Gear cable health

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peetee
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Gear cable health

Post by peetee »

There have been a lot of posts regarding Indexed gear change issues and with each come enquiries regarding the health of the cables fitted. If I ever come across poor indexing on a bike that hasn’t been dropped or damaged investigating the cables is my first step. I’d just like to add this new post to illustrate a few common issues. It’s worth adding that there is no direct correlation between quality of bike and quality of workmanship and I have seen such issues on expensive and cheap bikes alike. Some of these issues are age-related and others are shoddy workmanship that (usually, but not exclusively) cause problems from day one.
6CD64DB7-0231-459C-A5F0-02E18933015F.jpeg
The first photo shows the end of a gear cable outer with the cap removed.
Problem 1; It can be seen that the metal strands are exposed. This is because the outer plastic sleeve has shrunk. Some cables are more prone to this than others and it’s worth checking regularly for this problem which can cause the wire strands to splay and cause problem two:
Problem 2 is the split running down the cable. again this can allow the strands to splay, allow moisture and dirt in and more rapid deterioration of inner cable and outer due to compression splay propagating the split. This issue also comes about when second-rate cable cutters are used. The cable is pinched too hard before it is cut and the outer casing is crushed and splits.
Problem 3; The metal strands which take the bulk of cable compression force are cut such as that they do not do an equal share of that force. They should be cut directly across the cable so they are of even length. Note that bends in the cable should be maintained when inspecting as straightening out a cable may result in an uneven appearance to the length of those strands.
Problem 4 is shrinkage of the inner liner. Not a great deal on its own but it usually accompanies shrinkage of the outer and indicates cables that are past their best. On cables that are tightly routed or cut to a less than ideal length this shrinkage may cause friction and wear if the inner cable contacts the outer cable strands on tight turns.
Problem 5; the cut cable strands have ‘chisel-point’ ends that are likely to cut into and even break through the plastic end caps. This is particularly problematic at the shifter and I have seen these strands work their way right into a shifter mechanism wrecking it.
15E51669-5E49-4ADB-9632-B80333A04439.jpeg
Picture two shows a cable that has been cut correctly with sharp, dedicated bicycle cable cutters. Following this the ends are filed flat to provide a perfectly even, flat surface that allows the entirely of the cable outer to resist the inner cable tension and give clean accurate shifts every time and significantly lengthen the service life of the cable. Where possible the cable should be cut to replicate the curvature it takes when sited on the frame. As mentioned above, long or tight bends such as can be found by some rear gear mechs will result in strands on the inside of that bend protruding from the cable end.
Last edited by peetee on 5 Feb 2023, 8:00pm, edited 4 times in total.
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rjb
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Re: Gear cable health

Post by rjb »

I use a grinding wheel to dress the cable end perfectly square then use a pointy thing to form the inner liner whilst it's still warm and soft. A scriber works well for this or a thick needle point. :wink:
Filing the cable end is not always satisfactory as a single core can catch in the file and rip the outer sleeve IME.
gxaustin
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Joined: 23 Sep 2015, 12:07pm

Re: Gear cable health

Post by gxaustin »

Never had a problem with filing. I can't imagine how you could dislodge a strand of outer unless very ham fisted, or maybe using a rasp :wink:
francovendee
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Re: Gear cable health

Post by francovendee »

I touch the end lightly with a grinder. I also have a cup of water nearby to cool it before heat makes the plastic shrink.
The final thing I do is to use a fine drill in the Dremel to clear any burrs in the hole.
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Mick F
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Re: Gear cable health

Post by Mick F »

Never had any issues with gear outers or cutting them. Never needed to dress them or use a grinder.

To cut them, use a pair of good quality cable cutters, but slide a suitable length of inner inside. So, when you cut, the outer doesn't crush.

