On 2022-05-11 1:19 p.m., Andy Burnelli wrote:
> sms wrote:
>
>> Unfortunately, just replacing the warped rotors with the same OEM
>> rotors is not a long-term fix, the problem will come back.
>
> The "problem" most of the time is the driver's own foot, so, yeah.
> It will come back.
> It will continue to come back until the driver learns that warped rotors
> (as in potato chip) are a myth.

Your own sources disagree.

Vic Smith wrote:

> The author quoted above says - in the same article - "The excessive heat from the pads can
> cause the discs to overheat, resulting in disc warping."

We've had this discussion many times, where I'm well aware that there is
conflicting information even in any one given article on the subject.

What we have is a difference in terminology and measurement skills.

For example:
*The Mystery of Warped Brake Rotors*
<https://trade.mechanic.com.au/news/solved-the-mystery-of-warped-brake-rotors>
"Contrary to popular belief, brake rotors, and especially brake rotors
supplied by a reputable manufacturer such as DBA don't warp, no matter
how aggressively a vehicle is driven. Yet, as we know, brake pedal
pulsation caused by out-of-true brake rotors is a fairly common problem
that is almost invariably attributed to warped rotors, which is almost
invariably confirmed by excessive amounts of rotor run out that is easy
to "prove" with a dial gauge."

*Nuts & Bolts: Warped Rotor Myth*
<https://www.motortrend.com/how-to/1808-nuts-and-bolts-warped-rotor-myth/>
"It's exceedingly rare to actually warp a rotor. Instead, the cause
of the shudder you feel through the pedal is an uneven buildup
of brake pad material on the rotor itself."

The conflicting information is why you heard me say a few times in the
beginning that I wasn't saying it can't happen, but that it doesn't.
[I'm well aware some reliable references say it can't happen also.]

Given of the 100% of people who _say_ their rotors warped, 0% of them
actually measured it (and probably only 10% would know how), it's not warp.

> You'll probably find this study interesting:
> https://link.springer.com/article/10.1007/s11665-012-0397-7#article-info
> Let me know what you think of it.

Nice catch. Right down my line.

*The Effect of Residual Stress on the Distortion of Gray Iron Brake Disks*
<https://link.springer.com/article/10.1007/s11665-012-0397-7#article-info>

From the first two sentences, it appears they studied:
a. "thermal distortion"
b. of "gray iron brake disks"
c. due to "residual stress"
d. on both a heat-treated & non-heat-treated gray iron disk (singular)
e. measured by "neutron scattering"
f. and by "dynamometer tests" to measure "disk runout" during braking
g. and by "high temperature tensile tests" for "plastic deformation"
h. all due to "residual stress" *_during_* "brake applications.

It's a bit confusing but they _also_ added a separate action of
"heat treating in a vacuum furnace" to "simulate distortion at
high temperatures", um, so, um, they purposefully distorted the
discs, it appears... and _then_ they tested them for distortion
under pressure. (I admit that's a bit confusing to swallow.)

Also notice they're talking _during_ the brake application,
and that they're comparing residual stress between a single
heat treated & a single non heat treated gray iron rotor.

Nothing wrong with a test of just one component, but let's keep
that in mind (although I'm not saying anything was done wrong).

Presumably, if these numbers are meaningful, heat treating works:
"The results showed that the average residual stress of the '
heat-treated disk (47.6 MPa) was lower than that of the
non-heat-treated disk (99.6 MPa)."

"Dynamometer tests at high temperatures (up to 600�C/1112�F) indicated
that the residual stress pronounced the runout: the increase in disk
runout after the tests for the non-heat-treated sample was more than
twice that for the heat-treated sample."

Notice this is testing at high heat _during_ braking only; not afterward.
Their conclusion was that heat treating works, and that disks improperly
manufactured (i.e., no "stress relaxation" performed on them during the
manufacturing process) could be "deformed _during_ severe braking".

After first reading the abstract (which is how you read scientific
peer-reviewed papers, and yes, I've been published myself), you jump
to the conclusion next.

In the conclusion they state their goal was to study the difference
between heat treated and non heat treated gray iron rotors on high
heat distortion _during_ braking. At elevated temperatures, they
found the heat treated rotor (singular) distorted less than the heat
treated rotor (singular - as they only used two rotors for the test).

I found their conclusion interesting in that after they purposefully
introduced runout, they found that the largest increase was found
"along the circumference near the edge", which they opined
"indicates the necessity for a more refined design of the casting
process and the disk shape."

At that point I started to read how they ran their experiment,
but let's not summarize that here as I don't see anything wrong
with what they did (nor am I'm qualified to critique them).

On 2022-05-11 1:49 p.m., Andy Burnelli wrote:
> Vic Smith wrote:
>
>> The author quoted above says - in the same article - "The excessive
>> heat from the pads can
>> cause the discs to overheat, resulting in disc warping."
>
> We've had this discussion many times, where I'm well aware that there is
> conflicting information even in any one given article on the subject.
>
> What we have is a difference in terminology and measurement skills.
>
> For example:
> *The Mystery of Warped Brake Rotors*
> <https://trade.mechanic.com.au/news/solved-the-mystery-of-warped-brake-rotors>
>
> "Contrary to popular belief, brake rotors, and especially brake rotors
> supplied by a reputable manufacturer such as DBA don't warp, no matter
> how aggressively a vehicle is driven. Yet, as we know, brake pedal
> pulsation caused by out-of-true brake rotors is a fairly common problem
> that is almost invariably attributed to warped rotors, which is almost
> invariably confirmed by excessive amounts of rotor run out that is easy
> to "prove" with a dial gauge."
>
> *Nuts & Bolts: Warped Rotor Myth*
> <https://www.motortrend.com/how-to/1808-nuts-and-bolts-warped-rotor-myth/>
> "It's exceedingly rare to actually warp a rotor. Instead, the cause  of
> the shudder you feel through the pedal is an uneven buildup  of brake
> pad material on the rotor itself."

Tell me, Mr. Well-educated:

Does "exceedingly rare" actually mean "impossible"?

>
> The conflicting information is why you heard me say a few times in the
> beginning that I wasn't saying it can't happen, but that it doesn't.
> [I'm well aware some reliable references say it can't happen also.]
>
> Given of the 100% of people who _say_ their rotors warped, 0% of them
> actually measured it (and probably only 10% would know how), it's not warp.

This is your idea of only stating facts, is it?

Claiming things you cannot possibly know?

>
>> You'll probably find this study interesting:
>> https://link.springer.com/article/10.1007/s11665-012-0397-7#article-info
>> Let me know what you think of it.
>
> Nice catch. Right down my line.
>
> *The Effect of Residual Stress on the Distortion of Gray Iron Brake Disks*
> <https://link.springer.com/article/10.1007/s11665-012-0397-7#article-info>
>
> From the first two sentences, it appears they studied:
> a. "thermal distortion" b. of "gray iron brake disks" c. due to
> "residual stress"
> d. on both a heat-treated & non-heat-treated gray iron disk (singular)
> e. measured by "neutron scattering"
> f. and by "dynamometer tests" to measure "disk runout" during braking
> g. and by "high temperature tensile tests" for "plastic deformation"
> h. all due to "residual stress" *_during_* "brake applications.
>
> It's a bit confusing but they _also_ added a separate action of
> "heat treating in a vacuum furnace" to "simulate distortion at high
> temperatures", um, so, um, they purposefully distorted the discs, it
> appears... and _then_ they tested them for distortion
> under pressure. (I admit that's a bit confusing to swallow.)
>
> Also notice they're talking _during_ the brake application, and that
> they're comparing residual stress between a single
> heat treated & a single non heat treated gray iron rotor.
>
> Nothing wrong with a test of just one component, but let's keep
> that in mind (although I'm not saying anything was done wrong).
>
> Presumably, if these numbers are meaningful, heat treating works:
> "The results showed that the average residual stress of the '
>  heat-treated disk (47.6 MPa) was lower than that of the
>  non-heat-treated disk (99.6 MPa)."
>
> "Dynamometer tests at high temperatures (up to 600�C/1112�F) indicated
>  that the residual stress pronounced the runout: the increase in disk
>  runout after the tests for the non-heat-treated sample was more than
>  twice that for the heat-treated sample."
>
> Notice this is testing at high heat _during_ braking only; not afterward.
> Their conclusion was that heat treating works, and that disks improperly
> manufactured (i.e., no "stress relaxation" performed on them during the
> manufacturing process) could be "deformed _during_ severe braking".
>
> After first reading the abstract (which is how you read scientific
> peer-reviewed papers, and yes, I've been published myself), you jump
> to the conclusion next.
>
> In the conclusion they state their goal was to study the difference
> between heat treated and non heat treated gray iron rotors on high
> heat distortion _during_ braking. At elevated temperatures, they found
> the heat treated rotor (singular) distorted less than the heat
> treated rotor (singular - as they only used two rotors for the test).
>
> I found their conclusion interesting in that after they purposefully
> introduced runout, they found that the largest increase was found
> "along the circumference near the edge", which they opined
> "indicates the necessity for a more refined design of the casting
>  process and the disk shape."
>
> At that point I started to read how they ran their experiment, but let's
> not summarize that here as I don't see anything wrong
> with what they did (nor am I'm qualified to critique them).

