Can anyone tell the difference between rotors and pads (truthfully)?

On Sat, 04 Mar 2006 06:31:47 GMT, "Stuart A. Bronstein"
> wrote:

>> This is nonsense. Excessive braking can result in warped rotors, but
>> braking on turns has nothing to do with it.
>
>According to this article (probably the best on the Internet)
>http://www.babcox.com/editorial/bf/bf100326.htm
>
>"Many technicians are under the impression that a "warped" rotor is one
>that has too much runout. They also attribute this "warping" to why the
>brake pedal pulsates. This is not true. Runout will NOT cause pedal
>pulsation in most cases."
>
>So, I'm back to being confused about whether or not brake rotor
>pulsation is really caused by "warped" rotors or not. It seems not.
>
>But we learn more every day about brakes so time will tell for all.
>Stu

Confused? Why? ****ing take your car in and have the rotors
machined, and when the pulsation stops, you can ****ing bet it is
because the pads now have a flat surface to grip.

*************************
Dave

DTJ > wrote in news:g17k02pllgnipo1po1p6o9u9olc54hkj4o@
4ax.com:
>>According to this article (probably the best on the Internet)
>>http://www.babcox.com/editorial/bf/bf100326.htm
>>
>>"Many technicians ... attribute "warping" to why the
>>brake pedal pulsates. This is not true.

> Confused? Why? ****ing take your car in and have the rotors
> machined, and when the pulsation stops, you can ****ing bet it is
> because the pads now have a flat surface to grip.

Hi Dave,

According to more than one well-informed article, that's exactly what most
technicians do, and, that's exactly the wrong approach.
http://www.babcox.com/editorial/bf/bf100326.htm

I am just looking to find the proper way to resolve this problem long term
and, just the uneducated technician who thinks high octane gas is "better"
gas, there's a lot of ignorance posing as fact out there.

I'm simply trying to properly diagnose, isolate, and repair my first case
of brake pedal pulsation at highway speeds on a Toyota 4Runner truck.

I'm realizing neither machining the rotors nor simply replacing them will
solve the problem, long term. I'm getting closer to the answer though, with
your help, and I hope those who read this thread in the future benefit.

Stu

Stuart A. Bronstein wrote:
snip
> According to more than one well-informed article, that's exactly what
> most technicians do, and, that's exactly the wrong approach.
> http://www.babcox.com/editorial/bf/bf100326.htm
>
> I am just looking to find the proper way to resolve this problem long
> term and, just the uneducated technician who thinks high octane gas
> is "better" gas, there's a lot of ignorance posing as fact out there.
>
> I'm simply trying to properly diagnose, isolate, and repair my first
> case of brake pedal pulsation at highway speeds on a Toyota 4Runner
> truck.
>
> I'm realizing neither machining the rotors nor simply replacing them
> will solve the problem, long term. I'm getting closer to the answer
> though, with your help, and I hope those who read this thread in the
> future benefit.
>
> Stu

It seems to me you've found one article that you want to believe over all
the other articles available, as well as the advice from learned
technicians, based on their education and experience. Many of these techs
I've read in this thread are either experts in the field of brakes or are
Master Diagnostic Technicians, which would lead one to believe the majority
opinion of these is true.
Are you possibly overanalyzing your situation?
davidj92

"Stuart A. Bronstein" wrote:

> I'm realizing neither machining the rotors nor simply replacing them will
> solve the problem, long term.

What do you mean by "long term". As far as I can tell you are resisting
the idea of fixing your brakes because eventually they will require
fixing again. If you are hard on the brakes you can expect to have to
repair them quite often. If you put your mind to it you can easily wear
your brakes out in days.
Nevertheless, if you develop a pulsation in the brakes and you replace
the pads and rotors you can reasonably expect that to fix the problem
and it should last as long as the originals did if you drive the same as
before. Anybody who knows what they are doing will also make sure the
calipers and pistons are clean, that they move freely and are generally
in good working order and if not they should be fixed also.
In most cases buying replacement rotors costs the same or very little
more than having the rotors turned so just buy the rotors and you won't
have to worry about the rotors not being turned properly. That should
address most of the worries from the article you are so fond of.

