myth of warped disks

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On Tue, 4 Nov 2014 20:13:31 +0000 (UTC), "Danny D."

Well, I went into the puddle with perfectly functioning brakes. When I braked coming out of the puddle, my brakes were pulsating and stayed pulsating until I changed the rotors and pads. What do you suggest was the problem?
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clare wrote, on Tue, 04 Nov 2014 19:46:54 -0500:

What matters is *how* you measured the warp.
In my experience, I've *never* yet seen anyone who "said" a rotor was "warped", actually *measure* the warp.
It's *easy* to "say" it's warped; but, it's much more detailed to *measure* it, and, in "my" experience, anyone who bothered to measure things (as I do), has never said it was warp, in the end.
It was runout. It was BTV. It was DTV. It was bad bushings. Bad ball joints. Even bad suspension components. But, when measured, it has never (in my experience) ever been true "warp" in a street machine.
Again, I'm not every saying that rotors "can't" warp; I'm just saying that the most common causes of brake-related pedal pulsation hand steering wheel vibration are decidedly not warp.
And, by the way, I'm not the only one. https://www.google.com/search?client=ubuntu&channel=fs&q=the+myth+of+brake+rotor+warp&ie=utf-8&oe=utf-8

Yup. The *last* thing I'd look for, if I had pedal pulsation or steering wheel vibration under braking, is warped rotors.
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Vic Smith wrote, on Tue, 04 Nov 2014 20:46:32 -0600:

It wasn't warp.
https://www.google.com/search?client=ubuntu&channel=fs&q=the+myth+of+brake+rotor+warp&ie=utf-8&oe=utf-8
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clare wrote, on Tue, 04 Nov 2014 19:43:01 -0500:

Pedal fade is a different thing altogether, and we all know about the effect of heat on friction materials.
Likewise, we all know about the problems with brake fluid, which, as we all know, is hygroscopic, so, it "can" boil, given the right conditions of water + heat.
Either one, or both of which are far more likely to be the problem than a warped rotor, as in a potato chip.
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clare wrote, on Tue, 04 Nov 2014 19:53:17 -0500:

Actually, that's runout, not warp.

Again, that's not warp. https://www.google.com/search?client=ubuntu&channel=fs&q=the+myth+of+brake+rotor+warp&ie=utf-8&oe=utf-8

A truly warped rotor would be trash, almost certainly, I agree.

Like I said, the *short term* solution to a rotor affected by DTV or BTV due to pad deposits or to 'true' warp would be the same, which, given the economics of replacing a rotor versus the manpower and equipment to machine it, is to replace it. I don't agree.
But, the *long-term* solution is different, depending on the reason for the pulsation.
By the way, don't believe me. Believe the experts. https://www.google.com/search?client=ubuntu&channel=fs&q=the+myth+of+brake+rotor+warp&ie=utf-8&oe=utf-8
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Mayayana wrote, on Tue, 04 Nov 2014 18:22:11 -0500:

