And here we have another popular brake myth! barring improper installation rotors don't "warp"
Anybody who tells you have warped rotors (again assuming they were installed right) doesn't know how brakes work. Here's Stoptech, a major brake manufacturer who would have a pretty strong financial interest in convincing you rotors warp so you buy new ones from them, telling you it's a myth, and explaining in detail what is actually happening when JimBob at Brakes-R-Us is telling you they 'warped'
Not only does he explain what's
actually happening, he explains how to avoid/prevent/fix it too.
The fact you do it to virtually all your cars is further evidence it's a driver problem, not a rotor problem.
-Warped- Brake Disc and Other Myths
Good article for newcomers and worth repeating ...
Myth # 1 – BRAKE JUDDER AND VIBRATION IS CAUSED BY DISCS THAT HAVE BEEN WARPED FROM EXCESSIVE HEAT.
The term "warped brake disc" has been in common use in motor racing for decades. When a driver reports a vibration under hard braking, inexperienced crews, after checking for (and not finding) cracks often attribute the vibration to "warped discs". They then measure the disc thickness in various places, find significant variation and the diagnosis is cast in stone.
When disc brakes for high-performance cars arrived on the scene we began to hear of "warped brake discs" on road going cars, with the same analyses and diagnoses. Typically, the discs are resurfaced to cure the problem and, equally typically, after a relatively short time the roughness or vibration comes back. Brake roughness has caused a significant number of cars to be bought back by their manufacturers under the "lemon laws". This has been going on for decades now - and, like most things that we have cast in stone, the diagnoses are wrong.
With one qualifier, presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification, in more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history - I have never seen a warped brake disc. I have seen lots of cracked discs, (
FIGURE 1) discs that had turned into shallow cones at operating temperature because they were mounted rigidly to their attachment bells or top hats, (
FIGURE 2) a few where the friction surface had collapsed in the area between straight radial interior vanes, (
FIGURE 3) and an untold number of discs with pad material unevenly deposited on the friction surfaces - sometimes visible and more often not. (
FIGURE 4)
In fact every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc. This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures.
MYTH # 2 - RACING BRAKE DISCS ARE MADE FROM STEEL
To digress for a moment "steel discs" are a misnomer frequently used by people who should know better. This group includes TV commentators and drivers being interviewed. Except for some motorcycles and karts, all ferrous discs are made from cast iron - an excellent material for the job. While steel has a higher tensile strength, cast iron is many times stronger than disc brake requirements. Its thermal transfer characteristics are significantly better than those of steel so that the heat generated at the interface between pad and disc is efficiently carried through the friction faces to the interior surface of the disc and into the vanes from where the heat is dissipated into the air stream. Cast iron is more dimensionally stable at elevated temperature than steel and is a better heat sink - so let us hear no more talk of "steel" brake discs.
MYTH # 3 - A SOFT BRAKE PEDAL IS THE RESULT OF PAD FADE
The all too familiar mushy brake pedal is caused by overheated brake fluid, not overheated pads. Repeated heavy use of the brakes may lead to "brake fade". There are two distinct varieties of brake fade
A) When the temperature at the interface between the pad and the rotor exceeds the thermal capacity of the pad, the pad loses friction capability due largely to out gassing of the binding agents in the pad compound. The brake pedal remains firm and solid but the car will not stop. The first indication is a distinctive and unpleasant smell which should serve as a warning to back off,
B) When the fluid boils in the calipers air bubbles are formed. Since air is compressible, the brake pedal becomes soft and "mushy" and pedal travel increases. You can probably still stop the car by pumping the pedal but efficient modulation is gone. This is a gradual process with lots of warning.
MYTH # 4 - BOILED BRAKE FLUID WILL BE SERVICABLE AFTER IT COOLS.
Once the brake fluid inside the caliper has boiled, it has lost a significant percentage of its original boiling point and should be replaced. It is not necessary to remove all of the fluid in the system, just bleed until clear fluid appears.
MYTH # 5 - BECAUSE THEY ARE NON-HYGROSCOPIC SILICON BASED BRAKE FLUIDS ARE SUITABLE FOR USE IN HIGH PERFORMANCE CARS
DOT 3 AND DOT 4 brake fluids are ether based and are hygroscopic in nature - i.e. they absorb water vapor. As the braking system in not quite airtight, a significant amount of water can be absorbed from the atmosphere in the course of a year. A 3% water content in brake fluid drops the boiling point as much as 170 degrees F. Brake fluid should be completely replaced annually.
DOT 5 fluids are silicon based and are non-hygroscopic, which is good. They are also subject to frothing from high frequency vibration, which gives a soft pedal. Soft brake pedals may be OK in non-high performance cars (in fact, most drivers accept mushy brake pedals as normal) but they are not acceptable in any situation where the driver intends to modulate braking at high force values.
MYTH # 6 - The brake fluid reservoir should be topped up during routine service.
In most modern passenger cars, the brake fluid reservoir is designed with a specific volume and is equipped with an internal float. The volume corresponds to the amount of fluid that will be displaced when the pads have worn to the point of replacement plus a generous reserve. When the replacement point is reached, the descending float completes an electrical circuit and a light appears on the dash warning the driver that the pads should be replaced. If the brake fluid is topped up the first warning of warn out pads will be the screech of steel backing plate against iron disc. This will be both annoying and expensive.
