I think that this is a worthwhile read and it taught me something.
http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths
One point I can note is that judder isn't always from thickness variation, if you mount a rotor to the hub with junk between it and then clamp it
up you can get actual rotor run-out too, which ends up picking up extra friction material and starting that wonderful process of ever increasing
judder.
One of the biggest killers of rotors is sitting after a hard braking session with the pads clamped to the disc (some people like to sit with the
brakes on at junctions for some odd reason) - you're effectively sintering pad material onto the surface!
quote:
Originally posted by coyoteboy
One of the biggest killers of rotors is sitting after a hard braking session with the pads clamped to the disc (some people like to sit with the brakes on at junctions for some odd reason) - you're effectively sintering pad material onto the surface!
I use ATE Dot4 , so will try bleeding the breaks after a track day if I've boiled the fluid and see if that makes a difference
Interesting read.
quote:
Originally posted by Slimy38
quote:
Originally posted by coyoteboy
One of the biggest killers of rotors is sitting after a hard braking session with the pads clamped to the disc (some people like to sit with the brakes on at junctions for some odd reason) - you're effectively sintering pad material onto the surface!
Whilst you have a very good point, and it's something I try and avoid, an automatic car practically encourages that approach. Unless you shift into neutral, or you're on a very steep hill, an auto will creep forward. My current C class even has a brake hold function that is activated by pressing further down on the brake pedal, it locks the pads in place until you're ready to move off.
quote:
Originally posted by coyoteboy
, apart from anything I hate the "BRAKE LIGHTS IN THE FACE" situation you get at junctions - trashing your night vision!
I formally apologise to all those
sat behind me with my high level brake light leaving them with red spots! (It's an estate so it's even worse!) Disc warping is NOT a myth, it can and does happen. However, vibration from pad deposits and discs mounted on badly cleaned/uncleaned hubs are far more common.
quote:
Originally posted by MikeRJ
Disc warping is NOT a myth, it can and does happen. However, vibration from pad deposits and discs mounted on badly cleaned/uncleaned hubs are far more common.
The solid discs on my mk5 fiesta were warped. They were terrible after one particular hoon and never smoothed out throughout the rest of the pads
life.
I was more than aware not to sit stopped with the brakes on so np chance of pad material on the rotor.
quote:
Originally posted by britishtrident
quote:
Originally posted by MikeRJ
Disc warping is NOT a myth, it can and does happen. However, vibration from pad deposits and discs mounted on badly cleaned/uncleaned hubs are far more common.
100% with you on this
Very interesting read, thanks for posting.
Brake disc warping story. Back in my Imp racing days we used to fit Viva hubs to get front disc brakes. With HB Viva discs the discs would warp on
cooling down after every race. Viva HC discs were listed all the after market suppliers as the same part number the thickness had been increased
slightly although they still cleared the same calliper, when Lockheed Viva HC discs were fitted we never had another warped discs.
Capris used to drive garages mad with front brake vibrations often fitting new discs wouldn't cure it but fitting new anti-roll bar bushes
would even although there was no apparent wear in the originals would -- for those who don't know Capri suspension ant-roll bar was also the
brake reaction tie bar.
Later Girling sold special abrasive coated brake pads and fitting these in combination with new bushes was almost a copper bottomed cure.
It's clearly possible for warping to happen, it only takes residual stresses in the casting process to not be fully relieved in post production
or overheat unevenly cooling. I think the problem is "my discs have warped" is thrown around rather too freely, which is why I am a bit of a
pedant when it comes to online discussions
Yeah, I've seen claims that there's no such thing as a warped rotor before. If I'd bothered to keep them around instead of sending
them to the scrapyard, I could put up some pictures of rotors warped enough to see with the naked eye.
I've never seen any sign of "pad pick-up" like Stoptech claims, but I have seen rotors that varied as much as .010" in thickness;
usually whitish lumps hard enough to make carbide tooling skitter off. I figure that's due to impurities in the iron collapsing into some other
lattice. "Cast iron" is actually a crystalline structure, and it can do bizarre things when heated.
It warps, too...
Never seen a warped disc this side of a tardis. My discs on the porker juddered, was cleared off after braking from warp speed a few times.
[Edited on 29/8/15 by ian996]
[Edited on 29/8/15 by ian996]
Had Sierra ones warp where the face distorts inwards at the ventilated spaces.
quote:
Originally posted by Dingz
Had Sierra ones warp where the face distorts inwards at the ventilated spaces.
http://www.hendonpub.com/resources/article_archive/results/details?id=1787
I think the point is that 'warped discs' (used as a term for shudder in the brake pedal) are not caused by heat. I used to run 380mm discs
on the RS4 and even the smallest run-out from manufacture/installation would lead to judder in the pedal. I've never actually had warped discs
though.
interesting!
My M3 discs went above the heat sensor scale after a few laps at Combe 
But they didn't warp
It isn't so much the peak temperature of a disk that can causes warping as the cooling down process. Because the disc is rotating the heat build
up is evenly distributed around the disc problem arises during the cooling down when the vehicle is stopped the area disc under the caliper cools much
more slowly because the surface of the pad remains much hotter than the rest of the disc and will continue to transfer heat to the disc. . This can
both warp the disc and leave deposits in the the surface of the disc.
[Edited on 2/9/15 by britishtrident]
But a ventilated disc can never cool, or heat evenly due to the variations in thickness/mass where the bridging ribs are.