This question is *always* the next question when the conversation comes to the question of what people 'think' is warp.
First, before I answer that question, do realize that there are many (i.e., scores) of reasons for pedal and steering wheel vibration upon braking, which range from myriad suspension components to unsprung components such as worn bearings and bent components, etc.
However, if we *limit* our discussion to *brake rotor* related issues, then the number of things that can cause pedal pulsation is reduced.
The main three components that are disc-only related are: a. DTV b. BTV c. runout
Let's forget runout, for our purposes, because that's a mechanical problem, e.g., someone mentioned lug nuts disproportionately tightened. Runout can also be caused by rust developing under the rotor between the hub and the rotor. Let's ignore runout, which is generally easy to measure with a dial gauge attached to some sturdy anchor point.
DTV and BTV are harder to measure, simply because they are caused by really small variations on the rotor.
We're talking in the range of ten thousandths of an inch for pad deposits to build up such that they make a "hill" or a "slick spot", where the hill is the DTV and the slick spot is the BTV (both of which cause pulsations).
How is this "hill" or "slick spot" most commonly caused?
Well, think about what happens when you cruise down an exit ramp, at a starting speed of 80 mph and you stop at the light at the bottom and hold your foot on the brake pedal for 30 seconds or more.
What can you get? A pad imprint is what you may get.
What happens if you do this over and over again? More pad imprints.
Sometimes they form hills (I'm not really sure, chemically, why, but they do). Sometimes they form slick spots.
The hills cause DTV and the slicks spots cause BTV. So, what do you do to prevent that?
Two basic things:
Mentally change your braking habits: 1. Coast to a stop, and roll if you can, and lift off the pedal if you can, and, 2. Rebed your brakes, in effect, constantly.
In suggestion #1 above, the common argument is you don't have the room, but, I have been doing it for years, and you *often* don't even have to stop, because a light is finite, so, you can often roll up to the light until it's green, and, even so, you at least are allowing the rotors to cool if you have to stop, and even then, if you left a few feet, you can roll a bit more also. It's a mental decision to change your braking habits.
In suggestion #2 above, if you already *know* what rebedding is, you can do mini rebedding, simply by braking hard, once a month or so, on that very same stop, and, in effect, redistributing the bedding layer on the rotors. This is more subjective, and, here in California, I do it on the five-mile long hills of the mountains, as it's difficult to do on a flat straightaway, but, that's the second mental challenge. Rebed your brakes all the time.
That's really it.
Of course, take none of this from me. Take all of this from the literature. From people who should know. https://www.google.com/search?client=ubuntu&channel=fs&q=the+myth+of+brake+rotor+warp&ie=utf-8&oe=utf-8
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On Wed, 5 Nov 2014 03:03:25 +0000 (UTC), "Danny D."

old fart - so that was a lot of years.
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On Tue, 04 Nov 2014 20:46:32 -0600, Vic Smith

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On Wed, 5 Nov 2014 03:06:28 +0000 (UTC), "Danny D."

You can't even read? I said the rotors shattered. He litterally LOST HIS BRAKES. The rotors both disintegrated - TOTALLY.

Danny - you are NOT a mechanic. Iam. I also drove competetively for several years.
I HAVE seen warped rotors - even on street driven vehicles - and I HAVE measured them. You've just read about it. You don't really KNOW anything about it.
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On Wed, 5 Nov 2014 03:09:35 +0000 (UTC), "Danny D."

And what causes the runout to suddenly appear? Warpage. Temperature induced deformation of the steel rotor by any other name is WARPAGE.

brake pulsations are not warped rotors - but warpage DOES occur. It is a real problem that is overdiagnosed.
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On Wed, 5 Nov 2014 03:22:30 +0000 (UTC), "Danny D."

Changes in thickness are not warpage. Parallelism changes are not warpage.
According to you, a "wobble" isn't warpage.
Define warpage. You cannot say it does not exist if you cannot define it.
I've defined it, and measured it, yet you say it does not exist.
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On Tue, 04 Nov 2014 23:11:18 -0500, snipped-for-privacy@snyder.on.ca wrote:

Well, he just gave me a Google link with the "myth" argument. Even the brake experts only say that rotors "rarely" warp. I know the rotors warped. It's really semantics anyway. I know about pad deposition and scoring, and usually just say "I need new rotors." This time I said "My rotors warped." Good enough for me.
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'Danny D.[_15_ Wrote: > ;3304579']