-jim

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"davidj92" > wrote in
:

> It seems to me you've found one article that you want to believe over
> all the other articles available ... [you should] believe the majority
> opinion ... is true.


Hi David,

Actually I found many articles, some with conflicting ideas.

For example, some say we should replace with softer brake pads, others
say we should always true brand new rotors, other say never true rotors
off the vehicle, others say use the parking brake instead of the pedal
when stopped at a light due to cooling differences, etc.

The majority is often wrong, by the way. The majority will tell you, in
and of itself, that high octane gas is "better" gas just like the
majority of chiropracters will tell you your spine needs "adjustment".

There is only one truth, and I'm simply searching for that one truth.

Here's a quick summary to date of some of those articles
Stu


What causes high-speed brake induced shimmy?

Vibration felt in the steering wheel only when the brakes are
applied is not a front end alignment problem, but a brake problem.
http://www.trustmymechanic.com/besttires.html

The steering wheel is vibrating because the front brake
rotors are warped (we call this vibration "shimmy").
http://www.trustmymechanic.com/brakewarp.html

Cold judder occurs primarily as a result of a non-uniform
circumferential rotor (friction ring) thickness, which causes a
cyclic variation in the brake torque output during braking (1 -
2). These microscopic variations in the cross-sectional thickness
of the disc brake rotor, axiomatically referred to as Disc Thickness
Variations (D.T.V. or R.T.V. (Rotor Thickness Variation)) may arise
during rotor manufacture as a product of the machining process
(typical manufactured D.T.V. < 7 m), or, as laboratory and field
trial testing have demonstrated, may be generated throughout their
lifetime in-service.
http://www.eurac-group.com/technote4.htm

Warping can be caused by excessive heat build up, which softens the
metal ... however with most ventilated discs ... the sensation of
warped brakes (wheel shimmy under braking) most often is a matter of
a brake pad material operating outside of its designed temperature
range and it has left a thick(er) than normal deposit in one area
of the disc surface, creating a "sticky" spot that will grab every
revolution of the disk. In cars with automatic transmissions the
driver applies brakes when the car is stopped ... the brake pads
remain in contact with the disc and the discs will cool unevenly
.... leading to warping.
http://en.wikipedia.org/wiki/Disk_brake

Wheel shimmy during braking is often caused by thickness variation
of the rotor disc. If the rotor has runout, a thin spot will develop
by the continuous touch touch touch as the rotor turns while the
brakes are not applied. When this thickness variation increases to
approximately 0.007 inch, the pulsation can be felt by the driver.
http://en.wikipedia.org/wiki/Disk_brake

The accepted cause of brake-induced vibrations is disc thickness
variation. Disc thickness variation generated by off-brake running,
uneven transfer of lining material to the disc surface, disc
corrosion, and distortion of the disc under thermal loading. The
variations in rotor disc thickness cause the brake fluid pressure
in the caliper to fluctuate, resulting in torque variations.
http://support.mscsoftware.com/cgi-b...ake_Roughness_
2001_NAUC.pdf

Pre-loaded wheel bearings have no end play to "absorb" hub and rotor
run-out. Hence, almost 100% of any axial run-out of the hub and
brake rotor are transmitted to the brake pads. This axial run-out or
wobble in the rotor causes the brake pads to wear the rotor unevenly
over time, producing two sections of the rotor, 180 degrees apart,
where the rotor thickness becomes thinner than the other two sections.
This difference in thickness is called Disk Thickness Variation or DTV.
http://www.rtitech.com/latheinfo.htm

In general, any run-out greater than 0.002" (50 microns) will
lead to an increase in DTV of about 0.0004" (10 microns) in about
3000-5000 miles. In most cars, when DTV reaches 0.0004" (10 microns)
or only 4 ten-thousandths of an inch, the driver will complain of
pedal pulsation, steering wheel shimmy, or brake shudder. The most
important fact to consider here is that the installation of the
wheel will almost always increase hub/rotor run-out by 0.001-0.0015"
(25-40 microns), even if the lug nuts are carefully torqued.
http://www.rtitech.com/latheinfo.htm

On many vehicles, such as my '94 Jeep Grand Cherokee, it is important to
torque the front wheel lugs to a specified point, on my Jeep it is 90
foot/pounds. If this isn't done, my rotors warp in a very short time...

