Jack,
I don't know exactly what you just said but I think I soundly disagree. If you
assume the master cylinder is exerting a constant pressure, the size
of the slave will determine the line pressure and the resulting pressure output
of the slave.
If you don't believe it, go to your garden hose and turn it on full blast with
nothing on the end. Then try it with a nozzle attached to the end with
the thing turned on full blast. Note the difference in the pressure of the
water coming out. It works the same way with clutch hydraulics (and
electric current flow as well). Restrict the flow and pressure increases.
Of course (as Jim G. points out) the pressure required to press the pedal
increases with smaller slave cylinders so in reality, you cna't divorce any
part of the system from the rest in designing hydraulics. But the original
question was about the size of brake cylinders and I think that most
people will agree that if the original master cylinder is still in place, going
to the original wheel cylinders is the proper thing to do.
Regards,
Joe
P.S. I'll have to continue this discussion later today. I'm late for an
appointment!
Jack Brooks wrote:
>
> Joe,
>
> No. Since the pressure exerted by the master cylinder is constant, no matter
> what the slave cylinder size, the smaller slave cylinder would receive that
> constant pressure spread out over a smaller area and therefore provide LESS
> force than a larger cylinder.
>
> The pressure on the back of the slave piston is constant. Having a larger
> piston allows the constant pressure to work on a larger surface, generating a
> larger force.
>
> Think of it this way. What is psi?
>
> PSI is Pounds per Square Inch, or a loading based on an area.
>
> You have a constant pressure in the braking system, say 1,000 psi, or 1,000
> pounds for every square inch of surface. If you have 1 square inch of slave
> cylinder piston, you generate 1,000 pounds of force. If you have 2 square
> inches of slave piston surface, you are applying 1,000 pounds per square inch,
> BUT now you have 2 square inches, so you have 2,000 pounds of force. More
> square inches for the pressure to be applied to, yields more force applied to
> the pads.
>
> Yikes, here we go again, but it can be confusing,
>
> Jack Brooks
>
> >-----Original Message-----
> >From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net]On
> >Behalf Of Joe Curry
> >Sent: Wednesday, June 20, 2001 10:51 AM
> >To: Randall
> >Cc: Jim Gambony; Cwn74@aol.com; tedtsimx@q1.net; MJSUKEY@cs.com;
> >fot@autox.team.net; Triumphs@autox.team.net
> >Subject: Re: GT-6/Spitfire brakes
> >
> >
> >Actually, The question came up in relation to the clutch slave
> >rather than brakes. The delimma I had was whether to use a larger
> >or smaller slave
> >cylinder. The explanation I got is that since the pressure exerted
> >by the master cylinder was constant, the smaller slave cylinder
> >would receive that
> >constant pressure spread out over a smaller area and therefore give
> >more force than a larger cylinder.
> >
> >Think about it this way: If the master and slave cylinders were the
> >same size, the force of your foot would be what is driving the
> >clutch. As the
> >size of the slave is reduced and the master left alone, the
> >resulting pressure on the clutch would increase. Therefore, smaller
> >creates more pressure
> >in relation to the master. I can't find any fault with that argument.
> >
> >oe
> >
> >Randall wrote:
> >>
> >> Joe :
> >>
> >> It gets confusing here, since there are many different places to measure
> >> pressure.
> >>
> >> The force exerted by a hydraulic piston is the hydraulic pressure times
> >> the area of the piston. So, if the system pressure stays the same, a
> >> larger slave piston means more force applied to the shoes.
> >>
> >> Perhaps your authority said the _pedal_ pressure (or the hydraulic
> >> pressure), would be higher with a smaller cylinder (for the same braking
> >> force). Or, perhaps he was talking about the master cylinder (where a
> >> smaller piston gives you more braking force for the same pedal
> >> pressure).
> >>
> >> Randall
> >>
> >> Joe Curry wrote:
> >> >
> >> > Someone (who is supposed to know these things) once told me that
> >if you use a smaller wheel (or slave) cylinder, you will actually
> >get a higher
> >> > pressure than if you use a larger one. It makes sense to me
> >since the ratio between the size of the master and slave cylinders
> >is what determines the
> >> > pressure exerted on the thing that the hydraulics are driving.
> >> >
> >> > So, would going to a smaller wheel cylinder give you lower
> >pressure? According to this source, it would be greater.
> >> >
> >> > Anyone care to weigh in on this issue?
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