need opinion of hyundaitech

"Matt Whiting" <whiting.DeleteThis@epix.net> wrote in message
news:hzYIi.59$2n4.2754@news1.epix.net...
> Mike Marlow wrote:
>> "Matt Whiting" <whiting.DeleteThis@epix.net> wrote in message
>> news:5PFIi.53$2n4.2401@news1.epix.net...
>>
>>> I haven't measured many with a dial indicator, but I've never yet found
>>> one warped significantly. And I've had a couple of "warped" rotors that
>>> were "fixed" with 5-10 hard stops to redistribute the pad material. A
>>> mechanically warped disk would not get better with additional heating
>>> cycles.
>>
>> I too have "fixed" an occassional pulsing pedal this way, but it's the
>> exception. That's not fixing a warped rotor which has many more times
>> proven the case for me. Whether I tested them with a dial caliper or put
>> them on a lathe, they were verifiably warped. It's very common with a
>> lot of the cheap aftermarket rotors out there. Trying to make these
>> rotors better with brake cycles won't work.
>
> No, they were not "verifiably" warped if you didn't measure them.
>

Did you not read what I wrote?

>
>>> We'll have to agree to disagree. However, I suggest that anyone who
>>> thinks their disks are warped should take the time to check them with a
>>> dial indicator. I'll bet most times they will find no warpage.
>>>
>>
>> It's ok to disagree - you know I'm fine with that. I would only tweak
>> your closing comment by suggesting what I do - when faced with pulsing,
>> first try to clear the problem with braking techniques as you referenced.
>> When that does not fix the problem, simple be aware that rotors do warp,
>> and when buying new don't go cheap. Going better does not cost that much
>> more but works much better. Good quality rotors and ceramic pads. And
>> don't be alarmed by warped rotors - it's more and more common as
>> manufacturers cheapen up the rotors they build with.
>
> Except that rotors don't warp in general.
>

Whatever you say.

--

-Mike-
mmarlowREMOVE.DeleteThis@alltel.net
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Mike Marlow wrote:
> "Matt Whiting" <whiting RemoveThis @epix.net> wrote in message
> news:hzYIi.59$2n4.2754@news1.epix.net...
>> Mike Marlow wrote:
>>> "Matt Whiting" <whiting RemoveThis @epix.net> wrote in message
>>> news:5PFIi.53$2n4.2401@news1.epix.net...
>>>
>>>> I haven't measured many with a dial indicator, but I've never yet found
>>>> one warped significantly. And I've had a couple of "warped" rotors that
>>>> were "fixed" with 5-10 hard stops to redistribute the pad material. A
>>>> mechanically warped disk would not get better with additional heating
>>>> cycles.
>>> I too have "fixed" an occassional pulsing pedal this way, but it's the
>>> exception. That's not fixing a warped rotor which has many more times
>>> proven the case for me. Whether I tested them with a dial caliper or put
>>> them on a lathe, they were verifiably warped. It's very common with a
>>> lot of the cheap aftermarket rotors out there. Trying to make these
>>> rotors better with brake cycles won't work.
>> No, they were not "verifiably" warped if you didn't measure them.
>>
>
> Did you not read what I wrote?

A dial caliper can't easily measure run-out and a lathe doesn't measure
anything, so I basically don't believe you have ever checked a brake
rotor. A caliper could measure thickness variation, but not warpage. A
dial indicator in conjunction with a lathe could measure warpage, but
only if the rotor was installed true in the lathe and that wouldn't be
easy. The least little off-axis mounting would look like warpage when
the lathe was spun.

Easiest is to just spin the rotor on the car with a magnetic mount dial
indicator.

Matt
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"Matt Whiting" <whiting.TakeThisOut@epix.net> wrote in message
news:cYaJi.61$2n4.3193@news1.epix.net...

>
> A dial caliper can't easily measure run-out and a lathe doesn't measure
> anything, so I basically don't believe you have ever checked a brake
> rotor. A caliper could measure thickness variation, but not warpage. A
> dial indicator in conjunction with a lathe could measure warpage, but only
> if the rotor was installed true in the lathe and that wouldn't be easy.
> The least little off-axis mounting would look like warpage when the lathe
> was spun.