"Stuart A. Bronstein" > wrote in message
. com...
> "davidj92" > wrote in
> :
>
>> It seems to me you've found one article that you want to believe over
>> all the other articles available ... [you should] believe the majority
>> opinion ... is true.
>
>
> Hi David,
>
> Actually I found many articles, some with conflicting ideas.
>
> For example, some say we should replace with softer brake pads, others
> say we should always true brand new rotors, other say never true rotors
> off the vehicle, others say use the parking brake instead of the pedal
> when stopped at a light due to cooling differences, etc.
>
> The majority is often wrong, by the way. The majority will tell you, in
> and of itself, that high octane gas is "better" gas just like the
> majority of chiropracters will tell you your spine needs "adjustment".
>
> There is only one truth, and I'm simply searching for that one truth.
>
> Here's a quick summary to date of some of those articles
> Stu
>
>
> What causes high-speed brake induced shimmy?
>
> Vibration felt in the steering wheel only when the brakes are
> applied is not a front end alignment problem, but a brake problem.
> http://www.trustmymechanic.com/besttires.html
>
> The steering wheel is vibrating because the front brake
> rotors are warped (we call this vibration "shimmy").
> http://www.trustmymechanic.com/brakewarp.html
>
> Cold judder occurs primarily as a result of a non-uniform
> circumferential rotor (friction ring) thickness, which causes a
> cyclic variation in the brake torque output during braking (1 -
> 2). These microscopic variations in the cross-sectional thickness
> of the disc brake rotor, axiomatically referred to as Disc Thickness
> Variations (D.T.V. or R.T.V. (Rotor Thickness Variation)) may arise
> during rotor manufacture as a product of the machining process
> (typical manufactured D.T.V. < 7 m), or, as laboratory and field
> trial testing have demonstrated, may be generated throughout their
> lifetime in-service.
> http://www.eurac-group.com/technote4.htm
>
> Warping can be caused by excessive heat build up, which softens the
> metal ... however with most ventilated discs ... the sensation of
> warped brakes (wheel shimmy under braking) most often is a matter of
> a brake pad material operating outside of its designed temperature
> range and it has left a thick(er) than normal deposit in one area
> of the disc surface, creating a "sticky" spot that will grab every
> revolution of the disk. In cars with automatic transmissions the
> driver applies brakes when the car is stopped ... the brake pads
> remain in contact with the disc and the discs will cool unevenly
> ... leading to warping.
> http://en.wikipedia.org/wiki/Disk_brake
>
> Wheel shimmy during braking is often caused by thickness variation
> of the rotor disc. If the rotor has runout, a thin spot will develop
> by the continuous touch touch touch as the rotor turns while the
> brakes are not applied. When this thickness variation increases to
> approximately 0.007 inch, the pulsation can be felt by the driver.
> http://en.wikipedia.org/wiki/Disk_brake
>
> The accepted cause of brake-induced vibrations is disc thickness
> variation. Disc thickness variation generated by off-brake running,
> uneven transfer of lining material to the disc surface, disc
> corrosion, and distortion of the disc under thermal loading. The
> variations in rotor disc thickness cause the brake fluid pressure
> in the caliper to fluctuate, resulting in torque variations.
> http://support.mscsoftware.com/cgi-b...ake_Roughness_
> 2001_NAUC.pdf
>
> Pre-loaded wheel bearings have no end play to "absorb" hub and rotor
> run-out. Hence, almost 100% of any axial run-out of the hub and
> brake rotor are transmitted to the brake pads. This axial run-out or
> wobble in the rotor causes the brake pads to wear the rotor unevenly
> over time, producing two sections of the rotor, 180 degrees apart,
> where the rotor thickness becomes thinner than the other two sections.
> This difference in thickness is called Disk Thickness Variation or DTV.
> http://www.rtitech.com/latheinfo.htm
>
> In general, any run-out greater than 0.002" (50 microns) will
> lead to an increase in DTV of about 0.0004" (10 microns) in about
> 3000-5000 miles. In most cars, when DTV reaches 0.0004" (10 microns)
> or only 4 ten-thousandths of an inch, the driver will complain of
> pedal pulsation, steering wheel shimmy, or brake shudder. The most
> important fact to consider here is that the installation of the
> wheel will almost always increase hub/rotor run-out by 0.001-0.0015"
> (25-40 microns), even if the lug nuts are carefully torqued.
> http://www.rtitech.com/latheinfo.htm

