Re: [CR]Was: 57mm Campy calipers.. Now: tuning Campy brakes

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From: "dddd" <dddd@pacbell.net>
To: "Classic Rendezvous" <classicrendezvous@bikelist.org>
References: <000301c6335d$82eb9490$6501a8c0@maincomputer>
Subject: Re: [CR]Was: 57mm Campy calipers.. Now: tuning Campy brakes
Date: Fri, 17 Feb 2006 04:26:24 -0800
reply-type=original

The deflection of metal springs is linear, unless and until the configuration is altered by gross geometry changes, hardly applicable here.

The reduction of pre-load tension follows through the entire travel. It's less of a % of the total tension as the tension increases with lever travel, but a 10# reduction remains a 10# reduction even as the pads clamp the rim.

My own experience with NR calipers had me doing everything but bending in the springs, and when that still didn't cut it I finally bent each side of the springs inward several mm using some twisting action with a pair of pliers, off the bike. I measured and reduced the static pre-load by about half.

I was really surprised how much the power improved, especially from the hoods! It used to take much of my strength just getting the pads to the rim, but now a good pull (more like a twist) from the tops translates into stoppage and it's plenty of response for paceline work. I have since done the same tweak to Weinmann and Superbe calipers with equally satisfying result, and it's never so slack as to allow the levers to rattle. Next I might try this with some 750 center pull calipers on my Pedersen, but disassembling those things to get a grip on the short, stiff springs just doesn't sound much like fun.

David Snyder


----- Original Message -----
From: Ken Freeeman
To: 'Raymond Dobbins'


> Ray, springs are not really my field, but what you say seems to make

\r?\n> sense.

\r?\n> We're dealing with the stiffness of the spring wire in a bending

\r?\n> deformation, and the difference between the compressive stress and the

\r?\n> tension stress is greater with greater diameter. Re-setting the spring

\r?\n> might reduce pre-load, which might reduce resistance at the idle or

\r?\n> "unbraked" position.

\r?\n>

\r?\n> Come on, other engineers, I (a poor EE) need some smart ME's to tell us

\r?\n> what's really going on here!

\r?\n>

\r?\n> Ken Freeman, Ann Arbor, MI

\r?\n>

\r?\n>

\r?\n> dale,

\r?\n>

\r?\n> somewhere i read instructions on how to decrease the tension of the

\r?\n> caliper springs, and it involved bending each side an equal distance using

\r?\n> a

\r?\n> hammer and punch. but i wonder if that really does anything for the

\r?\n> tension.

\r?\n> my non-engineer mind thinks that the only thing that would accomplish, is

\r?\n> change the outermost position of the spring arms. wouldn't tension in the

\r?\n> springs be determined primarily by the gauge of the metal? so even if you

\r?\n> move them in, the tension wouldn't change.

\r?\n>

\r?\n> engineers, what say you?

\r?\n>

\r?\n> ray dobbins