Do you know of engineering papers for what people call brake rotor'warp'?

Joe Mastroianni wrote:
> On Sat, 16 Feb 2013 11:01:24 -0600, jim wrote:
>
>> If it does not mean "run out" what else would warp mean?
>
> Warp and runout are totally different things (to me, anyway)!
>
> 1. Warp means, to me, the rotors are 'wavy' (like a potato chip).
> 2. Runout merely means, to me, the rotors aren't spinning on
> on the same axis as the hub is.
>
> So, for example, let's assume a PERFECT ROTOR!
> If you put it on the hub crooked, it will have runout but not warp.
>
> How could you put it on crooked?
> I don't know all the ways, but one way is to have uneven
> rust on the hub. That 'tilts' the rotor so that the hub
> and the rotor aren't spinning on the same axis.
>
> The results in runout - which you measure with a dial gauge
> firmly affixed to something relative to the hub center axis.
>
> The way I understand warp, you'd NEVER be able to measure it
> on the vehicle (not anywhere near accurately, anyway).
>
> You measure warp on the bench. I suppose it's something that every
> rotor manufacturer measures as part of their quality control.
>
> The faces need to be parallel to each other.
>
> Now, having said that (which is pretty obvious stuff), I must
> then ask you (or anyone else) what THEY think the difference is
> between warp and runout - as it's pretty simple stuff (to me).

To me, a rotor could have runout but not be warped.
A warped rotor will usually have runout.

On Sat, 16 Feb 2013 19:39:24 -0600, Paul in Houston TX wrote:

>> The faces need to be parallel to each other.
>>
>> Now, having said that (which is pretty obvious stuff), I must
>> then ask you (or anyone else) what THEY think the difference is
>> between warp and runout - as it's pretty simple stuff (to me).
>
> To me, a rotor could have runout but not be warped.
> A warped rotor will usually have runout.

I agree.

A PERFECT rotor could easily have runout if it is mounted where
there is rust on the hub, for example. The axis of rotation of
the hub would be DIFFERENT on the rotor - so the rotor would
have runout. But it is still a perfect rotor - so it would not
have warp.

Now, if the rotor was actually warped, that means, to me, that
it's "wavy" (like a potato chip), and, as you said, it's ALSO
going to have runout.

And, I guess, if it has low spots and high spots (i.e., disc
thickness variation), then again, it's going to have runout.

HOWEVER ... the DTV that causes judder is sooooo tiny (15 microns
in some cases as reported by the aforementioned scientific papers!)
that we will be hard pressed to MEASURE DTV runout accurately
with our standard DIY garage micrometers.

All this is how "I" understand it though - but clearly, warp
needs to be measured on the bench. Nobody can possibly say their
rotors warped, in my opinion, if they didn't measure them on
the bench (off the vehicle).

On Sun, 17 Feb 2013 00:55:46 +0000 (UTC), Joe Mastroianni
> wrote:

>
>Now, having said that (which is pretty obvious stuff), I must
>then ask you (or anyone else) what THEY think the difference is
>between warp and runout - as it's pretty simple stuff (to me).

What you said. This pad deposition is new to me. Makes sense,
especially to those selling "scrubber" pads, which are advertised as
truing up rotors.. But why are they still cutting metal off rotors?
Seems pad deposition would be cut off and the metal would be barely
touched by an accurate lathe.
Never seen rotors cut, so I'm guessing the blade cuts the entire rotor
diameter, not just the pad wear area. Probably most rotor cutting is
done with a not very precise machine, and poor measurement.
Those scrubber pads don't seem a good idea either. I suspect they are
never an exact match in size compared to the permanent pads.
Anyway, I have very little experience with rotors that cause
pulsation. Only times it happened with me was with old worn rotors
that needed replacing anyway because they were grooved and eating
pads.
But here's what makes me believe that rotors CAN warp. And I'm not
NOT saying that it the cause of most brake pulsation.
I once went through a deep puddle with hot rotors. When I went into
the puddle the brakes were smooth. When I came out of the puddle I
had a severe pulsation on the right front.
The rotors were old and deeply grooved and ready for replacement
anyway.
Since rotors for my cars are usually 20-30 bucks each - cheaper than a
good pad set - I just replace them when I see/feel grooving.
Here's something else. I had a real good mechanic do the work on my
cars when I was busy with my work. Never doubted him at all.
But talking to him about brake jobs one time, he told me new rotors
must be lathed before using them.
I don't buy that. I've put maybe 4 sets of new rotors on my cars, and
just cleaned the preservative off them. They all worked out fine.
These are all the standard GM single piston brakes.

On Sat, 16 Feb 2013 19:55:59 -0600, Vic Smith wrote:

> This pad deposition is new to me.

The "theory" (as I understand it) for the uneven pad deposition
based brake judder is that a little "hill" of as little as
15 microns (according to one of the papers we listed) will cause
low frequency (around 100 Hz) brake judder.

I'm still trying to figure this out, but apparently two things
happen at the same time when the pads hit the deposition "hill".

1. The pads "push back" causing the vibration to be felt in the
brake pedal.
2. The force varies, causing the entire suspension to shudder.

At least that's how I understand it after reading the (complex)
papers a few times. I'm still reading them though, so consider
this a preliminary explanation.

On Sat, 16 Feb 2013 19:55:59 -0600, Vic Smith wrote:

> I have very little experience with rotors that cause
> pulsation. Only times it happened with me was with old worn rotors
> that needed replacing anyway because they were grooved and eating
> pads.

An interesting aside is that we all have seen grooved rotors,
and we all know the "fingernail test" (i.e., if it catches your
fingernail, it's too deep) - but - if you LOOK UP the specs for
grooves, they have to be absolutely huuuuuuge (like the thickness
of a dime!) to fail a rotor.

