Surprisingly no one brought up the relationship between temperature and pressure.
Guillaume Amontons was the first to empirically establish the relationship between the pressure and the temperature of a gas (~1700), and Joseph Louis Gay-Lussac determined the relationship more precisely (~1800). Because of this, the P–T relationship for gases is known as either Amontons’s law or Gay-Lussac’s law. Under either name, it states that the pressure of a given amount of gas is directly proportional to its temperature on the kelvin scale when the volume is held constant. Mathematically, this can be written:
P∝TorP=constant×TorP=k×T

 

Regardless of what the truth is - when the result is a shuddering, shaking or vibration when braking, chances are you are nearing a point when the rotors will need to be replaced. I've had numerous cars where this has happened and I tried to have them turned only to have the issue return a few months later. The answer was a full brake replacement - rotors and pads (and to be sure pistons within the calipers were operating correctly). Issue then never returned.

 

From my understanding the major source of brake squeal or chirping is caused by the pad rattling/vibrating in the caliber. Putting hi-performance brake grease on all of the moving surfaces usually fixes the problem. The other cause is hard racing pads and or rotors. You usually don't want these pads and rotors for street use.

 

Rotors are not made out of gas.

 

I'd like to add different facts to the discussion.

Warped/distorted rotors -
One doesn't have to melt the rotor to get distortion. You just have to get it to the yield point. I'd bet all of us has taken a piece of steel we want to bend and can't at room temp, but heat it red hot and it bends pretty easily. The hotter the easier it is to bend, but once it gets to the yield point but not glowing hot, keeping pressure on it for a long time at that lower temp. will give the same result. The steel is not melted in any way because the yield point is well below the melt point. I'm sure you all have seen movies of racing cars at night with the rotors glowing like the sun. Cast iron bends too. We bend aluminum too, not by getting it red hot but by heating it below that temp (which would melt the Al). The yield point of Al is much closer to the melt point. Certainly, the complex shape of the rotor with air paths between the 2 sides would be harder to bend than a rotor like my Spridget which is a plain 3/8" thick not hollow rotor. Given that the pads put even pressures on both sides of the disk, it shouldn't bend.
So what could cause different pressures on both sides of the disk? Race cars and expensive street cars have the caliper mounted firmly to the suspension/upright which fixes both sides of the caliper/brake piston holders in space. Ergo the distance from the rotor to either face of the caliper stays the same and it is only the pistons and pads that move. Any difference in pad wear is taken up by the individual pistons moving the pads in and out as required. This goes for the life of the pads. In most street cars (like a Toyota), the caliper is mounted to the suspension/upright which fixes only one side of the caliper a certain distance from the rotor face, but the other side of the caliper slides in and out on pins to adjust to differences in pad wear. This works pretty well when first assembled with everything clean and new lubricated pins, but the pins are steel and they rust and get dirty. When one lives up north where they use salt on the roads, it might be less than 1000 miles before the pins start to rust, and before road dirt gets into the hole the pins slide on. An easy example of a condition a rusted pin/dirty pin hole might cause is when you come to a hard stop and keep a decent amount of pressure on the brakes after braking, perhaps on a hill. You are putting a lot of pressure on one face of the rotor where the fixed pad is, but not on the other face.
Another reason you get distortion is that inside and outside pads wear at different rates almost all the time, which means the rotor gets more wear on one side. I've built and raced sports cars for the best part of 40 years (FP National Champion in 1995) and used to do my own street brakes too, and I have never seen inside and outside pads wear the at the same rate. The pad that shows the most wear will show more wear on the rotor. Sure you can turn a rotor down to get it smooth again but the best advice is to never turn a rotor, replace it! The mass of the rotor is part of the design requirements. When you turn a rotor you decrease the mass which means for identical stops the turned rotor gets hotter; ergo more susceptible to distortion
A couple of other points on brakes.
Cooling holes on rotors look great, but they make the rotors more susceptible to cracking at the holes. When doing a brake job, the rotors have to be very carefully inspected for any cracking at the holes
Cryogenic treatment (slowly down to very low temperature and slowly back up) will lengthen the life of a rotor, but perhaps more importantly will improve breaking. Each breaking experience will be identical to the previous one. I'm told the pads should be treated too, but I don't understand the science behind that.

 

Next time you feel brakes shudder like it has a warped disc, just try the bedding brake procedure. If you do it right and they clear up, youll know if you warped the rotors or stood on the brakes at a stop light with hot brakes depositing pad material unevenly

and squeaks are caused by the pad vibrating on the piston or the guides. Apply the red anti brake squeal goo to the back of the pad and some caliper grease to the contact points and go for a ride. If the squeak disappears and comes back, the contact areas where the pad rides on the caliper bracket might be worn too much causing the grease to dissipate quickly so you need a new bracket and pad

 

About the squeals… reminds me, my father was a semi-professional rally driver… 60’s and 70’s. He had the opinion that he liked the squeal on disc brakes. It assured him everything was working correctly prior to the start.

