Rotors bad after one year?

[jolly8286]

they also make pieces for runout if didn't know. BUT I don't know how it all actually works or if it does.

 

[Kevinm]

Brake pedal pulsation is not due to rotor runnout due to heat now I've heard it all!
As little as .000 5 in. (that's five ten-thousandths!) is the maximum, and you can believe that you'll feel a lot of disc pulsation at .0008 in.
Overheating can also cause rotors to warp. Overheating may be the result of severe abuse or dragging brakes. Defects in the rotor casting, such as thick and thin areas can also cause uneven cooling that leads to warpage. Hard spots in the metal due to casting impurities can be yet another cause.
Volumetric expansion is based on the mechanical properties of the metal being used! Brake rotors are made from ferious metals and depending on their carbon category will vay in expansion. Rotors being heat treated and the alloy being used will have a significant result on their longevity and the resisitance to heating and cooling.

Sorry but it's a fact and is documented in all OEM and third party repair manuals and by reputable brake companies. Don't believe me just do a little homework.I ageree there are other causes that can have the same effect, but to say overheating of a rotor does not cause runnout which causes pedal pulsations is just wrong!

 

[Rara]

Brake pedal pulsation is not due to rotor runnout due to heat now I've heard it all!
As little as .000 5 in. (that's five ten-thousandths!) is the maximum, and you can believe that you'll feel a lot of disc pulsation at .0008 in.

You can feel shudder in the car, but not in the pedal, due to pure runout of the rotor. I think you are seriously confusing pure runout, with Disc thickness variation; which is unfortunately extremely common. Pure runout means you can measure the runout on the face, but, the back face is still parallel to the front face, I suspect you have NEVER measured runout on both faces of the rotor simultaneously, and compared the two surfaces to each other directly;, I have, and I have done it a lot. Pure runout does not cause the caliper piston to move relative to the caliper body, therefore it does NOT drive pressure back up through the system and does NOT cause pedal pulsation. Disc thickness variation, or DTV, DOES cause the piston to get pressed back into the caliper body and DOES result in pedal shudder. Pure runout can lead to DTV due to uneven wear from contact with the pad during off-brake travel (as I believe the case with the OP is, starting with pure runout due to bearing runout)

Some cars I've worked on, you could definately feel down to 12 micron (~ 5 thousandths) of DTV (disc thickness variation). But it would generally take a decent bit more of pure runout before you could feel any vibration through the chassis or steering, but it would never come through the pedal, unless there was 10 micron or more DTV as well.

Overheating can also cause rotors to warp. Overheating may be the result of severe abuse or dragging brakes.

In my professional experience, "warped" rotors are virtually non-existant. Overheating leads to uneven pad deposition or uneven wear on the face of the rotors. Most typically, on street car pads, the actual cause is pad material deposition on the rotor, sort of "smearing". And its not always visible to the naked eye. I've had many sets of development rotors that had to be sent back for analysis to determine how much pad deposition there really was. Even on my team's race cars, I've never had a rotor "warp". I've had my drivers melt and bend pad backing plates, and weld them to the pistons, and still no "warped" rotors.

Defects in the rotor casting, such as thick and thin areas can also cause uneven cooling that leads to warpage. Hard spots in the metal due to casting impurities can be yet another cause.

I've seen localized cracking due to variations in rotor cheek thickness, but never warping. And I've seen hard spots lead to uneven wear, and uneven pad material deposition, but never to warping.

Volumetric expansion is based on the mechanical properties of the metal being used! Brake rotors are made from ferious metals and depending on their carbon category will vay in expansion. Rotors being heat treated and the alloy being used will have a significant result on their longevity and the resisitance to heating and cooling.

First, its "ferrous" not "ferious". Second, heat related issues that build up internal stresses in the rotors lead to CRACKING, not to warpage. Every rotor will eventually see cracking from the built up thermal stresses, provided it doesn't wear out the rotor face first.

Sorry but it's a fact and is documented in all OEM and third party repair manuals and by reputable brake companies. Don't believe me just do a little homework.I ageree there are other causes that can have the same effect, but to say overheating of a rotor does not cause runnout which causes pedal pulsations is just wrong!