Did I call it?

:-)

Alan wrote:

> Did I call it?

You must be a speed reader because your post is 3 minutes after his
during which time you read the article Vic proposed & his response.

What is your summary of what Vic Smith's article said?
And how does your assessment differ from his?

You have three minutes.

Andy Burnelli wrote:

> Unless new data has arisen, there are fundamentally two types of articles
> that will use the word "warp", namely...
> a. Those that _know_ warp doesn't happen, and,
> b. Those that don't know warp doesn't happen.
>
> For the articles that know warp doesn't happen, they will always explain
> how the shudder occurs (e.g., TV or runout or whatever), while those that
> don't know will be clueless. They'll call _everything_ warp.

Btw, since Steve has repeatedly insisted warp occurs, I must make the point
that _every_ article proposed by Steve has been in the latter category.

That is, as Steve did with his fabricated FCC maps (he never knew they
showed _zero_ 3G and 5G coverage until I looked it up and _told_ him that),
Steve, the consummate politician, purposefully selects the least reliable
articles to make his claims.

As if we're _all_ not aware that there are billions of people out there,
who want to sell you new rotors who will claim that your rotors warped.

BTW, if any shop does that, then think about the horrendous conditions that
it would take to warp a rotor, and not only should that rotor be thrown
away, but likely the entire car should be junked...

Simply because the conditions to truly warp a rotor are nigh near
impossible to attain, and if they were attained, you'd boil your fluids and
most of your rubber components would be marshmallows, and your pads would
shatter, etc.

In summary, anyone who tells you your rotors warped, and his solution is
anything other than to junk that car, then he's clearly bullshitting you.
--
If the proposed solution to true rotor warp isn't to junk the car, then
you're being bullshitted because warp conditions destroy more than rotors.

On 2022-05-08 12:36, NY wrote:
> "Alan" <nuh-uh@nope.com> wrote in message
> news:t57i62$p1k$1@dont-email.me...
>
>> Do the math on a single stop from highway speed.
>>
>> My 2012 BMW 135i MSport Edition weights 4,255lbs, so stopping it from
>> 60mph must dissipate 694,273 Joules.
>>
>> We'll assume that all the energy of the stop remains in the rotors
>> themselves, and that BMW has done it's job properly and that therefore
>> the front and rear brake rotors are proportional in mass to the energy
>> each must dissipate.
>>
>> So we can take the total mass of the rotors, the heat capacity of
>> steel and calculate the change in temperature.
>>
>> The mass of those rotors is 34.47kg
>>
>> The specific heat of steel is about 420 joules per kilogram per degree
>>
>> 420J/kg*c
>>
>> So with 34.47kg, we get 14,477.4 J per degree C temperature change,
>> and dividing the 694,273 joules we've got, we get a temperature change
>> of...
>>
>> ...just about 48 degree.
>>
>> If it's a warm summer day, you're not going to want to touch the
>> rotors, as they will now be above the boiling point of water (about
>> 120°C)...
>>
>> (Provided you ignore the energy lost to the airflow and also
>> dissipated by the mass of the pads and calipers themselves, as well
>> was the energy conducted into the hub of each wheel)...
>>
>> ...but it's hardly going to be enough to deposit brake pad material
>> onto the disk.
>>
>> This is why brake bedding procedures call for MULTIPLE retardations
>> from highway speed in order to get the disks hot enough to deposit an
>> even layer of pad material onto the surface.
>>
>> I know this, because in my amateur racing "career", I'm also a senior
>> racing instructor, and because our students are driving road cars for
>> sessions where the brakes actually WILL get to the temperatures that
>> can cause that kind of deposition, we always tell them not to apply
>> the parking braking when returning to the paddock after a session.
>
> I remember many years ago watching a "for schools and colleges" TV
> science programme at school about "energy". It talked about converting
> kinetic energy into other forms. As an example, they rigged up a camera
> on a car, pointing at the front brake disc. They they took it on a
> racing track (they emphasised that this was off-road!), and repeatedly
> accelerated to 70 and then braked hard to a stop. After a few cycles of
> this, the discs were glowing cherry red. I was quite surprised that
> discs would get *that* hot, and that brake pads would withstand contact
> with red-hot metal.

I worked for a company where we made industrial test beds (I was the
programmer). One of those was for testing brakes. During testing at the
brake factory where this machine was installed, the chap there actually
brought the disk to that hot. The testing procedures included braking
from 40, 60, & 80 down to 0, several times in a row, while graphing disk
temp, fluid pressure, torque...

He said a good pad material would not degrade or "fade" suddenly when
too hot, but would lose the friction coefficient gradually as
temperature increases, thus warning the driver of the danger.

--
Cheers,
Carlos E.R.

On 5/11/2022 5:47 AM, NY wrote:

<snip>

> I wonder what effect that high temperature had on the pads once they
> were red hot. Would you want to ride in that car afterwards - would the
> pads have been made less effective? How hot do discs get if you descend
> a long hill (let's say a mile long, average 1:4 aka 25%) using brakes
> only. My wife remembers a friend descending such a hill (Porlock Hill in
> Devon, England) in a motor caravan which may have had a mixture of discs
> and drums. By the end of the hill, there was smoke coming from the
> wheels (brake pads, presumably) - the driver learned an important
> lesson: to engage a low gear on a long steep hill so there is a bit of
> transmission braking to supplement the normal friction braking.

Decades ago I replace the brake pads on a VW Rabbit (Golf in other
regions) with pads that I ordered online from JC Whitney, a mail-order
parts house. Descending a steep hill, in San Francisco, the pads glazed
over from the heat. The rotors were fine. Did another brake job
immediately, using high-quality pads from an import car parts store.

Unfortunately, in the U.S., not a lot of vehicle owners still do their
own car maintenance so the number of auto parts stores is greatly
reduced. In my town of 60,000 people we've lost all three of our auto
parts stores as well as a fourth that's just across the city boundary. I
now buy my oil at Costco or Walmart and I order my oil filters from a
dealer that sells OEM parts on eBay.

Two of our vehicles are hybrids and because of regenerative braking the
brakes last a very long time, easily more than 100K miles. On my old VWs
I had to do brake jobs every 25K-30K miles.

On 5/11/2022 5:20 AM, Xeno wrote:

<snip>

> Nope, they were warped and wouldn't clean up *before* they went below
> minimum thickness. In the early days I tried a few, found I was wasting
> my time machining them, then started relying on *measurements* to
> determine serviceability after machining. It's only involves simple
> arithmetic. Discs these days are like spark plugs - the cost of repair
> due to time involved is outweighed by the low cost of new items.

