Theo, et Listers,
Nice job Theo. I hope everyone recognizes a sound explanation when the read it.
Bob
At 09:38 AM 2/3/99 -0700, Theo Smit wrote:
>I was pretty sure that the 'serial' systems incorporated two pistons
mounted on
>a common pushrod and are therefore equivalent to two 'parallel' systems.
>The thing to recognize is that the brake master piston area is the sum of the
>two individual pistons. Let's say that an original system used a single 13/16"
>master cylinder piston, and that 300 psi line pressure was required to produce
>incipient lockup. So then the pushrod force is 300 psi * 0.518 square in.
= 155
>lb. With a pedal ratio of 5:1 that works out to about 30 lb at the pedal -
>pretty light. So my numbers are wrong, but the math will work out.
>
>Now assume a dual master system was installed with identical 5/8" bores. Since
>it will still take 300 psi *in each system* to produce incipient lockup
>(disregarding brake balance problems), the pushrod force required is 300 *
>0.3066 + 300 * 0.3066 = 184 lbs. Strictly speaking, the pushrod force is the
>sum
>of (line pressure * master piston area) for all master pistons. Using the same
>5:1 pedal ratio gives about 37 lb pedal pressure. Note that due to the
>increased
>master piston area, the pedal travel required to take up mechanical slack in
>the
>pads and shoes has been proportionately reduced. The pedal will feel
firmer, as
>well as requiring more force to stop the car.
>
>The line routing does not affect the braking force required one iota since the
>brake fluid does not 'flow' in the system. The only thing that will affect
>pedal
>firmness is flex in the calipers and rotor assemblies, and rubber line
stretch.
>
>Theo Smit
>tsmit@novatel.ca
>B382002705
>
Robert L. Palmer
Dept. of AMES, Univ. of Calif., San Diego
rpalmer@ames.ucsd.edu
rpalmer@cts.com
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