You are grossly oversimplifying a very complex phenomenon and attributing failure modes to the wrong root causes. I don't fault you too much for believing it, because it is a common and long held misconception. I no longer work on brake components in my day job, but I did for a long time, and I have several million OEM vehicles on the road with brake components that I either designed, or developed; and I'm not even the most experienced/knowledgable person on brakes that regularly posts on this site, there are two others that have significantly more expertise than I do on the subject, (ironically they both have the same first name) and both of them would state the same things I have. Just because you share a popularly held opinion, doesn't mean it is correct.

 

[Kevinm]

Well I am done. if you really think heat only causes cracking! Then you really don't understand metalurgy at all! Now I understand where you are basing opinion! Quit frankly you have some major flaws in your assumptions, of which that's all they are. Basing assumptions on brake repair is really all opinion and no science to back it! Unless you have failure data done by a reputable testing lab, it's all speculation.
Physics of metalurgy is known science. To correct me based on a minor typo is just a dig that has no significance!
Please go do your homework on alloys and the different types of expansions involved. I bet you don't understand the difference in volumetric expansion vs. linear expansion! If you did you would not just say heat causes cracking!
Lets just leave it as is!

 

[BrApple]

lol, this is funny, practical experience and book experience are not equal. reminds me of one of my mechanical engineering courses I took. It was a "shop" class. we learned all the equations and theory behind machining of metals, cutting fluids etc. Now take my father who is a machinist. I am not sure that he knows of the theory and equations etc behind what he does, but he knows what he does and how to do it from actually doing it. However I can not say that because I know the theory that i can actually do it myself.

 

[SicSE]

Years ago turning was an accepted practice not so much anymore!

I'm not aware of any mechanic, at any shop/dealership that DOESN'T turn rotors, so I have to ask what you're basing this statement on?

the best way to do it is on the car.

That is most definitely a matter of opinion and completely dependant on the machining tech, the rotor setup, and available equipment.

This runout/distortion due to heat, often called warped rotors is extremely rare, and very difficult to make happen. So much so that its nearly a modern myth, despite many mechanics swearing by that diagnosis out of ignorance.

I would be one of those mechanics. You've made a very compelling argument, as usual, but this one is pretty hard to let go for two big reasons.

1. One day a long time ago, my girl drove over to my house and I washed her car for her. I washed the car and cooled her rotors, which were steaming from the cold water hitting them - yes, I was a retard at that point in time. Anyway, she complained about a pedal pulsation on the way home, that wasn't there when she drove it to me. I had deducted that to be "warpage", and atrributed it to the rapid cooling of the rotor... if you disagree with that deduction, what would you attribute the sudden pedal pulsation to?

2. Cylinder head warpage - I though the same basic principles applied to rotors?

 

[Rara]

Well I am done. if you really think heat only causes cracking! Then you really don't understand metalurgy at all! Now I understand where you are basing opinion! Quit frankly you have some major flaws in your assumptions, of which that's all they are. Basing assumptions on brake repair is really all opinion and no science to back it! Unless you have failure data done by a reputable testing lab, it's all speculation.
Physics of metalurgy is known science. To correct me based on a minor typo is just a dig that has no significance!
Please go do your homework on alloys and the different types of expansions involved. I bet you don't understand the difference in volumetric expansion vs. linear expansion! If you did you would not just say heat causes cracking!
Lets just leave it as is!

First, for volumetric thermal expansion, you're telling me that when the rotor heats up, it expands in all directions according to the coefficient of volumetric thermal expansion for the material (and I totally agree so far), but that somehow, as it cools back down, that some areas of the rotor contract at a different rate than it expanded at, and resulting in a rotor that no longer has the same shape as before? You're throwing a ridiculous strawman argument in here. Yes, of course rotors will expand and contract with temperature changes, but the raw material strength, even at the elevated operating temperatures, prevent the geometry from being permanently altered. Cast grey iron doesn't even start to stress relieve much until above 1000*F. The expansion and contraction of the material in its numerous heat cycles lead to high internal stresses that lead to localized cracking, or "heat checking" as it is commonly called in racing envorinments where it is encountered on a regular basis.

