Hey, you got it right! Bigger wheel cylinders = more pressure on the pads.
I was amazed at the opposite opinions. We increased the size until we went
too far & loacked up the rear wheels easily and then came back. @ $12 a
cylinder it was the easiest way.
Think about a trolley floor jack. A small pump pistons pushes a large
piston in the lifting ram. A small piston pushing a large one takes more
strokes but the large piston will exert more force (but with less travel).
Greg Burrowes
GM Holden Torana XU1 #50
Historic Touring Cars Australia
-----Original Message-----
From: owner-vintage-race@autox.team.net
[mailto:owner-vintage-race@autox.team.net] On Behalf Of Simon Favre
Sent: Wednesday, 12 May 1999 4:21
To: Haynes, Mark
Cc: 'Greg Burrowes'; Vintage Race
Subject: Re: beginners tech question
What you apply to the pedal is a force. Multiply that by whatever pedal
ratio you have and you still have a force. Divide that by the area of the
master cylinder piston and you get a pressure. Multiply that pressure by
the total area of wheel cylinder pistons and you get back to a force which
is applied to the brake pads or shoes. It's the ratio of master cylinder
area to wheel cylinder (or caliper) piston area that determines stopping
power. A smaller master cylinder piston means more pressure in the lines
because the force is divided by a smaller area. This makes for less pedal
effort, at the expense of more pedal travel. A larger master cylinder gives
less brake line pressure because the force is divided by a larger area.
This makes for greater pedal effort, and reduced pedal travel. The opposite
is true for wheel cylinders. A smaller wheel cylinder produces less force
on the shoes or pads for the same line pressure. On some cars, it's easier
to change the master cylinder, on some the wheel cylinders.
At the wheel cylinder, the relationship is intuitive, that is, bigger
cylinder = more stopping power = less pedal effort. At the master cylinder,
the relationship is counter-intuitive, that is, SMALLER cylinder = more
stopping power = less pedal effort.
"Haynes, Mark" wrote:
>
> Greg- By my recollection (which may be faulty) of hydraulic theory, if you
> take a specific traveling volume of fluid (hydraulic line), and apply the
> pressure over a larger applied area (i.e. a larger piston diameter) you
wind
> up with less pressure per unit area, thus decreasing the braking effect
> (actually the same pressure over a greater area). Anyone know for sure if
> my theory of hydraulics is correct??
> Mark Haynes
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