"Back in the olden days" I kept a spare set of rotors so when I was
doing a brake job I didn't have to stop and take the rotors to be
machined in the middle of the work. I'd then take the rotors that I
removed to be put on a lathe (for free since my relative had a repair
shop) and they'd be ready for the next brake job in 25,000 miles or so.

But back then discs were thick and heavy and could be machined multiple
times before they were too thin. Nowadays rotors are so thin they can
usually not be machined even once, but they've also become less
expensive (when adjusted for inflation).

My brother-in-law saw a lot of vehicles with warped rotors back in the
mid-1990's to 2000's, when the manufacturers started making them very
thin without the material science knowledge of how to prevent warping.
Just one serious overheating and the rotors were warped beyond repair.
There was one GM brand, that is now defunct, that was particularly
susceptible to warped rotors. His shop was in San Francisco and there
are lot of very steep hills (when San Francisco was first laid out the
proposal was to not do a grid because of the hills, but to have roads
winding up the hills; real estate people protested that this would be
too complicated).

Is someone actually claiming that disc rotors don't warp? That would be
very surprising since nearly every car mechanic in the world is well
aware of this issue
<https://www.sandiegouniontribune.com/cars/click-and-clack/story/2019-05-02/warped-rotors-give-this-pony-the-shakes>,
<https://www.cartalk.com/blogs/dear-car-talk/warped-brake-discs-are-bad-news>,

On 5/11/2022 5:20 AM, NY wrote:
> That word "warped" is misleading because it makes people think "wavy".

Yes, in many cases "uneven" would be a better adjective than "warped"
but there are still cases where the steel brake rotor is deformed from heat.

On 2022-05-11 4:41 p.m., sms wrote:
> On 5/11/2022 5:20 AM, NY wrote:
>> That word "warped" is misleading because it makes people think "wavy".
>
> Yes, in many cases "uneven" would be a better adjective than "warped"
> but there are still cases where the steel brake rotor is deformed from
> heat.

"Warped" is a perfectly fine descriptor and no one would argue that a
2x4 piece of lumber was "warped" simply because all it had was (say) a
twist.

On 2022-05-11 2:47 p.m., Andy Burnelli wrote:
> Andy Burnelli wrote:
>
>> Unless new data has arisen, there are fundamentally two types of articles
>> that will use the word "warp", namely... a. Those that _know_ warp
>> doesn't happen, and, b. Those that don't know warp doesn't happen.
>>
>> For the articles that know warp doesn't happen, they will always explain
>> how the shudder occurs (e.g., TV or runout or whatever), while those that
>> don't know will be clueless. They'll call _everything_ warp.
>
> Btw, since Steve has repeatedly insisted warp occurs, I must make the point
> that _every_ article proposed by Steve has been in the latter category.
>
> That is, as Steve did with his fabricated FCC maps (he never knew they
> showed _zero_ 3G and 5G coverage until I looked it up and _told_ him
> that), Steve, the consummate politician, purposefully selects the least
> reliable
> articles to make his claims.
>
> As if we're _all_ not aware that there are billions of people out there,
> who want to sell you new rotors who will claim that your rotors warped.
>
> BTW, if any shop does that, then think about the horrendous conditions that
> it would take to warp a rotor, and not only should that rotor be thrown
> away, but likely the entire car should be junked...
>
> Simply because the conditions to truly warp a rotor are nigh near
> impossible to attain, and if they were attained, you'd boil your fluids and
> most of your rubber components would be marshmallows, and your pads would
> shatter, etc.
>
> In summary, anyone who tells you your rotors warped, and his solution is
> anything other than to junk that car, then he's clearly bullshitting you.

What a load of bullshit.

sms wrote:

> Decades ago I replace the brake pads on a VW Rabbit (Golf in other
> regions) with pads that I ordered online from JC Whitney, a mail-order
> parts house. Descending a steep hill, in San Francisco, the pads glazed
> over from the heat. The rotors were fine. Did another brake job
> immediately, using high-quality pads from an import car parts store.

High quality?
How did you know?
By the advertising?

HINT: What's the cold/hot friction rating (coefficient) of those pads?
DOUBLEHINT: It's printed on every passenger vehicle pad sold in the USA.

> Unfortunately, in the U.S., not a lot of vehicle owners still do their
> own car maintenance so the number of auto parts stores is greatly
> reduced.

Is that true?

Do people do less of their maintenance now that it's easier than ever
before to do typical maintenance on a car for a whole bunch of reasons:
a. Cars require less maintenance nowadays (e.g., no points)
b. Videos abound on YouTube for how to do all sorts of maintenance
c. Cars are simpler now than they have ever been (IMHO)
d. The Internet makes finding & buying the correct parts super easy
etc.

Were auto parts stores more prevalent in the past than they are now?

> In my town of 60,000 people we've lost all three of our auto
> parts stores as well as a fourth that's just across the city boundary. I
> now buy my oil at Costco or Walmart and I order my oil filters from a
> dealer that sells OEM parts on eBay.

Maybe that (and Internet shopping) is why you lost your auto parts stores?
Why do you think that loss is only due to a presumed lack of home DIY?

> Two of our vehicles are hybrids and because of regenerative braking the
> brakes last a very long time, easily more than 100K miles. On my old VWs
> I had to do brake jobs every 25K-30K miles.

I still have a RWD vehicle with drum brakes, whose shoes lasted, oh, about
180K miles (and which were still meaty when I replaced them), and, let's be
clear, I live on the top of a mountain which is clearly tough on them.

The fronts go more frequently of course...
--
Each post to Usenet should strive to add value to what people already said.

On 2022-05-11 3:25 p.m., sms wrote:
> On 5/11/2022 5:47 AM, NY wrote:
>
> <snip>
>
>> I wonder what effect that high temperature had on the pads once they
>> were red hot. Would you want to ride in that car afterwards - would
>> the pads have been made less effective? How hot do discs get if you
>> descend a long hill (let's say a mile long, average 1:4 aka 25%) using
>> brakes only. My wife remembers a friend descending such a hill
>> (Porlock Hill in Devon, England) in a motor caravan which may have had
>> a mixture of discs and drums. By the end of the hill, there was smoke
>> coming from the wheels (brake pads, presumably) - the driver learned
>> an important lesson: to engage a low gear on a long steep hill so
>> there is a bit of transmission braking to supplement the normal
>> friction braking.
>
> Decades ago I replace the brake pads on a VW Rabbit (Golf in other
> regions) with pads that I ordered online from JC Whitney, a mail-order
> parts house. Descending a steep hill, in San Francisco, the pads glazed
> over from the heat. The rotors were fine. Did another brake job
> immediately, using high-quality pads from an import car parts store.

Some brake compounds aren't compatible with what came before and the new
pads can do that.

>
> Unfortunately, in the U.S., not a lot of vehicle owners still do their
> own car maintenance so the number of auto parts stores is greatly
> reduced. In my town of 60,000 people we've lost all three of our auto
> parts stores as well as a fourth that's just across the city boundary. I
> now buy my oil at Costco or Walmart and I order my oil filters from a
> dealer that sells OEM parts on eBay.
>
> Two of our vehicles are hybrids and because of regenerative braking the
> brakes last a very long time, easily more than 100K miles. On my old VWs
> I had to do brake jobs every 25K-30K miles.

On 2022-05-11 2:03 p.m., John Doe wrote:
> Alan wrote:
>
>> Did I call it?
>
> You must be a speed reader because your post is 3 minutes after his
> during which time you read the article Vic proposed & his response.

Why would I have had to read the article then and there?

The article was posted (checking) at 11:35, and I replied to Vic at
12:53pm with my prediction.

>
> What is your summary of what Vic Smith's article said?
> And how does your assessment differ from his?
>
> You have three minutes.

Sorry, but I'm not into the game playing.

Brake rotor warping can be and has been demonstrated by me with actual
video of warped rotors.