I will throw you a bone, that occasionally, depending ont he design of a particular rotor, you will see a conicity of the rotor because of the assymetry of the hat design, but even then, its not remotely like what you're calling "warping".

Second, you think my comments are based on being a simple brake repairman? You call me out on not providing data? lol. Notice I said there are millions of vehicles out there with brake parts I either designed or developed. Kind of hard to do that many working as a brake repairman. I've personally generated and reviewed mountains of brake test data working for an OEM, with help from two of the most respected independant brake test labs in the world, as well as a number of the Tier 1 brake suppliers and thier labs whose components I was involved with designing and/or testing. All the data I've worked with is proprietary, and can't be shared.

What about you? do you have anything better than "but, but, the repair manuals tell me its called warped rotors, and I can measure runout on one face of the rotor . . ." or trying to apply volumetric thermal expansion completely inappropriately.

The simple fact is that rotors just plain don't "warp" as the common myth says. measured runout on one face is only a small piece of the puzzle, and is virtually always coupled with the real culprit of pedal pulsation, which is DTV. And DTV is caused by uneven wear, or uneven pad material deposition.

 

[Rara]

That is most definitely a matter of opinion and completely dependant on the machining tech, the rotor setup, and available equipment.

I'm going to have to disagree. On-car turning is the best choice for sure whenever available. It's the only way you can account/compensate for variation in the other components on the car. That said, off-car turning is generally more than adequate.

I would be one of those mechanics. You've made a very compelling argument, as usual, but this one is pretty hard to let go for two big reasons.

1. One day a long time ago, my girl drove over to my house and I washed her car for her. I washed the car and cooled her rotors, which were steaming from the cold water hitting them - yes, I was a retard at that point in time. Anyway, she complained about a pedal pulsation on the way home, that wasn't there when she drove it to me. I had deducted that to be "warpage", and atrributed it to the rapid cooling of the rotor... if you disagree with that deduction, what would you attribute the sudden pedal pulsation to?

2. Cylinder head warpage - I though the same basic principles applied to rotors?

I'll see what I can offer on your two reasons . But, I will say up front that, I understand why the myth has perpetuated, because the methods to determine EXACTLY what the root cause of brake roughness is, are generally too expensive to use in a typical repair shop scenario, and honestly, completely unnecessary to go into that level of detail. It's become common practice to simply attribute the problem to "warped rotors" and replace or turn them.

1. Without having been there, and knowing a lot of exact details of the scenario, its tough to do any more than speculate, but I'll see what I can do First, I don't recall saying that warping a rotor was impossible to do under any circumstance, and this case may in fact be one of those ultra-rare scenarios, which certainly falls outside the realm of "normal use". But, what I do think is even more likely than that, is that your act of spraying water onto the rotors, did a very effective job of hardening the surface of the rotor in a very uneven manner. This could very quickly lead to uneven wear on that face of the rotor since the hardened surface would no longer wear nearly as quickly. Another, often overlooked aspect that would be in play here is that the coefficient of friction would have changed noticably in the hardened areas, as well as how the pad material is deposited. This results in brake torque variation, sort of a "stick-slip" type scenario, that also results in a very odd feel between the pedal and chassis. It should also be noted that many people have a very difficult time accurately describing brake roughness, and often say something is coming through the brake pedal, when it isn't, but is simply occuring whenever the brake pedal is pressed.

2. In regards to warped cylinder heads, you are right that the same mechanical properties in regards to thermal expansion apply, but the scenario is quite different. Remember that a brake rotor is designed to be as rotationally symmetrical as possible to avoid any imbalance issues, and that the loading on the rotor is very consistant, with the vast majority applied very consistantly and evenly around its entire circumferance as the rotor spins. And the cooling airflow is as even as possible through the rotor, picked up in the center at the hat, and delivered outward by the spinning vanes. A cylinder head, on the other hand, is very non-symmetrical in almost every way. One side of the head is typically much hotter than the other, with some areas that are locally much hotter than others. Cooling in the head is also non symmetrical. You also have very complex loads applied to the head, from the valvetrain components, to the combustion chambers altering back and forth according to firing order. When a cylinder head overheats, it is often locally instead of the entire head, and the non-symmetric loading can distort the head. And again, it is physically possible to warp a brake rotor, but the strength of the material, even at temperature, and the lack of significant non-tangential loading makes it extremely unlikely, and very very rare in actual practice.

