Why does my rear derailleur cable housing keep ripping?

[comish83]

Of course on vacation without any of my tools :crap:, my rear derailleur cable housing snapped/frayed one mile into my ride. Of course being by a local bike store I struggled my bike over there in the 11T cog and they replaced the cable and housing (which was less than 3 months old).

25 minutes of cycling later, the same thing happened. What causes this? I did notice the plastic guide under my bottom bracket appeared to be broken. So maybe when I shifted from 39X23 to 39x21 this is what caused the break because the guide maybe moved out of place putting tension on the housing? Im so lost and just want to ride on vacation.....

[rustychisel]

Mechanical? I apologise if my thinking is way off base here, but in the last couple of years I've been thinking...

... cyclists are no longer taught to change gears properly or effectively. Since the advent of Ergo/STI I have seen many more cyclists forcing through changes at full torque, particularly when ascending hills, and I hear the grind-grind-kerCHUNK as the chain is forced across.

... back in the day all cyclists with downtube shifters were taught to ease off the pedalling slightly whilst changing gear.... NOT stop pedalling... but have the drivetrain under less load until the shift is completed. Took but a fraction of a second.

In the last 10 years I've seen a good number of twisted up chain plates and bent front derailleur cages and, also, torn up cable housing as a result of this.

Is your cable housing properly installed. With the correct endcaps and ferrules which should protect the housing itself. Might the above have anything to do with it?

Enjoy your holiday

[carpediemracing]

I'm a "full power shifter", I shift probably literally every time I sprint, and specifically exactly at the same time I initiate my first power downstroke, aka "my jump". I've been doing this since hardened pins came out and probably a little before. Such shifting doesn't mess up properly set up cables/housing. I generally get a few years out of my cables and then I change levers or frames and I replace the gear wire (same housing). I just did that recently, new gear wire in previously used housing, due to a lever change.

I have had derailleur housings fail on me in short periods of time. Once was when I had to turn my bars 90 deg to get the bike to fit in the car. Combined with the very long stem and very low bar position, I have very little extra housing. The Campy housing did a spiral fracture of sorts and just exploded every 2-3 months. This is something that happened a couple times. I went to segmented housing to avoid this problem, and haven't had a problem since.

So for what I read in the first post my thoughts are:

1. It might be that your BB guide was either loose or improperly secured. This could cause there to be more tension on the housing, but, unless you're in the biggest cog, there actually isn't that much more tension. It's the same tension to hold the derailleur in place. It's just the that shifting into the biggest cog might be off because the cable isn't being pulled as expected.

2. Your cables may have been very loose during travel/shipping and then reassembled with some significant piece in the wrong place or loose. I've inadvertently gotten my cable beneath my BB guide as well as over one of the end guides (that keep the cable from falling out of the groove). I've also squished my cable with the washer on the BB guide. Any of these will dramatically increase friction in the cable system and increase the chances of other things happening.

3. If your housing failed spectacularly a few months in then it might be that the housing was curved too much. Either too short, squished in shipping/travel, squished or turned significantly when putting into a car, or even during assembly.

4. Spiral wound housing needs to be capped so the spiral wire doesn't just out too much, otherwise the housing starts to un-spiral. It takes longer than just 3 months though, so I don't think this is the problem.

I think the housing was turned/pulled/squished/curved too much. That kind of force doesn't mix well with spiral wound housing. It's why I use segmented housing. Zero failures since switching over in 2004? It was maybe a year after I got the Z, and fitting the bike in the back of the car was not easy. The failures occurred in the housing between the downtube and the bars, where it had to curve hard when I turned the bars. The housing by the derailleur was fine.

Eventually I had a system for the car where I could fit 5 wheels (2 for the bike plus 3 spares), a full size floor pump, a toolbox, a 50 lbs gear bag, 2 helmets, and a cooler, and not put a single thing in the front seat. I could even bring extra stuff, like a few quarts of oil. But I blew through a bunch of housing packing the bike the first summer I had the car. This picture is just the bike and one pair of wheels.
http://1.bp.blogspot.com/_TbmplkIYLx8/SFu17V-yevI/AAAAAAAAAqc/kE0JQ1Y5QtQ/s800/100_3179-Z-with-bike.JPG

[ultraman6970]

No idea OP, never had that problem, neither seen a person with the problem ever.

[swaterfall]

Very weird problem to have re-occur. Do you have any pics?

I think​ the only explanation would be excess friction and/or tension on the cable. The broken guide could explain that. Stressed​ from shifting while pedaling should not transmit to the cable housing.

[dgauthier]

Pictures would be nice.

Is your rear derailleur cable long enough, like the example in this link?
http://www.parktool.com/blog/repair-help/cutting-and-sizing-cable-housing#article-section-3

[cmbicycles]

Where did the cable fray/break?

[comish83]

The cable housing broke/frayed right at the end towards the rear derailleur. This is what happened both times. The first time I was climbing a very slight incline shifting into an easier gear and the second time I was going downhill shifting into a smaller cog but there was little to no resistance when doing so. I think this was due to the guide under the bottom bracket being out of place and the person (which shop will not be named) not fixing that and causing this issue. I could be wrong. PIC of housing attached

-Mt. Mitchell here I come (once I repair this myself)!!