No, actually NO ONE in the world actually understands friction, let alone the effect heat has on friction.
Friction is one of those things that we realize exists, but no one truly understands what causes it. If you ask an "expert", he'll mumble something about inter-molecular forces and s#it like that before telling you that that no one really knows.
In fact, our current method of dealing with friction is to use a standard lab test to measure the amount of force needed to drag a block made of one material over a surface made of a different material. So, you have a myriad of different "coefficients of friction" of different material blocks being dragged over different matieral surfaces.
'Friction - Wikipedia, the free encyclopedia' (http://en.wikipedia.org/wiki/Friction)
Also, there is both static friction and dynamic friction, and each exists for thousands of different pairs of materials. Like the static coefficient of friction for rubber on concrete, or rubber on ice, or glass on glass, or asbestos on steel or lead on copper, and none of those coefficients account for the temperature of the block that's being dragged nor the temperature of the surface it's being dragged over. So, in a problem where a car looses control and slides off the road, we take the co-efficient of friction for rubber on concrete and apply that ratio to the weight on each tire. But, if that accident happened during the winter in Northern Manitoba when the rubber was harder or in the sweltering heat of an August day in Death Valley, the amount of friction actually occuring could and would be very different than what we'd calculate from lab tests where we pull a room temperature block of rubber over room temperature concrete.
What we do know is that dynamic friction is generally lower than static friction. Static friction is essentially the force you have to overcome to get the block to START moving. Dynamic friction is the force you have to overcome to get the block to KEEP moving. So, since static friction is generally higher than dynamic friction, for a car sliding sliding down an icy hill, once it starts sliding, it generally keeps sliding until it reaches the bottom of the hill. But, why that SHOULD be the case is something no one on this planet understands.
So, for example, our way of calculating the force of friction between a rubber tire and a concrete roadway is to take 1/4 the weight of the car and multiply it by the coefficient of friction for rubber on concrete. But, any race car driver will tell you that WIDER tires grip the road better, and that's something that's not accounted for in our current method of calculating friction. Also, any race car driver will tell you that heating up the tire rubber by doing a "burn out" before the race starts will give better traction during the race, and that's also something we don't know how to account for either. We don't know if that's only true for rubber on concrete, or for all materials. Thirdly, speed has an effect on friction too. The faster the motion, the lower the friction. So, for example, the total force required for a drywall gun to drive a drywall screw into wood at 12,000 rpm is much less than the total force required to wrist twist it in by hand with a #2 Phillips screw driver. No one can explain that. It all undoubtedly has to do with the inter atomic or inter molecular forces between the two materials in contact, surface roughness and stuff like that, but no one really knows what's happening or why.
So, when you say "we all know about the effect of heat on friction materials", what you really mean is that we all know that hot brake pads rubbing on hot steel has a lower coefficient of friction than cold brake pads on cold steel. But, there's not a single person in this world that can explain why that should be the case.
Sorry for disagreeing, but I just couldn't let that statement go by without commenting on it.
http://www.engineershandbook.com/Tables/frictioncoefficients.htm
--
nestork


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Vic Smith wrote, on Tue, 04 Nov 2014 22:44:06 -0600:

I've had this discussion so many times, I know exactly how it goes.
There are a few more steps, but, the step is always said by those who insist that their rotors warped (even though absolutely *none* of them actually measured, and most don't even know *what* to measure, nor how) that they meant the word differently.
You'll notice in my initial posts, I was *very clear* about what "I" meant by "warp".
So, those who insist their rotors "warped", change the definition, which, is fine (I've seen this happen every time).
There are still a few more stages to go through, but, we cannot proceed until people read what the experts have to say. It matters not what "I" have to say. Read the links found by the Google search.
Note: If folks actually read those links, we'd proceed to the next stage, which is that they'd see that even the experts don't agree on all points - so then we go down the semantics road again - but we aren't there yet... :)
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clare wrote, on Tue, 04 Nov 2014 23:14:29 -0500:

Ok. Show me a picture of the measurements on a street-use rotor.
(I've been asking this question for at least a decade, and *nobody* has ever provided a picture of them measuring warp on street-use rotors, mainly because they didn't measure them.)
They're all just guessing.
The best we ever get is a measurement of runout.
Watch and see. (I've been down this road scores of times before...)
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nestork wrote, on Wed, 05 Nov 2014 06:32:23 +0100:

What I go by are the ratings of my brake pads, which, as you all know, is required printing on all passenger vehicle pads sold in the USA.
I would never put in anything less than FF, for example, for the cold/hot friction ratings. Maybe even GG, if I get them for a good price.
And, yes, I've been down the argument that the government mandated friction ratings don't test the real world - but it beats marketing innuendo (ceramic and all that hogwash notwithstanding).
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clare wrote, on Tue, 04 Nov 2014 23:19:23 -0500:

You didn't read a single one of the references. And, you're changing the definition.
I was *very clear* on my definition. Runout is runout; it isn't warp (as in potato chip).
But, don't believe me. Read what the experts have to say.
https://www.google.com/search?client=ubuntu&channel=fs&q=the+myth+of+rotor+warp&ie=utf-8&oe=utf-8
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clare wrote, on Tue, 04 Nov 2014 23:23:20 -0500:

Same way you measure warp for an engine block.
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Danny D. wrote, on Wed, 05 Nov 2014 07:25:02 +0000:

Here are some found by that simple google search ...
Police care about rotor warp, right? http://www.hendonpub.com/law_and_order/articles/2013/11/maintenance_and_idle_hours
Professional car tech bloggers care about rotor warp, right? http://www.brakeandfrontend.com/brake-tech-feature-8-myths-that-could-be-holding-you-back-from-performing-the-best-brake-job/
Companies that sell brake components care about rotor warp, right? http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths
Car enthusiasts care about rotor warp, right? http://www.mossmotors.com/SiteGraphics/Pages/brake_discs.html
Braking enthusiasts care about rotor warp, right? http://www.skimmydiscs.co.uk/blog/warped-brake-discs-myth/
How about the Raybestos brake tech school? http://www.hendonpub.com/resources/article_archive/results/details?id 87
Of course, then there are the people who say one thing, and then another: http://blog.fcpeuro.com/2014/08/08/warped-rotors-reality-or-myth/
But, overall, the evidence is pretty clear (although, as I said, I've read every single article there is on this, and they don't all agree).
Note: I'm positive you'll find articles that "assume" rotor warp, as I've been down this road many times. However, in *every* one of those cases, what you *won't* see is a balanced discussion of the argument that rotors don't typically warp. You'll quickly notice that those who say rotors don't warp *know* all about the counter argument, while those who say rotors warp invariably are clueless about the counter argument.
And, nobody who says their street rotors warped ever measured it and proved that they did (they all *say* they did, but none can provide a picture).
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Vic Smith wrote, on Tue, 04 Nov 2014 22:44:06 -0600:

Look at my very first post on this subject ...

The main reason for *understanding* what is going on is *not* to solve the short-term problem (which is always to replace or machine or rebed or retorque the rotors for all rotor-specific DTV/BTV/runout problems).
The main reason for understanding what is really going on is to formulate the correct *long term* solution.
If you think your street rotors warped (like a potato chip), then you will implement the wrong long-term solution, but the right short-term solution.
I've been down this road so many times, I know where we are going, but you have to read what the experts have to say.
Bear in mind, they don't all agree on all topics, and also bear in mind you will certainly find articles that state that true warp actually exists - but - you'll *never* find an article that says that, while acknowledging that the counter argument exists.
Whereas, you'll *always* find the counter argument explained in all the threads from experts who say it's a myth that street rotors commonly warp.
It's just like people saying you'll catch cold if you go outside without a hat and coat on in the freezing rain. You won't, and you can't - but they'll never believe it ... but those who know how you catch cold know BOTH SIDES of the argument while those who insist they caught cold in the cold, don't even UNDERSTAND the other side of the argument.
Same thing with warp. Lack of understanding is the problem. Until that's fixed, you can't come up with the correct long-term solution to the problem.
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