Matt - you get too hung up on little things and overlook the obvious. Claim
what you will, but if you've never mounted and turned a rotor I'm not going
to spend any time arguing about what "could" be happening. I'm happy to let
you believe what you read on a web site as the hidden answer to rotor
problems, and I'll simply bumble along fixing cars in my ignorance. I'm
really not going to spend a lot of time trying to satisfy your needs for
empiracle evidence to refute something you read.

>
> Easiest is to just spin the rotor on the car with a magnetic mount dial
> indicator.
>

And I do stand corrected on this point, in that I should have said dial
indicator. Don't know how the word caliper slipped in there unless it was
in the front of my mind - this being a brake discussion. Regardless, if
you'd have worked on pulsing pedal problems you'd certainly have verified
warped rotors with an indicator.

Let me challenge that article this way Matt - how much depositing and
imprinting is necessary to cause a noticeable pulse in the pedal? How much
to create wild pulsing at highway speed? How does this buildup occur in
such varying depths around a 10" disk that is turning at highway speeds with
(near) constant brake pressure, while 5 hard stops is all it takes to clean
it up?

--

-Mike-
mmarlowREMOVE.TakeThisOut@alltel.net
 >> Stay informed about: need opinion of hyundaitech 

"Mike Marlow" <mmarlowREMOVE DeleteThis @alltel.net> wrote in message
>
> Let me challenge that article this way Matt - how much depositing and
> imprinting is necessary to cause a noticeable pulse in the pedal? How
> much to create wild pulsing at highway speed? How does this buildup
> occur in such varying depths around a 10" disk that is turning at highway
> speeds with (near) constant brake pressure, while 5 hard stops is all it
> takes to clean it up?

The buildup thing kind of puzzled me also. I'd think that if there was
buildup turning the rotors would remove it and leave the rotor in spec.
Certainly some shop would have noticed they are cutting brake lining, not
metal.

Do you think it is possible to generate enough heat and the spinning would
actually unwarp the rotors? Since repeated stops are necessary, that is the
only possibility I can think of.
 >> Stay informed about: need opinion of hyundaitech 

Mike Marlow wrote:
> "Matt Whiting" <whiting.RemoveThis@epix.net> wrote in message
> news:cYaJi.61$2n4.3193@news1.epix.net...
>
>> A dial caliper can't easily measure run-out and a lathe doesn't measure
>> anything, so I basically don't believe you have ever checked a brake
>> rotor. A caliper could measure thickness variation, but not warpage. A
>> dial indicator in conjunction with a lathe could measure warpage, but only
>> if the rotor was installed true in the lathe and that wouldn't be easy.
>> The least little off-axis mounting would look like warpage when the lathe
>> was spun.
>
> Matt - you get too hung up on little things and overlook the obvious. Claim
> what you will, but if you've never mounted and turned a rotor I'm not going
> to spend any time arguing about what "could" be happening. I'm happy to let
> you believe what you read on a web site as the hidden answer to rotor
> problems, and I'll simply bumble along fixing cars in my ignorance. I'm
> really not going to spend a lot of time trying to satisfy your needs for
> empiracle evidence to refute something you read.

I've never mounted a rotor on a lathe as I never had a lathe. I've
always used a dial indicator with the rotor on the car as that is THE
most accurate way to check for warp. And thickness variation is checked
just as easily on a car as well. And thickness variation would cause
much more severe pulsing anyway. Warp just moves the calipers side to
side in their mount. Since they are designed to move this way anyway,
this doesn't cause much problem. The severe pulsing is caused from
variations in friction as the rotor turns and this is either from
variations in coefficient of friction around the circumference of the
rotor or from variations in clamping force around the circumference.
The former is caused by uneven pad material deposition or nonuniform
changes in the metal properties as described in the article. The latter
is caused by uneven thickness of the rotor (also extremely rare). Warp
just about never happens and even if it did, it would cause very slight
vibration and would NOT cause the car to shudder as will the other two
problems.


> And I do stand corrected on this point, in that I should have said dial
> indicator. Don't know how the word caliper slipped in there unless it was
> in the front of my mind - this being a brake discussion. Regardless, if
> you'd have worked on pulsing pedal problems you'd certainly have verified
> warped rotors with an indicator.

No problem, brain farts happen. However, I have to admit when I hear
someone use the incorrect nomenclature it causes me to question the
veracity of their message.


