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Old July 26th 05, 02:24 AM
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Default Brake Trouble / Road Bike

Sheldon Brown writes:

I just changed the brake cable on my old Miyata Road bike... When
I apply the Shimano 105 rear brake, one pad stays on the rim and
does not spring back when released. The brake levers are also 105
AERO and not STI. How can I fix this problem? Am I installing
the cable wrong?


It's not the cable!


Actually, it could be. If the loop of cable running from the back
end of the top tube to the brake caliper is too short, and possibly
even if it's too long, it can do this.


Let's assume that much about brake adjustment is understood. tension
in the cable should have little effect on centering, at least to the
amount that they might not move equally.

See: http://sheldonbrown.com/cables for tips on cable installation.


Dual Pivot brakes were introduced to prevent the asymmetric pad
movement you describe.


But he doesn't have those.


Who said he had dual pivot brakes? I only mentioned that because this
is a classic problem in single pivot brakes.

You'll notice that the return spring slides in the caliper when the
brake is used. This sliding assumes that both spring ends are
perfectly lubricated, which they are not. Therefore, brake pads in
single pivot, and even centerpull brakes, generally do not retract
equally after use in rain or dusty terrain.


Shimano SLR calipers use nylon or Teflon pads that the spring bumps
against, which generally don't require wet lubrication.


I installed Teflon sleeves in my Campagnolo brakes in the 1970's and
realized that the effect was minimal. We wouldn't have dual pivot
brakes today if plastic sleeves were an adequate fix for that problem.

These are the finest single-pivot calipers ever made. I've got these on
my fixed gear tandem...


Unfortunately, bicycle repair shops, unaware of the cause, use hammers
and punches to bend the offending spring


That technique was appropriate for some older sidepulls, models dating
from the early '70s and older, and was the only way to regulate the
centering of the caliper.


I don't believe it was ever appropriate. The anchor bolt on those
brakes could be rotated and the springs lubricated just the same as on
later more expensive brakes. It was on Universal side pull brakes
that I first recognized the problem and cringed when I saw the hammer
routine.

or repeatedly rotate the center bolt


Campagnolo invented the center bolt with wrench flats to permit it
to be turned/held with a cone wrench for correct centering. This
was a major breakthrough.


As I said, you could rotate the center bolt without the 13mm wrench
flats and I did. It was one of my disappointments with Campagnolo
because since those days I designed a return spring that does not have
(cosine error) slip when returning the caliper. It's coil is
concentric with the center bolt and does not have this problem.

For the Shimano single-pivot sidepulls, the end of the center-bolt
is the point to turn/hold, using either a 5 mm Allen wrench or a 12
mm box wrench. Best to loosen the mounting nut, turn the center
bolt to center the caliper, then tighten the mounting nut while
holding the center bolt from turning.


instead of cleaning the contact and giving it a drop of oil. Just
a drop of oil is often enough.


Since the spring does not change, logically only cleaning and
lubrication is the right response. It has nothing to do with whether
there is a solid lubricant at the spring contact.

The oil is the way to go for calipers that have metal/metal contact
between the spring and the arm.


Sheldon "Symmetry" Brown


Dual pivot brakes are not symmetrical and that's where we're at!

Jobst Brandt
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