# Drilled and slotted brake rotors better than solid?



## HotRodx10 (Aug 24, 2017)

I've been looking for brake pads and rotors for a friend, and I see O.E. rotors, and the supposedly "upgrade" ones that have drilled holes and/or slots for only a few bucks more. Are the drilled or slotted rotors really any better?


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## Nealtw (Jun 22, 2017)

Better cooling.


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## HotRodx10 (Aug 24, 2017)

Nealtw said:


> Better cooling.


I understand that's the theoretical advantage, but I don't know if it produces any tangible differences for normal driving conditions.


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## runagate (6 mo ago)

HotRodx10 said:


> I've been looking for brake pads and rotors for a friend, and I see O.E. rotors, and the supposedly "upgrade" ones that have drilled holes and/or slots for only a few bucks more. Are the drilled or slotted rotors really any better?


At first one would say better cooling, BUT it is a maybe.
What is does is offer better break performance.
How?
As the break pads friction against the disk, there is a brake erosion material building up between the brake and rotor that negatively impact brake performance. It is acting like powder lubricant. The holes or slots, allow that layer to escape.


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## mark sr (Jun 13, 2017)

IMO for normal driving the standard non slotted disc are fine.


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## Old Thomas (Nov 28, 2019)

As brake pad material is vaporized by the heat of intensive spirited driving it produces gasses that have to escape to reduce brake fade. Drilled and/or slotted rotors help to vent those gasses. For a plain Jane daily driver it will be hard to notice a difference. The brakes will feel better simply because new pads and rotors are present. Drilled/slotted can result in slightly shorter pad life because they wipe off pad material faster. That, too, is hard to quantify because so many cars with d/s rotors are driven and braked harder. My pickup warps OEM plain rotors in about 20k miles so I might try d/s because they don’t cost more and pads are a cheap half hour job, just to see what happens. If your friend drives hard and lives in mountain country, why not? For my old man flat land driving I don’t expect to notice better braking other than maybe better warp resistance but I have no proof of that. It is flat here, we can see a mile down the road, and we roll out to a stop and hardly use the brakes.


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## SPS-1 (Oct 21, 2008)

HotRodx10 said:


> I understand that's the theoretical advantage, but I don't know if it produces any tangible differences for normal driving conditions.


The tangible advantage is that it looks better (on a sporty car).


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## HotRodx10 (Aug 24, 2017)

Old Thomas said:


> If your friend drives hard and lives in mountain country, why not?


Not alot of hard braking for this gal, and I don't think she drives the mountain passes much.


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## HotRodx10 (Aug 24, 2017)

SPS-1 said:


> The tangible advantage is that it looks better (on a sporty car).


Yeah, I don't think the rotors are even visible on her Highlander.


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## runagate (6 mo ago)

Old Thomas said:


> As brake pad material is vaporized by the heat of intensive spirited driving it produces gasses that have to escape to reduce brake fade. Drilled and/or slotted rotors help to vent those gasses. For a plain Jane daily driver it will be hard to notice a difference. The brakes will feel better simply because new pads and rotors are present. Drilled/slotted can result in slightly shorter pad life because they wipe off pad material faster. That, too, is hard to quantify because so many cars with d/s rotors are driven and braked harder. My pickup warps OEM plain rotors in about 20k miles so I might try d/s because they don’t cost more and pads are a cheap half hour job, just to see what happens. If your friend drives hard and lives in mountain country, why not? For my old man flat land driving I don’t expect to notice better braking other than maybe better warp resistance but I have no proof of that. It is flat here, we can see a mile down the road, and we roll out to a stop and hardly use the brakes.





Old Thomas said:


> My pickup warps OEM plain rotors in about 20k miles


What makes them fail ? How do they look ?


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## Nealtw (Jun 22, 2017)

10 Drilled and Slotted Rotors Pros and Cons – Green Garage (greengarageblog.org)


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## SW Dweller (Jan 6, 2021)

Most of the sports cars I have driven and ridden in do not have drilled/slotted breaks from the MFG. I would think if the MFG's could get 10 feet less distance stopping they would use them.
As many as a MFG would buy the cost difference would be nothing. 
I am a guy that figures the engineers at the factorys are paid to come up with the best product. Me with out an degree in engineering will only muck it up by changing to non standard parts.


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## Steve2444 (Sep 28, 2020)

If you are towing, or drive aggressively, bat outta hell. Yea get them.
Otherwise, it's up to you, for a few bucks... why not.


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## SPS-1 (Oct 21, 2008)

HotRodx10 said:


> Yeah, I don't think the rotors are even visible on her Highlander.


Go solid.


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## Jeekinz (Jan 29, 2007)

I run Detroit Axle pads/rotors, have 10k miles on the front and 3k on the rears. No problems. They did seem a bit "grabbier" at first going from oem Audi brakes.