On 2022-05-11 5:21 p.m., Andy Burnelli wrote:
> sms wrote:
>
>> Decades ago I replace the brake pads on a VW Rabbit (Golf in other
>> regions) with pads that I ordered online from JC Whitney, a mail-order
>> parts house. Descending a steep hill, in San Francisco, the pads
>> glazed over from the heat. The rotors were fine. Did another brake job
>> immediately, using high-quality pads from an import car parts store.
>
> High quality?
> How did you know?
> By the advertising?
>
> HINT: What's the cold/hot friction rating (coefficient) of those pads?
> DOUBLEHINT: It's printed on every passenger vehicle pad sold in the USA.

TRIPLEHINT: The cold/hot friction rating is not all that matters.

>
>> Unfortunately, in the U.S., not a lot of vehicle owners still do their
>> own car maintenance so the number of auto parts stores is greatly
>> reduced.
>
> Is that true?

Probably, yes.

Vehicles have become far more complex.

I can do my own brake pads if I care to, and I do do so for my 1998 Van
Diemen RF98-2 Formula F.

>
> Do people do less of their maintenance now that it's easier than ever
> before to do typical maintenance on a car for a whole bunch of reasons:
> a. Cars require less maintenance nowadays (e.g., no points)
> b. Videos abound on YouTube for how to do all sorts of maintenance
> c. Cars are simpler now than they have ever been (IMHO)
> d. The Internet makes finding & buying the correct parts super easy
> etc.
>
> Were auto parts stores more prevalent in the past than they are now?

Easily, yes.

>
>> In my town of 60,000 people we've lost all three of our auto parts
>> stores as well as a fourth that's just across the city boundary. I now
>> buy my oil at Costco or Walmart and I order my oil filters from a
>> dealer that sells OEM parts on eBay.
>
> Maybe that (and Internet shopping) is why you lost your auto parts stores?
> Why do you think that loss is only due to a presumed lack of home DIY?
>
>> Two of our vehicles are hybrids and because of regenerative braking
>> the brakes last a very long time, easily more than 100K miles. On my
>> old VWs I had to do brake jobs every 25K-30K miles.
>
> I still have a RWD vehicle with drum brakes, whose shoes lasted, oh, about
> 180K miles (and which were still meaty when I replaced them), and, let's be
> clear, I live on the top of a mountain which is clearly tough on them.

Let's be clearer:

You talk bullshit on a regular basis.

sms wrote:

> "Back in the olden days" I kept a spare set of rotors so when I was
> doing a brake job I didn't have to stop and take the rotors to be
> machined in the middle of the work. I'd then take the rotors that I
> removed to be put on a lathe (for free since my relative had a repair
> shop) and they'd be ready for the next brake job in 25,000 miles or so.
>
> But back then discs were thick and heavy and could be machined multiple
> times before they were too thin. Nowadays rotors are so thin they can
> usually not be machined even once, but they've also become less
> expensive (when adjusted for inflation).

I wonder if _anyone_ here realizes _why_ there's a minimum thickness spec?

HINT: It's not what everyone intuits (e.g., it's not for heat dissipation).

> My brother-in-law saw a lot of vehicles with warped rotors back in the
> mid-1990's to 2000's, when the manufacturers started making them very
> thin without the material science knowledge of how to prevent warping.

It's amazing how you concoct your own imaginary belief systems, Steve.

> Just one serious overheating and the rotors were warped beyond repair.

If a rotor got hot enough to warp your rubber brake lines turned into
marshmallows & your brake fluid boiled off & your pads disintegrated.

> There was one GM brand, that is now defunct, that was particularly
> susceptible to warped rotors. His shop was in San Francisco and there
> are lot of very steep hills (when San Francisco was first laid out the
> proposal was to not do a grid because of the hills, but to have roads
> winding up the hills; real estate people protested that this would be
> too complicated).

Again, you fabricate purely imaginary belief systems, and then you
frantically strive to find the most insane reasons to bolster it up.

> Is someone actually claiming that disc rotors don't warp?

Yeah. Like the entire world. That's a lot more than "someone", Steve.

> That would be
> very surprising since nearly every car mechanic in the world is well
> aware of this issue
> <https://www.sandiegouniontribune.com/cars/click-and-clack/story/2019-05-02/warped-rotors-give-this-pony-the-shakes>,
> <https://www.cartalk.com/blogs/dear-car-talk/warped-brake-discs-are-bad-news>,

It's always amazing how you find all the bullshit on the Internet and yet
you _miss_ all the reliable references, where you _aim_ for bullshit, Steve.

There are half a dozen materials rotors are made of though, so we'd have to
look up the melting point of each of them to be more precise about melting.
1. cast iron
2. steel
3. stainless steel
4. laminated steel
5. high carbon iron (e.g., Sparta CX3.5)
6. ceramic

<https://ricksfreeautorepairadvice.com/warped-brake-rotors/>
"To get cast iron hot enough to soften the metal you'd need to generate
almost 2,300�F range. There isn't a factory stock automotive brake
system in the world that's capable of generating that kind of heat.
In fact, you would experience brake pad fade, pad disintegration,
brake fluid boiling and rotor discoloration long before you
reached 1,000�F."

"To pass the J2928 rotor test, rotors must withstand at least
150 heat cycles on a dynamometer without cracking or showing
any structural or dimensional failure. "

