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I think so... OEM is crap these days
I am going to have to disagree on that, in particular to brake rotors.

I once witnessed an OEM brake rotor manufacturer dialing in machining centers on a new brake rotor machining system. Tolerances were very tight. Took them better part of a week to get everything just right.
 

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Some OEM brakes are good/perform well and some are the opposite. Often it has to do with the size of the brakes, not their actual quality. I had a Dodge minivan, the kind of car intended to load with the family and stuff. It had small brakes that stopped the car, but never lasted over about 25k miles. Now my wife has a 6 cylinder Mustang convertible. Since it is supposed to be a sporty kind of car, it has way bigger brakes than I expected, and it is not a car that has room for lots of people or cargo. At 60k miles I replaced the brakes because they were glazed and rumbled, but they still looked like new with very little wear.
 

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It does happen to an extent, I believe it's why we end up seeing the glossy finish on rotors and while it may account for some thickness variation, I've had enough rotors on a lathe to also see that metal gets removed not just adhered friction material to get a rotor flat again.

Mostly when I see pad material fused to a rotor it's because a vehicle hasn't been driven and some sort of reaction happens between the friction material and the rotor leaving a noticeable build up(real common on 07-16 Honda CR-V rear rotors). As a professional tech we would just resurface them but realistically you could grind the build up off with an abrasive disc on an angle grinder. Not sure how long that fix would work/last though.

The other thing I have noticed when they do leave a build up from sitting, even when you resurface them you can get the rotor flat but still see the outline of the brake pad where the build up was.
Glossy finish is glazing. Again, from misuse or excessive heat (faulty components).

If you guys can come up with more than one dumb website saying brake pad material transfers/bonds to rotors/drums I may believe you. But for now and from my long term experience, its b.s.
 

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Glossy finish is glazing. Again, from misuse or excessive heat (faulty components).

If you guys can come up with more than one dumb website saying brake pad material transfers/bonds to rotors/drums I may believe you. But for now and from my long term experience, its b.s.
Every rotor I've ever seen glazes, google what glazing is, transfer of pad material to the rotor.

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Also I'm not a hobbyist, I fix cars at a high volume dealership for a living, 15 years in the industry, ASE Master certified with L1 and Honda Master certified.
 

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If you guys can come up with more than one dumb website saying brake pad material transfers/bonds to rotors/drums I may believe you. But for now and from my long term experience, its b.s.
Doesn't that happen during "bedding the brakes" and is listed as the proper break-in on practically every website about brakes?

Bedding in your brakes is just an industry term to explain breaking in your new brakes. Bedding in your brakes helps transfer an even layer of brake pad material onto the brake rotor which assists in smoother brake operation and improved braking power.
 

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So if you want more to argue about discuss the difference, benefits, issues between metallic and what we'll call Nao type pads, those being the run of the mill pads that 99.9% of cars use. Lets see how many false/inaccurate/I've done it that way for 30 years comments that brings up.

I'm really amazed at all the false, misleading, ignorant posts here about rotors despite some accurate posts that get dismissed. And, just because something happened one time does not make it reality.
 

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Discussion Starter · #68 ·
So if you want more to argue about discuss the difference, benefits, issues between metallic and what we'll call Nao type pads, those being the run of the mill pads that 99.9% of cars use.
I'd be interested in hearing from someone knowledgeable on the subject, which you seem to be. I've read alot that says ceramic are the best, but that comes from places that are trying to sell them, so I don't know if that's really true.
 

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Glossy finish is glazing. Again, from misuse or excessive heat (faulty components).

If you guys can come up with more than one dumb website saying brake pad material transfers/bonds to rotors/drums I may believe you. But for now and from my long term experience, its b.s.
Sorry to bump an old thread but I had a perfect example of pad material transferring/bonding to the rotor, not from driving but from sitting for an extended period.

Before
Tire Wheel Automotive tire Tread Synthetic rubber


Cleaning the deposited material off with a Scotch Brite roloc disc on a mini angle air grinder.
Tire Wheel Automotive tire Tread Synthetic rubber


After resurfacing the rotor - you can still see somehow the pad material has effected the rotor metal - not sure exactly what happens.
Automotive tire Wood Rim Gas Metal
 

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Discussion Starter · #70 ·
Those are some interesting pictures, LawrenceS. It does support the transfer of pad material to the rotors.