At least in my experience.

If anyone actually has a bona-fide "groove" specification for their
rotor - please share!

On Sat, 16 Feb 2013 19:55:59 -0600, Vic Smith wrote:

> But here's what makes me believe that rotors CAN warp.
> And I'm not NOT saying that it the cause of most brake pulsation.

I should clearly state that I too believe rotors CAN warp!

However, what MOST people "call" warp, isn't warp at all.
It's merely brake judder.
Which, as we've seen from the dozen papers, can be caused by a LOT
of things. And, as shown by the industry advertising anyway, most
of the time it's NOT warp.

Plus, how would anyone know it's warp if they didn't measure the
rotors on the bench, as that's the ONLY way to tell a warped rotor
(as far as I can tell).

On Feb 16, 8:55*pm, Vic Smith > wrote:
> But why are they still cutting metal off rotors?
> Seems pad deposition would be cut off and the metal would be barely
> touched by an accurate lathe.
> Never seen rotors cut, so I'm guessing the blade cuts the entire rotor
> diameter, not just the pad wear area. *Probably most rotor cutting is
> done with a not very precise machine, and poor measurement.

I haven't seen rotors cut in decades, I'll have to make a call.

As I recall the lathe was "marked" in .001 increments (and a
"standard" cut was .003) but "infinitely" variable. My buddy set it
up once then left me to finish the job, so I played with it.

Being cautious, since it was my rotor, I set the bit to barely touch
and dialed it in slowly and could see it hit high spots, small and
large, short and tall.

Whether that was the result of warp, even wear or molecular deposits,
I couldn't guess.
-----

- gpsman

On Feb 16, 9:18*pm, Joe Mastroianni > wrote:
> On Sat, 16 Feb 2013 19:55:59 -0600, Vic Smith wrote:
> > But here's what makes me believe that rotors CAN warp.
> > And I'm not NOT saying that it the cause of most brake pulsation.
>
> I should clearly state that I too believe rotors CAN warp!
>
> However, what MOST people "call" warp, isn't warp at all.
> It's merely brake judder.
> Which, as we've seen from the dozen papers, can be caused by a LOT
> of things. And, as shown by the industry advertising anyway, most
> of the time it's NOT warp.
>
> Plus, how would anyone know it's warp if they didn't measure the
> rotors on the bench, as that's the ONLY way to tell a warped rotor
> (as far as I can tell).

my caravan carries a lot of weight, and the pads wear out
fast.........

Used to be garages demanded we turn the rotors, in my application they
would warp fast.

so now i just buy new rotors any time the pads get replaced.

my neighbor a highly skilled guy does lots of my vehicle repairs,
sadly i must find someone new.

he is a smoker and has lung cancer stage 4......

he is a good hard working guy i will miss him

In article >,
Joe Mastroianni > wrote:

> We're having a conversation among friends when one casually mentions
> his wife's rotors "warped".
>
> The other jumps on him and declares that street-use rotors don't warp (in
> general). An Internet search bears him out, as MANY articles say rotor
> warp is a myth.
>
> Googling, we find that brake torque variation is mostly from uneven pad
> deposition buildup (i.e., disc thickness variation) and axial runout. But
> then it gets confusing as the more enlightened sources begin to mention
> thermo elastic instability hotspots and breaking judder into low
> frequency cold judder and high frequency hot judder.
>
> The heated discussion went on. And so did the confusion.
> For more than a few beers.
>
> My question?
>
> While we now know rotors rarely actually warp, does anyone know of a good
> scientific or engineering paper explaining the TRUE causes of brake
> related judder in street cars?

It can happen but not as often as those selling "rotor turning" say so.

In every car that I've had, shaking was caused by the calipers not being
properly lubricated. The viscosity is important to prevent sticking and
produce motion dampening.
--
I will not see posts from Google because I must filter them as spam

On 02/17/2013 07:48 AM, Kevin McMurtrie wrote:
> In article >,
> Joe Mastroianni > wrote:
>
>> We're having a conversation among friends when one casually mentions
>> his wife's rotors "warped".
>>
>> The other jumps on him and declares that street-use rotors don't warp (in
>> general). An Internet search bears him out, as MANY articles say rotor
>> warp is a myth.
>>
>> Googling, we find that brake torque variation is mostly from uneven pad
>> deposition buildup (i.e., disc thickness variation) and axial runout. But
>> then it gets confusing as the more enlightened sources begin to mention
>> thermo elastic instability hotspots and breaking judder into low
>> frequency cold judder and high frequency hot judder.
>>
>> The heated discussion went on. And so did the confusion.
>> For more than a few beers.
>>
>> My question?
>>
>> While we now know rotors rarely actually warp, does anyone know of a good
>> scientific or engineering paper explaining the TRUE causes of brake
>> related judder in street cars?
>
> It can happen but not as often as those selling "rotor turning" say so.
>
> In every car that I've had, shaking was caused by the calipers not being
> properly lubricated. The viscosity is important to prevent sticking and
> produce motion dampening.
>

The odd thing is that the one car I've had (actually a company car) that
had chronic "warping" issues was nearly new, so you wouldn't think that
this would be the issue?

OTOH I have had all sorts of cars that go years without any brake
maintenance other than every two years fluid flushes and never had any
brake oddness... Last really long term car I think I did repack the
front wheel bearings once for insurance but just put the brakes back
together, I suppose I must have cleaned and lubed the sliders because it
would make sense to do so... Others just stopped fine until I had to
address the brakes for whatever reason (usually the pads wearing out
eventually) and continued stopping fine afterwards.

Now I do make sure that if the rotor sits on a hub and is not a one
piece that the interface is clean, but you'd think that that would be a
best shop practice as well.

nate


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