On 2018-04-30 13:02, jbeattie wrote:
On Monday, April 30, 2018 at 9:24:31 AM UTC-7, Joerg wrote:
On 2018-04-30 08:19, jbeattie wrote:

[...]

... Did you change the housing after the failures?


No, though I did smooth the channels a little with fine-grit
sandpaper and polishing paste. Couldn't help much though because
the heads simply pulled out of the cables.

Besides, why do we as end users a.k.a. consumers have to correct
design mistakes on bicycles so often?

Most cable failures occur over time and involve breaking of
individual strands -- which should be noticed with routine
maintenance. There are housing, lever, adjuster and ferrule
designs/installations that can hasten cable failure, but a
catastrophic failure probably means a defective cable. IIRC, Shimano
did recall some cables 10+ years ago because of ends popping off.
And most of the "design" problems with other brake parts usually
result in symptoms long before the failure, like brakes that are
stiff, sticky, etc. These are usually symptoms of a cheap bike, too.

More curious tech problems: I currently have an Avid BB7 rear cable
disc on my commuter that is in housing all the way from the lever to
the caliper. I expect drag, and the return springs on the Avid
brakes are not great -- better than the first generation BB7, but
still not great. So, I expect cable drag from the housing and even
some pad drag caused by the weak return spring.


What I occasionally do is let the bike rear up against a wall, propping
it all up so it won't slide back down. Then I tie a cotton chunk around
the cable where it comes out the jacket at the rear caliper and fasten
the lever slightly pulled. Now I drip some oil on at the lever and let
that run down the cable. A few drops every hour or so, whenever I happen
to be in the garage for other reasons. Eventually the cotton ball gets
oily and then I stop and clean it up. Similar with the front brake but
then I need to lay the bike. I like to keep things nicely lubed.


What I didn't expect is that the brakes would self-tighten. It's the
oddest thing. The brakes just tighten up, and the torque arm is
fully retracted -- so its not a stuck cable. In some instances, I
think it is because the rear axle has smooth faces, and the wheel can
get cocked under load (and with a tight QR), but I've even had the
brake drag after dropping the wheel to make sure it is straight. It's
like I have a haunted rear brake caliper.


Car drum brake pads had that since a long time on some of the better
models. Decades. As the pads wore, a little "sticky cog" would be
slightly turned and that made the pads not retract as far as when they
were new. That saved a lot of frequent maintenance. I always wondered
when the bike industry would learn this but maybe the 100-year learning
curve isn't up yet :-)

At least your bike seems to have "inadvertent self-adjust".

One thing I never liked about many mechanical disc brakes is that they
only have a piston on one side. As the pads wear the rotor gets pulled
sideways more and more. They could have done a better design job.

--
Regards, Joerg

http://www.analogconsultants.com/