Campagnolo 12 speed chorus frayed cable

[hainy]

3 months ago the cable at the anchor bolt on the rear derailleur frayed and now it has happened again. I have never had this problem before with Campagnolo. Does someone know what could be causing it to fail? They are standard campagnolo cables.

Thanks in advance for any help.

Cheers

Hainy

[dddd]

The most frequent cause that I can correlate to short cable fatigue life would be the lo-limit adjustment on the derailer being too "tight", which causes over-stress on the cable every time that the largest cog is engaged.

This can happen because the mechanic wants to stay on the "safe" side of having the chain move into the spokes.

Another cause is that someone re-adjusts the cable tension to accomodate a slight difference of cassette positioning on a different rear wheel. The cable gets re-tensioned but they don't re-visit the lo-limit screw to allow the rear derailer to move with the tighter cable.

Especially when the shifter isn't UltraShift, where the cable spool thus won't rotate "out of the way" of an over-tight cable when shifting to the largest cog, the cable tension can go very high, and even higher yet every time the rider's pedaling stroke flexes the frame.

[gfk_velo]

Originally Posted by hainy

3 months ago the cable at the anchor bolt on the rear derailleur frayed and now it has happened again. I have never had this problem before with Campagnolo. Does someone know what could be causing it to fail? They are standard campagnolo cables.

Thanks in advance for any help.

Cheers

Hainy

I read dddd's reply with interest but I'd be surprised if the lever could generate enough tension for that to occur, based on the release tension of the clutch.

If the RD was that "hard" against the low limit screw, I don't think the clutch in the lever would have a strong enough "hold" to keep the bike in that gear, I think it would jump "up" a gear. The release tension on the clutch (UltraShift levers) / index springs (if an older lever) is only around 2.5kg. Repeatedly exerting that much force against lever 2 would also probably result in L2 failure. Historically we have seen that, usually with poorly set front derailleurs and LH levers.

That wouldn't necessarily preclude fraying by that method - maybe if an Escape / Powershift lever was in use, where the ratchet mechanism is gated and can't be pulled "backwards" - but I'd have thought it would have to happen an awful lot of times before fraying would occur & that the user would notice the excessive force needed to engage the biggest sprocket ...

I'd take a look at the reverse of the cable clamp plate and check whether the entry point to the channel that the cable sits in is smooth (the channel itself is slightly ridged but the point at which the cable comes into it, is slightly funnelled to allow for angular movement of the cable).

I am assuming that the clamp plate is correctly oriented and that the cable isn't clamped under the 90-degree "hook" on the clamp plate (that is there to prevent the clamp plate from turning when the pinch bolt is tightened, it is not the cable clamp itself. Using it as a clamp results in poor shifting & may indeed fray the cable).

Repeat tightening - especially over-tightening - of the pinch bolt can also eventually flatten the cable. That can result in individual strands starting to break. I's quite easy to over-tighted with a long 5mm allen key, we see it with trainee mechanics all the time, where they don't use a torque wrench to learn the "feel" of the clamping torque..

[cgolvin]

Originally Posted by gfk_velo

If the RD was that "hard" against the low limit screw, I don't think the clutch in the lever would have a strong enough "hold" to keep the bike in that gear, I think it would jump "up" a gear.

Apologies for the thread drift, but wow, what a timely post. I recently changed wheelsets and noticed that with higher watts in the lowest gear the RD would drop to the next largest sprocket (and I could force the jump if I manually pulled the cable). I just put the bike on the stand, where I could reproduce the behavior, loosened the low limit screw and …*problem fixed.

Always appreciate gfk_velo's contributions here, thanks again.

[hainy]

If you make a large adjustment to the b-tension screw how does this effect the limit screws and cable tension.

[bikeboy1]

The B screw wasnt suggested as having anything to do with the cable tension. They were talking about the H and L limit screws which are the two screws side by each. The thought was having the screw adjusted in a little too much when shifting the chain up to the largest cog on the cassette. Graham didnt think that would actually be the cause of your frayed cable and was directing you toward the groove that the cable is supposed to run through where it is clamped. It is hard to see but if you take the screw out of the mount and pull the plate away you will see a groove where the cable sits and is clamped to by the block and the clip. Always make sure you have the end caps on the cable to protect it and keep it from fraying as well.

[dddd]

Originally Posted by gfk_velo

I read dddd's reply with interest but I'd be surprised if the lever could generate enough tension for that to occur, based on the release tension of the clutch.

