particular in the third smallest cog the chain jumps around.

The only change I had made prior to this was installing a new cable several weeks ago, and moving the routing from the 'front' channel to the 'rear' channel. I have put several hundred miles on this cable with it working fine.

Aside from having the hanger checked (which I have no reason to suspect), and possibly replacing the cable, any suggestions?

Thanks

[AngryScientist]

hmmm.

I would inspect the entire body very closely. It sure sounds like something structural has cracked and the whole unit does not have the rigidity it needs to keep everything in check. That's what I'm betting on based on those symptoms.

[Mark McM]

If the change in shifting was sudden, my first suspect would be derailleur hanger alignment. If the hanger is bent inward, it would effectively rotate the derailleur inward and upward, with the combined affect of offsetting the indexing, moving the jockey wheel upward at the big sprocket, and also affecting the ratio of lateral travel to cable travel (which would result in the indexing getting worse at the ends of the cassette).

In other words, all the symptoms you describe can be caused by a bent hanger.

[oldpotatoe]

Originally Posted by AngryScientist

hmmm.

I would inspect the entire body very closely. It sure sounds like something structural has cracked and the whole unit does not have the rigidity it needs to keep everything in check. That's what I'm betting on based on those symptoms.

The first thing that comes to mind for me(well second, first is der hanger) is the cable is failing at the shifter. Maybe der housing split somewhere.
Then maybe the RD is wacked somehow. Barrel adjuster at the RD broken?

[elvisthehorse]

ive had b adjustment. vibrate loose and effect shifting. free and easy,

and make sure no body parts have cracked. had that happen too.,

[elvisthehorse]

double post, sorry

[cgolvin]

Checked hanger alignment: off by a small amount, repaired, minor improvement but nowhere near right.

Replaced housing: no change.

Replaced cable: no change.

Replaced chain (needed doing anyway, wasn't expecting a result): no change.

Next step: new derailleur (though I wish I could borrow one first, kind of spendy when I'm not certain it's a fix).

Must admit some disappointment regarding the longevity of Campy 12 components, at least in my minuscule sample. In more than 4 decades of riding Campy I had never broken a FD, RD, or chainring tooth but (will) have replaced all those with 17k miles on this groupset.

[oldpotatoe]

Originally Posted by cgolvin

Checked hanger alignment: off by a small amount, repaired, minor improvement but nowhere near right.

Replaced housing: no change.

Replaced cable: no change.

Replaced chain (needed doing anyway, wasn't expecting a result): no change.

Next step: new derailleur (though I wish I could borrow one first, kind of spendy when I'm not certain it's a fix).

Must admit some disappointment regarding the longevity of Campy 12 components, at least in my minuscule sample. In more than 4 decades of riding Campy I had never broken a FD, RD, or chainring tooth but (will) have replaced all those with 17k miles on this groupset.

Warranty? BUT, is there anything cracked or broken on RD?

ott@campagnolona.com

[cgolvin]

Originally Posted by oldpotatoe

Warranty? BUT, is there anything cracked or broken on RD?

ott@campagnolona.com

Thanks OP. I bought the groupset more than 3 years ago so it's out of warranty. I still have to remove the RD to give it a close examination, so far I can't say there's anything broken though it does look to me like the cage is misaligned. Once I have it off I plan to contact Jerry & Steve, no harm in asking, right?

[dddd]

When you replaced the rear derailer cable, did you feed the length of the cable through the shifter before starting to feed it into the lever body and cable housing port?

Often when this is done, the cable forms a very tight loop that must be forced into the body/port/housing, which bends the cable sharply and which is then hidden from view inside of the cable housing.

At the small end of the cassette, where cable tension is usually minimal, the bent cable starts acting like a spring that takes up some cable length, messing with the precise relationship between the shifter's indexed movements and the rear derailer's movements.

So I always "stuff" the short loop of cable into the body/port/housing before more than a few inches of the cable has been fed into/through the shifter, with any bent-up section of cable then getting cut off past the rear derailer's cable binder bolt. The cable can also be easily inspected and straightened as long as it isn't hidden in the cable housing just behind the shift lever.

Another thing I've noticed is that when a cable is fed into a sharply-bent cable path, that it goes in under lengthwise compressive force and tends not to become bent. But when cables are pulled through such a bent path, the cable tends to become curved like macaroni.

Lastly, as I feed a cable's length into and through it's full path at the lever, I apply a thin film of cable-specific, silicone-PTFE lubricant to the cable every single time. The cable lube not only is the best lube for the metal-on-plastic interface, it also prevents sticky, old lube in the existing housing from sticking to... ...anything.

[dddd]

Oh, heck, one more thing to consider:

Were the cable housings replaced?

Often when an old cable is pulled out, an exposed (and very dirty) length of the cable gets pulled through the housings, severely contaminating the clean inside of the cable housing.

Any resulting friction in the rear-most loop of housing effects some push-and-pull force on the cable there, and which unfortunately affects the entire length of the cable relative to the shifter's precise, indexed movements..
So with the entire cable feeling this added change in cable tension force, the cable acts noticeably more elastic, degrading shifting accuracy.

So I always at least replace the rear loop of cable housing when I don't feel like messing with the bar tape.
And I cut off the dirty exposed length of cable and then wipe clean the short stub of cable that I might try to push into the old/retained cable housing before pulling it through said housing and out of the shifter.

[cgolvin]

Originally Posted by dddd

When you replaced the rear derailleur cable, did you feed the length of the cable through the shifter before starting to feed it into the lever body and cable housing port?

My wheel guy, who is also a very good mechanic, fashioned a tool out of one of my broken Shamal spokes. This tool allows me to route the cable through the lever body without introducing any bend in the cable.

After removing the derailleur I'm pretty certain that the problem is that both cages are bent. It's not super clear in the photo below, but if you look at the bottom of the cages (top of the picture) there is a clear bend inward. I need to price out the cage replacement versus just buying a new derailleur.

[dddd]

I can't see anything wrong with the derailer cage in your photo, but I also can't see the end of the mounting bolt which is what I totally reference my visual inspection off of.

The end surface of the mounting bolt should at least be visibly parallel to the pulleys, indicating that the derailer is not bent in a way that might change the effective adjustment when changing from one chainring to another (which would be the most pronounced symptom of a bent derailer, that the needed cable tension adjustment seems to change when a different chainring is selected.

I don't think that the derailer itself is likely the problem based on similar experiences.

[dddd]

Is there any possibility of the cable deviating from it's path along the groove adjacent to the binder/pinch bolt at the rear derailer?

Modern derailers swing the outer arm through a greater angle range, which puts the cable at more of an angle to the groove when the derailer hits the high-limit stop while you are fastening the cable. I suggest inverting the bike and really inspecting that area, removing and then replacing the screw and washer/plate part so as to visually inspect the groove.
Being even a cable's thickness off of the groove's entry point will alter the derailer's actuation leverage and fowl up the indexing movement.
The cable needs to be nice and round to engage the groove as intended.

[herb5998]

For your pulley adjustment, which method did you use?


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