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Brake Trouble / Road Bike



 
 
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  #21  
Old July 27th 05, 07:23 PM
Werehatrack
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Default Brake Trouble / Road Bike

On Wed, 27 Jul 2005 13:41:05 -0400, Sheldon Brown
wrote:

Quoth Jobst Brandt:
I don't see why that [bending the spring] was the only available
method. How did you initially poisition the brake caliper was with
pads adjacent to the rim? Why could the centerbolt not be
rotated? I don't believe it was riveted or welded in place.


The block on the centerbolt that had the groove for the middle of the
spring also had a concave groove on the other end.

The front one had a large radius to match the curvature of the front of
the fork crown.

The rear one had a smaller radius, transversely oriented groove that fit
snugly against the seatstay bridge.

These parts could not be rotated because of the curved interface to the
frame/fork.

Bending the spring was the _only_ way to adjust the centering.


And even when the springs and pivots were lubricated appropriately,
they often didn't stay centered very well. These were not high-tech
units with a lot of attention to good engineering. They were made to
be simple to install (even if that required some inelegant field
adjustment) and simple to service. That the installation and
servicing sometimes involved the use of two pairs of pliers or a
hammer to bend the spring was considered acceptable procedure. I've
seen various attempts to overcome the lack of reliable centering,
often including the use of a Nylock nut left somewhat loose at the
back end of the mounting so that the caliper could float a bit. That
latter technique was fairly common in the late '60s. It was
considered preferable to have it rub *lightly* but able to deflect
instead of having the brake rub hard on one side when it didn't return
properly for some reason...which was more often than a lot of people
could ignore.


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  #22  
Old July 27th 05, 09:07 PM
Sheldon Brown
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Default Brake Trouble / Road Bike

Jobst Brandt wrote:

Somehow these threads drift off into unrelated topics, probably to
defend a defenseless position that no one else knows the writer holds
until defended here.


You were the one who brought up the issue of using a hammer and punch,
with your categorical statement that "I don't believe it was ever
appropriate."

The subject of this thread was centering a modern high quality Shimano
brake, not steel caliper Raleigh brakes of decades ago. Even those
brakes recognized the problem and made spring bosses pressed onto
knurled center bolts that were pressed in place to assist adjusting
brake position.


That's not correct. The "spring bosses" were either threaded onto the
center bolts (for the cheaper models) or were a slip fit over the center
bolts. The part involved was a single casting, nothing knurled, no way
to rotate the front vs the back.

Let's leave the hammer and punch in the historic bin.
There is no place for them on any recent aluminum alloy brake caliper.


That's true.

Sheldon "Loves Old Raleighs" Brown
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  #23  
Old July 27th 05, 09:54 PM
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Default Brake Trouble / Road Bike

Sheldon Brown writes:

Somehow these threads drift off into unrelated topics, probably to
defend a defenseless position that no one else knows the writer
holds until defended here.


You were the one who brought up the issue of using a hammer and
punch, with your categorical statement that "I don't believe it was
ever appropriate."


I still believe that because, as I mentioned, I never used that
method with those old brakes that did not have wrench flats as the
later Campagnolo brakes did. I got to see many different brakes in
the days when the brake design concept was as volatile as it is today
but with less understanding of the problems being addressed.

The subject of this thread was centering a modern high quality
Shimano brake, not steel caliper Raleigh brakes of decades
ago. Even those brakes recognized the problem and made spring
bosses pressed onto knurled center bolts that were pressed in place
to assist adjusting brake position.


That's not correct. The "spring bosses" were either threaded onto
the center bolts (for the cheaper models) or were a slip fit over
the center bolts. The part involved was a single casting, nothing
knurled, no way to rotate the front vs the back.


Some were, while others were one piece and yet others were knurled and
pressed into the base block. That doesn't change the cause of brakes
retracting asymmetrically with longer use, primarily a result of
friction at the spring contacts... the subject of this thread if I
recall correctly.

Let's leave the hammer and punch in the historic bin. There is no
place for them on any recent aluminum alloy brake caliper.


That's true.


Just the same, it is worth mentioning up because the method is still
in use in bicycle maintenance on the basis that it had been done
before by noted mechanics... much like tying and soldering spokes.
These things live forever.

Should they be challenged or is bicycling lore the poorer for it?

We could delve into the sham of Gore-tex (R) next.

http://www.thebackpacker.com/beginners/goretex.php

just for starters.

Jobst Brandt
 




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