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Author: Subject: Warped brake discs - a myth!
Ivan

posted on 17/8/15 at 08:29 AM Reply With Quote
Warped brake discs - a myth!

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

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coyoteboy

posted on 17/8/15 at 09:21 AM Reply With Quote
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!





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Slimy38

posted on 17/8/15 at 09:53 AM Reply With Quote
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.

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matt5964

posted on 17/8/15 at 10:02 AM Reply With Quote
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.





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coyoteboy

posted on 17/8/15 at 10:05 AM Reply With Quote
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.


Yep, my 370Z has this function too - I'm not keen on it, especially with rotor prices as they are for that car!

I always just try to remember the handbrake (most cars don't run the normal pads as the handbrake pads and even so the rears are usually a lot colder), apart from anything I hate the "BRAKE LIGHTS IN THE FACE" situation you get at junctions - trashing your night vision!





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Slimy38

posted on 17/8/15 at 11:04 AM Reply With Quote
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!


Oddly enough, that's why I try and use the brake hold function as much as possible, assuming that it worked like the handbrake... unfortunately as I was finding the name of the hold function, I found out that it doesn't extinguish the brake lights!! 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!)

The handbrake on a Merc isn't as easily accessible, mine is a small button under the dash that has more in common with the bonnet release than something to use while driving!

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MikeRJ

posted on 17/8/15 at 11:16 AM Reply With Quote
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.
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britishtrident

posted on 17/8/15 at 01:40 PM Reply With Quote
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





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[/I]

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bi22le

posted on 17/8/15 at 06:49 PM Reply With Quote
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.





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dilley

posted on 17/8/15 at 08:43 PM Reply With Quote
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


That makes 200%! Discs are generally fine, it's what they're mated to that is the problem.

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micksalt

posted on 18/8/15 at 07:09 AM Reply With Quote
Very interesting read, thanks for posting.
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britishtrident

posted on 18/8/15 at 07:11 AM Reply With Quote
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.





[I] What use our work, Bennet, if we cannot care for those we love? .
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[/I]

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coyoteboy

posted on 18/8/15 at 09:53 AM Reply With Quote
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





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TRX

posted on 29/8/15 at 06:17 PM Reply With Quote
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...

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ian996

posted on 29/8/15 at 09:09 PM Reply With Quote
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]

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Dingz

posted on 29/8/15 at 10:22 PM Reply With Quote
Had Sierra ones warp where the face distorts inwards at the ventilated spaces.





Phoned the local ramblers club today, but the bloke who answered just
went on and on.

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Ivan

posted on 30/8/15 at 07:52 AM Reply With Quote
quote:
Originally posted by Dingz
Had Sierra ones warp where the face distorts inwards at the ventilated spaces.


Yes - that problem is mentioned in the article.

I must say that the author of the article (Carrol Smith) impressed me as one of the foremost race engineers in the world and well respected author of race oriented books as someone who knows what he is talking about.

That being said I am sure that there are examples of badly manufactured (Poor material and not de-stressed) and designed discs that do warp but I think the point being made is that if you have disc related problems it's unlikely to be warped discs.

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jeffw

posted on 30/8/15 at 08:17 AM Reply With Quote
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.






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r500_2015

posted on 1/9/15 at 08:50 PM Reply With Quote
interesting!

My M3 discs went above the heat sensor scale after a few laps at Combe But they didn't warp

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britishtrident

posted on 2/9/15 at 07:10 AM Reply With Quote
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]





[I] What use our work, Bennet, if we cannot care for those we love? .
― From BBC TV/Amazon's Ripper Street.
[/I]

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Dingz

posted on 2/9/15 at 08:28 AM Reply With Quote
But a ventilated disc can never cool, or heat evenly due to the variations in thickness/mass where the bridging ribs are.





Phoned the local ramblers club today, but the bloke who answered just
went on and on.

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