Re: Brake Piece

["Joe Zaccaria" <jzaccaria@xxxxxxxxxxxxxx>]

Thomas you are correct.  It seems that most of us have studied hydraulics at
some point.  It is simply another way of benefitting from the physical
properties of mechanical advantage.

Zac
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- ----- Original Message -----
From: "Thomas Emberson" <thomas@xxxxxxx>
To: <ST@xxxxxxxxxxxxxx>
Sent: Monday, February 12, 2001 1:35 PM
Subject: Re: Brake Piece


>
> From the discussions I think one point has not been made clear. When
> the lever is full dis-engaged, that is no hands on it, all the way
> out etc.  there is a completelopen path of fluid from the reservoir
> to the slave cylinders.  Which is why the MityVac works :-)
>
> The pads will always travel in as far as they are pushed. Which is
> why brakes will require more pull distance is the rotor is warped
> a bit, as the pads will get pushed in further. As pads wear they
> do not push in as far thus more brake fluid stays in the slave
> cylinders.
>
> You could have pads that start out 12" thick, as long as you had
> the travel in the slave cylinders and enough fluid the master
> cylinder reservoir. In fact, in such as case the brakes would
> actually get firmer as they wear, because as they wear, become
> thinner the friction material would be less compressible as it is
> thinner. And as we all know brake fluid is not compressible.
>
> In other words, the master cylinder only has to be big enough for
> the instantaneous movement of the slave cylinder, not for the over
> all movement of the life of the pads.
>
> Anyway, if you look at you bike, and how much surface area there
> is on the slave cylinders, you can see why you would come close to
> emptying the reservoir through the complete life of a set pads. In
> fact, what we are talking about is the power of hydrolics, the
> master cylinder moves save 1 cm with 20 lbs of force, where the
> slaves travel 1mm with 200 lbs of force.
>
> Thus, stoppies for all. It's in the constitution :-)
>
> I shut up again.
>
> t.
>
> On Mon, 12 Feb 2001, Paul Fox wrote:
>
> > zac -- thanks for the reply...
> >  >
> >  > There are some basic laws of physics that apply here.  First if there
was a
> >  > size mismatch between the master and slave cylinders the brakes would
never
> >  > work properly whether or not the pads were worn.  You see one of the
great
> >  > benefits of the disc brake caliper system is that they are self
adjusting.
> >  > What this means is simply that as the pads wear, the calipers retain
a bit
> >  > more fluid so the volume of fluid under pressure required to apply
the
> >  > brakes never changes.  Therefore the concept of the brakes being less
> >  > effective when the pads have worn is an incorrect one.
> >
> > yes, after sending my question i realized that that would normally be
> > the case.  the problem would come if the total volume of the slave
> > cylinder with worn pads were greater-than, or maybe even
> > nearly-equal-to, the volume of the master.  in that case, pulling the
> > lever the whole way in would _not_ yield adequate pressure on the
> > pads, right?  the lever would bottom out before the system had
> > pressurized.  i'm not saying this is the Sprint problem, i'm just
> > pointing it out as a possible design flaw.  this could result from
> > a late change in the specification for the pads, for instance -- if
> > they had lower wear limits than the system was designed for, the slave
> > cylinder would need to be bigger.
>
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