Chain riding on sprocket teeth (Campagnolo 12 speed)

[alcatraz]

Cal,

I know your preference towards having a small gap between the top pulley to the largest cog. Next time when you have a Shadow-based Di2 bike in your hands, adjust the B screw for a small gap and try shifting from the second largest cog to the largest cog, and see if you hear a clunk on a small percentage of shifts. I tried to reduce the pulley wheel gap on my bike but I get the 'clunk' on perhaps 20% of the shifts from the second largest to the largest cog. Increasing the gap solves the problem. I don't think the noise is an indication of a bad or missed shift. But the noise just doesn't sound good when all other cogs shift without any noise. Perahaps this is a Shadow Di2 specific problem. I now have Di2 on my tandem as well and it does the same thing. I'm just curious if you can duplicate the problem on another Di2 bike you have access to.

The gap can't be zero for two reasons.

1. When the chain derails it's riding the cog and eating into the distance.

2. The derailleur (and guide pulley) moves in a line over the cogs, not sideways then height adjusts.

So when in 2nd gear and starting a downshift you already at this point need the complete minimum cog-riding pulley distance for the 1st gear which you don't have yet.

So adjust until the noise disappears and keep testing shifting 2nd to 1st.

When the pulley is offset from cage pivot point it complicates things if you're on 2x becauese the pulley distance changes depending on which chainring you are in. Offset is usually but not always found on 1x derailleurs.

[pdlpsher1]

So adjust until the noise disappears and keep testing shifting 2nd to 1st.

Basically that's what I do. I increse the distance until the noise goes away on 100% of the shifts. I don't go by the installation manual since the gap is really hard to measure.

But when someone says 'I've adjusted the pulley to be as close as possible to the largest cog' it's difficult to discern if they are referring to a gap or a noise-free 2nd largest to the largest cog shift. I imagine most people do it visually.

[Calnago]

@PdlPshr1: I have tested every combo possible as you know, and done it extensively. I even purposely adjusted the gap to more than it should be just to verify that the shifting is less crisp than when the pulley is as close as possible. It was definitely less crisp. And when properly adjusted there is no “clunk”. It was nothing but silky smooth. Any cog. Any shift combo... it’s an effortless shift.
Did you ever get the new hanger installed on your bike? As I’ve said before, unless it was a custom hanger I doubt it will end up within Shimano’s road spec either. It’s a function of the position the dropouts were welded to the stays. They’re angled too far forward on that bike you pictured and that’s a function of how the frame was built.
I know you’re very happy with your shifting. So all good. But having to have the derailleur so far from the cogs is not how it was designed to be. And I have indeed verified that the closer you can get it the better.
I’m not really sure what Alcatraz is talking about saying there can’t be zero gap, because of course there can’t be as there would be no room for the chain to pass. But as long as the gap is enough to allow the chain to pass without any jamming or jitters, then it’s big enough.
Furthermore. We’re talking about Campy here, but the principles of having the upper pulley as close to the cogs as possible applies equally to Shimano

Anyway, that’s all I got.

[pdlpsher1]

Cal,

Well, my experience is always different from yours. I have two bikes from two different manufactures. Both have Di2. The closer the pulley wheel gets to the largest cog the worst the 2nd largest to the largest shift. The clunk doesn't happen all the time, just on some of the shifts. Backing off the pulley wheel the noise goes away. The noise has nothing to do with the RD hanger. Perhaps Campy doesn't have this issue. That's why I mentioned up front that I'm on Di2 in my first reply. Anyways what am I doing on a Campy thread...

[graeme_f_k]

Hoping to have some guidance. This happens intermittently (probably 1 out of every 10 times or so...) when I shift to the 25T and/or 32T sprocket, the chain would sometimes ride on the sprocket teeth and then reseat itself (see pic below). When climbing, this would cause a jolt of course. Aside from this, every other sprocket shifts fine.





Current setup: C60 frame with Campagnolo SR 12, with 11-32 cassette. Rear derailleur hanger is straight (vertical, horizontal), chain is not stretched (i.e. fairly new), 11-32 cassette is fairly new as well, cassette is tightened to correct torque settings, upper pulley wheel is close as possible to cassette (5-6mm), high and low limit screws adjusted, cable tension adjusted (more on slacker side, if the cable tension is more tight, then shifting isn't that great).... I've played around with cable tension, B screw, etc... to no avail

Any guidance is much appreciated.

Top jockey is too close to the 32.

The "close as possible" note in the set-up info also mentions that there has to be space for the chain to pass through and for the shift to be clean, without any risk of the jockey cage touching the sprockets.

At the other end of the cassette you also need to ensure that the run of chain from the guide pulley up to the 11 is either level with the floor (when the bike is on the floor) or slightly "uphill" as the chain passes from the guide pulley to the 11 sprocket.

If these two conditions are not satisfied, you won't get consistent shifting.

[Calnago]

I think the reason it looks too close in his picture is because the chain is essentially riding on top of the cogs of the 32, essentially creating the effect of having a bigger cog on there than the 32. So yeah, if he’s got it set up for a 32 then placing the chain like it is in the photo (as if there’s a 33 or 34 tooth cog, then that isn’t going to help that gap and it ends up looking like it is. But if the chain was placed on the cogs properly, his gap is likely ok, so long as the chain can pass freely between the cogs and the upper pulley in all combos... which is of course, close as possible.

[mag]

We'd need a photo of normal situation on the 32t sprocket I think.
But I like that photo. He gets a free help in the form of a temporary 34t sprocket or so and yet he has to complain... Some people can never be happy.

[Calnago]

ha, “free help” aside, agree that a pic in the normal position would be good in the end, but I really think the fact it can ride up on the teeth like that is the result of a pretty simple adjustment issue, again.... making a big assumption that everything else is ok.