> Let me challenge that article this way Matt - how much depositing and
> imprinting is necessary to cause a noticeable pulse in the pedal? How much
> to create wild pulsing at highway speed? How does this buildup occur in
> such varying depths around a 10" disk that is turning at highway speeds with
> (near) constant brake pressure, while 5 hard stops is all it takes to clean
> it up?

Very little is required. All it takes is enough to change the
coefficient of friction from one circumferential location to another.
One pad imprint can do it. It is a little bit like oil. It takes a
very thin film to radically change the coefficient of friction of a surface.

Matt
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Edwin Pawlowski wrote:
> "Mike Marlow" <mmarlowREMOVE.TakeThisOut@alltel.net> wrote in message
>> Let me challenge that article this way Matt - how much depositing and
>> imprinting is necessary to cause a noticeable pulse in the pedal? How
>> much to create wild pulsing at highway speed? How does this buildup
>> occur in such varying depths around a 10" disk that is turning at highway
>> speeds with (near) constant brake pressure, while 5 hard stops is all it
>> takes to clean it up?
>
> The buildup thing kind of puzzled me also. I'd think that if there was
> buildup turning the rotors would remove it and leave the rotor in spec.
> Certainly some shop would have noticed they are cutting brake lining, not
> metal.
>
> Do you think it is possible to generate enough heat and the spinning would
> actually unwarp the rotors? Since repeated stops are necessary, that is the
> only possibility I can think of.
>
>

I don't think the issue is build up in the sense of changing the
thickness measurably. I think it is more an issue of changing the
coefficient of friction in a nonuniform way around the circumference.
That only takes a layer a few atoms or molecules thick... I'd have to
read the article again as I don't remember all of the details, but I
think they also talk about other phenomenon occurring as well.

I think the odds of changing a mechanically warped rotor back to a true
one are simply astronomical. That is the reason that I started to
believe this article had merit. That and measuring a handful of rotors
that pulsed severely and finding that they were true well within the
manufacturers specs. After "fixing" a few "warped" rotors with very
hard stops, I knew that I wasn't "unwarping" the rotor and something
else had to be going on here. I also break in new pads per the article
and I now almost never have a problem with pulsing brakes.

However, I'm not saying you should believe me or even the article. Try
it yourself. Next time your brakes pulse, put a dial indicator on them
and see if they are really warped (moving side to side as they spin).
I'll bet the odds are very high that you have nothing outside of the
manufacturer's specs. Then go out and make several very hard stops per
the article and see if the pulsing changes. Then measure axial run-out
of the rotors again and see if anything has changed. I'm betting
nothing has changed, but I'll also bet that your brakes pulse less. It
will never go completely away as you can't undo completely the damage
caused by improper brake-in or other use such as making a hard stop and
then holding the brakes on at a light or such and severely imprinting
the brakes. Only shaving metal off the rotors or replacing them will
restore you completely to normal.

However, as I said earlier, if you are at the point of replacement
anywhere, what have you got to lose by trying the hard stop treatment?

Matt
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"Matt Whiting" <whiting.TakeThisOut@epix.net> wrote in message
news:SztJi.66$2n4.4032@news1.epix.net...

>
> Very little is required. All it takes is enough to change the coefficient
> of friction from one circumferential location to another. One pad imprint
> can do it. It is a little bit like oil. It takes a very thin film to
> radically change the coefficient of friction of a surface.
>

That's the part I don't buy Matt. How fast are those rotors turning at
highway speed? How does this deposit occur from one circumfrential location
to another? If imprinting was as real a factor as this guy suggests, every
single car that has ever put a mile on a road would have suffered this after
the first stop at the end of a highway exit ramp. It's a great sounding
theory for a guy's web site, but it's bull - at least as he presents it.

--

-Mike-
mmarlowREMOVE.TakeThisOut@alltel.net
 >> Stay informed about: need opinion of hyundaitech 

Mike Marlow wrote:
> "Matt Whiting" <whiting RemoveThis @epix.net> wrote in message
> news:SztJi.66$2n4.4032@news1.epix.net...
>
>> Very little is required. All it takes is enough to change the coefficient
>> of friction from one circumferential location to another. One pad imprint
>> can do it. It is a little bit like oil. It takes a very thin film to
>> radically change the coefficient of friction of a surface.
>>
>
> That's the part I don't buy Matt. How fast are those rotors turning at
> highway speed? How does this deposit occur from one circumfrential location
> to another? If imprinting was as real a factor as this guy suggests, every
> single car that has ever put a mile on a road would have suffered this after
> the first stop at the end of a highway exit ramp. It's a great sounding
> theory for a guy's web site, but it's bull - at least as he presents it.