On Sun, 05 Mar 2006 18:21:06 GMT, "Stuart A. Bronstein"
> wrote:

>"davidj92" > wrote in
:
>
>> It seems to me you've found one article that you want to believe over
>> all the other articles available ... [you should] believe the majority
>> opinion ... is true.
>
>
>Hi David,
>
>Actually I found many articles, some with conflicting ideas.
>
>For example, some say we should replace with softer brake pads, others
>say we should always true brand new rotors, other say never true rotors
>off the vehicle, others say use the parking brake instead of the pedal
>when stopped at a light due to cooling differences, etc.
>
>The majority is often wrong, by the way. The majority will tell you, in
>and of itself, that high octane gas is "better" gas just like the
>majority of chiropracters will tell you your spine needs "adjustment".
>
>There is only one truth, and I'm simply searching for that one truth.
>
>Here's a quick summary to date of some of those articles
>Stu
>
>
>What causes high-speed brake induced shimmy?


Generally the last 3 articles pretty well nail it, while many of the
others contain truth.

Rotor quality is one BIG variable - and todays rotors are not "aged"
before finishing. The "green" castings relieve after machining - so
often arive out of true from the factory.
Warpage, in itself, seldom causes pedal pulsation OR steering shimmy
unless it is quite sizeable. Thickness variation causes problems even
if very close in tolerance.
Vented rotors often have "callapse" problems, where several "fins"
move in tolerance as the rotor ages, or in use.
Particularly in the "salt belt" todays pads often cause a "glaze" on
the rotors, which traps moisture and pits the rotor away. When it
pits, the oxide layer expands behind the glaze, clausing "blisters"
that cause pulsations.

Machining the rotor temporarily solves the problem, but reduced
thickness and mass makes warpage more likely.

As for surfacing new rotors, SOME need surfacing. On Car machining
will usually give you a truer disk - but since runout is NOT the big
problem, off-car machining on a good lathe will sometimes give better
parallellism than on-car machining, where vibrations can have an
effect.
Pad composition is one thing you CAN change to prevent or greatly
reduce break pulsation problems. Anything with an iron metallic is
going to cause problems in salt-belt areas. Brass metallic is MUCH
better, from early Toyota experience, and carbon metallic or ceramic
pads have proven to be a great improvement in my experience with later
model Ford and GM vehicles.

