myth of warped disks

Mayayana wrote, on Tue, 04 Nov 2014 18:22:11 -0500:

> So what should one do? Avoid hard braking?

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 a
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...utf-8&oe=utf-8

On Wed, 5 Nov 2014 03:22:30 +0000 (UTC), "Danny D."
> wrote:

>Mayayana wrote, on Tue, 04 Nov 2014 18:22:11 -0500:
>
>> So what should one do? Avoid hard braking?
>
>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 a
>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...utf-8&oe=utf-8
OK Danny - how would YOU measure warpage? What is your definition?
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.

clare wrote, on Tue, 04 Nov 2014 23:23:20 -0500:

> OK Danny - how would YOU measure warpage?

Same way you measure warp for an engine block.

Thanks. I'l give your tips a try. I have noticed that
the oscillation is not always there, so your explanations
make sense.

Mayayana wrote, on Wed, 05 Nov 2014 07:54:13 -0500:

> Thanks. I'l give your tips a try. I have noticed that
> the oscillation is not always there, so your explanations
> make sense.

As you rebed the brakes the pad deposits can change, and what oftne
happens is that the "character" of the vibration changes (either the
speed at which it starts and stops, or severity, or whatever).

That's a good clue that you're dealing with deposition and not some
mechanically different problem, such as warp.

Rebedding would *never* change the character of warp.
Rebedding *often* changes the character of what people "call" warp.

The long term solution is different when there's real warp involved from
when it's merely DTV or BTV due to uneven pad deposition.

Good luck. Let us know how it works out.
Once you understand this beast, you can drive with more finesse on the
brakes.

On Wed, 5 Nov 2014 07:25:58 +0000 (UTC), "Danny D."
> wrote:

>clare wrote, on Tue, 04 Nov 2014 23:23:20 -0500:
>
>> OK Danny - how would YOU measure warpage?
>
>Same way you measure warp for an engine block.
You still have not said how you measure warpage of a rotor. Measuring
warpage of an engine block is totally different - and I know how to do
that too. To measure warpage of a block you need to measure not only
un-evenness of the block deck, but also twist and alighnment both
vertically and horizontally of the bearing bores and trueness,
roundness, and alignment of the cyl bores.

All of this is done without rotating the block.

Not how you check a rotor for warpage - not even close.

The rotor is a lot simpler.

You still have not explained how you measure warpage on a rotor -
possibly because you don't believe it is possible to measure it
because it does not exist..

How then do you measure to prove a rotor is NOT warped????

On Wed, 5 Nov 2014 07:54:13 -0500, "Mayayana"
> wrote:

> Thanks. I'l give your tips a try. I have noticed that
>the oscillation is not always there, so your explanations
>make sense.
>
The chances that you have actually experienced a warped rotor ARE
pretty slim.

On Wed, 5 Nov 2014 19:02:53 +0000 (UTC), "Danny D."
> wrote:

>Mayayana wrote, on Wed, 05 Nov 2014 07:54:13 -0500:
>
>> Thanks. I'l give your tips a try. I have noticed that
>> the oscillation is not always there, so your explanations
>> make sense.
>
>As you rebed the brakes the pad deposits can change, and what oftne
>happens is that the "character" of the vibration changes (either the
>speed at which it starts and stops, or severity, or whatever).
>
>That's a good clue that you're dealing with deposition and not some
>mechanically different problem, such as warp.
>
>Rebedding would *never* change the character of warp.

So now you are admitting that actual warpage "can" exist???
>Rebedding *often* changes the character of what people "call" warp.
>
>The long term solution is different when there's real warp involved from
>when it's merely DTV or BTV due to uneven pad deposition.
>
>Good luck. Let us know how it works out.
>Once you understand this beast, you can drive with more finesse on the
>brakes.

On Tuesday, November 4, 2014 5:22:42 PM UTC-10, Danny D. wrote:
> Mayayana wrote, on Tue, 04 Nov 2014 18:22:11 -0500:
>
> > So what should one do? Avoid hard braking?
>
> 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 a
> 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...utf-8&oe=utf-8

As a practical matter, I like to be careful about imprinting my rotors - especially after a rapid stop or when braking while going downhill. I think it's just good policy. I'll leave word definitions to you car techs. :-)