hydrolic disk brakes and wear of the pads...

[RootsAndRocks]

I've had my new bike for a few weeks only, and I'm wondering how the brakes behave as the pads keep wearing off. Will travel of the lever increase to engage the brake? It's different than in a car, as in my Shimano brakes there is a pads-spreading spring, so I think a worn-out pad would have to travel further to touch the disk.

[FullMonty]

no, the pistons self-adjust for pad wear. your lever travel should be fairly consistent until perhaps the very end of the pad life.

[RootsAndRocks]

I hear you, but I don't fully understand...

[schoenrock]

Originally Posted by RootsAndRocks

I hear you, but I don't fully understand...

mAybE u sHooD cAll da hYdrOlic xperTz

[FullMonty]

Originally Posted by RootsAndRocks

I hear you, but I don't fully understand...

as the pads wear out, the caliper pistons compensate by "starting" closer to the rotor. fluid will automatically pump from the reservoir in the lever and keep the pistons farther out.

[skimtb1]

Originally Posted by RootsAndRocks

I hear you, but I don't fully understand...

as your brake pads wear, the pistons retract less and less back into the caliper.

when you replace the brake pads you will have to push the pistons back into the caliper in order to fit the new pads in.

[boomforeal]

^this is my experience but i'll admit to not really understanding how its possible. in a closed hydraulic system, the fluid (optimally) takes up all available "space" between the master (lever) and slave (caliper) cylinders - applying pressure to the master displaces fluid within the system, actuates the slaves, pushing the pads towards the rim, and a spring pushes back to reset the brakes.

Originally Posted by skimtb1

as your brake pads wear, the pistons retract less and less back into the caliper.

so where does this extra "space" come from (when your pads wear) and go (when you install new pads and pry the pistons apart)?

[Lady Gravity]

good grief, are you an engineer? just ride the bike, and check your pads periodically.

[RootsAndRocks]

Originally Posted by skimtb1

as your brake pads wear, the pistons retract less and less back into the caliper.

makes sense, thanks. I think it's pretty cool how modern bikes are built...

[FullMonty]

Originally Posted by boomforeal

^this is my experience but i'll admit to not really understanding how its possible. in a closed hydraulic system, the fluid (optimally) takes up all available "space" between the master (lever) and slave (caliper) cylinders - applying pressure to the master displaces fluid within the system, actuates the slaves, pushing the pads towards the rim, and a spring pushes back to reset the brakes.



so where does this extra "space" come from (when your pads wear) and go (when you install new pads and pry the pistons apart)?

technically pretty much every modern disc brake isn't a fully closed system. basically there is a really tiny hole in the master cylinder between the bore itself and the reservoir in the lever. the reservoir is covered by a flexible bladder which allows expansion with heat. when you squeeze the lever, the master cylinder piston seal goes past this hole, seals that portion of fluid, and activates the caliper. you can actually see this happen if you bleed a shimano brake. my understanding of how the actual adjustment works is limited, but I'm gonna guess that when the master cylinder is activated and not enough pressure builds, more fluid is allowed to flow into the system. anyway, it works, and I am happy that we're not all running old Hope C2s where you had to play with a dial to adapt for pad wear and heat build-up.

[boomforeal]

Originally Posted by FullMonty

technically pretty much every modern disc brake isn't a fully closed system. basically there is a really tiny hole in the master cylinder between the bore itself and the reservoir in the lever. the reservoir is covered by a flexible bladder which allows expansion with heat. when you squeeze the lever, the master cylinder piston seal goes past this hole, seals that portion of fluid, and activates the caliper. you can actually see this happen if you bleed a shimano brake.

i've bled shimano hydraulic brakes and all of this makes sense.

my understanding of how the actual adjustment works is limited, but I'm gonna guess that when the master cylinder is activated and not enough pressure builds, more fluid is allowed to flow into the system.

this is what doesn't make sense to me. where does the "more fluid" come from? in a closed system you would need mo fluid to push mo cylinder to compensate for worn brake pads, but with the shimano's, somehow, you don't. this is what i'm wondering about.

anyway, it works, and I am happy that we're not all running old Hope C2s where you had to play with a dial to adapt for pad wear and heat build-up.

qft!

[mattj]

Originally Posted by boomforeal

this is what doesn't make sense to me. where does the "more fluid" come from? in a closed system you would need mo fluid to push mo cylinder to compensate for worn brake pads, but with the shimano's, somehow, you don't. this is what i'm wondering about.

Full Monty very effectively explained that the brakes are NOT closed system. The "extra" fluid comes from the reservior. That leftover space in the reservoir is then taken up by the expansion of the bladder. When you "reset" the pistons you are pushing fuild back from the brake into the reservoir.


-m

[boomforeal]

Originally Posted by mattj

Full Monty very effectively explained that the brakes are NOT closed system.

still confused (i thought the expanding bladder just dealt with heat levels, and get this part) but thanks for your effort and patience.

[slider32]

The "reservoir" on the brakes is NOT, the master cylinder. the master cylinder is the small tube that the piston is in that the lever pushes, This draws fluid from the reservoir. When the pistons move out further, they draw more fluid from the reservoir, into the master cylinder.

[philly56]

^ DING DING! we have a winner!