 

Alcon Brakes Myth Of Warped Brake Discs

 

Post #18: Post #48: Alcon Brakes is a manufacturer of high performance brake systems and an OEM supplier to Jaguar Cars. You can believe what they said in Post #48: "In almost every case, this problem is not caused by a warped discs, but that the brake pad material transferred unevenly to the surface of the disc." (Emphasis mine). That's the same thing I said in Post #18: "rotors usually don't warp".

I'm getting dizzy ... aren't you?


Time for a Moderator to close this discussion. What else is there to say?

 

At least we’re not arguing anymore. I’d think information posted from the experts would actually be invaluable to future readers.

 

Listen, you guys are great and really respect you both, but all you are doing is searching out and finding opinion pieces that match your belief and post them as expert testimony. The original article from the OP was an editorial by a lady from some brake website. Jahummers link is NOT Alcon but a company called MotoSports in Naperville IL that operates an AlconKits website. They have revenue of $157,000 according to D&B. So no, moderators shouldn't close out with your mis-information. You may be right about warped discs, that I am not going to argue about, but your reference material is flawed along with the assumption that you have given the end-all of information here.

About Alconkits.com

Motodelta Company Profile | Naperville, IL | Competitors, Financials & Contacts - Dun & Bradstreet (dnb.com)

 

I really wish this thread was dead. Deleted. Gone forever.
All I KNOW, with personal in-my-own-eyes information is that I've personally with my eyes I have seen rotors that were not 'flat', hence 'warped'. Build-up was not a factor. The frikkin' thing was not flat and true to the hub, that is the fact. Nothing anyone in the entire universe could ever say with nine hundred trillion words and a quadrillion pictures would ever alter what I saw. With my eyes. I don't care how it got that way. I don't care if dog-almighty came down and damned it to die in a volcano in the center of hell. I don't care if it got hot then wet then hot then wet then hot then wet then cold then hot then cold and wet.
It was warped.
This thread is not what it should be.

 

Respectfully, you are making assumptions without even asking how or why these links are being shared. As a matter of fact I have not done ANY searches for warped disc info. This particular link was featured on an Alcon website I was researching replacement rings for my alloy hats. The only specific research I did was cited above where I asked a seasoned mechanic his take on this entire thread and "warped" discs.

EDIT: Also, I do not think this thread should be closed because someone who disagrees wants to have the final word.

 

Metal will deform with heat and pressure. If it didn't, there would be no 'minimum thickness' and no 'serviceable thickness' limits on rotors - because they would never get thinner.

I can't imagine this is done evenly and uniformly along the face of the rotor, hence a warping/distorting.

If you don't believe your rotors are physically changing shape over years of use, then you can go join the 911 conspiracy theorists who say jet fuel doesn't burn hot enough to melt steel. In that case, maybe we should start making turbine blades out of steel instead of nickel super alloys!!

It doesn't have to be hot enough to melt, it just has to be hot enough to weaken.

 

I do not think this thread should be closed because someone who agrees with it wants to have the final word. ;-)

 

I would believe the arguing will never stop because there are significant differences of opinion.

Empirical evidence culled from a local tech no matter how seasoned is just not enough to sell me. I really don't care how you got there, so you didn't search warped rotors but in other research you stumbled across an article that you felt was relevant to your beliefs and posted. There, you got me, I will stipulate you are right and you didn't research the topic. Once stuart jumped on thinking that is an OEM Alcon article which it is not, you piped in that expert info has been supplied. The alconkits website has this composed by "site admin" and is littered with advertisements for their Rotor reconditioning kit, it is a sales ploy written from info commonly found on the internet.

I dispute that we have heard from any experts, honestly I can't find any verifiable scientific study published that supports or debunks warped rotor. Only opinion pieces. In the end I don't find any of this upsetting so no worries.

 

I completely disagree. I've ruined two or three skillets by heating them on the stove and then running cold water over them. The metal was no where near it's melting point, but the skillets still warped. Once I figured out why my skillets were warping I stopped doing that and I haven't had a problem since.

And like a previous member stated, I have seen warped rotors with my own eyes, so I know they exist.

 

You're putting words in my mouth. I'm just tired of reading the same thing over and over. What's the point?


And, please, someone reply so I don't have the last word. 🤐

 

Reply.

 

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