On 12/5/2022 5:58 am, Alan wrote:
> On 2022-05-09 8:39 a.m., Andy Burnelli wrote:
>> 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.
>
> <https://youtu.be/glIik3KHcOs>
>
> What's that if it's not warp, Arlen?

Looks a lot like *warp* to me. ;-)

I don't think I would be bothered even starting to machine that one -
binned!

--
Xeno

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