Quote:
Originally Posted by paradocs98
...now the dead space is improved and there is no sponginess, just power and solid bite. Interestingly, there is still a little bit of play or dead space at the top of the pedal travel...
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There's play at the top of the pedal throw because the master cylinder needs it. There's a fluid duct from the brake fluid reservoir that enters the master cylinder from the side or the top. When you push down on the pedal, you start the piston moving into the master cylinder. The first bit of piston travel closes the duct off as the piston slides past. Until this open duct to the reservoir is cut off, the brake pedal has no back pressure. Once the duct is fully closed off by the piston, the piston starts to build pressure against the the pads in the calipers, but there's still a bit of play because the pads back away from the rotors by the amount of any float or runout in the rotor and wheel bearing assembly. The two factors together are good for an inch or a bit more of brake pedal travel. Once you're actually pushing the pads against the rotors, things firm right up. Note that none of this has anything to do with the design or construction of the calipers.
Quote:
Originally Posted by paradocs98
...The shop owner thinks it's just the way StopTechs feel, because he explained to me that the OEM BMW setup and some aftermarket kits like Brembo use a spring tensioner that keeps the brake pads snugged up against the rotors, resulting in an immediate bite, while StopTech does not use a spring, instead allowing the pads to "float" a bit, being held in place by the locating pins coming from the rotors, and resulting in the slightest bit of pedal travel before biting...
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For pure race cars burdened with excess bearing or knuckle flex under braking and cornering, there are "anti-knockback" springs that can be installed in the caliper cylinders to gently push the caliper pistons and pads against the rotor when the brakes are not applied. This is a race-car only application, and I don't know of any street vehicle that's so weak that it needs this kind of intervention. No BMW does.
What I can guarantee is that the pads are not
"held in place by the locating pins coming from the rotors". There are bolts and anti-rattle springs that keep the pads from banging around in the caliper pad pockets (or falling out onto the road) when the brakes aren't applied, but that has nothing to do with pedal travel. On this point, I have no idea what he's talking about.