Michael D. Porter wrote:
> Now, extrapolate that fixed circumstance to the two differently-sized
> wheel cylinders. The smaller bore cylinder _will_ extend more for a
> given amount of fluid delivered than the larger cylinder, and its
> applied force will be less, and because its displacement is more, it
> will extend further for a given volume of fluid. That's hydraulics.
That is hydraulics if the systems were seperate and unloaded. Neither
is true in a Triumph.
> But this does _not_ have an effect on the fluid
> delivered to one half or all of the system. That is wholly dependent
> upon the amount of fluid delivered by the master cylinder, and that is
> dependent upon the distance of the delivered stroke of the master
Hydraulics is not about fluid. The fluid is a carrier of
pressure. Hydraulics is about pressure.
> Yes, I agree that at the point that all friction material is in firm
> contact with braking surfaces is the point at which pressure builds.
...it is also the point at which appreciable movement stops, and
therefore APPRECIABLE FLUID FLOW STOPS. The fluid is effectively
incompressible, and all parts are essentially not moving after
this point. This is why fluid flow is not an issue here.
> If the shoe moves in closer contact with the drum
How can the shoe move closer to the drum after it's already
touching the drum? This makes no sense. Brake pads are nearly
incompressible, especially since the contact area is large.
Touching is touching is touching. After that, it's just more
force making it push harder on the surface.
Let's prove by negation.
The pad contact area on both sides is the same. The wheel
that locks first is getting "more friction" from the pad
than the other side. Friction depends on three things, the
coefficient of surface friction, the contact area, and the
Since the pads are equal, the coefficient of friction
and the contact area is the same, meaning the applied
force is higher on the lock-up side.
If we assume (falsely, but to prove by negation) that the
smaller cylinder is locking up first, then it is
exerting more pressure on the pad. This pressure comes
from the fluid, therefore the SURFACE OF THE SMALL PISTON
facing the fluid is receiving more pressure than the
surface of the larger piston.
This pressure is the pressure of the fluid, times the
surface area of the cylinder face. We'll make up a ratio,
and say that the smaller piston has 2/3 of the surface area
of the larger one. Therefore, the hydraulic pressure in
that wheel cylinder must be MORE than 1.5 times the
pressure in the other cylinder for the wheel to lock first.
So in order for all the above statements to be true,
the pressure in the smaller cylinder has to be more than
1.5 times that of the other. Since the cylinders are
connected, the pressure is not larger, it is always
the same. Therefore this reasoning is false.
/ Trevor Boicey 1992 Celica GT 1975 MG Midget /
`----- firstname.lastname@example.org -------...so close, but so far, gosensgo--'