why do disc brakes fade?

[toph99]

i can see why drums do, they get hot, expand and the pads can't make contact anymore, but why do disc brakes fade? i keep reading about it happening on cars in magazines, but i'd think if the disc expands it would just make harder contact with the pads. can soemone explain it to me?

 

[Rallispec]

another question about disc breaks-- why do they warp?

my old car had brakes that were warped and cuased wabbling when i had to brake hard.

 

[The Stigenator]

Solid discbrakes fade more often than slotted discs.. the slots are used to cool down the break pad.

The rotor gets screwed up because you got to remember its made of bimetalallic strips, when heated one expands more than the other and it warps.. that is why now high perfornance cars and F1 cars use carbon fiber or carbon impegranted steel as a braking system.

 

[yakko]

Heat.

 

[JC]

<< i can see why drums do, they get hot, expand and the pads can't make contact anymore >>



Well actually, that's not why drums fade....your foot's on the pedal, if the drum expanded the shoes would move out more to compensate

It's the heat that causes the friction material to lose its friction properties, causing the fade. Drums are less able to shed the heat rapidly to avoid the fade. Vented (not solid) rotors
cool better than solid rotors, and drilled rotors help shed the worn-off pad material.

Another cause of brake fade is vaporizing of the brake fluid, from the brake heat being transferred to the fluid. Bad, very bad.



<< The rotor gets screwed up because you got to remember its made of bimetalallic strips, when heated one expands more than the other and it warps >>



Huh? Most rotors are 100% cast iron. Warping sets in when the rotor can't shed the heat, causing permanent warpage. Machining may straighten it out, but the resulting thinner rotors
are even more susceptible to warping.

JC