How brakes work

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    psbarham
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    Join date : 2010-07-04
    Age : 43
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    How brakes work

    Post  psbarham on Mon Jul 12, 2010 2:38 pm

    i wrote this ages ago for a mate of mine who was having a few problems after fitting brembo calipers to his car , i thought this might be of interest to someone

    how brakes work

    The master cylinder is the heart of the hydraulic system. It converts the force exerted on the brake pedal into hydraulic pressure that applies the brakes. Depressing the brake pedal moves a push rod in the master cylinder. Mounted on the push rod, are a pair of pistons (primary and secondary) in tandem (one after the other) that exert force against the fluid in the master cylinder bore. This creates pressure, which along with the fluid that's displaced by the pistons is routed through the brake lines to each of the wheel brakes.
    Because brake fluid is incompressible, it acts like a liquid linkage between the master cylinder and each of the wheel brakes. Any increase in pressure that is created in the master cylinder is instantly transferred to each of the brakes. So as the pistons in the master cylinder push against the fluid, it displaces fluid through the brake lines. This pushes the disc brake caliper and wheel cylinder pistons outward to apply the brakes.
    When the brake pedal is released, the spring-loaded piston assembly in the master cylinder returns to its rest position. The fluid that was displaced by the pistons is pushed back to the master cylinder as the disc brake pads kick out away from the rotors and springs inside the drums retract the brake shoes. The fluid returns to the fluid reservoir through the "compensating ports," which are small openings between the master cylinder bore and fluid reservoir just ahead of each of the pistons.

    why the pedal was soft
    I hope that made sense to everybody, you! at the back, wake up it is about to get even more boring and less likely to make sense , judging from the description Derek has given me is down to the ratio between the master cyl and the calipers , the master cyl will only displace a set amount of fluid in one stroke for example 10cc now in his old calipers this was enough to push his pistons out by 10mm, enough to apply the brakes firmly without the pedal hitting the floor ( I know it isn’t 10mm in reality but it is an easier no. to work with ) now with his new calipers the surface area has increased by a considerable amount not only at the front, up from 2 pots to 4 pots , but also at the back ,up from 1 pot to 2 pots , this now means that the total surface area of the pistons has gone up and that the 10cc of fluid that was moving the pistons 10mm before is now only moving them 5mm , the only way to over come this is to find a master cyl with a bigger piston area so it displaces more fluid in one stroke preferably about 20 to 25 cc this will give you the 10mm of piston travel , I’m assuming that an evo 7 master cyl will fit the bill to match the calipers , this will hopefully restore his brakes .

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