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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" <spamtrap@lexregia.com> wrote in message
news:m_FOf.56512$dW3.24778@newssvr21.news.prodigy.com...[color=blue]
> "davidj92" <davidj92REMOVE@sigecom.net> wrote in
> news:l9GdndF_XfPAvpbZRVn-gw@sigecom.net:
>[color=green]
>> 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.[/color]
>
>
> 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.
> [url]http://www.trustmymechanic.com/besttires.html[/url]
>
> The steering wheel is vibrating because the front brake
> rotors are warped (we call this vibration "shimmy").
> [url]http://www.trustmymechanic.com/brakewarp.html[/url]
>
> 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.
> [url]http://www.eurac-group.com/technote4.htm[/url]
>
> 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.
> [url]http://en.wikipedia.org/wiki/Disk_brake[/url]
>
> 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.
> [url]http://en.wikipedia.org/wiki/Disk_brake[/url]
>
> 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.
> [url]http://support.mscsoftware.com/cgi-bin/kb_files/Ford_Brake_Roughness_[/url]
> 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.
> [url]http://www.rtitech.com/latheinfo.htm[/url]
>
> 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.
> [url]http://www.rtitech.com/latheinfo.htm[/url][/color]