Carbon Metallic pads on my 90 Aerostar improved rotor life by over
400%, and pad life by 100% over factory parts. Brake effectiveness was
also GREATLY improved - allowing me to actually lock the front wheels
on dry pavement, which was absolutely impossible with the factory
pads.
>
>Vibration felt in the steering wheel only when the brakes are
>applied is not a front end alignment problem, but a brake problem.
>http://www.trustmymechanic.com/besttires.html
>
>The steering wheel is vibrating because the front brake
>rotors are warped (we call this vibration "shimmy").
>http://www.trustmymechanic.com/brakewarp.html
>
>Cold judder occurs primarily as a result of a non-uniform
>circumferential rotor (friction ring) thickness, which causes a
>cyclic variation in the brake torque output during braking (1 -
>2). These microscopic variations in the cross-sectional thickness
>of the disc brake rotor, axiomatically referred to as Disc Thickness
>Variations (D.T.V. or R.T.V. (Rotor Thickness Variation)) may arise
>during rotor manufacture as a product of the machining process
>(typical manufactured D.T.V. < 7 m), or, as laboratory and field
>trial testing have demonstrated, may be generated throughout their
>lifetime in-service.
>http://www.eurac-group.com/technote4.htm
>
>Warping can be caused by excessive heat build up, which softens the
>metal ... however with most ventilated discs ... the sensation of
>warped brakes (wheel shimmy under braking) most often is a matter of
>a brake pad material operating outside of its designed temperature
>range and it has left a thick(er) than normal deposit in one area
>of the disc surface, creating a "sticky" spot that will grab every
>revolution of the disk. In cars with automatic transmissions the
>driver applies brakes when the car is stopped ... the brake pads
>remain in contact with the disc and the discs will cool unevenly
>... leading to warping.
>http://en.wikipedia.org/wiki/Disk_brake
>
>Wheel shimmy during braking is often caused by thickness variation
>of the rotor disc. If the rotor has runout, a thin spot will develop
>by the continuous touch touch touch as the rotor turns while the
>brakes are not applied. When this thickness variation increases to
>approximately 0.007 inch, the pulsation can be felt by the driver.
>http://en.wikipedia.org/wiki/Disk_brake
>
>The accepted cause of brake-induced vibrations is disc thickness
>variation. Disc thickness variation generated by off-brake running,
>uneven transfer of lining material to the disc surface, disc
>corrosion, and distortion of the disc under thermal loading. The
>variations in rotor disc thickness cause the brake fluid pressure
>in the caliper to fluctuate, resulting in torque variations.
>http://support.mscsoftware.com/cgi-b...ake_Roughness_
>2001_NAUC.pdf
>
>Pre-loaded wheel bearings have no end play to "absorb" hub and rotor
>run-out. Hence, almost 100% of any axial run-out of the hub and
>brake rotor are transmitted to the brake pads. This axial run-out or
>wobble in the rotor causes the brake pads to wear the rotor unevenly
>over time, producing two sections of the rotor, 180 degrees apart,
>where the rotor thickness becomes thinner than the other two sections.
>This difference in thickness is called Disk Thickness Variation or DTV.
>http://www.rtitech.com/latheinfo.htm
>
>In general, any run-out greater than 0.002" (50 microns) will
>lead to an increase in DTV of about 0.0004" (10 microns) in about
>3000-5000 miles. In most cars, when DTV reaches 0.0004" (10 microns)
>or only 4 ten-thousandths of an inch, the driver will complain of
>pedal pulsation, steering wheel shimmy, or brake shudder. The most
>important fact to consider here is that the installation of the
>wheel will almost always increase hub/rotor run-out by 0.001-0.0015"
>(25-40 microns), even if the lug nuts are carefully torqued.
>http://www.rtitech.com/latheinfo.htm

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"Stuart A. Bronstein" wrote:
>
> jim > wrote in
> :
> > What do you mean by "long term". ...
> > Anybody who knows what they are doing will also make sure
> > the calipers and pistons are clean, that they move freely and are
> > generally in good working order and if not they should be fixed also.
> > In most cases buying replacement rotors costs the same or very
> > little more than having the rotors turned so just buy the rotors
>
> Hi Jim,
>
> You are the words of wisdom.
> - I will replace the rotors (I already ordered them from the best Toyota
> Internet dealership in the USA according to these newsgroups).
> - I will replace the pads and hardware too (already ordered them too).
> - I agree it is important to check that the four pistons in each caliper
> are moving freely as the disc thickness variation (DTV) is what caused the
> runout in the first place (not heating & cooling warpage).