[cmbicycles]

That piece of housing looks really short for the rear derailleur loop, unless it is going into a sram mtn derailleur or something where it inserts into the front of the derailleur instead of the rear. See the Park link above for a good visual, although I think the one they show as "ok" is just a tad long.

[carpediemracing]

+1 on length. Looks like a housing that runs down from a seat stay mounted stop, not a chainstay one. And a really low chainstay mounted stop at that.

Are the pivots okay in the derailleur? Seems like the cable is pulling harder than should be.

[sales guy]

First thing, according to the giant book of Shimano for manufacturers and frame builders, that piece of housing is to be 292mm exactly from ferrule to ferrule. This is based on the placement of the cable stop and the dropout/length of dropout hanger. This can of course change based on the derailleur you have also like a SRAM or new DA style routing. But the original measurement was 292mm.

Yes, an odd number and very specific. if you go too far out from that-short or long, it can mess up your shifting.

Second, housing is made poorly. It can break very easily. I have seen what the OP has had happen many many times. I save it to show off to people. Kind of cool but sucks when you're on a ride.

Housing is effected by weather and UV rays. I have a brand new set of Campagnolo Record housing in black, it's already cracking! I just pulled it out of the package for a build. Heat, UV, major temp changes, it all affects them. And you end up with the housing cracking or blowing thru.

What stops it, new housing. I find real shimano housing to be better with less issues like this. I used to see it on Suntour housing all the time. Especially the XCD shifter bikes on old Schwinns like the Crosstour. So really old bikes with really old housing.

If your new piece failed that quickly, it's probably cheap housing that had been sitting for quite awhile.

[stien]

Yeah I can see that housing getting awfully stressed because it's so short.

Also, electronic shifting. :ducks:


Funny anecdote: I had put 4000 miles on a bike with 5800 on it and was at the end of a pretty epic riding vacation when my shifting went super wonky. I fiddled with the barrel adjuster and made it a little better but it wasn't where it should be. I had decided to go Etap on this bike and I picked up a group the day I got home. The minute I put the bike in the stand to check out the shifting for the last ride on the 5800 the right shifter cable head snapped clean off in the shifter. It wasn't going to stand for getting replaced without a fight!

[dustyrider]

The cable housing broke/frayed right at the end towards the rear derailleur. This is what happened both times. The first time I was climbing a very slight incline shifting into an easier gear and the second time I was going downhill shifting into a smaller cog but there was little to no resistance when doing so. I think this was due to the guide under the bottom bracket being out of place and the person (which shop will not be named) not fixing that and causing this issue. I could be wrong. PIC of housing attached

-Mt. Mitchell here I come (once I repair this myself)!!

Looks like a housing issue I had on an older full suspension mtb frame.
The internal routing through the chain stay, pain to fish housing in, coupled with a sram x9 rear mech. had my housing splitting exactly like that. There was just no way to route the housing to relieve the pressures of shifting with that particular rear derailleur and bike.

[weisan]

Try again. If it breaks again... You need an exorcist, not a mechanic.

[Tony]

I agree, housing looks too short.
May want to try something like this.
https://fairwheelbikes.com/alligator-mini-i-link-shift-housing-cable-kit/

Have on my road bike for the last three years, light and smooth shifting.

[tctyres]

BTW, if you have a screwdriver in your toolkit, you shouldn't have to limp in the smallest cog.

The guys at GCN show two different ways of dealing with a snapped cable.


https://youtu.be/obUkL-Ya8dE

[Tony]

BTW, if you have a screwdriver in your toolkit, you shouldn't have to limp in the smallest cog.

The guys at GCN show two different ways of dealing with a snapped cable.


https://youtu.be/obUkL-Ya8dE

I always carry zip ties, can be used instead of the cable.

[oldpotatoe]

I agree with others, housing too short and find some shimano or Jagwire 5mm der housing and find some Wheels 5mm BRASS ferrules', not the crappy plastic ones.

Or maybe the housing was 291mm...ya know, and that's why it split...:eek::rolleyes:

[sevencyclist]

I think your cable runs down the seatstay and loop back into the rear deraileur. However, the loop can sometimes rotate inwards and gets rubbed by the cassette, thereby wearing out the cable housing and fraying the cable.

Perhaps you can ziptie the cable to the seatstay towards the outside, preventing the loop from rotating into the cassette.

Hope this helps.

[sales guy]

I agree with others, housing too short and find some shimano or Jagwire 5mm der housing and find some Wheels 5mm BRASS ferrules', not the crappy plastic ones.

Or maybe the housing was 291mm...ya know, and that's why it split...:eek::rolleyes:


I know it sounds stupid. But seriously, 292mm.

I had a shop at the time I found this out. I was a Merlin dealer back when Rob V was there. So ages ago. And we were building up a custom Merlin Tri bike. I couldn't get the rear to shift well. It was a full Dura Ace kit with Dura Ace hubs for the training wheels and Zipp's for the race wheels. No matter what I did it wouldn't shift.

I ended up calling up Merlin and Rob told me the 292mm measurement. I laughed and told him I didn't buy it. Sure enough, it worked.

I had never seen the book until I worked for a frame company and then a components manufacturer. But it worked and that was the recommended size.

Again, a few mm's or two either way works. But past that you can end up with shifting issues and of course cracked housing.

Oh, and remember, 5mm housing is supposed to have 1.2mm inner wires. 1.1 is for 4mm housing.