*Stop the "Warped" Rotors Myth and Service Brakes the Right Way*
<https://www.brakeandfrontend.com/warped-rotors-myth/>
Rotors are cast in extreme heat at three to five times greater
than the most aggressive braking situation. Physically 'warping'
a rotor would require a similar application of extreme heat,
which is impossible."
---
*The 'Warped' Brake Disc & Other Myths of the Braking System*
<https://centricparts.com/getmedia/bd69395a-b65c-481d-93f7-b26b1bd0638d/Centric_and_APC_Technical_Whitepaper_B1-Warped-Brake-Disc-8-2018_1.pdf>
<https://www.ipdusa.com/Articles/528/The-Warped-Brake-Disc-and-Other-Myths-of-the-Braking-System>
"In more than 40 years of professional racing, including the
Shelby/Ford GT 40s - one of the most intense brake development
programs in history - I have never seen a warped brake disc."
---
<https://www.brakeandfrontend.com/brake-rotors-dont-warp-the-earth-is-not-flat/>
"By declaring a customer's brake pedal pulsation complaint is caused
by warped rotors is like saying the earth is flat. Both are cases where
the observation of the person is based on a tiny piece of evidence
that is false in nature and application."
---
<https://ricksfreeautorepairadvice.com/warped-brake-rotors/>
"Calling it brake rotor warp demonstrates a complete misunderstanding
of the metallurgy and the braking process"
---
<https://www.crossdrilledrotors.ca/blog/part-one-rotors-dont-warp>
"Brake rotors do not warp from heat, even when driven by the
most aggressive traffic officer."
---
*The Mystery of Warped Brake Rotors*
<https://trade.mechanic.com.au/news/solved-the-mystery-of-warped-brake-rotors>
"Contrary to popular belief, brake rotors, and especially brake rotors
supplied by a reputable manufacturer such as DBA don't warp, no matter
how aggressively a vehicle is driven. Yet, as we know, brake pedal
pulsation caused by out-of-true brake rotors is a fairly common problem
that is almost invariably attributed to warped rotors, which is almost
invariably confirmed by excessive amounts of rotor run out that is easy
to "prove" with a dial gauge."
---
**Why Do Brake Rotors Warp?**
<https://www.buybrakes.com/help/why-do-brake-rotors-warp/>
"The thing is, rotors don�t actually permanently warp. It may feel that
way when braking, but what really happens is that they become irregular
due to excessive lateral run out of the rotor face. You can feel through
the brake pedal as little as .002" of run out. This amount of run out is
far smaller than you can see. In other words, rotors always remain true,
but they can wear out irregularly for several reasons."
1. Lug torque
2. Hub rust
3. Hub runout
---
*Brake Rotors Warp From Heat -- Myth Busted*
<https://www.hansonsubaru.com/service/information/brake-myths.htm>
"there's simply no way that a brake rotor can get hot enough to warp
or deform on an ordinary passenger car."
---
*Nuts & Bolts: Warped Rotor Myth*
<https://www.motortrend.com/how-to/1808-nuts-and-bolts-warped-rotor-myth/>
"It's exceedingly rare to actually warp a rotor. Instead, the cause
of the shudder you feel through the pedal is an uneven buildup
of brake pad material on the rotor itself. As little as 0.0004 inch
can be felt through the pedal & 0.001 inch can be downright annoying"
---
**Everything You Need to Know About High-Tech Rotors**
<https://www.motortrend.com/how-to/understanding-disc-brake-rotors/>
"The most persistent myth about rotors is that they warp. It takes a
lot of heat, the kind of heat used in the casting process, to actually
warp a rotor. The two common problems that cause pedal pulsation are
lateral run-out and disc thickness variation. Lateral run-out is
typically caused by run-out from the hub face, wheel bearing, uneven
lug nut torque, or a buildup of rust and corrosion between wheel and hub.
Disc thickness variation is most often caused by excess pad transfer,
the very thin layer of pad material that bonds to the rotor surface,
and uneven wear from an improperly mounted caliper. "
---
*Warped Brake Rotors - Vibrating Reality or Internet Myth?*
<https://blog.fcpeuro.com/warped-brake-rotors-vibrating-reality-or-internet-myth>
"Traditionally, this was blamed on warped rotors, and the prescription
was to either get the rotors machined or to replace the rotors.
Technically this wasn't wrong, but it's not completely right either.
To understand what is going on, lets examine how the brake pads
and rotors interact. It's not as simple as it seems on the surface,
and relies on complex interaction between friction materials.
Technically yes, the rotor is warped because the buildup of pad deposits
is a few thousandths of an inch thick. To restore proper smooth braking
performance, the uneven deposits need to be removed, and a fresh uniform
layer of friction material needs to be laid down."
---
*Stop the "Warped" Rotors Myth and Service Brakes the Right Way*
<https://www.brakeandfrontend.com/warped-rotors-myth/>
"Myths take hold �because either A) they seem completely logical or
B) they are so often repeated that they just become common knowledge.
The warped rotor myth is a little bit of both. A rotor that
contributed to a pulsation condition certainly appears 'warped.'
Plus, everyone says it - even technicians that know the rotor isn't
really warped will say it as shorthand. Rotors are cast in extreme heat
at three to five times greater than the most aggressive braking
situation. Physically 'warping' a rotor would require a similar
application of extreme heat, which is impossible."
---
*Six Brake Rotor Myths Debunked*
<https://www.onallcylinders.com/2017/05/19/6-biggest-brake-rotor-myths-debunked/>
Brake Rotors Warp - Rotors don't warp.
Back in the 1970s, in what was probably a scene right out of the
movie Dazed and Confused, someone came up with a theory about
brake-rotor "warping," and it totally stuck. Why? Probably because,
in layman's terms, it makes sense.
But then real life happens and this faulty explanation doesn't
hold up to scientific scrutiny.
What is often described as "warping" is actually the presence of
two separate phenomena that can happen in isolation or in combination
with each other, and neither has anything to do with warping.
These phenomena are:
a. Brake torque variation (BTV), and
b. Disc thickness variation (DTV)

sms wrote:

> On 5/11/2022 5:20 AM, NY wrote:
>> That word "warped" is misleading because it makes people think "wavy".
>
> Yes, in many cases "uneven" would be a better adjective than "warped"
> but there are still cases where the steel brake rotor is deformed from heat.

There are half a dozen materials rotors are made of though, so we'd have to
look up the melting point of each of them to be more precise about melting.
1. cast iron
2. steel
3. stainless steel
4. laminated steel
5. high carbon iron (e.g., Sparta CX3.5)
6. ceramic

<https://ricksfreeautorepairadvice.com/warped-brake-rotors/>
"To get cast iron hot enough to soften the metal you'd need to generate
almost 2,300�F range. There isn't a factory stock automotive brake
system in the world that's capable of generating that kind of heat.
In fact, you would experience brake pad fade, pad disintegration,
brake fluid boiling and rotor discoloration long before you
reached 1,000�F."

"To pass the J2928 rotor test, rotors must withstand at least
150 heat cycles on a dynamometer without cracking or showing
any structural or dimensional failure. "

*Stop the "Warped" Rotors Myth and Service Brakes the Right Way*
<https://www.brakeandfrontend.com/warped-rotors-myth/>
Rotors are cast in extreme heat at three to five times greater
than the most aggressive braking situation. Physically 'warping'
a rotor would require a similar application of extreme heat,
which is impossible."
--
The problem with people who believe their own intuition more than facts, is
they believe the craziest things, like the earth is flat & rotors warp.

On 2022-05-11 5:33 p.m., Andy Burnelli wrote:
> sms wrote:
>
>> "Back in the olden days" I kept a spare set of rotors so when I was
>> doing a brake job I didn't have to stop and take the rotors to be
>> machined in the middle of the work. I'd then take the rotors that I
>> removed to be put on a lathe (for free since my relative had a repair
>> shop) and they'd be ready for the next brake job in 25,000 miles or so.
>>
>> But back then discs were thick and heavy and could be machined
>> multiple times before they were too thin. Nowadays rotors are so thin
>> they can usually not be machined even once, but they've also become
>> less expensive (when adjusted for inflation).
>
> I wonder if _anyone_ here realizes _why_ there's a minimum thickness spec?
>
> HINT: It's not what everyone intuits (e.g., it's not for heat dissipation).

But you'll avoid actually providing an answer.

>
>> My brother-in-law saw a lot of vehicles with warped rotors back in the
>> mid-1990's to 2000's, when the manufacturers started making them very
>> thin without the material science knowledge of how to prevent warping.
>
> It's amazing how you concoct your own imaginary belief systems, Steve.
>
>> Just one serious overheating and the rotors were warped beyond repair.
>
> If a rotor got hot enough to warp your rubber brake lines turned into
> marshmallows & your brake fluid boiled off & your pads disintegrated.

Utterly wrong.

Metal can warp when temperature rises enough to release stresses left
over from the manufacturing process.

I have an aluminum engine that came with my Van Diemen Honda that was
removed because it warped at temperatures only a little bit above the
boiling point of water.

>
>> There was one GM brand, that is now defunct, that was particularly
>> susceptible to warped rotors. His shop was in San Francisco and there
>> are lot of very steep hills (when San Francisco was first laid out the
>> proposal was to not do a grid because of the hills, but to have roads
>> winding up the hills; real estate people protested that this would be
>> too complicated).
>
> Again, you fabricate purely imaginary belief systems, and then you
> frantically strive to find the most insane reasons to bolster it up.
>
>> Is someone actually claiming that disc rotors don't warp?
>
> Yeah. Like the entire world. That's a lot more than "someone", Steve.

Ummmm... ...no.

>
>> That would be very surprising since nearly every car mechanic in the
>> world is well aware of this issue
>> <https://www.sandiegouniontribune.com/cars/click-and-clack/story/2019-05-02/warped-rotors-give-this-pony-the-shakes>,
>> <https://www.cartalk.com/blogs/dear-car-talk/warped-brake-discs-are-bad-news>,
>>
>
> It's always amazing how you find all the bullshit on the Internet and
> yet you _miss_ all the reliable references, where you _aim_ for
> bullshit, Steve.

I've shown you the video, Arlen.

>
> There are half a dozen materials rotors are made of though, so we'd have to
> look up the melting point of each of them to be more precise about melting.
> 1. cast iron
> 2. steel
> 3. stainless steel
> 4. laminated steel
> 5. high carbon iron (e.g., Sparta CX3.5)
> 6. ceramic

Warping can take place at much lower temperatures than melting, Arlen.

