Ferguron

I have a Dura-Ace 11 speed groupset. Last week I had the RD shift cable break...again. The same thing happened only like 2500 miles ago. The cable broke in the shifter...about 1 1/2 inches from the end.

I maintain the shifters carefully...cleaning and lubricating at least once a year.

Admittedly I shift a lot...probably more than most people but it seems to me the cable should still last a lot longer than 2500 miles.

This time a added a thick layer of grease in the channel that carries the cable in the shifter.

Anybody have similar experience / suggestions to prolong the life of the cable?

Troul 

Are you shifting under load often? If everything is proper, I'd try a different (reputable) brand cable.

Ferguron

I generally avoid ****ting under load. I forgot to say...I used either Shimano or Jagwire cables.

Chuck M 

There are other threads on this. Apparently it isn't unusual. A set of cables isn't that expensive and they are easy to replace. I've started doing it preemptively since I read that thread.

datlas 

I too have experienced that my Shimano RD shifter cable frays/breaks inside the shifter every 2500 miles or so. I believe this is a design defect by Shimano that puts too much stress on the cable as it makes a very tight turn inside the shifter. My thinking is those of us that shift frequently suffer from this.

alcjphil

The more often you shift, the more often you will have to replace cables

Andrew R Stewart 

The more you ride the more often you will have to replace shift cables.

We have a few customers who are especially hard on their cables, as in replacing every 6 months or so. Others who could go years with the OEM ones. The one thing that can be said as a fact is that replacing the cable before it breaks will keep you from finishing a ride in a high gear and you'll never have to replace a shift lever from a jammed in it cable strand. I think most here can do their personal math on this risk management. Andy

cxwrench

That won't help. The cable breaks because it fatigues from shifting...getting pulled around the shift drum then let go. Just like bending a paper clip, just takes longer. It's not the friction of the cable rubbing against anything so grease won't help. Just learn from this time and change your cable at 2000 miles. This happens to tons of people, you're definitely not the only one.

Troul 

If the change in brand has no positive outcome, I'd set a calculated miles ridden reminder to replace it as a proactive maintenance item. I try to keep up on mine with like such recommended reminder, but sometimes I'm premature to that even & it has shown me I was borrowed time.

JohnDThompson 

It's not so much a "design defect" as it is a design limitation. The experimental aircraft folks have a rule-of-thumb regarding control cables, where cable failure is a far more serious matter than on a bicycle: to prevent cable fraying failures, any cable guide or pulley through which a cable passes should have a radius of about 50 times the diameter of the cable. It's simply not practical to pack that into a bicycle shift lever, whether incorporated into a brake lever or even mounted on a down tube.

FBinNY 

+1

Cables fail strand by strand owing to metal fatigue where the cable is repeatedly bent and straightened at the lever mechanism.

As stated, there is a design limitation, but it's made worse by a change in how cables are made. Engineering guidelines for cable pulley radius depend on the type of cable. Wire rope, that some people call braided, ie. 7x7 or 7x19 is more supple than the single center cables, ie. 1x7 typical of gear and and brake cables on bikes.

Over the years we've seen those types of gear cables used on very small diameter lever pulleys like those on downtube shifters with no problems.

However, as I mentioned, there's been a change. In order to make cable run more smoothly in lined housings modern cables are die drawn, distorting the outer wires and squashing it all into a more cylindrical, smoother shape. This lowest friction but at the same time work hardens the wire making it more brittle and increasing the necessary pulley diameter creating today's problem.

Ironically, some people experiencing excessive cable breakage might do better with less expensive gear wires which are not die drawn, being more supple and forgiving of repeated flexing, and extending the amount of time before metal fatigue sets in.

Crankycrank

I started using this Aligator 31-strand Superior Shine Slick Stainless Shimano/ Sram 1.1mm cable on my rear derailleur. ALLIGATOR 31-STRAND INNER CABLE (alligatorcables.com) Uses more but thinner strands than Shimano or Jagwire and compatible with both housings at 1.1mm diameter. Lots of hype and I have only put on about 2.5k miles on it so far and I usually get 4-5k on the J or S's best cables. I'll try to remember to update when it starts to fray but may be awhile. Found the best prices on Ebay and usually a little less expensive than the others best cables. I'm hoping the better flexibility will help to last longer but might try FBinNY's suggestion in post #11 if it doesn't work out.

UPDATE: OK, just a few days after I posted this the cable started fraying right in the area near the cable head where most of my shifting wraps around the pully. About 2k miles less than what I usually get with the J and S cables. I have a second Aligator on hand so hopefully this was a fluke but I'm not sure I would recommend these at this point. Bummer.

Troul 

I would also expect the load (derailleur tension) to which a bicycle cable endures is another factor. Seems like the major brands that supply OEMs with derailleur's have reduced the spring rate. BITD; when I would remove a rear wheel & had to manually swing the derailleur during the process, it would act like napping turtle if I for some reason slipped my grip. Nowadays, it's less aggressive.

FBinNY 

Actually tension in the ranges involved has little or nothing to do with the problem.

It's purely about the degree and frequency of flex. Anytime you flex a solid material the part of it outside the curve has to stretch while the part inside contracts. The greater the bend, the greater the differential in length inside to outside, and that's the problem in a nutshell.

Up to a limit known as the free bend radius, it doesn't matter because the relative changes in length are within the spring range of the material. But sharper bends stretch the outer edges beyond the elastic limit and cause internal distortions within the metal which accumulate, leading to eventual fatigue. This is actually no different than how spokes eventually fail from metal fatigue and most experienced mechanics are used to that phenomenon.

Cable has a smaller free band radius than wire, because the individual strands can alter their position, so they don't have to stretch as much. However, in die drawn cables, the individual strands cannot move as much, and the cable begins act more like a solid wire and therefore fatigues that much faster.

So, as noted by someone above it's not about miles, it's about shift frequency. Specifically it's about the frequency of the most common shifts which bend the cable at the same place each time.

cxwrench

Nope, that doesn't have anything to do with it. It's purely the flexing of the cable that causes this particular failure.

easyupbug 

I ride in the summer in the Bighorn foothills where I shift a lot and am starting to think Di2 and/or eTap might be getting closer to worth the +++$ and fussing, charging and all.

SoSmellyAir

Definitely, if the internal routing paths of the bike frame is not well thought out. Mine is OK, so I am just resigned to replacing the shift cables (and housings while at it) every 18 months or so.

oldbobcat

Two words for that. SRAM Doubletap. I've never replaced a cable that frayed inside a Doubletap lever.

SoSmellyAir

Does the SRAM Doubletap shifter design somehow avoid pulling the shift cable through a tight radius bend?

oldbobcat

Not as tight as Shimano's. Cable fraying in Shimano STI levers goes at least as far back as the 5600-6600-7800 generation. Of course, people have other reasons for not choosing SRAM, but I'm not one of them.

Ferguron

I am just going to make a note to replace the cable every 1500 - 2000 miles.

It might be a PITA but it sucked having to make the call of shame for a ride home...there was no way I was going to make it the up the hills in he remaining 15 miles of my ride on the 11 tooth sprocket.