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.
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?
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.
On Fri, 15 Feb 2013 16:51:20 -0800, jim beam wrote:
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
AKEBONO: Brake Noise, Vibration, Harshness, causes
POWERBRAKE: The final word on brake judder and "warped" discs
BREMBO: Judder caused by improper bedding procedure
Rotors warp for the same reason that lugs break off: idiots with lug wrenches.
It is correct that rotors do not warp by themselves, but I have seen plenty
of cases of warped rotors, all of which can probably be traced to some idiot
"C'est un Nagra. C'est suisse, et tres, tres precis."
right, but that's not warping in the permanent sense that you can
measure off the vehicle, only in the elastic distortion sense that
disappears again as soon as you sort the wheel interface out properly.
I had a 1979 Plymouth Champ Twin-Stik I bought new. With about 5K
miles on it, I took it on a hairball trip through the Sierras. By the
end of the trip, the rotors were definitely warped. The dealer didn't
have the special tool that car needed to remove the rotors, no one had
needed it yet. So given the choice of waiting several weeks for one
to be shipped from Japan, or machining their own tool, they made their
own tool. At least, that's what they told me, and I can't imagine
them making up stories to make more problems, work and expense for
Man, that was a little pocket rocket, before the term was invented.
And I thought that coming from a '63 Vette.
Thanks for the judder links, Joe.
@home.com is bogus.
Near my work: http://www.nbclosangeles.com/news/local/Tustin-Orange-County-
On Fri, 15 Feb 2013 16:48:16 -0800, jim beam wrote:
The proletariat be damned, I reach out to the literati to explain
what "really" causes brake judder (because it's not rotor warp)!
Googling, I found these on the bimmer boards so far that I'm reading:
"Aspects of disc brake judder"
Proceedings of the Institution of Mechanical Engineers,
Part D: Journal of Automobile Engineering
Analysis of the vehicle brake judder problem by employing a simplified
Acoustics and Dynamics Laboratory,
Department of Mechanical Engineering,
The Ohio State University, Columbus, Ohio, USA
A Parametric Study of Brake Roughness
Robert Bosch Corporation
Judder, Diagnosis, & Prevention,
Mohamed Khalid Abdelhamid, AlliedSignal Automotive, Europe
Improved mathematical models of vehicle brake judder and experimental
Osman Taha Sen, Rajendra Singh
Acoustics and Dynamics Laboratory, Department of Mechanical and Aerospace
The Ohio State University,
Judder vibration in disc brakes excited by thermoelastic instability
Oscar Altuzarra, Enrique Amezua, Rafael Avilés, Alfonso Hernández, (2002),
Engineering Computations, Vol. 19 Iss: 4, pp.411 - 430
Experimental Analysis of Disc Thickness Variation Development in Motor Vehicle
School of Aerospace, Mechanical & Manufacturing Engineering (SAMME)
Thermal Brake Judder Investigations Using a High Speed Dynamometer
David Bryant, John Fieldhouse, Andrew Crampton and Chris Talbot, University of
Braking Process in Automobiles: Investigation of the Thermoelastic Instability
M. Eltoukhy and S. Asfour, Department of Industrial Engineering, College of
Engineering, University of Miami
Brake Vibration and Noise - A Review and Discussion
Dihua Guan, State Key Laboratory of Automotive Safety and Energy,
Tsinghua University, Beijing, China
NVH Simulation Technology for Disc Brake Calipers
Hitachi, Suzuki Yoichi Kumemura Hayuru Inoue Yuichi Takagi Shinji Suzuki
SURFACE TEMPERATURE DISTRIBUTION IN A COMPOSITE BRAKE ROTOR
A.A. Adebisi1, M.A. Maleque1 and Q.H. Shah
Department of Manufacturing and Materials Engineering
DISCUSSION OF THE CHARACTERISTICS OF BRAKE JUDDER AND THE NECESSARY DATA
ACQUISITION SYSTEM FOR COMPLETE ANALYSIS
D. Bryant, A. Crampton, J. Fieldhouse and C. Talbot
University of Huddersfield, Queensgate, Huddersfield HD1 3DH, UK
Order domain analysis of speed-dependent friction-induced torque in a brake
Osman Taha Sen, Jason T. Dreyer, Rajendra Singh
Acoustics and Dynamics Laboratory,
Department of Mechanical and Aerospace Engineering,
The Ohio State University, Columbus, OH 43210, USA
quickly scanning, i see nothing on caliper asymmetry.
that one presumes disk thickness variation, nothing on caliper dynamics.
i'll try to look at the rest, but seriously, most people who don't know
are chasing their tails. those that do know aren't going to say much
because they're not going to do two things:
1. they're /definitely/ not going to kill a cash cow which is selling
new disks way before they're worn.
2. they're not going to stop using single-sided calipers because they're
essential to macpherson strut suspension being able to have a negative
so you're just going to have to keep sucking it up and coughing it up.
On Fri, 15 Feb 2013 18:34:14 -0800, jim beam wrote:
I'm reading those papers, as you are, and they talk about hot and cold
judder and they speak of high and low speed judder (mostly we're talking
around 100Hz here so that's low speed judder).
There's a lot of stuff about hot spots (I 'think' that's thermoelastic
instability) and disc thickness variation (I 'think' that's uneven
pad deposition) and axial runout (I think that's plane old runout).
It will also take me a while to read them all, but I don't see anything
(yet) about the single piston caliper design.
I believe that what happens is that there's some transference of pad
material onto the iron disk at a molecular level. You can't measure it
because we're not able to measure tolerances to that level. It does,
however effect the frictional coefficients between the two surfaces at
localized areas. This causes the hot spots. Well, that's my
understanding about it anyway.
The pad material transference occurs mostly when the pads are hot. As a
practical matter, I try to ease up on the brake pressure after coming to
a stop after heating up the brakes.
dude, absolutely there's transference "at the molecular level" - you
can't have friction without it. but to be grasping at straws as if
there's some kind of ghost in the machine that can't be explained any
other way is just ridiculous.
nothing personal to you, but that's complete b.s.
only in some cases, with some kinds of pads. maybe 10% at most. all
the rest is plain old mechanical misalignment coupled [literally] to
poor dynamics of an unevenly weighted caliper.
it seems this is another one of those hose flap and antifreeze
electrolysis topics - a knowledge gap into which some people feel
compelled to inject good old underinformed guessing.
dude, seriously, how do you think adding a "molecular layer" to a disk
surface makes the slightest difference? surface roughness is in the
order of 10 microns. that's at least 10,000 times bigger than even a
huge "molecular layer".
oh, and oem runout tolerance is ~10 times greater than that.
i'm glad i didn't bother! i spent years of my life measuring stuff to
microns and below, so if you think i'm going to try to educate a guy
who's clutching at "molecular layer" straws and being hostile about it
because he can't be bothered to pay attention to fact or can't be
bothered to google, you need to think again.
just as i suspected, the relevant stuff is way over your head.
On Monday, February 18, 2013 5:29:50 AM UTC-10, jim beam wrote:
Yeah, don't bother to respond to me if you can't even understand what the s
ubject is. You're talking about brake runout but I'm not talking about that
. What I'm talking about, dude, is the transference of pad material onto th
e surface of the cast iron surface of the rotor. This layer is invisible to
the naked eye and you can't measure it as runout because the whole idea of
seating new pads is to get an even layer of this stuff onto the surface of
the rotor. I'm not interested in getting sucked into your discussion about
warped brakes and disk runout - dude.
P.S., If you think that machining a rotor results in a grooved surface... w
ell that just explains everything.
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