>
> <https://ricksfreeautorepairadvice.com/warped-brake-rotors/>
> "To get cast iron hot enough to soften the metal you'd need to generate
>  almost 2,300�F range. There isn't a factory stock automotive brake
>  system in the world that's capable of generating that kind of heat.
>  In fact, you would experience brake pad fade, pad disintegration,
>  brake fluid boiling and rotor discoloration long before you  reached
> 1,000�F."

How does an aluminum engine warp at temperatures much lower than the
temperature necessary to soften aluminum?

>
>  "To pass the J2928 rotor test, rotors must withstand at least  150
> heat cycles on a dynamometer without cracking or showing  any structural
> or dimensional failure. "

Which wasn't a standard until 2013.

There are lots of cars with rotors older than 10 years.

<snipping the repetitive, self-serving bullshit>

On 2022-05-11 5:46 p.m., Andy Burnelli wrote:
> sms wrote:
>
>> On 5/11/2022 5:20 AM, NY wrote:
>>> That word "warped" is misleading because it makes people think "wavy".
>>
>> Yes, in many cases "uneven" would be a better adjective than "warped"
>> but there are still cases where the steel brake rotor is deformed from
>> heat.
>
> There are half a dozen materials rotors are made of though, so we'd have to
> look up the melting point of each of them to be more precise about melting.
> 1. cast iron
> 2. steel
> 3. stainless steel
> 4. laminated steel
> 5. high carbon iron (e.g., Sparta CX3.5)
> 6. ceramic
>
> <https://ricksfreeautorepairadvice.com/warped-brake-rotors/>
> "To get cast iron hot enough to soften the metal you'd need to generate
>  almost 2,300�F range. There isn't a factory stock automotive brake
>  system in the world that's capable of generating that kind of heat.
>  In fact, you would experience brake pad fade, pad disintegration,
>  brake fluid boiling and rotor discoloration long before you  reached
> 1,000�F."
>
>  "To pass the J2928 rotor test, rotors must withstand at least  150
> heat cycles on a dynamometer without cracking or showing  any structural
> or dimensional failure. "

1. A test that didn't exist until 2013.

2. A test that no manufacturer is required to pass.

On 12/5/2022 12:37 am, Andy Burnelli wrote:
> Xeno wrote:
>
>> You don't trust intuition, you listen to it, you make some
>> assessments, and then you *test* what it is telling you.
>
> I'm all for testing, as my cars are a quarter of a century old and when
> they break, I form an hypothesis and then I test that hypothesis so as to
> replace the part that needs to be replaced.
>
> One place I need your intuition on is this sentence in this reference:
>
>  *The 'Warped' Brake Disc & Other Myths of the Braking System*
> <https://www.ipdusa.com/Articles/528/The-Warped-Brake-Disc-and-Other-Myths-of-the-Braking-System>
>
> "In fact every case of "warped brake disc" that I have investigated,
>  whether on a racing car or a street car, has turned out to be friction
>  pad material transferred unevenly to the surface of the disc.  This
> uneven deposition results in thickness variation (TV)  or run-out due to
> hot spotting that occurred at elevated temperatures."

As I have stated, you can have a *warped disc* and *not experience*
judder, shudder or the like. You see, a warped disc does *not* lead to a
*thickness variation*, it's more akin to a *buckle* and, as such will
much more likely cause an effect in the *steering*, a *shimmy*.
>
> The fact they say "runout" in the same sentence as "TV" seems incongruent
> to me, where I think I understand what they're saying, but the reason it's
> disconcerting is that "normally" the solution for runout is _different_
> than the solution for DTV.
>
> Of course, TV will cause an "apparent runout" on the dial gauge, but it's
> not the same kind of runout you'd get with, oh, say, rust around the hub.

Correct. If the actual disc warps, you will get the same kind of runout
as you experience with the disc not sitting flat on the hub. I have had
runout of that nature on discs that are *integral* with the hub. In most
cases, but not all, that runout is caused by incorrect wheel nut tightening.
>
> The reason the semantics matter is that the _solution_ to each problem is
> different, where, for example, the solution to a truly warped rotor (as in
> potato chip) would be to junk that rotor, while the solution to DT is
> typically to smooth out the bumps, and the typical solution to runout is to
> figure out what caused the roter to be mounted off kilter (in most cases).

These days, given the disposable nature of discs, it is probably
advisable to dispose of discs rather than trying to dress them up on the
lathe. Back in the day, discs were a rather expensive item, these days
not so much.
>
> All show up, eventually, as "runout" but each cause has a different
> remedial solution so the fact you can measure an out-of-spec variation on a
> dial gauge doesn't tell you _which_ problem caused the runout.

You look at *several* symptoms, not just the runout alone.
>
>>> If the rotor met thickness, cracking, gouging specs, then you wasted
>>> a good
>>> rotor.
>>
>> Nope, they were warped and wouldn't clean up *before* they went below
>> minimum thickness. In the early days I tried a few, found I was
>> wasting my time machining them, then started relying on *measurements*
>> to determine serviceability after machining. It's only involves simple
>> arithmetic. Discs these days are like spark plugs - the cost of repair
>> due to time involved is outweighed by the low cost of new items.
>
> I agree on the cost factor weighing in as I've replaced perfectly good
> rotors for kids who no longer live at home even though the rotors were
> within specs because I had to buy the parts ahead of time and because I
> knew that a new rotor will last longer for the kids than an old rotor (even
> though the old rotor was within thickness specs).
>
> I get rotors for $15 to about $35 each, although I'm well aware they can
> easily cost many times that (especially for the bullshit drilled and
> slotted rotors - which are sold to morons who are intuitive people).
>
>>> HINT: If "warp" was truly a wavy rotor, then why does rebedding often
>>> work?
>>
>> Because people cannot discern or determine the *difference* in symptoms.
>
> Yup.
>
> That's why it matters what _word_ we use.
> a. If it truly warped, then any sane person would junk the rotors.
>   (Because the conditions to cause warp would have been horrendous.)
> b. If it's simply pad deposits, then a sane person might try to
> "scrape" them off with a simple re-bedding process.
>   (Or machine them off.)
> c. If it's simply that there is rust buildup between the rotor and the
> hub or maybe lug bolts/nuts torqued too tightly on one side, then
>   the runout can be cured by cleaning up the rust & retorquing the nuts.
>
> What I've seen on innumerable forums is people replace not only the rotors
> and then _blame_ the new rotors for "warp" but on some forums, they resort
> to _larger_ calipers and rotors, thinking that their vibration was "warp"
> caused by the brakes being designed to be too small.

Inability to discern the difference - common issue.
>
> I'm sure you're well aware, for example, of the infamous "Tundra upgrade"
> to Toyota SUVs. There's zero chance of convincing them that it's a myth.

Don't think we had the Toyota Tundra in this part of the world.
>
>> As I said, *measurement* will tell you where matters have gone awry.
>
> The main problem with the measurement is we're looking at puny differences
> which are extremely difficult to measure in terms of pad imprints.
>
>> I can *measure* the warp.
>
> Did you read in the references how puny the DTV is for a sensible vibration
> while braking? I have really nice dial gauges and calipers and yet even I
> can't measure to that accuracy & precision (for a variety of reasons).

Using either a micrometer or dial indicator, I can measure variations to
half a thou. I could go better but I would need to spend a lot more
money on the equipment and it simply isn't necessary. Nor do they make
brake specific measuring equipment to, say, 0.0001" accuracy.
>
> What's the best accuracy and precision of your measurement equipment?

See above.

