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

Here's 8 pages of "words"... that conform to what I think I might have once known.

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- 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.

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

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 source?path?receiver model 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 observations Osman Taha Sen, Rajendra Singh Acoustics and Dynamics Laboratory, Department of Mechanical and Aerospace Engineering, 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 Brakes 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 Huddersfield Braking Process in Automobiles: Investigation of the Thermoelastic Instability Phenomenon 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 experiment 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.

source?path?receiver model

that one presumes disk thickness variation, nothing on caliper dynamics.

etc.

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Huddersfield

Phenomenon

Engineering, University of Miami

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ACQUISITION SYSTEM FOR COMPLETE ANALYSIS

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 scrub radius.

so you're just going to have to keep sucking it up and coughing it up.

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 mistorquing lugs.

--scott

did you mic them?

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'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.

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.

indeed.

as said before, that's comparatively uncommon [and very rare on bmw!] and pursuit of that as an explanation is not going to yield meaningful results to a big picture understanding other than being something some people will latch onto if there's any visible clues. ordinary looking disks without deposition are the norm, and any explanation has to be able to account for them too.

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well, it's pretty obvious if you consider the relative masses as a dynamic system being agitated by a waving disk sat in its middle.

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.

I'll regret it but OK, I'll bite - how would you measure rotor runout that's only a few molecules thick?

If it does not mean "run out" what else would warp mean?

Warp and runout are totally different things (to me, anyway)!

1. Warp means, to me, the rotors are 'wavy' (like a potato chip).
2. Runout merely means, to me, the rotors aren't spinning on on the same axis as the hub is.

So, for example, let's assume a PERFECT ROTOR! If you put it on the hub crooked, it will have runout but not warp.

How could you put it on crooked? I don't know all the ways, but one way is to have uneven rust on the hub. That 'tilts' the rotor so that the hub and the rotor aren't spinning on the same axis.

The results in runout - which you measure with a dial gauge firmly affixed to something relative to the hub center axis.

The way I understand warp, you'd NEVER be able to measure it on the vehicle (not anywhere near accurately, anyway).

You measure warp on the bench. I suppose it's something that every rotor manufacturer measures as part of their quality control.

The faces need to be parallel to each other.

Now, having said that (which is pretty obvious stuff), I must then ask you (or anyone else) what THEY think the difference is between warp and runout - as it's pretty simple stuff (to me).

To me, a rotor could have runout but not be warped. A warped rotor will usually have runout.

I agree.

A PERFECT rotor could easily have runout if it is mounted where there is rust on the hub, for example. The axis of rotation of the hub would be DIFFERENT on the rotor - so the rotor would have runout. But it is still a perfect rotor - so it would not have warp.

Now, if the rotor was actually warped, that means, to me, that it's "wavy" (like a potato chip), and, as you said, it's ALSO going to have runout.

And, I guess, if it has low spots and high spots (i.e., disc thickness variation), then again, it's going to have runout.

HOWEVER ... the DTV that causes judder is sooooo tiny (15 microns in some cases as reported by the aforementioned scientific papers!) that we will be hard pressed to MEASURE DTV runout accurately with our standard DIY garage micrometers.

All this is how "I" understand it though - but clearly, warp needs to be measured on the bench. Nobody can possibly say their rotors warped, in my opinion, if they didn't measure them on the bench (off the vehicle).

On Sun, 17 Feb 2013 00:55:46 +0000 (UTC), Joe Mastroianni wrote:

What you said. This pad deposition is new to me. Makes sense, especially to those selling "scrubber" pads, which are advertised as truing up rotors.. But why are they still cutting metal off rotors? Seems pad deposition would be cut off and the metal would be barely touched by an accurate lathe. Never seen rotors cut, so I'm guessing the blade cuts the entire rotor diameter, not just the pad wear area. Probably most rotor cutting is done with a not very precise machine, and poor measurement. Those scrubber pads don't seem a good idea either. I suspect they are never an exact match in size compared to the permanent pads. Anyway, I have very little experience with rotors that cause pulsation. Only times it happened with me was with old worn rotors that needed replacing anyway because they were grooved and eating pads. But here's what makes me believe that rotors CAN warp. And I'm not NOT saying that it the cause of most brake pulsation. I once went through a deep puddle with hot rotors. When I went into the puddle the brakes were smooth. When I came out of the puddle I had a severe pulsation on the right front. The rotors were old and deeply grooved and ready for replacement anyway. Since rotors for my cars are usually 20-30 bucks each - cheaper than a good pad set - I just replace them when I see/feel grooving. Here's something else. I had a real good mechanic do the work on my cars when I was busy with my work. Never doubted him at all. But talking to him about brake jobs one time, he told me new rotors must be lathed before using them. I don't buy that. I've put maybe 4 sets of new rotors on my cars, and just cleaned the preservative off them. They all worked out fine. These are all the standard GM single piston brakes.