Nick wrote:
> Assume the master cylinder will move 10cc of brake fluid to the rear
> circuit, every time the pedal is pushed down. That leaves 5cc per cylinder.
> Now when the 3/4" piston moves say 3/8", the volume left behind is 5cc, the
> exact amount of fluid availavble from the cylinder. Now on the 5/8"
> cylinder, that same 5cc change in volume might move the piston 1/2" because
> the bore is smaller and the fluid has no where else to go, so it MUST move
> the piston further out to make room for that same 5cc's. When the piston
> moves further on the smaller cylinders, the rear brake shoe contacts the
> drum sooner than it would with the larger cylinders, hence the smaller
> cylinder will lock up the rear brakes sooner.
Well, fluid displacement is not really a valid way of looking
at the problem to be blunt.
Essentially, a hydraulic system works like a lever. Just
like moving the fulcrum of the lever will increase power
at the expense of travel, so will shrinking or growing
the piston.
Think of it more this way. When you depress the pedal, let's
say you pump the system up to 100psi. It can be much higher, but
100psi is a nice round number.
The pressure that is pushing the brake shoes against the
drum comes from this 100psi pressure pushing on the
piston face. A larger piston has more face, and gives more
pressure. In other words, if you have one large piston
and one small piston, the large piston will take more
of the fluid to travel to the drum, but will deliver
more pressure when you hit the "hard point" of the
pedal.
It's a leverage question. Just like a longer wrench
will given you more power but make you move your arm
further, a larger piston will take more fluid but
will exert more pressure.
In a "braking" situation, the fluid travel is almost
irrelevant. The pads move to contact the drums/discs,
and then they really don't move since the pads are not
really that compressible. At this point, pressing
with your foot just pushes harder on the pads. With
different cylinders, you aren't pushing equally
hard on both wheels. That's bad.
--
.---------------------------------------Ottawa-Canada-GOSENSGO-----.
/ Trevor Boicey 1992 Celica GT 1975 MG Midget /
`----- tboicey@brit.ca -------...so close, but so far, gosensgo--'
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