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## Marq1 (May 31, 2021)

12.1659036887.1961699


> My pickup warps OEM plain rotors


Rotors don't actually warp, the pad material builds up a very small film on the surface, that causes them to pulsate due to thickness variation. it's called brake judder.


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## Old Thomas (Nov 28, 2019)

Mine are warped, no doubt about it. I frequently towed a landscape trailer that is a little under 3000 lbs. with the mower on it so brakes are not required. I think it stressed my brakes too much. Last year I gave that trailer to my son and I bought one with brakes and it helped.


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## HotRodx10 (Aug 24, 2017)

Old Thomas said:


> Mine are warped, no doubt about it.


How would you know? The only effect of warped rotors would be that the caliper slides back and forth on the slide pins alot, but it doesn't affect how the brakes respond. If you're assuming they're warped because the brake pedal goes up and down when you press on the brakes, that's not because the rotors are warped; it's because they have pad material fused to them, making them thicker in some areas than others. If you want to assumed they are warped, go right ahead. Rotors that are actually warped cannot be turned (machined), but those affected by having pad material on them could be. However, for either problem, the easiest, and often the most economical solution is to replace the rotors, anyway.


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## 1865wingate (12 mo ago)

Have you ever driven for hours in stop and go traffic? slotted or holes help dissipate the heat quicker. warped rotors can give the brake pedal a pulsating feel. Every rotation they produce heat, and more wear, with each contact.


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## HotRodx10 (Aug 24, 2017)

Warped Brake Rotors—The Facts



> The fact is: The discs were never warped at all. Every warped brake disc that we’ve investigated with the assistance of our suppliers shows uneven patches of friction material from the brake pads on the surface of the disc. These patches cause variation in thickness (run-out) and the vibration under braking. Brake manufacturers have been struggling to deal with this situation for years because warped discs are so readily blamed for brake-related vibrations.


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## 1865wingate (12 mo ago)

HotRodx10 said:


> Warped Brake Rotors—The Facts


I'll buy that but the outcome is the same, high and low points. Of course even when they turn them they probably can't tell the difference. It would be like, same poop, different pile to some of them. I'll put this one in my little book of helpful things to know.


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## HotRodx10 (Aug 24, 2017)

1865wingate said:


> Of course even when they turn them they probably can't tell the difference.


I wouldn't know. I haven't had any rotors turned in the last 25 years. Even when I could still find a machine shop to do it, the hassle wouldn't have been worth the few bucks (if any at all) I could save.


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## FM3 (Aug 12, 2019)

HotRodx10 said:


> I understand that's the theoretical advantage, but I don't know if it produces any tangible differences for normal driving conditions.


They don't.

And drilled rotors can crack easier.
And slotted rotors can wear down the pads more.


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## 1865wingate (12 mo ago)

Well, maybe if you are going for a 6 second Saturday night drive, running in the 24 haures le Mans, or live at the Bonneville Salt Flats they might be good.........But they LOOK so cool!


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## LawrenceS (Oct 21, 2020)

HotRodx10 said:


> Warped Brake Rotors—The Facts


While that may be true in some instances, I have seen plenty of rotors that are actually warped as a professional automotive tech. In the Honda world the 09-15 pilots and 12-17 odysseys constantly have rotors warping. The exact reason I am unsure, but I speculate it had something to do with the front and rear brakes being undersized for the vehicles. Front's being undersized allowing for a greater build up of heat in the rotors and rears being undersized causing the fronts to work harder. For the odysseys Honda even updated the rotor design for improved cooling.


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## Old Thomas (Nov 28, 2019)

We had a Dodge Caravan that ate pads and rotors every 25K miles. Now my wife has a Mustang convertible and it’s large brakes last almost forever.


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## mark sr (Jun 13, 2017)

My 2010 jeep JK has 90k on it, the rear pads have been replaced twice, the front once. Never owned a vehicle before that wore out rear brakes quicker than the fronts.


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## HotRodx10 (Aug 24, 2017)

LawrenceS said:


> While that may be true in some instances, I have seen plenty of rotors that are actually warped as a professional automotive tech. In the Honda world the 09-15 pilots and 12-17 odysseys constantly have rotors warping. The exact reason I am unsure, but I speculate it had something to do with the front and rear brakes being undersized for the vehicles. Front's being undersized allowing for a greater build up of heat in the rotors and rears being undersized causing the fronts to work harder. For the odysseys Honda even updated the rotor design for improved cooling.


I don't doubt that both conditions may happen, but as I said, the preferred solution is the same regardless - replacement of the rotors.

There's some good info on bedding the brakes in the article, though, to minimize the occurrence of the build-up problem.