 

[Rara]

Holy crap did I use the word "very" a lot in this thread.

I am very sorry for that.

 

[Kevinm]

So grey steel which has the same properties as carbon steel as i said in my previous posts can have internal streses if uneven cooling due to differing cross sectional areas or uneven cooling brought about by mould chill or heat treatment or realized shrinkage of castings onto solid cores. When grey iron is hardened to about 600 deg C it increases it's stress relief, but graphite may form of which reduces the physical strength of the hardening process. Carbon steel has a coeficient of expansion of 8.666xx micro inch per degree farenheit. So as I said before in a very early post, the quality control of the part and it's processes will dictate the actual characteristics. One thing you continue to discount.
BTW if you think it's a myth then please explain the garden hose incident as one other has posted! Think this thread is worn out!

 

[BrApple]

BTW if you think it's a myth then please explain the garden hose incident as one other has posted!

he did ....

 

[Dyoel182]

BTW if you think it's a myth then please explain the garden hose incident as one other has posted! Think this thread is worn out!

I think you wore the thread out. What does spraying a hot piece of metal with cold water have to do with normal brake use?

 

[Rara]

So grey steel which has the same properties as carbon steel

First, its grey cast iron, and second, no, no no, grey cast iron and mild steel do NOT have the same properties. Further, there are a number of compositional variations of grey iron and and an even greater number of variations of plain carbon steel, each having properties tailored to specific applications. Is there overlap? most certainly, but to say they are the same makes you look silly.

as i said in my previous posts can have internal streses if uneven cooling due to differing cross sectional areas or uneven cooling brought about by mould chill or heat treatment or realized shrinkage of castings onto solid cores.

So now we are discussing the manufacturing techniques for rotors? I thought we were safe to assume a reasonable level of quality in a typical street car rotor . . . especially an OEM replacement . . .
OEM brake rotors have very strict quality controls in production, from specs for mold cooling rates to shrinkage control specs to heat treatment specs (including stress relieving). Aftermarket rotors have less stringent controls, but in general, even the cheap crap rotors are halfway decent these days.
IIRC, rotors are generally stress relieved, and THEN the faces are ground resulting in flat, parallel rotor surfaces. In the very poor quality rotors, you do occasionally get rotors that produce brake roughness right out of the box because the faces are not parallel, or not flat because they didn't relieve them before grinding the braking surfaces.

When grey iron is hardened to about 600 deg C it increases it's stress relief, but graphite may form of which reduces the physical strength of the hardening process.

This doesn't even make sense, hardening and stress relief are directly opposite. And graphite most definately will and does form in grey iron; that is part of the point of grey iron, to form flake graphite, and is a big part of why grey iron is a common choice for rotor material. The graphite is what makes the rotor face machinable, ie easily ground or turned to make flat parallel faces. It is also what provides such a high damping factor that prevents many of the unwanted high frequency noises that could occur in a brake system. You talk down to me about not knowing my metallurgy and then you spring this nonsensical garbage?

Carbon steel has a coeficient of expansion of 8.666xx micro inch per degree farenheit. So as I said before in a very early post, the quality control of the part and it's processes will dictate the actual characteristics. One thing you continue to discount.

And gray iron has a coefficient of volumetric expansion of between 6.5 and 7.5 10^-6/F, depending on the particular composition and temperature range, noticably lower than carbon steel. but what does that have to do witht he price of rice in China? You're all over the map here.
And yes, quality control is extremely important, I've never discounted it, and much of my day job is ensuring the parts I design are being manufactured with the appropriate quality control measures in place. As I said above, rotor manufacturing is done with significant quality control measures in place. And if you are really that concerned about it, make sure you only buy rotors from known reputable vendors. But for the sake of argument here, I think we are safe to assume some level of quality as delivered, and any gross alteration from that is usually readily apparent from the beginning of use. I mean, if we take your concerns to its farcical conclusion, perhaps I should worry about the rotor manufacturer quality control being so bad, that it accidentally ships me a rotor made of C4 and my car is going to explode.

