On 08 Sep 2009 01:31:55 GMT, Jobst Brandt wrote:

Steve who? wrote:

I have a 10-speed Ultegra equipped road bike in which the rear
derailleur cable keeps breaking strands near the shifter which
necessitates a cable replacement. The broken strands occur about
3/4" from the barrel. This is currently happening every 3000 miles
or so.

Originally I was using Jagwire replacement wires as that seems to be
what most local shops now carry. At the last replacement I decided
to opt for real Shimano inner wires. When removing the old cable I
compared the cable diameter and found that the Jagwire inner wires
were .010-.015" smaller in diameter compared to the new Shimano
inner wire. Also at this time I replaced the plastic ferrules with
the aluminum variety as recommended by the LBS that sold me the
cable.

Fast forward about 6 months. This weekend I was cleaning and
inspecting the bike in preparation for the upcoming MS 150 event
next weekend. Much to my surprise I found a broken strand in the
new Shimano cable necessitating yet another cable replacement.

As You probably noticed, a new cable cannot be broken with all the
force possible with a shift lever. Bowden cables break when a strand
on the inside of a (sharp) curve wears half way through. Because all
strands pass that point when shifted, they are all worn half through
in the inside of the curve and can then be easily broken by bending
under even light tension.

When removing the old cable rather than unwinding the broken strand
I picked up a pair of regular needle nose pliers that happened to
have side cutters built in and to my amazement these cutters went
right through the cable! In the past I can remember these steel
cables being un-cutable by this method. For identification purposes
the side of the cable barrel has an "R" stamped in the side of it.

Cutting with diagonal cutters (the kind you used) is good practice and
does not splay the cable, because the cable snaps back to its helical
wound shape. The important thing is to get rid of that sharp bend
where the break occurs. That is usually a kink in the cable housing,
so get a new one or cut the old ones kinked end off. The same goes
for brake cables. If you see a cable housing come off its anchor at
an angle, that is a sharp (damaging) bend for the cable.

So is this a characteristic of the newer cables or does Shimano have
several different grades of shifter cables? If so how do I know
which one best and which one I am getting?

There are various kinds with different strand diameters, single wound
and compound wound. Compound wound is often used to make the control
cable more flexible, something we inherited from the short bends used
for cables that follow handle bar contours. The were first common on
Campagnolo bar end shifters.

Any other things that I should check that might be causing these
premature cable failures?

Do it!

Jobst Brandt

Jobst,

I don't see any obvious bend in the housing near the broken strand but
I will probably replace the housing anyway. The main bend I see in the
inner wire is where the cable wraps around the drum in the shifter
itself.

Steve