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## Marq1 (May 31, 2021)

> slotted or holes help dissipate the heat quicker


Actually they don't, you have removed mass from the rotor with the holes/slots. It's the mass of the rotor that helps absorb and dissipate the generated heat.

Unless your driving a Nascar you will not see any benefit from those openings, they may look cool, but they are of no benefit!


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## SPS-1 (Oct 21, 2008)

NASCAR rotors are not cross-drilled. They do have small slots however.


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## Brainbucket (Mar 30, 2015)

If you ever turned rotors on a brake Laeth, then you would see rotors warp. No question.


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## jazzwineman (Aug 11, 2021)

HotRodx10 said:


> I've been looking for brake pads and rotors for a friend, and I see O.E. rotors, and the supposedly "upgrade" ones that have drilled holes and/or slots for only a few bucks more. Are the drilled or slotted rotors really any better?


What kind of vehicle do you have and what type of driving do you do. There is no need at all for slotted rotors for a standard driver. It is just a "bling" sort of thing for some drivers and since I drive a variety of Jaguars, I have found no need for them. I would spend the money an quality pads like Pagid or the like and that will give you better brake performance.

TBB


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## rickwhoo (Nov 4, 2014)

Marq1 said:


> 12.1659036887.1961699
> 
> 
> Rotors don't actually warp, the pad material builds up a very small film on the surface, that causes them to pulsate due to thickness variation. it's called brake judder.


Rotors do warp... I have resurfaced hundreds of rotors because of warping as a mechanic.


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## HotRodx10 (Aug 24, 2017)

rickwhoo said:


> Rotors do warp... I have resurfaced hundreds of rotors because of warping as a mechanic.


Not trying to start a fight. You're sure that these hundreds are rotors were actually the same thickness face to face at all locations, but 'shifted' forward and back as they went around? They weren't actually thicker in some areas than others?


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## jazzwineman (Aug 11, 2021)

HotRodx10 said:


> Not trying to start a fight. You're sure that these hundreds are rotors were actually the same thickness face to face at all locations, but 'shifted' forward and back as they went around? They weren't actually thicker in some areas than others?


none of this really answers the person's original question.


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## rickwhoo (Nov 4, 2014)

HotRodx10 said:


> Not trying to start a fight. You're sure that these hundreds are rotors were actually the same thickness face to face at all locations, but 'shifted' forward and back as they went around? They weren't actually thicker in some areas than others?


All I know is that they were in fact warped and resurfacing them cured their shaky steering wheels while braking afterwards. I've been repairing and maintaining cars and trucks for over 45 years now.


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## jazzwineman (Aug 11, 2021)

rickwhoo said:


> All I know is that they were in fact warped and resurfacing them cured their shaky steering wheels while braking afterwards. I've been repairing and maintaining cars and trucks for over 45 years now.


If they were truly warped you would have to take a lot of surface material off and that is the opposite of what one wants with a rotor.


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## HotRodx10 (Aug 24, 2017)

jazzwineman said:


> none of this really answers the person's original question.


No, but my question was answered a while ago. Now, we're exploring some other side topics.


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## HotRodx10 (Aug 24, 2017)

rickwhoo said:


> All I know is that they were in fact warped and resurfacing them cured their shaky steering wheels while braking afterwards.


So you're saying you never measured the thickness of the rotors, you just machined them until the faces were flat? If that's the case, you don't really know if they were warped or just thicker in some areas.


rickwhoo said:


> I've been repairing and maintaining cars and trucks for over 45 years now.


Good for you. Many others could claim the same. That doesn't prove that you're right. Since machining the rotors works for either problem, the fact that maching the rotors resolved the issue is not evidence that your assumption of the cause is correct.


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## rickwhoo (Nov 4, 2014)

As far as my replacing rotors with drilled and slotted, I find they work a little better. I'm not racing around too much also.


HotRodx10 said:


> So you're saying you never measured the thickness of the rotors, you just machined them until the faces were flat? If that's the case, you don't really know if they were warped or just thicker in some areas.
> 
> Good for you. Many others could claim the same. That doesn't prove that you're right. Since machining the rotors works for either problem, the fact that maching the rotors resolved the issue is not evidence that your assumption of the cause is correct.


Seriously???


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## HotRodx10 (Aug 24, 2017)

rickwhoo said:


> Seriously???


Yes, seriously. Did you ever measure the thickness of the rotors or did you just turn them?


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## rickwhoo (Nov 4, 2014)

HotRodx10 said:


> Yes, seriously. Did you ever measure the thickness of the rotors or did you just turn them?


Yes, I measured for minimum thickness and made sure to not go thinner as I resurfaced them for being warped.


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## rickwhoo (Nov 4, 2014)

HotRodx10 said:


> No, but my question was answered a while ago. Now, we're exploring some other side topics.


