As I know the cause of especially suspension problems in a car can be very complicated. I wonder how did you describe the problem cause so exactly . . .
Anybody who has worked on a car absolutely knows that describing a problem cause so detailed on a car which you have never seen comes just from an ***** (you fill it) man. I had never heard of that before. Saying that it happens on highway driven cars means that you have repaired so many of highway driven cars with the same symptom, and other cars in the same condition but not highway driven!!!
bob, I have spent a number of years designing brake components and developing entire vehicle braking systems for an OEM vehicle manufacturer. This includes thousands of hours of testing with hundreds of vehicles, and constantly replacing components on each of these vehicles, and recording mountains of data on everything, including a number of things that the average mechanic (professional or DIY) can't do, and would have no idea would even be significant. The three biggest items a brake development engineer spends his time on are brake roughness, dust, and noise. There are a few common root causes of brake roughness, and the description from the original poster very clearly fits one of these common causes that I am intimately familiar with from many hours of testing related to it. And honestly, its one of the primary reasons that the specification for the wheel bearings used on the Ford Fusion are much tighter than the specification for its platform-mate, the Mazda 6, to give a relevant and practical application.
That said, and as much as I hate to admit it, I have been wrong before, and probably will be wrong again. I am not infallible, and never claimed to be. This is why my suggestion clearly stated to verify the condition of the wheel bearings as a first step, and proceed from there, including verification of the condition of the control arm bushings as well. That said, those who know me well, particularly on here, know that I won't post detailed responses on subjects that I don't have significant knowledge and experience with. It bothers me to no end when people post "technical" information that is simply regurgitated from someone else without clearly stating so. This is how modern myths and incredibly stupid modification ideas spread, things like "warped" rotors, and "gutted" MAFS. Because it bothers me so much when other people do it, I work VERY hard to not do it myself, and when I am able, to correct it when other people do it.
Here as I understand the best helpful answers are the suggestions for solving the problems based on the writer’s experience. What does anybody gets HERE from quoting coefficients of expansion of steel? Quoting that even does not support your opinion (look where you say: …
I did not check it to see if it is right or not! But assuming it is right it means that cast iron deforms less than steel under heat and it is why they use it. There is absolutely possibility of wrapped and deformed cast iron rotors because of heat.
You are absolutely right, the coefficient of volumetric thermal expansion is completely irrelevant in the original discussion, but someone else quoted it for carbon steel and stated it was the same for grey cast iron, I was simply correcting that inaccurate statement. And it does nothing to support or to not support my statements, as the actual value is again, irrelevant to the actual discussion. And again, you are right that the
possibility of warping (please stop using "wrapped", it makes you look silly, unless you are talking about giving rotors away as Christmas gifts this year) or deformation due to heat always exists, but this is entirely seperate from how likely it is to occur. It is always possible that I could be struck by an airplane falling out of the sky, but it is extremely unlikely.
Typical street rotors rarely see temperatures beyond 600-700F under normal usage. Under hard usage (including track usage), even on vehicles with borderline thermal capacity (ie, rotor mass) rotor temps virtually never exceed 1000-1100F. If you were to strike a brake rotor at 1100F with a sledge hammer on the face, you would most likely deform it noticably, but a brake caliper applies the load around the circumference of the rotor, with minimal relative side load (this is something that engineers work on heavily in design to minimize this) so the load into the hot rotor is applied in a direction where the rotor is exceptionally strong, and extremely unlikely to cause any permanent deflection at all. the side loading applied by the caliper squeezing the rotor is minimal by having a floating caliper body that squeezes the rotor pretty evenly on both sides, and even less so on a fixed caliper with opposing pistons squeezing both sides directly. Rotors are still pretty strong even in the extreme 1000-1100F temperature range (I'm not going to try to dig up the tensile strength vs. temp data) but when they get that hot on a typical street car (including the CSVT) other things start causing issues before enough load gets into the rotors to deflect them (and they limit further temperature increase in the rotor) pad material starts to lose its friction level (ie pad fade, brake pedal stays firm, but car doesn't stop as well) or the fluid starts to boil (ie, fluid fade, brake pedal gets mushy and car doesn't stop as well).
On street cars, the more common heat related problem (and often called warped rotors by those that don't know better) is the uneven pad deposition I mentioned before. All brake pads deposit material on the rotor face, they are supposed to, and it works better that way anyway (I'm not going to get into the tribology, so you'll have to trust me). It is a very thin layer, and effectively invisible to the naked eye. When the rotor and pad get very hot, more pad material gets transferred, and it gets smeared around, resulting in a wavy uneven surface. these "waves" of pad material aren't very high, but they don't have to be, because, as was said before, it only takes 10-12 microns of rotor thickness variation on many vehicles before brake roughness can be felt. This is often called "warped" rotors as well, because the transferred pad material can still be invisible to the naked eye, and the mechanic will either turn the rotors, or replace them, and when the problem goes away, it is inaccurately confirmed in his/her mind that the problem was in-fact "warped" rotors, when in reality it was simply pad material transferred. Of course, some types of pads are more prone to this than others, and some specifically include materials to "scrub" the rotor face to limit pad material build up. Generally, the less prone a pad is to "smearing" while hot, the faster the rotor face itself will wear.
With
You say: “Wrapped rotors are virtually not existent” what does it mean?!
There are thousands of articles on internet about wrapped rotors , All are false?! Even if somebody reads this thread concludes that there is possibility of wrapped rotor!! Your own discussion even supports this opinion that the mentioned car can have wrapped rotors!
I would say most of them are inaccurate on describing the root cause. But thankfully, most of them are correct in how to manage the issue, so its not the end of the world for non-technical people. If you recall, people thought the earth was flat for a LONG time before popular opinion was finally corrected. And once more I will state, that it is physically possible to warp rotors, but extremely unlikely, and requires some unique circumstances outside of common use.
I know that you appreciate other people opinion, even when you do not agree with and there is high possibility that they are right.
Absolutely, however, in this particular case, based on my extensive experience in the area, I'd say there is a very low possibility of my "opinion" being wrong.
