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Broken Rear Derailleur Cable - Common Problem?

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Broken Rear Derailleur Cable - Common Problem?

Old 10-10-11, 05:06 AM
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The Chemist
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Broken Rear Derailleur Cable - Common Problem?

Hello All,

Tonight I was riding home from work and I noticed that the rear derailleur suddenly became very difficult to shift. After a couple of minutes there was a snap and the rear derailleur cable broke inside the shifter housing.

Now, I don't know if this is a common thing or not, so I'm not sure if it's a faulty cable, or it's just normal wear and tear. I bought the bike 6 months ago and have ridden it for nearly 4200km. The rear derailleur is Sora, and the shifter is Deore, if that's important.

It's not a big thing to me as it's a pretty simple thing to replace (I think) but I just want to know in future if I'll need to replace the cable regularly to prevent this kind of thing from happening again.

Thanks in advance.
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Old 10-10-11, 07:09 AM
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No, it's not a common problem. But I reckon every rider has been caught out by a snapping cable on some occasion. If the break was really inside an unbroken portion of housing I'd suspect that the cable had been kinked prior/during installation, and then slowly working itself apart ever since. Breaks at point where it's a more obvious local load, as in/out of housings, anchor points etc are far more common - or rather less uncommon.
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Old 10-10-11, 08:27 AM
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Luke: I'd suggest that while you are at it you treat yourself to a new cable housing. They don't cost much and you'll enjoy the smooth shifting a new set will give you.
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Old 10-10-11, 08:47 AM
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It's not common. I've never broken one in over 150,000 miles of riding and I only replace mine every 7000 miles or so on each bike. However, I always use stainless steel drawn cables which are both smooth and rust resistant. They cost a bit more than plain or galvanizzed cables but their durability is worth it.
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Old 10-10-11, 08:52 AM
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Originally Posted by HillRider View Post
It's not common. I've never broken one in over 150,000 miles of riding and I only replace mine every 7000 miles or so on each bike. However, I always use stainless steel drawn cables which are both smooth and rust resistant. They cost a bit more than plain or galvanizzed cables but their durability is worth it.
Just astonishing stats. You are my hero, Hillrider

I've never broken a cable, but then I do regularly re-grease and check for damage fairly regularly. You should be fine for next time.
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Old 10-10-11, 11:49 AM
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Uptick a ways to quality die-drawn slick cable of Stainless steel ,
and a quality Teflon lined housing.
Insure the line the whole thing takes from the front to back is smooth, and kink free
and the replacement will last a long time.

But Metal fatigue happens, and rust never sleeps
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Old 10-10-11, 12:04 PM
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200 plus bikes rehabbed in the last couple of years, many of them in very neglected condition. I have never found a broken cable yet (plenty of them rusted solid and siezed, but not broken). And I have never broken a cable on a personal bike in 40+ years of riding.
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Old 10-10-11, 12:28 PM
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Originally Posted by wrk101 View Post
200 plus bikes rehabbed in the last couple of years, many of them in very neglected condition. I have never found a broken cable yet (plenty of them rusted solid and siezed, but not broken). And I have never broken a cable on a personal bike in 40+ years of riding.
Right. Not all that common.

However, it can happen. Had a young guy come into the coop a week ago with a broken shift cable. Apparently, it had been like that for years.
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Old 10-10-11, 12:57 PM
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Originally Posted by dsbrantjr View Post
Luke: I'd suggest that while you are at it you treat yourself to a new cable housing.
Yes!!! Though cables may break, get frayed or kink, it's usually worn housings that make shifting iffy. The usual culprit is the RD loop.
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Old 10-10-11, 01:53 PM
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I've fixed a lot of cheap BSO/xMart bikes over the years. No broken or about to be broken FD/RD cables, except near the clamp on the derailleur or for that matter the brake where over-tightening has damaged the cable.
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Old 10-10-11, 02:17 PM
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I'm reading this a bit differently. It sounds like it happened inside the shifter (as in inside the housing of the shifter not inside the shifter cable housing). If that is the case, this is one place where it is more common for cable to break as it is often subject to a lot of bending.
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Old 10-10-11, 03:17 PM
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I broke a shift cable once, on a rear derailleur. From what I remember, it snapped at the pinch bolt. It was very old, the bike dates to the late '80s and hadn't been serviced much till I got it, so the cable could have been 25 years old. I also broke a Sturmey-Archer 3-speed shift cable once, again, it was very old. I've never broken a shift cable that was new enough to have been fitted by me. You must have just been very unlucky.
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Old 10-10-11, 04:52 PM
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Originally Posted by CACycling View Post
I'm reading this a bit differently. It sounds like it happened inside the shifter (as in inside the housing of the shifter not inside the shifter cable housing). If that is the case, this is one place where it is more common for cable to break as it is often subject to a lot of bending.
Yes, that's correct - right near where it attaches to the shifter (not exactly sure how far away as I haven't actually opened up the shifter to have a closer look. I use my rear shifter quite a bit, so I guess I'm not surprised it broke there.

No commuting for me today, but I'll try to get to the LBS tonight to get it fixed.