--
Xeno

Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On 12/5/2022 8:43 am, sms wrote:
> On 5/11/2022 5:20 AM, Xeno wrote:
>
> <snip>
>
>> Nope, they were warped and wouldn't clean up *before* they went below
>> minimum thickness. In the early days I tried a few, found I was
>> wasting my time machining them, then started relying on *measurements*
>> to determine serviceability after machining. It's only involves simple
>> arithmetic. Discs these days are like spark plugs - the cost of repair
>> due to time involved is outweighed by the low cost of new items.
>
> "Back in the olden days" I kept a spare set of rotors so when I was
> doing a brake job I didn't have to stop and take the rotors to be
> machined in the middle of the work. I'd then take the rotors that I
> removed to be put on a lathe (for free since my relative had a repair
> shop) and they'd be ready for the next brake job in 25,000 miles or so.
>
> But back then discs were thick and heavy and could be machined multiple
> times before they were too thin. Nowadays rotors are so thin they can
> usually not be machined even once, but they've also become less
> expensive (when adjusted for inflation).
>
> My brother-in-law saw a lot of vehicles with warped rotors back in the
> mid-1990's to 2000's, when the manufacturers started making them very
> thin without the material science knowledge of how to prevent warping.
> Just one serious overheating and the rotors were warped beyond repair.
> There was one GM brand, that is now defunct, that was particularly
> susceptible to warped rotors. His shop was in San Francisco and there
> are lot of very steep hills (when San Francisco was first laid out the
> proposal was to not do a grid because of the hills, but to have roads
> winding up the hills; real estate people protested that this would be
> too complicated).
>
> Is someone actually claiming that disc rotors don't warp? That would be
> very surprising since nearly every car mechanic in the world is well
> aware of this issue
> <https://www.sandiegouniontribune.com/cars/click-and-clack/story/2019-05-02/warped-rotors-give-this-pony-the-shakes>,
> <https://www.cartalk.com/blogs/dear-car-talk/warped-brake-discs-are-bad-news>,
>
Yes, this excerpt is *classic*.

My 2008 Mustang GT shakes at around 60-65 mph when braking.
The Hurst five-speed stick shakes, too. When this is happening,
the steering wheel moves from side to side.

I have had the *shimmy* (steering wheel moves from side) without any
other symptom such as Judder or shudder. A lot of people used to confuse
the issue with wheel balance or other steering defects and spend a
fortune chasing the real fault. The clue was, and is, in the fact that
the issue only occurs under braking, sometimes even very light braking.

--
Xeno

Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On 12/5/2022 4:31 am, Vic Smith wrote:
> On Wed, 11 May 2022 13:37:53 +1000, Xeno <xenolith@optusnet.com.au> wrote:
>
>>
>> Yeah, "as in a potato chip" would be a bit too extreme. OTOH, I have
>> *measured* warped rotors that were warped sufficiently to have an effect
>> on the *steering*, even some that were too far gone to machine whilst
>> still retaining minimum thickness. Note, not seen warping on ventilated
>> discs that I can recall, just the old solid discs. The ventilated discs
>> seem rather more robust.
>
> Ventilated rotors warp too. After a period of severe braking I unintentionally drove
> though a long, deep puddle. Went from a smoothly braking car to a shuddering
> beast at the next stoplight.

Well, yes, uneven rapid cooling of the disc, that would do it.

That said, my only experience of warped rotors is with the
non-ventilated variety.

--
Xeno

Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On 2022-05-11 6:00 p.m., Xeno wrote:
> On 12/5/2022 12:37 am, Andy Burnelli wrote:
>> Xeno wrote:
>>
>>> You don't trust intuition, you listen to it, you make some
>>> assessments, and then you *test* what it is telling you.
>>
>> I'm all for testing, as my cars are a quarter of a century old and when
>> they break, I form an hypothesis and then I test that hypothesis so as to
>> replace the part that needs to be replaced.
>>
>> One place I need your intuition on is this sentence in this reference:
>>
>>   *The 'Warped' Brake Disc & Other Myths of the Braking System*
>> <https://www.ipdusa.com/Articles/528/The-Warped-Brake-Disc-and-Other-Myths-of-the-Braking-System>
>>
>> "In fact every case of "warped brake disc" that I have investigated,
>>   whether on a racing car or a street car, has turned out to be friction
>>   pad material transferred unevenly to the surface of the disc.  This
>> uneven deposition results in thickness variation (TV)  or run-out due
>> to hot spotting that occurred at elevated temperatures."
>
> As I have stated, you can have a *warped disc* and *not experience*
> judder, shudder or the like. You see, a warped disc does *not* lead to a
> *thickness variation*, it's more akin to a *buckle* and, as such will
> much more likely cause an effect in the *steering*, a *shimmy*.
>>
>> The fact they say "runout" in the same sentence as "TV" seems incongruent
>> to me, where I think I understand what they're saying, but the reason
>> it's
>> disconcerting is that "normally" the solution for runout is _different_
>> than the solution for DTV.
>>
>> Of course, TV will cause an "apparent runout" on the dial gauge, but it's
>> not the same kind of runout you'd get with, oh, say, rust around the hub.
>
> Correct. If the actual disc warps, you will get the same kind of runout
> as you experience with the disc not sitting flat on the hub. I have had
> runout of that nature on discs that are *integral* with the hub. In most
> cases, but not all, that runout is caused by incorrect wheel nut
> tightening.
>>
>> The reason the semantics matter is that the _solution_ to each problem is
>> different, where, for example, the solution to a truly warped rotor
>> (as in
>> potato chip) would be to junk that rotor, while the solution to DT is
>> typically to smooth out the bumps, and the typical solution to runout
>> is to
>> figure out what caused the roter to be mounted off kilter (in most
>> cases).
>
> These days, given the disposable nature of discs, it is probably
> advisable to dispose of discs rather than trying to dress them up on the
> lathe. Back in the day, discs were a rather expensive item, these days
> not so much.
>>
>> All show up, eventually, as "runout" but each cause has a different
>> remedial solution so the fact you can measure an out-of-spec variation
>> on a
>> dial gauge doesn't tell you _which_ problem caused the runout.
>
> You look at *several* symptoms, not just the runout alone.
>>
>>>> If the rotor met thickness, cracking, gouging specs, then you wasted
>>>> a good
>>>> rotor.
>>>
>>> Nope, they were warped and wouldn't clean up *before* they went below
>>> minimum thickness. In the early days I tried a few, found I was
>>> wasting my time machining them, then started relying on
>>> *measurements* to determine serviceability after machining. It's only
>>> involves simple arithmetic. Discs these days are like spark plugs -
>>> the cost of repair due to time involved is outweighed by the low cost
>>> of new items.
>>
>> I agree on the cost factor weighing in as I've replaced perfectly good
>> rotors for kids who no longer live at home even though the rotors were
>> within specs because I had to buy the parts ahead of time and because I
>> knew that a new rotor will last longer for the kids than an old rotor
>> (even
>> though the old rotor was within thickness specs).
>>
>> I get rotors for $15 to about $35 each, although I'm well aware they can
>> easily cost many times that (especially for the bullshit drilled and
>> slotted rotors - which are sold to morons who are intuitive people).
>>
>>>> HINT: If "warp" was truly a wavy rotor, then why does rebedding
>>>> often work?
>>>
>>> Because people cannot discern or determine the *difference* in symptoms.
>>
>> Yup.
>>
>> That's why it matters what _word_ we use.
>> a. If it truly warped, then any sane person would junk the rotors.
>>    (Because the conditions to cause warp would have been horrendous.)
>> b. If it's simply pad deposits, then a sane person might try to
>> "scrape" them off with a simple re-bedding process.
>>    (Or machine them off.)
>> c. If it's simply that there is rust buildup between the rotor and the
>> hub or maybe lug bolts/nuts torqued too tightly on one side, then
>>    the runout can be cured by cleaning up the rust & retorquing the nuts.
>>
>> What I've seen on innumerable forums is people replace not only the
>> rotors
>> and then _blame_ the new rotors for "warp" but on some forums, they
>> resort
>> to _larger_ calipers and rotors, thinking that their vibration was "warp"
>> caused by the brakes being designed to be too small.
>
> Inability to discern the difference - common issue.
>>
>> I'm sure you're well aware, for example, of the infamous "Tundra upgrade"
>> to Toyota SUVs. There's zero chance of convincing them that it's a myth.
>
> Don't think we had the Toyota Tundra in this part of the world.
>>
>>> As I said, *measurement* will tell you where matters have gone awry.
>>
>> The main problem with the measurement is we're looking at puny
>> differences
>> which are extremely difficult to measure in terms of pad imprints.
>>
>>> I can *measure* the warp.
>>
>> Did you read in the references how puny the DTV is for a sensible
>> vibration
>> while braking? I have really nice dial gauges and calipers and yet even I
>> can't measure to that accuracy & precision (for a variety of reasons).
>
> Using either a micrometer or dial indicator, I can measure variations to
> half a thou. I could go better but I would need to spend a lot more
> money on the equipment and it simply isn't necessary. Nor do they make
> brake specific measuring equipment to, say, 0.0001" accuracy.
>>
>> What's the best accuracy and precision of your measurement equipment?
>
> See above.
>

Isn't it amazing how Arlen continues to argue with someone who quite
obviously has lots of hands on experience with the subject...

