Hey everyone, been doing some reading about my StopTech brake products and one thing I have found is a lot of misinformation on almost all car forums online regarding the myth of "warped brake rotors." Most people believe that fast cooling (ie washing when brakes are hot), unevenly torqued lugs, or extreme braking situations can cause abnormal vibration due to "warping." This is considered by StopTech, and several other industry experts, to be a complete falsehood:

http://www.stoptech.com/technical-su...nd-other-myths

Among the important excerpts from this page is:

"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."

There you have it. It is in fact thickness variation and not a warped rotor that is the cause of most vibration under braking - assuming the hub and other components are in good condition. Is this becoming common knowledge? Perhaps I'm telling you something you already know. But based on the number of threads I have seen stating differently, I thought I should post this. Probably the best solution in this case is to have the rotors resurfaced if a bedding procedure does not work to correct this.

Thanks!

 

My OEM MB rotors went 125,000 miles no issue before I replaced them due to wear thickness limits.

 

Yeah I have never had a set of "warped rotors" and my OEM brake rotors went for a very long time before I replaced them with R1 Concepts discs, which I love, but this was just something that needed to be addressed.

 

It's very unusual for me to see "warped" rotors at my shop. The only ones I recall were Tundras used in the oilfield. Very heavy tow loads creating a lot of heat then splashing through deep water at drill sites. I've seen a couple that were cracked.

Occasionally used to see rear rotors on Supras warp. But they were thin non-ventilated rotors that didn't like racing very much. Most people never get their rotors so hot they glow red so warping doesn't really happen.

On that note, if you've never been to the 24 Hours of Daytona, it's amazing seeing the brake rotors on the fronts glowing red at night as they brake into turn 1.

But yeah.......people call rotors "warped" when they get vibration under braking. Resurfacing rotors just removes the uneven deposit of pad material from the rotors.

 

^ Thank you, good endorsement from an expert. As you said it's only very rare and unique situations where you get warping and it usually comes on vehicles with heavy load. That is amazing though I've seen that out at HPR when their brakes get hot and they come into sharp turns, brakes become red hot and I've even seen smoke and fire on some.

 

I call B.S. I turn rotors all the time, and they are, in fact warped. I am not cutting off uneven deposits of pad material, I am removing metal. From the rotor. to make it flat again.

Often caused by sticking single piston calipers causing one pad to drag on one side, heating up the rotor unevenly.

Rotors do warp boys, that's a real thing.

 

Of course you take off metal. No one said you didn't. But you are taking off more pad material than you realize. If you put the shavings under a microscope you will clearly see the pad material bonded to the metal.

And I clearly stated that I had seen warped rotors. But the majority of the brake jobs I do where the customer complains of a brake vibration is caused by pad material unevenly distributed on the rotor surface, or the rotor itself wearing in un-even patterns. It takes way more heat to warp a ventilated steel brake rotor than 98% of customers can generate in a brake system under normal use.

If you will notice when you re-surface a rotor and you have a variation in thickness, those variations are not at the same location on both sides of the rotor. They are offset. That is because under braking the caliper assy moves laterally as the high spot passes under the pad, and the high spot on one side wears a trailing low spot on the other side of the rotor. The pattern can repeat several times around the rotor. Don't believe me, next time you turn a set of rotors, mark your high spot with one cutter bit, then slowly bring the opposite side bit in until it just touches the other rotor face. In almost every instance, the high spot on one side slightly preceeds the low spot on the other side. It's also not uncommon for both high spots to be in the same location on both sides of the rotor due to uneven pad residue, which would be impossible for a "warp" to cause unless the steel was at it's melting point. (2500 degree F) And disc brakes will fail long before that point as DOT 5 brake fluid will boil at around 350 degrees and at that point, the brakes will fade to nothing. Brake rotors just don't get hot enough under normal use to boil the fluid or warp a rotor. It takes a wide variation in temperature between sections of the rotors to generate the sort of metal fatigue necessary to actually "warp" a rotor.

In fact, on my most recent ASE re-certification test series, one of the questions under brake pulsation causes was:

Technician A says un-even rotor wear can cause brake pulsation. Technician B says pad material building up unevenly on the rotor can cause a brake pulsation. Which technician is correct.
a) Technician A
b) Technician B
c) Both Technician A and Technician B
d) Neither Technician A or Technician B

the correct answer was "c".

 

Rotors will be out of true up to half a millimeter or more. That is metal that has chosen a new shape. Pad materiel may in fact be on top of the surface, but it is a vanishingly small amount compared to the rotor.

Most rotors we turn are not in fact warped, but the ones that are do not merely suffer from a little scuff of pad materiel, the metal takes a new shape due to heat cycles.

Bad information is bad.

 

Did you read the link from StopTech or anything Otto said? I would not consider either of those sources "bad information" lol

 

I did read the link, it has lots of issues. For one thing he states that Dot 3 & 4 Brake fluid is
"ether" based, when it is actually glycol based, and it does in fact claim that rotors cause pulsation from pad materiel build up. My direct experience is different, and I turn rotors almost every day.

Think what you want, it makes very little difference to me.

 

Nice thread, Just read the whole thing.

Couldn't help but laugh at reading "I turn rotors everyday" every other response. Backed by no references except for "I turn rotors everyday".....Riiiight.

 

I would trust a brake manufacturer which is also an R&D company as well as a professional Mercedes-Benz technician (Otto) above most other sources, I guess as a synopsis it is possible but most situations are in fact unevenly transferred braking material. The higher performance the application I bet these figures change.

 

For most of use doing our own brakes, it is all academic.


Unless you are turning them yourself, new rotors are often price competitive with turning rotors.

 

Unless you drive any AMG with the newer two-piece rotor design lol, those are quite expensive to replace as we all know. I wonder if the new cryo brake rotor process reduces the possibility of uneven material transfer or, rarely, warping. I wouldn't think it would help at all for the former but possibly the latter for track use and super high performance applications where this happens.

 

I read this article because I was researching warped rotors because I thought that was my problem.


As it turned out it was pad material buildup. After reading the article, I took the beast out on the expressway and made s few stops to build some heat. Then I ran it up to about 85 and stood on the brake pedal till I was almost stopped and then accelerated back to cruising to cool everything down. Since that time, my brakes have been as smooth and vibration free as new.


The adjustment I have made to my braking habits is to NOT sit stopped with my foot on the brakes after a hard stop as that is when pad material is transferred.


I have 64000+ miles on the original pads & rotors.

 

Good input Kurtis, I had this problem with my mom's old Toyota as well and I ended up taking her car out and doing a brake bedding procedure much like you did and it ended up fixing the problem. Even when bedding in new brakes (which is an important step to prevent this from happening I feel) you do NOT stand on the brakes at a stop. Changing your brake pads can probably also help.