Also, either use Campag cables (lubricated for life) or Jagwire.
Mick F. Cornwall
TheBomber
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Joined: 16 Feb 2020, 8:18pm

Re: Gear cable health

Post by TheBomber »

peetee wrote: 22 Dec 2022, 9:38pm
Problem 1; It can be seen that the metal strands are exposed. This is because the outer plastic sleeve has shrunk. Some cables are more prone to this than others and it’s worth checking regularly for this problem…
Interesting - I’d be meaning to post asking this very thing as my (white) Shimano cables do this quite quickly. I’ve taken to leaving the outers a little long so that when it occurs it is possible to draw back the inner, trim a cm off the outer and then reassemble without having to replace the whole thing.
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531colin
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Re: Gear cable health

Post by 531colin »

TheBomber wrote: 23 Dec 2022, 1:36pm
peetee wrote: 22 Dec 2022, 9:38pm
Problem 1; It can be seen that the metal strands are exposed. This is because the outer plastic sleeve has shrunk. Some cables are more prone to this than others and it’s worth checking regularly for this problem…
Interesting - I’d be meaning to post asking this very thing as my (white) Shimano cables do this quite quickly. I’ve taken to leaving the outers a little long so that when it occurs it is possible to draw back the inner, trim a cm off the outer and then reassemble without having to replace the whole thing.
Is that then a (semi) permanent fix? ie once the white outer sheath has shrunk, is it then stable?
....and can you just trim off the few millimetres exposed when the outer shrinks without trimming the outer sheath itself?
TheBomber
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Re: Gear cable health

Post by TheBomber »

531colin wrote: 23 Dec 2022, 4:50pm Is that then a (semi) permanent fix? ie once the white outer sheath has shrunk, is it then stable?
....and can you just trim off the few millimetres exposed when the outer shrinks without trimming the outer sheath itself?
I’ve always thought of it as buying more time for an existing cable rather than a permanent fix, but now you mention it maybe the shortening is only required once. I have one that could be done now so perhaps I should report back in 12 months whether there has been further shrinkage.

I’ve always cut back into the plastic in order to get a clean cut but if you have very good cutters you could try trimming only the exposed wire strands.
TheBomber
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Re: Gear cable health

Post by TheBomber »

531colin wrote: 23 Dec 2022, 4:50pm
Is that then a (semi) permanent fix? ie once the white outer sheath has shrunk, is it then stable?
....and can you just trim off the few millimetres exposed when the outer shrinks without trimming the outer sheath itself?
Coming back to this topic from December last year. While the shifting on my bike was still working it felt spongy and less precise, so time for some cable maintenance. The plan was to trim the exposed wire strands and then reassemble with the same parts.

All the outers had shrunk as expected:

95D1B591-B7CC-44C5-AE40-B5117E1E1AFD.jpeg

so I chopped 8mm off each and put it all back together. Trouble is, this is a Shimano 10 speed bike with the old cable pull ratio so everything has to be perfect for it to work - and removing cable inners and replacing is not perfect. Maybe I could have tried greasing the inners but I don’t have the Shimano cable grease and have never found using bearing grease to work. So I got some new inners and outers from the draw and used them. Which means I won’t know whether the shrinkage is a one time thing or just keeps going.

But here’s a thing - the outer I took from the drawer is from the same length as the existing outers on the bike, but it hadn’t shrunk. It’s kept in the same environment as the bike - less than a metre away. The only difference is it hasn’t been flexed through use or exposed to much daylight. So clearly if you want your cables to last, then ride after dark in straight lines.
iandusud
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Re: Gear cable health

Post by iandusud »

I would add to this that there is considerable difference in quality of different gear inner wires. I have been struggling with downshifts to the inner chainring on our tandem with STI shifters, despite fitting new inner and outer cables. This issue was friction in the first cable run from the shifter. Replacing the inner wire with smooth finished one was the instant cure. The one it replaced was one a quantity of std stainless steel inner wires that I have however I don't think it coped well the tortuous routing imposed by the STI lever.
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