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

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

"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