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Re: [T3] Brake Pedal Set Up

andy wrote:

>>The reason is to ensure that there is enough movement possible for the pedal in
>>case one circuit fails, as the pedal then moves the full distance that circuit
>>allows before pressurising the other (hopefully OK) circuit.  You don't want it
>>to hit the bulkhead before it can do that.
>this doesnt make any sense to me. from my understanding....
>a dual circuit MC uses one circuit for the fronts and one for the rear.
>they are both always active. if you lose one you still have half of your
>brakes, unlike a single.
>the reason the mc needs to fully disengage is to allow the pressure
>release ports to open. otherwise there will always be pressure on the
>brakes, your mileage will suffer, they could overheat and they will wear
>out prematurely.
Having played around with my master cylinder on my bench, this is what I
think happens (and I very well could be wrong and grossly oversimplifying)

Assuming everything is working properly, when you press the pedal,
you're pushing the piston that drives the rear circuit first, and the
hydraulic pressure therein pushes the front circuit along also.
Something in the way the springs are tuned probably governs the
proportioning (since these cars don't have the proportioning valves you
normally see on more modern vehicles)

If the rear circuit fails, the rear circuit spring collapses and the
rear piston collides with the front pistion and you need all the pedal
travel you can to drive the front cylinder. If the front circuit fails,
the front circuit spring collapses and you need the travel to pressurize
the rear circuit once the front piston hits the end of the bore in the
master cylinder.

Thus, being able to maximize pedal travel is an important safety
adjustment. The master cylinder needs the slack to allow the master
cylinder to be fully disengaged, else the brakes will certainly drag and
overheat and fade (and boil the brake fluid if it gets hot enough).

Am I right here?

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