Well, for a 30" diameter tire, the RPM at 60 MPH is 672. Alternatively,
this is 11 revolutions per second. I don't follow your point though
about the RPM. Can you elaborate?

Most cars I've ridden in have suffered from this. I travel on business
fairly often and rent a lot of cars and almost every rental I drive has
pulsing brakes. Some fairly minor and some downright obnoxious.

Matt
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"Matt Whiting" <whiting.RemoveThis@epix.net> wrote in message
news:LhCJi.68$2n4.4379@news1.epix.net...
> Mike Marlow wrote:

>>
>> That's the part I don't buy Matt. How fast are those rotors turning at
>> highway speed? How does this deposit occur from one circumfrential
>> location to another? If imprinting was as real a factor as this guy
>> suggests, every single car that has ever put a mile on a road would have
>> suffered this after the first stop at the end of a highway exit ramp.
>> It's a great sounding theory for a guy's web site, but it's bull - at
>> least as he presents it.
>
> Well, for a 30" diameter tire, the RPM at 60 MPH is 672. Alternatively,
> this is 11 revolutions per second. I don't follow your point though about
> the RPM. Can you elaborate?

What I meant is that the rotor is tuning fast eniugh that if layering were
truly the culprit, it would be a much more consistent thing given the
rotational speed of the wheel. It would be difficult at best to create
layering of variable density.

>
> Most cars I've ridden in have suffered from this. I travel on business
> fairly often and rent a lot of cars and almost every rental I drive has
> pulsing brakes. Some fairly minor and some downright obnoxious.
>

Well, I don't drive rental cars anymore, like I used to. I've been more
local for the past two years (almost). I have not found brake pulsing to be
common in any rentals I ever did drive - and I used to be in 2-3 different
rental cars every week. I know that none of our cars display it unless
things are wearing out.

Let's go back for a sanity check though... We *are* talking about a wobble
and not a very faint low level pulse - right?

--

-Mike-
mmarlowREMOVE.RemoveThis@alltel.net
 >> Stay informed about: need opinion of hyundaitech 

In my opinion, most recent brake vibration problems I've seen have been caused by material transfer from the pad to the rotor. This causes variation in the cefficient of friction as the rotor turns, creating a vibration when the brakes are applied. I've fixed a few cars by making several hard stops, but most have a large enough problem that this will not work.

It's also true that runout doesn't typically cause significant vibration. As was said in an earlier post, runout just causes the caliper to slide back and forth, but doesn't change the distance between the pads. In fact, on most vehicles, runout can be very large (tens of times the allowable specification) and still only cause a very minor brake vibration. I know this from cases where I've actually measured runout with a dial indicator. Thickness variation and friction variation are much more likely to cause a significant vibration.

I, too, have measured very few rotors with a dial indicator. I have one in my box and will use it when necessary, but when making repairs, I'm typically not that interested in the rotor runout. Why? Because whether the rotor has excessive runout, excessive thickness variation, or excessive material transfer, the repair is the same: resurface or replace the rotors.

I do, however, tend to make a mental note of how the rotor turns on the lathe. And it is indeed possible to make runout checks on a lathe. The knobs on the lathe are indexed, so I can monitor how much metal I need to take off (within a couple thousandths) to remove the runout. While I agree the accuracy is nowhere near a dial indicator, it's enough to give me a general idea of what's occurring. Most rotors need only about .004" or .006" taken off before the bit contacts the entire rotor. This is enough to tell me that runout isn't the real issue in most cases. In fact, looking at the cut pattern is sufficient to tell me that, although more frequent than runout issues, thickness variation is also much less common that material transfer (which can often be seen visually on the rotor surface). Of course, if you really want to measure the thickness variation, the best way is to take about 8 micrometer readings around the rotor and compare them.

If I were doing an engineering analysis, I'd be interested in accurate and precise runout and thickness variation readings, as well as measurements of coeffecient of friction around the rotor. As far as the mechanic working on the brakes, it's just not that important. The answer is to true up the rotor or to take off the junk that's causing the friction to vary. Either way, you're cutting the rotors.
 >> Stay informed about: need opinion of hyundaitech