Thanks for the help everyone.
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Old 10-10-11, 10:07 PM
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Cables fatigue fray and break. it's normal, though their life expectancy varies tremendously. The cause is the winding and unwinding of the arc of the lever. It's like bending a paper clip back and forth, after a while it stiffens, gets brittle and finally snaps.

Note, that it's the bending action, not the tension that causes the problem, and the life expectancy depends not on how many miles you ride, but how often you shift. Folks riding in places like Pennsylvania, and Connecticut riding rolling terrain can expect much shorter life than folks in Kansas or even Colorado, where shifting is less frequent.

BTW- an interesting note is that modern die drawn wires such as used on the best systems are more prone to flex fatigue than the less expensive stuff. But all things considered, gear cable replacement is one of the lowest per mile maintenance costs, even in Connecticut.
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Old 10-11-11, 08:00 AM
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You have Shimano STI shifters, right? I've seen this happen several times. Even me - had one break on my first set of 600 8s shifters. Replace your STI shifter cables on a regular basis. Annually or every other year is a good idea.


And I've never seen this happen with a Campagnolo Ergo system.
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Old 10-11-11, 01:01 PM
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It may not be "common" but it certainly happens, and as mentioned above, has mostly to do with the quality of cables/housing involved. After a couple of years of owning my bike and only occasional cable lubricating, my rear cable broke at mile 51 of the Palm Springs century. Bummer. It broke at the same place as yours, right where the cable end wraps and unwraps around the barrel in the shifter. This is normal use, and a high quality cable should be able to handle this for over a year, and usually over 2 years. You can visually check this 'weak point' by pulling the brake lever back and shifting through the gears while watching inside the shifter. If any strands of the cable are broken, you'll be able to see it long before the whole thing reaches it's breaking point (at least with my ultegra levers, not sure if the sora levers allow the same visual access to the cable or not).

Many people replace brake and shift cables every year, whether they need it or not. If you're in a specifically bad climate and your bike is typically "rode hard and put away wet" then you'll have to adjust your maintenance schedule to accommodate.

-Jeremy
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Old 10-11-11, 08:30 PM
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Per a Shimano rep, their 10-speed STI shifters wind the cable taken up tightly inside and the cables are prone to breaking if not replaced regularly. My 5600 105 right (rear) shifter broke the cable inside the shifter after 3800 miles, then again in another 4400 miles. I now replace it regularly every 3000 miles and have still had a few broken strands at that point on maybe a third of my replacements.

It's not just that one shifter of mine. I'm on my third 105 right shifter, having worn out the pawl/ratchet gear on the other two after about 16,000 miles each. They have all been hard on cables; it wasn't just one aberrant set.

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Old 10-12-11, 08:18 AM
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We got one on a cop's bike yesterday. The officer who brought it in said the guy who was riding it was "A big fella," and that he was standing and hammering when shifting when he felt it snap.
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Old 01-14-12, 11:28 PM
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Had another cable snap in exactly the same place this week. Not sure why. I'm going to have all the housings replaced at the same time as the cable, though - maybe there's too much friction in the system and it's overstressing the cable at the shifter?
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Old 01-15-12, 12:01 AM
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There are industrial standards that speak of minimum drum and pulley diameter in relation to cable gauge. As the pulley diameter shrinks the life expectancy before metal fatigue sets in goes down. Most shift levers are near or below the standard design ratio because of space and other limitations.

Modern gear wires are also more prone to metal fatigue form flexing on the lever drum than older wires were because most today are die drawn, or squeezed tighter to be smoother on the outside. This trade off for smoother shifting has a significant cost in fatigue life.

Overall gear cable life depends on where you live and how you ride. It's measured not in days or miles but in the number of shift cycles. Interestingly, people in fairly flat areas may have the shortest life because they might be shifting back and forth between two or three gears, which means that they're always flexing the wire in the same place.

BTW- the wire will try to tell you when it's getting ready to let go. Near the end the wire may stiffen, or have a single strand or two fail changing shift performance. If you suddenly find yourself constantly fiddling with the cable adjuster, and it's been a long time since you replaced the wires, do so now before your 10 speed becomes a 2 speed.
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Old 01-15-12, 08:33 AM
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Originally Posted by FBinNY View Post
There are industrial standards that speak of minimum drum and pulley diameter in relation to cable gauge. As the pulley diameter shrinks the life expectancy before metal fatigue sets in goes down. Most shift levers are near or below the standard design ratio because of space and other limitations.
Bicycles violate industrial mechanical standards in almost all ways and the worst is chain operating conditions. An industrial chain drive will be set up with a precisely straight chainline, adhere to minimum cog tooth counts, stay within prescribed torque and rpm limits and be run in an oil bath or continuous lubrication. It will be expected to have a service life of at least 10,000 hours and often much longer. A derailleur bicycle chain violates nearly all of these conditions and is lucky to last 500 hours (7000 miles at an average of 15 mph is 466 hours).
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Old 01-15-12, 11:23 AM
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[QUOTE=The Chemist;13342439]Hello All,

Tonight I was riding home from work and I noticed that the rear derailleur suddenly became very difficult to shift. After a couple of minutes there was a snap and the rear derailleur cable broke inside the shifter housing.
[/QUOTE
I've seen it happen quite frequently but never to my own bikes. I can only suggest that you replace cables as soon as shifting starts to feel balky or notchy.
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