Do you know of engineering papers for what people call brake rotor 'warp'?

We're having a conversation among friends when one casually mentions his wife's rotors "warped".
The other jumps on him and declares that street-use rotors don't warp (in general). An Internet search bears him out, as MANY articles say rotor warp is a myth.
Googling, we find that brake torque variation is mostly from uneven pad deposition buildup (i.e., disc thickness variation) and axial runout. But then it gets confusing as the more enlightened sources begin to mention thermo elastic instability hotspots and breaking judder into low frequency cold judder and high frequency hot judder.
The heated discussion went on. And so did the confusion. For more than a few beers.
My question?
While we now know rotors rarely actually warp, does anyone know of a good scientific or engineering paper explaining the TRUE causes of brake related judder in street cars?
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> does anyone know of a good > scientific or engineering paper explaining the TRUE causes of brake > related judder in street cars?
Here's 8 pages of "words"... that conform to what I think I might have once known. http://www.powerbrake.co.za/downloads/tech_01_judder.pdf -----
- gpsman
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On 02/15/2013 10:52 AM, gpsman wrote:
>> does anyone know of a good >> scientific or engineering paper explaining the TRUE causes of brake >> related judder in street cars? > > Here's 8 pages of "words"... that conform to what I think I might have > once known. > http://www.powerbrake.co.za/downloads/tech_01_judder.pdf > ----- > > - gpsman >
words, but not a paper, just advertising.
their cited uneven disk thickness is relatively uncommon. distortion from the plane is very common indeed. it's the asymmetry of a caliper's component momenta that causes pulsing in the hydraulics. opposed pistons dynamically self-equilibrate - single sided calipers cannot.
--
fact check required

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On Fri, 15 Feb 2013 16:51:20 -0800, jim beam wrote:
> words, but not a paper, just advertising.
Yes, I'm looking for 'real' scientific engineering papers.
All these (which are decidedly NOT engineering papers!) say rotors aren't warping, but as you noted, it might just be advertising.
CENTRIC: Pad and Rotor Bed-In Theory, Definitions and Procedures http://www.centricparts.com/files/Centric%20White%20Paper%20C2-Bed-In%20Theory.pdf
AKEBONO: Brake Noise, Vibration, Harshness, causes http://www.akebonobrakes.com/company/media_center/white_papers/akebono_NVH.pdf
POWERBRAKE: The final word on brake judder and "warped" discs http://www.powerbrake.co.za/downloads/tech_01_judder.pdf
BREMBO: Judder caused by improper bedding procedure http://www.brembo.com/en/car/Racing/Street-products/Documents/USA%20CATALOGO.pdf
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Joe Mastroianni wrote:
> On Fri, 15 Feb 2013 16:51:20 -0800, jim beam wrote: > >> words, but not a paper, just advertising. > > Yes, I'm looking for 'real' scientific engineering papers. > > All these (which are decidedly NOT engineering papers!) say rotors > aren't warping, but as you noted, it might just be advertising. > > CENTRIC: Pad and Rotor Bed-In Theory, Definitions and Procedures > http://www.centricparts.com/files/Centric%20White%20Paper%20C2-Bed-In%20Theory.pdf > > AKEBONO: Brake Noise, Vibration, Harshness, causes > http://www.akebonobrakes.com/company/media_center/white_papers/akebono_NVH.pdf > > POWERBRAKE: The final word on brake judder and "warped" discs > http://www.powerbrake.co.za/downloads/tech_01_judder.pdf > > BREMBO: Judder caused by improper bedding procedure > http://www.brembo.com/en/car/Racing/Street-products/Documents/USA%20CATALOGO.pdf
You might do well in a.h.r because those guys know mechanical stuff.
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jim beam wrote:

Just to be clear, I never said the disks actually warped.
Anyone who says that rotors commonly warp is clearly heading back to the village missing its idiot.
However, to be 'fair', a lot of what people call warp is simply runout, which is what I think you're referring to (since you could never correct true warp short of machining the rotors).
A lot of other times, what people call warp is merely uneven pad deposition, which, oftentimes, a rebedding run (especially one with very harsh pads) will scrape clean & eliminate the judder.
Whatever they 'call' it, it's not warp because you can MEASURE warp and they never ever measure it! Those who do, find out that it's not warp. It's really that simple. Those who insist it's warp seem to have no resistance with the q-tips in the ears.
This thread seems to be going in the right direction which is to find the true cause of judder.
I will also try to read those scientific papers that were posted.
http://www.researchgate.net/publication/233988829_Analysis_of_the_vehicle_brake_judder_problem_by_employing_a_simplified_sourcepathreceiver_model/file/79e4150e7d38711887.pdf http://sem-proceedings.com/20i/sem.org-IMAC-XX-Conf-S17P04-A-Parametric-Study-Brake-Roughness.pdf http://sem-proceedings.com/14i/sem.org-IMAC-XIV-14th-Int-14-5-5-Judder-Diagnosis-Prevention.pdf http://www.mecheng.osu.edu/adl/files/adl/C12-1.pdf http://www.ehu.es/compmech/welcome/doc/Paper%20867%20Engineering%20Computations.pdf http://researchbank.rmit.edu.au/eserv/rmit:6260/Rodriguez.pdf http://eprints.hud.ac.uk/3878/1/2008-01-0818.pdf http://cdn.intechweb.org/pdfs/5380.pdf http://www.acoustics.asn.au/conference_proceedings/ICA2010/cdrom-ICA2010/papers/p46.pdf http://www.hitachi.com/ICSFiles/afieldfile/2009/12/25/r2009_07_107.pdf http://ejum.fsktm.um.edu.my/article/1146.pdf http://eprints.hud.ac.uk/3797/1/10_PAPER_Final_D_Bryant.pdf http://www.mecheng.osu.edu/adl/files/adl/J187.pdf http://pid.sagepub.com/content/217/6/419.full.pdf
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On Sat, 16 Feb 2013 19:55:59 -0600, Vic Smith wrote:

