After only 3,000 miles the Pinion gearbox shifting cable has failed where it exits a TRP Hylex lever (drop bar model). The fail point is left hand lever, circled in photo. This seems designed to fai: short radius, metal on metal. Any ideas on mitigating this? Anyone else have this issue? The dealer has no options for this.




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Doesn't look like the bag is helping matters, as it forces the cable in that area to bend in two different directions.

I would use thin cables, like SRAM's. And expect to replace them annually. This has been a Shimano problem for 35 years.

Ditto: the highest failure point is the area of tightest radius within the brifter. Only option is cable change at the earliest hint of
shifting resistance which suggests that the cable has begun to fray with in the shifter, or change the cable every year or so or
maybe when you change chains. It is worse on tandems, much worse. I don't think the bag has much to do with it.

Lousy design on a bike designed to travel the world. Never have I owned a bike that went through cables on a nearly annual basis, including our beloved ‘99 Burley Duet tandem… but obviously no brifters at that time.

Frequent inspection and early replacement are the best things for this problem.

What about better cable?
Covered cable?
Molybdenum disulfide grease?

Agree that the bag looks to be the major factor in the premature failure of the cable.

Compare the last generation of STI drop bar levers with decent shift cable longevity, the ones where the cables come straight out the inner side of the levers and then bend very gradually down and back.

Many people, including me, choose to run the cable to the opposite side of the down tube, to increase the radius of the bend (and thus the lifespan of the cable) even further.

The shift other cable on the OP's bike might be ready to go, too.

Yes, I noticed that as well. Without the bag it still has the bad angle, but will try to make the left more like the right with small adjustments.

if you can find a cable with smaller strand/higher count wires.. use it.
the thinner wires bend easier, reducing the flex forces.

other than that... change cables more often.. it's what is done by any of us that have ever fought to remove the broken remnants of drop bar brifter shift cables.

VERY common on some Shimano brifters, btw... TOO common.

it would be a good thing to look into... WHICH cables flex easier... it would be a popular article for sure.
higher nickel alloy stainless steels Should resist cracking better, too. Nickel lends ductility... Chrome and manganese are the opposite of nickel, in that respect...

plain old galvanized cables may hold up longer in the tight bends required in brifters.... ?....

Jagwire or Clark's need to get to work on brifter-specific cables, IMO. I'd buy a few pair!
although.. flexing is stretching, so...

Keep in mind that cables fail due to physical conditions, i.e. the tight bending radii that every manufacturer's brifters inherently have. It isn't a friction issue causing the problem, so lubricants or coverings aren't going to significantly mitigate the issue. I am not a materials engineer so I can't comment on what other SS alloys might be an option for a better quality cable. There may also be composites that could work for all I know. I do suspect though that alternative materials would cost more money and would have to have a much longer life to be cost effective vs replacing an inexpensive cable once a year. Probably the only real solution would be a radical redesign of the actuation methods that would result in less bending stress on the cable.
John

Although the hbar bag is forcing the cable and housing to follow a sharper curve, it is unlikely the cause or contributor to the failure of the cable. It is an age old problem that has no relief with the current design of brifters and the shifter shown in the original post. Simply put, do as others have said, change the cable before it breaks, and if that means annual replacement, so be it.
The rear der cable on my brifters lasts about 4 seasons, the front I have yet to replace as it does not get used nearly as much as the rear.

It's all about the bend radius, you can either use a similar but smaller* cable or find a more flexible one. The good ones have many fine strands twisted into small bunches which are then twisted together again, which is good for flexibility but doesn't make for slippery sliding - the multitwist cables like 7×7 can't be polished like those with 1×19 or similar construction. As with so many things, it's a compromise between performance, cost and durability. The best thing is to keep your cables clean and lubricated and well routed, and your derailleurs well adjusted and lubricated. Either replace cables on a schedule, perhaps every Easter, or as soon as you see a strand out of place during your frequent checks.


*recommended minimum bend radius is often expressed as a multiple of cable diameter, and generally ignored in the design of bike parts

I'll add that as well as checking for broken strands every so often, if you notice your shifting starts to get sloppy for some unknown reason, closely check the cable inside the shifter for any broken strands and stop using that shifter until you put a new cable in. Cables breaking off at the head inside the shifter can be a major PITA to remove and I once had a broken strand get caught in the mechanism and broke it. No way to repair it either.

+1 this. The experimental aircraft homebuilders have a rule-of-thumb: for cable direction changes, control cables should use a pulley with a radius 50x the diameter of the cable to reduce the likelihood of metal fatigue failure in use. That's not going to fit inside any brifter. And yes, downtube shifter are also subject to this issue, but there at least impending failure is far more obvious than with a cable hidden inside a brifter.

Do you also shift under load? This could contribute to this by adding load increases friction caused by the other factors stated in above responses.

Have to disagree. The shift cables in Shimano's early 9- and 10-speed STI shifters lasted far longer than the cables in the later versions with the cable housing routed under the handlebar tape. It's the abrupt, small-radius bend at the lever's exit point that's the culprit.

The OP might consider using a much smaller front bag or some other workaround. But installing high-quality, supple inner cables frequently is the simplest fix.

Filament technology's come quite a long way since wire rope was first invented then used so widely. I'm aware that modern sailing tech has become quite fond of replacing steel rigging with synthetic fiber that's far stronger than the metal stuff it's replacing while also being lighter and virtually corrosion-free.

I've not seen any mention made of whether this stuff (Dyneema, specifically) has seen any bicycling applications.

Friction and fatigue are the two material dynamics affecting these skinny metal cables where they're forced to perform dimensional changes in tight confines. I'm wondering if synthetics would offer any solutions albeit at some increase in expense?

Tons of 8, 9 and 10 speed external cable shifters were known to fail - and were much harder to get the cable remains out of.

Kevlar is hard to weld a cable head onto.

Sure. Down tube shifter cables, too, back when those were standard. Working the remnant of cable out of a Campy down tube shifter was always fun.

But no one was recommending replacing shift cables semi-yearly or yearly until drop bar shifters with concealed cables took over the market.

Yeah, I've messed with it enough to be aware of that limitation.

Dyneema's a different critter, slippery as all heck but reacts to heat a lot like nylon and polypropylene.


(Google's reply to my query)

I've formed 'stoppers' on some stuff I've done with it with a torch & concave mould; it takes some unusual efforts to get knots that'll work.

All the typical cable heads I've ever handled looked to be cast-in-place, not unlike soldered, usually what looked like a zinc or aluminum alloy material.

Yes, we were. I worked at a shop that had a basement ceiling decorated with external cable brifters that stopped working - at least half had cables stuck in them that no one could get out.

I think you'll find those cable heads are steel if you try to file them.

Forming a knot in rope decreases the tensile strength by as much as 50%. Steel is exceptionally strong by volume, and shift cables are limited by size, not weight. So you could certainly make a Dyneema or Kevlar bike cable system, but it probably would not be compatible with existing shifters.

It’s a Pinion gearbox so little to no shifting under a load allowed.

I am giving this a try… Shimano Optislick coated, die-drawn stainless steel… 10 bucks instead of 5. If they last 6000 instead of 3000 miles that’s worth it. Plus a two year warranty.