Xeno wrote:

>> You can't test warp on the vehicle (not reliably anyway).
>> It has to be tested on a known flat bench (or using known flat tools).
>
> Or mounted on a brake lathe

Agreed.
All you need is a long flat edge and feeler gauges as a minimum.

I'm all about facts.
I'll change my mind in a split second if that's where the facts lead.

Let's look at the facts in this discussion between two adults on Usenet.

My point is that nobody who says warp (as in potato chip) measures that
warp (as in potato chip), where I already know that warp (as in potato
chip) isn't what happens when a brake rotor is subject to intense heating &
cooling cycles.
"High quality brake rotors that pass SAE J2928 Brake Rotor Thermal
Cracking Procedure for Vehicles below 4,540 kg GVWR proves
they don't warp"

As I said, intuition is a terrible thing indeed.
"Calling it brake rotor warp demonstrates a complete misunderstanding
of the metallurgy and the braking process"

> I wasn't saying anything about rebedding at all.

OK. But the fact that rebedding works sometimes means that what it fixed
wasn't warp (as in potato chip). What it fixed wasn't runout either.

What it fixed is the only thing it _could_ fix, which is deposit buildup.

Intuition is a terrible thing indeed.
"The brake pads and rotors in a street vehicle can't possibly
generate enough heat to warp a brake rotor."

>> Almost nobody could machine a warped rotor (as in potato chip) back to
>> perfection simply because the amount of metal needed isn't going to be
>
> Depends on the amount of warp and whether the rotor still meets minimum
> specs afterwards. It only takes a very small amount of warp for the
> driver to be able to sense it.

Agreed.

However, any rotor that was subject to enough heat to truly warp it (as in
potato chip) was subject to _tremendous_ heat - almost impossible to attain
in a passenger vehicle (again, I'm not talking about the space shuttle
here).
"The heating and cooling that people refer to when discussing
'warped brake rotors' would cause cracking, not warping."

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

> The car showed *symptoms* of warp, the rotors, when measured showed
> *evidence* of warp. I drove the car, I felt the symptoms, I measured the
> rotor warp.

I'll leave it at that since I respect your experience.

Read this please, though (it's just one random hit of many of course):
*What causes warped brake rotors?*
<https://ricksfreeautorepairadvice.com/warped-brake-rotors/>
"brake rotors DO NOT WARP from normal driving or even race track use.
Yes, you read that correctly. A typical street vehicle can't possibly
generate enough heat to warp a brake rotor."

All the quotes in this one post are from that reference, but I can easily
find more because I know what I know and most people are intuitive.

Did I mention yet that intuition is a terrible thing?

>> I doubt it. Rotors are made of a variety of steels (e.g., motorcycle rotors
>
> I don't, I saw the evidence.

Again, I respect your experience.

However, you have to respect my knowledge that _reliable_ sources say
otherwise and that runout isn't warp (as in potato chip) and that if
rebedding worked, it wasn't warp (as in potato chip) after all.
"Even if you're traveling straight down the side of a mountain
with your brakes applied the entire way. Your brake pads will fade
and start to disintegrate long before you come close to heating
your rotors enough to soften them to the point where they could
possibly warp"

I even doubt machining could fix any appreciable warp (as in potato chip),
and even if it did, I wouldn't want any rotors from _that_ shop. :)
"In addition, if your brake system is working properly, it's applying
equal pressure to both sides of the rotor which means BOTH SIDES
are heating at the same rate. To warp a brake rotor, you must have
more heat on one side of the rotor than the other."

>> are often stainless steel) but even for the worst quality cast iron rotors,
>> look up the temperature it takes to melt them.
>
> Automotive rotors were pretty much all cast iron back in the era
> concerned. And the rotor did *melt* at the periphery, as I stated. It
> had been damn hot all over but the periphery was clearly melted.

I'm not going to argue with you on that as cast iron has a relatively low
melting point where our question is can a rotor typically get to that point
on a passenger vehicle whose owner suspects his rotor warped (as in potato
chip).

