Quote:
Originally Posted by jkv45
What you stated is true (pads wearing - I read it) but that takes time.
The issue I'm describing is happening any time you use the brake.
Do you see my point?
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i guess it sounds like i missed the part about where the fluid returns to the res....
i've only built one brake system from scratch so lets just describe the entire process for our collective education, yeah?
you have some fluid which is hard to compress. you want to push on something. you use a pump (master cylinder) to push that fluid (which you temporarily store in a brake fluid reservoir) into a tube (brake line) which hopefully wont expand much. that tube is connected to a bigger tube (caliper). that bigger tube has basically a plug in it (caliper piston). so when you pump fluid into that bigger tube as if the bigger tube was a balloon, the plug tries to push out. the more fluid you push into that bigger tube, the more pressure there will be on that plug trying to leave that tube. that plug then pushes on the brake pads which push on the brake rotor which slows you down or whatever. depending on the type of pump (master cylinder) you use to pressurize the cylinder, it may self-return with a spring, have passive return (the leftover fluid pressure pushes the pump back), or even have a mechanical stop to keep it where you set it. some are even controlled by electronics. for a basic rear brake on a motorcycle, you typically only have one caliper and one master cylinder but there are all sorts of different setups. the most common being two calipers on a splitter per master cylinder, or for cheap cars, one tandem res master cyl going into a splitter and then two ratio controls to get to all 4 wheels, but whats weird about cars is they are split cross-wise instead of front/back. so one system has the front left and right rear and the other has the front right and left rear. as you use up brake pad, the brake pad gets thinner, this means you need to push it out further. because the big cylinder (caliper) is fairly large compared to the small cylinder (master cylinder), it can take several times the volume of the small cylinder to move the large cylinder very much. this is why over the lifetime of the pads you need to add fluid into the system (from the brake fluid reservoir), because the fluid needs to physically take up more space inside the caliper to push the piston out far enough to have the pads touch when they are at the end of their lifetime.
what's cool about most car-style brake reservoirs is they are actually tandem in the sense that it looks like one and acts like one when its full, but if one system drains, it is actually two separate bottles inside (a bottle without a top inside the main bottle) so that if one of your systems leaks all the fluid out it doesn't take the fluid from the other system, but you don't have to confuse the drivers by having two fluid reserviors when "Theres only one brake pedal!"
did i get anything wrong?