If the RD was that "hard" against the low limit screw, I don't think the clutch in the lever would have a strong enough "hold" to keep the bike in that gear, I think it would jump "up" a gear. The release tension on the clutch (UltraShift levers) / index springs (if an older lever) is only around 2.5kg. Repeatedly exerting that much force against lever 2 would also probably result in L2 failure. Historically we have seen that, usually with poorly set front derailleurs and LH levers.

That wouldn't necessarily preclude fraying by that method - maybe if an Escape / Powershift lever was in use, where the ratchet mechanism is gated and can't be pulled "backwards" - but I'd have thought it would have to happen an awful lot of times before fraying would occur & that the user would notice the excessive force needed to engage the biggest sprocket ...

I'd take a look at the reverse of the cable clamp plate and check whether the entry point to the channel that the cable sits in is smooth (the channel itself is slightly ridged but the point at which the cable comes into it, is slightly funnelled to allow for angular movement of the cable).

I am assuming that the clamp plate is correctly oriented and that the cable isn't clamped under the 90-degree "hook" on the clamp plate (that is there to prevent the clamp plate from turning when the pinch bolt is tightened, it is not the cable clamp itself. Using it as a clamp results in poor shifting & may indeed fray the cable).

Repeat tightening - especially over-tightening - of the pinch bolt can also eventually flatten the cable. That can result in individual strands starting to break. I's quite easy to over-tighted with a long 5mm allen key, we see it with trainee mechanics all the time, where they don't use a torque wrench to learn the "feel" of the clamping torque..

Correct that if it's Ultrashift, likely the shifter springs might also be the parts to suffer, assuming that the lo-limit screw gets backed off only enough that the shifter doesn't slip, since the the cycling of cable tension will cause some cyclic motion short of slippage.

But that shift into low gear even using Ultrashift will momentarily over-stress the cable when the shift is being made, if the lo-limit is set to the tight side.
Shimano incorporated a firm travel-limiter in it's 11s levers (actually in the spool mechanism), that limited the spool travel range, seemingly to deal specifically with that over-tension that can occur during shifting to the largest cog (not because of any concern that the shifter would slip).

Having said all that, Campagnolo levers do seem to be more immune to cable failure than Shimano's hidden-cable shifters, seemingly having to do with the bend radius that the cable has to make.
So the OP's cable failure might just be from the cable getting traumatized by the pinch bolt washer (especially if the cable position gets changed slightly looser at the bolt after initial tightening of the bolt has crushed and work-hardened the cable slightly). As gfk_velo points out, the cable needs to be respected where the clamping occurs. I still remember how the very old bike components tortured their cables, but are today designed not to (until the newest Shimano derailers came along, re-introducing the sharp bend).

I try to always check that the shift up to the largest cog isn't causing any increase in the lever force above what is needed to shift up to the second-largest cog, and if it is, loosen the lo-limit screw slightly until the shift can be made unencumbered by any added force of the limit screw.

[hainy]

Thanks everyone

Dropped it into my mechanic today and he is having a closer look at all the possible causes with a particular focus on the clamping bolt.

Cheers

Hainy

[oldpotatoe]

Originally Posted by dddd

Correct that if it's Ultrashift, likely the shifter springs might also be the parts to suffer, assuming that the lo-limit screw gets backed off only enough that the shifter doesn't slip, since the the cycling of cable tension will cause some cyclic motion short of slippage.

Some snipped.

Which 'shifter springs' would that be? Unlike 10s, 2009 and older, there aren't really 'shifter springs' that hold the disc into position, rather notches held there with a wee ball bearing. One of the reasons Ultrashift..10s early 2009/10, 11s and 12s AND Ekar levers are so much more durable.

[dddd]

Originally Posted by oldpotatoe

Some snipped.

Which 'shifter springs' would that be? Unlike 10s, 2009 and older, there aren't really 'shifter springs' that hold the disc into position, rather notches held there with a wee ball bearing. One of the reasons Ultrashift..10s early 2009/10, 11s and 12s AND Ekar levers are so much more durable.

Sorry for my late reply!

I was referring to the replaceable "G" springs, that suffer fatigue after so much use. I did think that these were the "traditional" (serviceable) type and called UltraShift, similar to what was found inside of their former down tube levers.
But perhaps "UltraShift" refers to the external functionality of the levers and not the internals(?).