....because he's "well-educated".

:-)

On 5/11/2022 6:00 PM, Xeno wrote:
> On 12/5/2022 12:37 am, Andy Burnelli wrote:
>> Xeno wrote:
>>
>>> You don't trust intuition, you listen to it, you make some
>>> assessments, and then you *test* what it is telling you.
>>
>> I'm all for testing, as my cars are a quarter of a century old and when
>> they break, I form an hypothesis and then I test that hypothesis so as to
>> replace the part that needs to be replaced.
>>
>> One place I need your intuition on is this sentence in this reference:
>>
>>   *The 'Warped' Brake Disc & Other Myths of the Braking System*
>> <https://www.ipdusa.com/Articles/528/The-Warped-Brake-Disc-and-Other-Myths-of-the-Braking-System>
>>
>> "In fact every case of "warped brake disc" that I have investigated,
>>   whether on a racing car or a street car, has turned out to be friction
>>   pad material transferred unevenly to the surface of the disc.  This
>> uneven deposition results in thickness variation (TV)  or run-out due
>> to hot spotting that occurred at elevated temperatures."
>
> As I have stated, you can have a *warped disc* and *not experience*
> judder, shudder or the like. You see, a warped disc does *not* lead to a
> *thickness variation*, it's more akin to a *buckle* and, as such will
> much more likely cause an effect in the *steering*, a *shimmy*.
>>
>> The fact they say "runout" in the same sentence as "TV" seems incongruent
>> to me, where I think I understand what they're saying, but the reason
>> it's
>> disconcerting is that "normally" the solution for runout is _different_
>> than the solution for DTV.
>>
>> Of course, TV will cause an "apparent runout" on the dial gauge, but it's
>> not the same kind of runout you'd get with, oh, say, rust around the hub.
>
> Correct. If the actual disc warps, you will get the same kind of runout
> as you experience with the disc not sitting flat on the hub. I have had
> runout of that nature on discs that are *integral* with the hub. In most
> cases, but not all, that runout is caused by incorrect wheel nut
> tightening.
>>
>> The reason the semantics matter is that the _solution_ to each problem is
>> different, where, for example, the solution to a truly warped rotor
>> (as in
>> potato chip) would be to junk that rotor, while the solution to DT is
>> typically to smooth out the bumps, and the typical solution to runout
>> is to
>> figure out what caused the roter to be mounted off kilter (in most
>> cases).
>
> These days, given the disposable nature of discs, it is probably
> advisable to dispose of discs rather than trying to dress them up on the
> lathe. Back in the day, discs were a rather expensive item, these days
> not so much.
>>
>> All show up, eventually, as "runout" but each cause has a different
>> remedial solution so the fact you can measure an out-of-spec variation
>> on a
>> dial gauge doesn't tell you _which_ problem caused the runout.
>
> You look at *several* symptoms, not just the runout alone.
>>
>>>> If the rotor met thickness, cracking, gouging specs, then you wasted
>>>> a good
>>>> rotor.
>>>
>>> Nope, they were warped and wouldn't clean up *before* they went below
>>> minimum thickness. In the early days I tried a few, found I was
>>> wasting my time machining them, then started relying on
>>> *measurements* to determine serviceability after machining. It's only
>>> involves simple arithmetic. Discs these days are like spark plugs -
>>> the cost of repair due to time involved is outweighed by the low cost
>>> of new items.
>>
>> I agree on the cost factor weighing in as I've replaced perfectly good
>> rotors for kids who no longer live at home even though the rotors were
>> within specs because I had to buy the parts ahead of time and because I
>> knew that a new rotor will last longer for the kids than an old rotor
>> (even
>> though the old rotor was within thickness specs).
>>
>> I get rotors for $15 to about $35 each, although I'm well aware they can
>> easily cost many times that (especially for the bullshit drilled and
>> slotted rotors - which are sold to morons who are intuitive people).
>>
>>>> HINT: If "warp" was truly a wavy rotor, then why does rebedding
>>>> often work?
>>>
>>> Because people cannot discern or determine the *difference* in symptoms.
>>
>> Yup.
>>
>> That's why it matters what _word_ we use.
>> a. If it truly warped, then any sane person would junk the rotors.
>>    (Because the conditions to cause warp would have been horrendous.)
>> b. If it's simply pad deposits, then a sane person might try to
>> "scrape" them off with a simple re-bedding process.
>>    (Or machine them off.)
>> c. If it's simply that there is rust buildup between the rotor and the
>> hub or maybe lug bolts/nuts torqued too tightly on one side, then
>>    the runout can be cured by cleaning up the rust & retorquing the nuts.
>>
>> What I've seen on innumerable forums is people replace not only the
>> rotors
>> and then _blame_ the new rotors for "warp" but on some forums, they
>> resort
>> to _larger_ calipers and rotors, thinking that their vibration was "warp"
>> caused by the brakes being designed to be too small.
>
> Inability to discern the difference - common issue.

I recall my first vehicle with disc brakes. The rotors were thick,
heavy, and massive. The pads were very small. The rotors never warped
(or deformed, or whatever someone wants to call it) but the pads had so
little surface area that they wore out quickly and could overheat on
steep downhills if the driver didn't downshift to use engine braking.

It was not a great brake design but it was pretty simple to change the
pads, and I had to do that often.

On 12/5/2022 6:01 am, Alan wrote:
> On 2022-05-09 6:30 p.m., Andy Burnelli wrote:
>> sms wrote:
>>
>>> But the mass of thick rotors negatively affected fuel economy so much
>>> thinner rotors began to be used, and they usually can't be resurfaced
>>> even once, they have to be replaced at the same time the brake pads
>>> are replaced.
>>
>> Bullshit.
>> The time to replace rotors is when they no longer meet the specs, and
>> there
>> are a few specs that they need to meet (cracks, thickness, gouges, etc.),
>> but the main spec is the thickness.
>>
>> I've seen many people say the bullshit you say but the fact is you
>> measure
>> them, like Xeno and I do, and if they're within specs, you keep them.
>>
>> It doesn't matter how many brake pads you replaced.
>>
>>> They also warp much easier. It also actually became not that uncommon
>>> to replace warped rotors, but not the pads, since the pads were fine.
>>
>> More bullshit.
>>
>> Read this before you bullshit us please.
>> <https://ricksfreeautorepairadvice.com/warped-brake-rotors/>
>>
>> It's impossible for rotors to warp (as in potato chip), and everyone who
>> says they do, has _never_ measured it, least of all you, Steve.
>
> <https://www.youtube.com/watch?v=DiuwzN2mQuA&t=122s>

Yep, done that, seen the warp, many, many times!

I liked the way he did that final non-directional finish. I used to do
it the hard way, that looked easy in comparison.

--
Xeno

Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)