I'm still trying to figure out how warped rotors supposedly cause the brake pedal to pulse. Warped rotors would still be the same thickness everywhere. The entire caliper would potentially move, sliding on the pins, but the piston wouldn't move.
 

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Those are some interesting pictures, LawrenceS. It does support the transfer of pad material to the rotors.

I'm still trying to figure out how warped rotors supposedly cause the brake pedal to pulse. Warped rotors would still be the same thickness everywhere. The entire caliper would potentially move, sliding on the pins, but the piston wouldn't move.
If it was warped, as it rotates it might feel something. If the pads stay straight
Parallel Font Rectangle Graphics
 

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Those are some interesting pictures, LawrenceS. It does support the transfer of pad material to the rotors.

I'm still trying to figure out how warped rotors supposedly cause the brake pedal to pulse. Warped rotors would still be the same thickness everywhere. The entire caliper would potentially move, sliding on the pins, but the piston wouldn't move.

That type of pad material bonding to the rotor typically causes more of an audible thump versus a feeling in the pedal.

Warping may not be the proper term used in metallurgy for what happens to rotors but it has become the common place term to use. Technically pulsation comes from runout or parallelism. I understand what you are saying that if the metal warped one would expect the thickness/parallelism to be the same all around even and it would just have positive runout on one side and negative on the other side because the metal moved as one piece in 1 direction. Brake pulsation typically comes from the front rotors, which are all pretty much vented(the vanes in the middle between the two surfaces) so maybe it's something with the vanes warping and pulling one or both sides of the rotor inward because typically when cutting a rotor the warped area appears as a low spot not a high spot.

And even with warping like your envisioning, what ends up happening is it's felt more in the steering wheel because as the caliper is following the rotor it ends up pushing against the knuckle through the caliper causing the steering to move.
 

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Those are some interesting pictures, LawrenceS. It does support the transfer of pad material to the rotors.

I'm still trying to figure out how warped rotors supposedly cause the brake pedal to pulse. Warped rotors would still be the same thickness everywhere. The entire caliper would potentially move, sliding on the pins, but the piston wouldn't move.
I believe the pistons do move....when brake rotors warp you feel it in the brake pedal and steering wheel. The calipers take some of it but so do the pistons....to much going on there to not.

To answer earlier posts, when you turn discs and the meat of the rotor is off getting disc that have different thicknesses around the disc, it's bad casting. I see that with cheap foreign made rotors. Quality control issues for sure.
 

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It's not the metal, you can not "warp" rotors.

Nominal brake temps are around 400F, the forging temp of carbon steel (as an example) is 1200F so it's physically impossible to input sufficient heat via braking to cause the metal to dewform.

It's all in the minute layers of pad materials that coat the rotors, it's called PULSATION!!!
 

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Discussion Starter · #76 ·
It's not the metal, you can not "warp" rotors.

Nominal brake temps are around 400F, the forging temp of carbon steel (as an example) is 1200F so it's physically impossible to input sufficient heat via braking to cause the metal to dewform.

It's all in the minute layers of pad materials that coat the rotors, it's called PULSATION!!!
Of course you're right, but entrenched dogma is apparently difficult, and it seems sometimes impossible, to correct.
 

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Thermal shock can warp rotors. They don’t have to be at melting temperature. For example, glass has a melting point over 2000 degrees F. Put boiling water at 212 degrees in a glass, then dump it out and dump in ice water. The glass breaks at a tenth of its melt temperature. Rotors get up to hundreds of degrees in a stop. Then the car goes through a puddle and water gets splashed on the hot rotors. The rotors can warp. Warping and deforming are different from melting.
 

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I had two brake lathes when I was in my twenty's. One for drums and one for discs.....quick way brand.

When turning discs I would clean up scoring or the run out which I believe is a warped rotor. The cutting head would sometimes be way past the disc edge so in my opinion it can't just be brake pad absorption.

Once trude up, I would no longer have pulsation in the brake pedal.

Also, watching slow mo videos of breaks in auto shop I can assure you the brakes get way hotter than 400 degrees.
 
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