The "theory" (as I understand it) for the uneven pad deposition based brake judder is that a little "hill" of as little as 15 microns (according to one of the papers we listed) will cause low frequency (around 100 Hz) brake judder.
I'm still trying to figure this out, but apparently two things happen at the same time when the pads hit the deposition "hill".
1. The pads "push back" causing the vibration to be felt in the brake pedal. 2. The force varies, causing the entire suspension to shudder.
At least that's how I understand it after reading the (complex) papers a few times. I'm still reading them though, so consider this a preliminary explanation.
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On Sat, 16 Feb 2013 19:55:59 -0600, Vic Smith wrote:

An interesting aside is that we all have seen grooved rotors, and we all know the "fingernail test" (i.e., if it catches your fingernail, it's too deep) - but - if you LOOK UP the specs for grooves, they have to be absolutely huuuuuuge (like the thickness of a dime!) to fail a rotor.
At least in my experience.
If anyone actually has a bona-fide "groove" specification for their rotor - please share!
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On Sat, 16 Feb 2013 19:55:59 -0600, Vic Smith wrote:

I should clearly state that I too believe rotors CAN warp!
However, what MOST people "call" warp, isn't warp at all. It's merely brake judder. Which, as we've seen from the dozen papers, can be caused by a LOT of things. And, as shown by the industry advertising anyway, most of the time it's NOT warp.
Plus, how would anyone know it's warp if they didn't measure the rotors on the bench, as that's the ONLY way to tell a warped rotor (as far as I can tell).
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my caravan carries a lot of weight, and the pads wear out fast.........
Used to be garages demanded we turn the rotors, in my application they would warp fast.
so now i just buy new rotors any time the pads get replaced.
my neighbor a highly skilled guy does lots of my vehicle repairs, sadly i must find someone new.
he is a smoker and has lung cancer stage 4......
he is a good hard working guy i will miss him:(
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On 02/17/2013 12:39 AM, bob haller wrote:

which is what most people do. it "works" because the new disks are clean and thus seat properly. if old disks were properly cleaned, they would too, but since time is money for shops, and disks relatively cheap, replacement is in fact an economic option.

--
fact check required

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he has very little time according to his doctor.
its sad people get addicted to smoking then spend horrendous amounts of money to get sick and die
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On Mon, 18 Feb 2013 19:04:34 +0000, Tegger wrote:

Thanks for checking.
Googling for random manufacturer's specifications, I find this GM spec: http://www.procutinternational.com/supplier_gm.aspx Which says: Do not resurface rotors for light grooving. Resurface rotors only when grooves of 1.5 mm (0.060 in) or deeper are present.
"A dime may be used to determine disc brake groove depth. Place a dime in the groove, with Roosevelt's head toward the groove. If the dime goes into the groove beyond the top of his head, the groove exceeds 1.5 mm (0.060 in) and the rotor should be serviced. In Canada, if any portion of the letters of "Canada" are covered, the rotor should be serviced. If the groove is too narrow for the dime to be inserted, it is not a cause for concern."
Conversely this spec: http://www.raceshopper.com/tech.shtml Says: "Check disc for scoring or grooves over .012" depth. If either applies, resurfacing or replacement is required."
But, the point is that grooves have to be "really big" to fail a rotor.
PS: How did we get onto the side topic of rotor scoring anyway?
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Since I have a parking lot instead of a drive way, and two of the stalls in that lot are just plain hard to get into, I use those stalls for myself rather than try to sucker a tenant into renting them. So, with a spare parking stall, I go to auto auctions whenever I down to just one car in case I get into an accident and need a car in a hurry.
One time I was putting a recent acquisition up on concrete blocks (for storing it) immediately after a rain storm. When I eventually put that car back on the road, I had the worst brake pedal pulsation you can imagine.
What happened is that the rain water between the rotors and the pads caused the rotors to rust really badly under the pads. I'm thinking the water that got between the rotors and the pads couldn't dry out and simply kept rusting the rotors. I tried to drive it off, but it wouldn't happen, so I just replaced the rotors. When I took the old rotors off I could see they were both badly rusted in one area on both sides.
I'm willing to bet dollars to donuts that a lot of cars with "warped rotors" on used car lots are cars that were last driven immediately after a rain. Since then, I've made a point to be aware of the weather before putting up a car for storage and that same problem hasn't happened again.
--
nestork


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