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

"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."


This is sort of true but misleading. If the 2 sides of the disc stay
parallel, there won't be any pulsation even if there is warpage. This
may often be the case when the runout is small. Most rotors have
ventilation slots between the disc surfaces this makes it unlikely that
the surfaces stay nice and parallel when the warp is large.
If you have pulsation when braking on dry pavement then it is coming
from the disks not running true. This can develop in numerous ways. For
instance due to impurities in the metal or other reasons part of the
disk surface can become much harder than the rest. As a result the disk
will wear unevenly. Now you might choose to not call this "warping", but
the result is the same the disc surface doesn't run true and causes
pulsation in the brake pedal.


>
> 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.
>

Excluding pulsation due to ABS and malfunctioning ABS the only thing
that can cause pulsation in the brake pedal is a disk or drum that is
not running true. Stuck calipers can greatly magnify a small amount of
runout in a disk. So the problem may be more than the runout. But if the
discs/drums are running perfectly true you won't have any pulsation in
the pedal.

And incidentally, brake shudder and pulsation in the brake pedal are
not the same thing. If everything besides the rotors are generally in
good condition you can have a pulsation in the brake pedal alone. That
is, a passenger wouldn't notice anything at all. If you get a shudder
when you hit the brakes it may also be felt in the brake pedal or it
might not. A shudder or vibration might not even be a brake problem or
only partly a brake problem. Bad suspension components, out of balance
tires or out of round tires could all cause a vibration that is
triggered by applying the brakes. It is possible to have a condition
where the whole car shakes violently when the brakes are applied without
any pulsation in the brake pedal.

-jim

-jim

-jim



> But we learn more every day about brakes so time will tell for all.
> Stu
>
> jim > wrote in
> :
>
> >
> >
> > hob wrote:
> >
> >> > Even a first year engineering student can tell you how hard
> >> > braking with the linkage turned hard over bends (warps) the rotor
> >> > bell.
> >
> > That's just plain silly.
> >
> >
> >> > (imagine 2 tons moving forward trying to go over a tire turned
> >> > sideways
> >> > with the brake pads locked onto the rotor, a rotor designed for
> >> > transfer
> >> of
> >> > force into floating claipers and transversely into the axle.
> >
> > The caliper can move freely from side to side (floating calipers).
> > There is no side load at all due to steering.
> >
> >> > Guess how the force gets from the 2 ton moving vehicle mass into
> >> > the
> >> tire
> >> > tread in a turn-- through the shoes gripping the rotor and back
> >> > into the axle - forces across the rotor plane, unlike straight
> >> > ahead braking, where the forces are in the rotor plane)
> >
> > This is fantasy. The wheel is mounted solid to the axle with the rotor
> > sandwiched between. Even if the axle would deflect it couldn't
> > possibly deflect enough to exceed the side travel of the calipers. If
> > the car is sliding sideways the brakes see no load at all because
> > there would be no force to turn the wheels.
> > Heat build up is usually what causes rotors to warp. You don't
> > even
> > have to put the rotor on a car just toss it in a fire and it will
> > warp. Rust in the ventilation passages can also warp rotors. And
> > frozen calipers can also warp rotors - not so much because of uneven
> > force loads but uneven heat loads.
> >
> >> >
> >> > Any experienced engineer will tell you that if there is a problem
> >> > and it
> >> > goes way when you replace a part, the problem is gone.
> >> > Was the problem the root cause and will it return? Well, if it
> >> > wasn't
> >> part
> >> > of the problem, the problem would still be there in some form.
> >> > However, if it is only part of the problem, the problem will
> >> > later
> >> > manifest the same symptoms (E.g, if the driver brakes hard in
> >> > corners,
> >> part
> >> > of the problem, the rotors will again bend/wear the faces so that
> >> > in time the plane of the rotor surfaces are no longer within
> >> > tolerance, Before the driver got in and warped the new rotors, the
> >> > new rotors were just fine)
> >> >
> >
> >
> > This is nonsense. Excessive braking can result in warped rotors, but
> > braking on turns has nothing to do with it.
> >
> > -jim
> >
> >
> >> > ( Logically, when you change the rotor and then the problem goes
> >> > away,
> >> the
> >> > problem is gone.)
> >> >
> >> > and it seems
> >> > > nobody on this planet can really (reliably) tell the difference
> >> > > between brake friction materials (because there are no standards
> >> > > whatsoever) according to
> >> > > http://www.performanceoiltechnology....ingsystems.htm
> >> >
> >> >
> >> > the man ought to read the specs in the vehicle manuals, which do
> >> > indeed
> >> list
> >> > tolerances for rotors. And he ought to get some in depth background
> >> > first.
> >> > The internet is full of half-aware self-promoters with partially
> >> applied
> >> > theories. And AMSOIL, no less.
> >> >
> >> > FWIW - match mounting is a way to limit costly close tolerance
> >> > machining
> >> in
> >> > many mating parts- you make hundreds of parts all alike, and then
> >> > measure them - some will be way off and get tossed, most will be
> >> > within tolerance and used according to their tolerance, and some
> >> > may even be perfect. It's cheaper than making each one perfect.
> >> >
> >> > I'll put this quote from them in here for the experienced engineers
> >> > to get
> >> a
> >> > chcukle
> >> >
> >> > "DTV is when the rotor thickness is not the same all the way around
> >> > the rotor. DTV is typically caused by lateral runout. DTV can only
> >> > be
> >> measured
> >> > with very specialized laboratory testing equipment or with special
> >> > on vehicle capacitance probes."
> >> >
> >> > right.... ( or like a shop caliper or shop "mic", as noted in the
> >> > maintenance manuals.)
> >> >
> >> > Quote - "This [DTV] phenomenon is what many technicians refer to
> >> > as
> >> > "warping", however they actually think the rotor warped and needs
> >> > replacement."
> >> >
> >> > OK, so what they are saying is that the rotor isn't warped ( and
> >> > so the
> >> > rotor is true?) and the face of the rotor plane has just warped,
> >> > and so
> >> they
> >> > are saying that
> >> > instead of the rotor needing replacing because the thickness
> >> > varies,
> >> the
> >> > rotor needs replacing because the thickness varies and the esoteric
> >> > DTV measurements are lab things .(or you could just get refacing
> >> > done at a
> >> brake
> >> > shop, if enough material is left).
> >> >
> >> > enough of quoting their home-spun humor....
> >> >
> >> > >
> >> > > So, since I have horrible brake-induced wobble in my Toyota
> >> > > 4Runner, how DOES anyone buy the right parts given there are no
> >> > > regulations or standards to protect us?
> >> > >
> >> >
> >> > There are regulations - Check out the following standards for brake
> >> > materials: DE3A, BEEP, NHTSA FMVSS-105
> >> >
> >> > > We may as well close our eyes and choose randomly for all the
> >> > > lack of standards. Which leaves me to my most important question,
> >> > > having to
> >> trust
> >> > > in your judgement and experience (which I don't have).
> >> > >
> >> > > Where would YOU buy a good quality rotors & pads for a Toyota
> >> > > 4Runner?
> >> > >
> >> >
> >> > From Toyota -
> >> > why? aftermarket pads have few, if any standards. New-car brake
> >> > pads
> >> > (OEM) have to meet NHTSA standards, and thus actually do stop
> >> > better, are more reliable, and the dust around the kids and dogs is
> >> > less hazardous.
> >> >
> >> > nuff free stuff
> >> >
> >> > > Stu
> >> >
> >> >
> >
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