BTW if you think it's a myth then please explain the garden hose incident as one other has posted! Think this thread is worn out!

We covered that one already. Try to keep up. Btw, you keep calling my knowledge, education and experience into question here, but haven't made any indication of your background or experience . . . Where do you even get your information besides from google and wikipedia? Oh, and old service manuals, I almost forgot.

 

[SicSE]

this thread is worn out!

I would call it extremely informative, and I think if you would pull your head out of your ass, you would agree. I'm not trying to be a d*ck, but come on man. Don't get so caught up in being right that you're unable to explore the possibility of being wrong.

 

[Kevinm]

Rara - Grey steel does have similar properties as carbon steel!
I'm not here to brag about my qualifications lets just say, I have entensive engineering expierence and schooling. Do not use Wikepedia as you have mentioned. That surely is a cop out on your behalf! I have not metioned anything about your schooling, but for some reason you feel I have! It seems I have touched a nerve in some way! Lets just say, I have been schooled pretty extensively with over 35 years of expierence.

SicSe - okay you are right, rotors I am wrong, rotors never warp! It is not I who has his head in his a**. Tell that to the industry.

 

[Dyoel182]

Dyoel -your rotors never get wet! Good for U!

Dont be a smartass. What does spraying a warm rotor with water have to do with rotors naturally getting hot when pads drag on them?

 

[B3NN3TT]

I always figured that rotors were turned MANY YEARS ago when the technology was a little more scarce and costly. Additionally, most every 70's-and-up disc-equipped car had wheel bearings built into the rotors as well - another additional cost and hassle, what with re-packing or replacing those. So turning was implemented as a cost-effective solution.

Now that you can get a brand new OEM rotor for $25 and swap them on in 15 minutes, it seems silly to have them turned.

 

[bobdorit]

He says there is shuddering at mileage over 70 80mph too (beside brake vibration). this can not be because of brake rotor. I had exactly the same problems and balanced the wheels and changed the rotors and drums three times! I put three different brands! Although I balanced the wheels, and they were balanced I eventually changed the rims it became much better after that (both braking vibration and high speed shuddering) but there is still a little bit of vibration at braking... I think it has something with balancing of all the components including wheel, rotor, hub, drive shaft alltogether. any body remembers hunter wheel balancers which were used to balance the wheel on the car? they were awesome! they resolve high speed vibration which I see even the new hunter balancer can not! Somewhere I read that car makers advise the on-car balancing and on-car rotor lathe as ultimate cure of vibration.

 

[BrApple]

if you have vibration from braking at highway speeds I suggest checking the lower control arm bushings. when mine where worn and I had some brake problems I got a terible vibration that shook the dash when braking at highway speeds. change the rotors and pads and half of it went away. change the control arms and all of it went away.

 

[bobdorit]

My car is good enough, I changed the lower control arms too and I get along with it.
I just wanted to say to guys that their discussion is getting far from the problems addressed at the beginning of the thread. It is not only vibration under braking condition but vibration at high speed without braking, which does have something with balance.

If somebody thinks the brake vibration and bad rotor (what ever, run out, wrapping…) is not heat related. Let’s say this is a scientific claim! “Brake vibration has nothing to do with heat!” If I research this, first step is review of available literature. There are thousands and thousands articles about rotors runout and failure of rotors because of heat, in internet and scientific literature. So even if anybody does not know the difference of cast iron and mild steel, he can more confidentially say that IT IS HEAT RELATED rather than ISNT! While the MAIN REASON FOR CHOOSING CAST IRON FOR BRAKE ROTORS IS ITS BEHAVIOR UNDER HEAT. Cast iron stands heat stress much better than low carbon steel.