Well, I'm not sure I trust your analysis. It is quite likely that in one
way or another heat was a major factor that led to the problem
developing. That put another way, if you drive so that the brakes
never get hot it's likely they will last a very long time. All the
energy in a car moving at 70 mph goes into the brakes when you make a
sudden stop. You don't want to put your hand on the discs after doing
that. And if your rotors are truly not the same thickness that didn't
happen all at once - it happened over time and quite a number of things
could have started the process most all of them related to heat,
followed by rust, salt and dirt.
I assume you feel that your brakes needed replacement sooner than they
should have. That points to the driver as the most likely cause. Some
drivers regularly have to replace brakes every 10000 miles others can
get 100000 miles (altho that may be hard to do where salt plays a big
role in the deterioration of brakes). Also, some cars tend to have
brakes that last longer and take more abuse than others.

>
> I'm not just interested in fixing my brakes (otherwise I'd just take them
> to any mechanic on the block). I'm interested in learning why it happened
> and how to prevent it from happening in the future. And how to diagnose
> the problem properly.
>
> For example, if I follow your (correct) advice to check caliper and piston
> movement, it begs the question (which is NOT in the shop manuals)!
>
> How does one check that the front 2 calipers & 8 pistons move freely?


In order to change the brake pads and rotors you need to move the
calipers and pistons to their wide open position of there travel. You
should be able to tell if they are able to move normally. Rust of course
is what usually causes sticking problems. Disc brake pistons don't have
much clearance so it doesn't take much to jam them up.

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"Emmo" > wrote in news:ZDGOf.5257$gm.1937
@tornado.texas.rr.com:

> On my '94 Jeep Grand Cherokee, it is important to torque
> the front wheel lugs to 90 foot/pounds.
> If this isn't done, my rotors warp in a very short time...

Hi Emmo,
I agree and disagree (now that I've done some research).
I agree one should do a three pass tightening of the lug nuts, which, in
the case of the six-lug-nut 1998 Toyota 4Runner, is 84 foot pounds.

FIRST PASS: While the truck is in the air, tighten three lug nuts by hand
in a triangle pattern; then tighten the other three in a reverse triangle
pattern.

SECOND PASS: Back on the ground, tighten the second lug nut triangle to 1/2
the recommended torque (42 foot pounds for a 1998 Toyota 4Runner); then do
the same for the first triangle set of lug nuts.

THIRD PASS: Finally, tighten the first triangle to full torque; and then
the second triangel to full torque.

Of course, this assumes the hub was cleaned of all rust and was greased
with synthetic Mobil 1 grease to prevent rust creep (pushing out of the
rotors like tree roots push out a sidewalk or curb).

However, now that I've learned enough to be dangerous, I will disagree with
your assertion that the rotors will "warp" if you tighten lug nuts
incorrectly. Many articles have shown that brake discs almost never warp.
What people call warp is really disk thickness variation or rotor thickness
variation caused by the pad deposition being different on various parts of
the rotor.

See a more detailed explanation in the following reference:
http://www.stoptech.com/tech_info/wp...akedisk.shtml#

Stu

"Stuart A. Bronstein" > wrote in message
. net...
> However, now that I've learned enough to be dangerous, I will disagree
> with
> your assertion that the rotors will "warp" if you tighten lug nuts
> incorrectly. Many articles have shown that brake discs almost never warp.
> What people call warp is really disk thickness variation or rotor
> thickness
> variation caused by the pad deposition being different on various parts of
> the rotor.

Dear Stuart,
I know for a fact, that incorrectly tightening lugnuts will
warp rotors. (even brand new rotors).
I can prove it on just about any vehicle.
(not just hubless types)
Those websites are just playing on words mostly and also
must not know that even a 0 thickness variation can still have a
warp in the rotor if the wheels are not properly tightened.
You really should not listen to websites as if they are law..
Since if you do.
There are websites that have proof of many other things
that are far more silly than the "rotors can not warp" bologna
you are reading.


--
James M Driscoll Jr
Spaceman