[taylorpetie]

@Cal -- thanks again for your insights. It's always appreciated. I'm currently on travel and will report back once I undo everything this weekend and start from scratch with your instructions again. I think it maybe my starting point, but then again it may be just me. Some thoughts below.

Does the chain seem be over shifting a bit, as if a bit more would throw it into the spokes, or not quite shifting enough, as in it's thinking "I think I can I think I can" as it tries to climb to the larger sprocket.

It did seem like it overshifted awhile back, but i loosened the cable tension and most of the shifting (with the exception of the two problem child cogs) doesn't overshift, but also ensuring that it doesn't struggle to shift up ... i.e. the 'I think I can' shifting

Also, if I followed the campy manual, I've put the chain on the 5th cog and adjusted the tension to the point where i hear chain rub on the upper cog, than back off tension by counting how many clicks (or half turn of the tension barrel) before i hear chain rub on the lower sprocket... and then increasing the tension back to the middle point by counting half the clicks (or turns of the barrel). At this point, it still overshifted a little bit on certains cogs, and therefore, I release more tension with 2 or 3 clicks.

I ask because, despite you saying that it's shifting pretty well overall, I would question that and say it's shifting like crap, and it is, based on what you say and show. I think you're starting point is slightly off....

This was what I initially thought as well. So, awhile back I removed the rear derailleur tension cable (so chain rides on the smallest cog and big chain ring).
Adjusted the 'B' screw and found the middle point where chain wasn't rubbing. The odd thing was when I reattached the cable (without cable tension), clamped the cable, and then started to increase the barrel cable tension so that the rear derailleur will shift to the 2nd COG, 3rd COG, 4th and 5th COG... (this required around 3 or 4 counter clockwise barrel half turns), But, then dropping the shift back to smallest COG, there would be chain rub between 1st and 2nd COG...at which point I would have to slightly loosen the B screw to remove the noise. This in effect I think then screws up my starting point.

[taylorpetie]

ha, “free help” aside, agree that a pic in the normal position would be good in the end, but I really think the fact it can ride up on the teeth like that is the result of a pretty simple adjustment issue, again.... making a big assumption that everything else is ok.

yes, will post photos when I'm back in town.

[taylorpetie]

taylorpetie,

When you say your RD hanger is straight did you actually check it with a hanger alignment tool? Sometimes people say their hanger is straight but they have never checked it with a tool. A hanger can be misaligned on a brand new bike that's never been crashed or mishandled. Even the slightest hanger misalignment will cause shifting problems. Also another common problem is a loose hanger. Take your wheels off and make sure those two philips screws are tight. And wiggle the hanger with your hand to detect any movement. There should not be any movement on the hanger with the wheels off.

Yes, I used the park tool to ensure the hanger was straight to the wheels and had made sure the hanger was not loose. Thanks

[alcatraz]

If shifting from 3to2 and 1to2 puts the chain in different optimal positions by 1-2 barrel adjuster clicks I'd say that is normal. If more than that you have some issue somewhere.

You can't set the B-screw on the small cog unless you ride really small cassettes like 23-25t or and oversized derailleur. It will contact the large cog if you do.

Lets see some more pictures of the entire drivetrain. Small cog indexing issues could sometimes be because of a bad housing/chain length.

Do you notice differences in ability to shift into the small cog depending on which chainring you are in?

[Calnago]

Alcatraz, I think you’re confusing 11sp with 12sp. The “B” screw on 12sp has a lot of effect, like the B-Screw on the Shadow type Shimano derailleurs. I think what you might be referring to is the “H-screw” on the Campy 11sp, which you adjust while on the Small ring/big cog.
The 12sp mechanical derailleur works quite differently.

[alcatraz]

Thanks, I just checked the installation video and noticed that the derailleur has such an extreme travel angle (or what it's called) that even for a 32t cassette the upper pulley will clear the big cog when nearly touching the small cog.

Very nice I have to say. Shimano and sram can learn something here.

[taylorpetie]

So, I've started from scratch
1. Detached tension cable and loosened the adjuster barrel (around 5 turns)
2. In the smallest COG and big chain ring, adjusted the upper limit screw (i.e. the B screw) to find the middle point/alignment of the smallest cog and upper pulley. Pedaled while tightening the B-screw until there was chain rub against 2nd cog, then loosend until there was chain noise, then tightened screw to the quiet middle point (slightly to loose side). I'vd done this several times to find that quiet, mid point.
3. Re-attached tension cable
4. Adjusted tension betwen 1st and 2nd COG (i.e. 11T and 12T) -- required around 3 half barrel turns for derailleur to shift to 2nd cog. Additional 2 -3 half barrel turns to eliminate chain noise.
5. Shifted up to 3rd COG (13T). Slight chain noise, and therefore tightend tension to 4 clicks until no chain noise
6. Shifted to the remaining COGs fine without chain rub or chain riding on sprocket teeth (from 14T thru 22T ... anything higher was pretty much cross-chaining)
7. Dropped big chain ring to small chain ring, dropped rear derailleur position down to 13T... and shifted to 32T and then back down, and then back up
8. Seemed to shift fine until 25T and 32T where intermittent problem of chain riding on sprocket teeth
9. At this point, released some tension (1, 2, 3, 4 clicks) and even tried increasing tension (1, 2, 3, 4 clicks) and same result.


Below are pics of pulley distance from COG:

32T COG and small chain ring



Small COG and big chain ring alignment... The hanger was checked using a tool to ensure it's straight... but I just noticed that in the picture below, the upper pulley has a slight inward position and not straight... the lower pulley flares out which is normal (per the manual)... but is the top pulley seems to have a slight inward slant (even though I've doubled/tripled check that the hanger is vertically and horizontally straight.