"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."

>> I'm not saying it's impossible. But I doubt it happens for normal passenger
>> vehicles (I'm not talking space shuttle stuff or fighter plane stuff).
>
> Nor am I. I wasn't and never have been an aviation mechanic.

The only thing I harp on is I've never met a person who claimed it was
"warp" (as in potato chip) who actually measured it, and, worse, the remedy
often is something (like rebedding) which couldn't possibly have fixed warp
(as in potato chip).

Worse than even that, is all the reliable sources say passenger vehicle
rotors can't warp (as in potato chip) simply because brakes can't generate
enough heat.

>> Look it up.
>
> No need, I saw the evidence directly.

I knew what I'd find in brake warp when I just looked it up as I did my
research long ago (just as I did with cellphone caused accident rates).

Most people work solely on intuition.
Humans have the intuition of evolved monkeys.

Intuition serves humans well... sometimes.
But not always.

Read this _one_ reference for a starting point on fixing that intuition.
<https://ricksfreeautorepairadvice.com/warped-brake-rotors/>

If you don't like it, find another (there are plenty).

>> Yes. I know. But did you measure warp (as in potato chip)?
>
> Yes, I did, with a dial indicator. Definitely warp.

"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. "

>> You can't measure warp without a known straight surface to compare against.
>> A mic won't measure warp.
>> A dial gauge won't measure warp (unless it's a special setup).
>
> It was a special setup - a brake lathe. Runout and warp shows up very
> clearly when the hub and rotor assembly is correctly mounted.

Note that the link I am giving you has information from the brake rotor
manufacturers who themselves claim that their rotors can't warp (as in
potato chip) in passenger vehicles under _any_ circumstances.

Raybestos video titled "Rotors Can't Warp":
<https://youtu.be/LVRVe1cEBDI>

>> HINT: I've never seen anyone who did who said their rotors warped when what
>> really happened was something else (e.g., runout or pad deposition).
>
> Depending on the site, runout can be a symptom of warp. You verify it as
> warp by checking both sides.

I'm not going to harp on the issue other than to repeat my salient points.
a. Rotors don't warp (as in potato chip) in passenger vehicles. Period.
b. People who _say_ they did, didn't measure warp (as in potato chip).
c. The temperatures needed are unattainable in passenger vehicles.
>>> If they wouldn't clean up and still remain within specs, they would be
>>> replaced, and that could be determined from the measurements.
>>
>> I seriously doubt an actual warp (as in potato chip) could be machined, but
>> if it's only slight, then maybe, but what fool would want rotors that were
>> actually warped (as in potato chip) even after they were machined?
>
> Well, these days the rule is discard and renew, don't machine.
> Procedures have changed.

OK. But I can _easily_ find industry references that say rotors can't warp
(as in potato chip) simply because they are designed _not_ to warp (as in
potato chip), and, because the temperatures to cause warp (as in potato
chip) are unattainable.

What does that tell us about the intuition of human beings?

>> Did you machine stainless steel rotors?
>
> Nope. never saw a stainless steel rotor when I was involved in brakes.
> All seemed to have been cast iron of varying grades. That said, I didn't
> work on exotic cars nor did I work on motorcycles or aircraft. YMMV.

Xeno,
I respect you. If you can find a _single_ reference on this planet that is
reliable that can show brake rotors in passenger vehicles truly warping (as
in potato chip), I promise you I will _read_ that reference you find.

In summary, most people work 100% off of intuition, in my humblest of
experiences, where human intuition is that of an evolved monkey.

Just as cellphones don't change the accident rate is a completely
unintuitive fact, brake rotors don't warp (as in potato chip) in passenger
vehicles.

Please at least read the reference provided (which is just random as I can
find _plenty_ of references saying the same thing from brake manufacturers
like Centric - whom I've spoken to personally about this topic).
--
The problem with humans is they're intuitive, and intuition is a terrible
thing. It takes a different kind of person to check their intuition.