Yes we are... LoL


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## HotRodx10 (Aug 24, 2017)

rickwhoo said:


> Yes, I measured for minimum thickness and made sure to not go thinner as I resurfaced them for being warped.


...and were they the same thickness everywhere, or were they thicker in some areas and thinner in others?


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## Jeekinz (Jan 29, 2007)

Drums and rotors do in fact warp. As others, Ive spent enough time behind a brake lathe to know that. Anyone that says they do not warp have no idea what they're talking about. Min thickness is listed on the rotor, you make your cut then measure. 

Flywheels warp too, so do clutch packs.


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## Old Thomas (Nov 28, 2019)

I put a run out gauge on them and quantify the warpage.


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## rickwhoo (Nov 4, 2014)

HotRodx10 said:


> ...and were they the same thickness everywhere, or were they thicker in some areas and thinner in others?


Give it up man... Has enough people in here convince you to rotors warping?


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## HotRodx10 (Aug 24, 2017)

rickwhoo said:


> Has enough people in here convince you to rotors warping?


I never said rotors never get warped (See post #28). Neither did the article I linked to. I just called into question your assertion that all of the rotors you've machined over the years were all warped, as opposed to being thicker from deposited pad material. From what I've read, both conditions do occur. Only by putting a caliper on the rotor at multiple locations and comparing the measurements would you be able to tell which condition the rotors suffer from. The solution is the same, but the causes are different, and the issue with deposited pad material is preventable with proper break-in of new rotors and pads.


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## Jeekinz (Jan 29, 2007)

Ive never seen brake pad material (fuse) to rotors or drums. Thats on motorcycles to tractor trailers and everything in between.


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## HotRodx10 (Aug 24, 2017)

Jeekinz said:


> Ive never seen brake pad material (fuse) to rotors or drums. Thats on motorcycles to tractor trailers and everything in between.


I have, although it's not as obvious to the eye as you might think, especially with metallic pads. Pulsing brakes are a classic sign of this condition. Mine originated with an emergency braking situation and actually got worse over the next months.


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## Old Thomas (Nov 28, 2019)

Brakes pulsate, I buy new rotors. I don’t care whether it is brake pad deposits or warpage.


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## HotRodx10 (Aug 24, 2017)

Old Thomas said:


> Brakes pulsate, I buy new rotors. I don’t care whether it is brake pad deposits or warpage.


Me too. As I said, I posted the article about the brake pad deposits so people would be aware that proper bedding/break-in can prevent this problem. Also, many times warped rotors cannot be turned, because they would be too thin if you did, but ones with deposits could be. Granted, I can't find a machine shop around here that even turns rotors as a regular thing, so the prices to have it done are more than new rotors. There's also far less hassle and downtime to replace them.

I replace the rotors whenever the pads need replaced. Supposedly, you can change rotors every other time the pads are changed...if they're not too worn down/thin, warped, have pad deposits on them, and if they don't have grooves, and if half a dozen other things that I don't care to check are true...not worth the hassle to inspect them that closely, when it takes 5 minutes longer to replace the rotors while I have the calipers off, anyway. Of course, since I plan on that from the beginning, I don't replace the pads until the pad material is completely gone. I trim, remove, or bend the little warning tabs, so I don't have to worry about them squeaking until I hit the metal of the backing.


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## Jeekinz (Jan 29, 2007)

HotRodx10 said:


> I have, although it's not as obvious to the eye as you might think, especially with metallic pads. Pulsing brakes are a classic sign of this condition. Mine originated with an emergency braking situation and actually got worse over the next months.


Let me preface by saying (again) Ive worked on many cars/trucks. Also ran a fleet of 18 vehicles (which itself is another ballgame) But if what you and that web page are saying is true, rotors would all warp before they wore out. Which is not true. 99 times out of 100 the reason for warped rotors is heat. Riding the brakes, bad caliper, line or pins, etc. The vehicles in my fleet would run 500-800 miles per day. Id install probably 5-6 sets of pads on the same set of rotors without any warping (or the mysterious buildup as you say). Just tossing the rotors from wear.
And this wasnt in fly-over country USA, but NY/NJ with plenty of traffic.


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## Old Thomas (Nov 28, 2019)

If I have a choice, I buy expensive pads and cheap rotors. Then they are both shot at the same time.


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## Marq1 (May 31, 2021)

> 99 times out of 100 the reason for warped rotors is heat


I'm guessing 9 years as an OEM brake engineer doesn't count for much compared with all the "experience" posted here but you simply can't get rotors hot enough, with normal usage, to metallurgically cause them to warp. But we really didn't bother testing the really cheap crap so I cant disagree with all the experts here!


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## rickwhoo (Nov 4, 2014)

Marq1 said:


> I'm guessing 9 years as an OEM brake engineer doesn't count for much compared with all the "experience" posted here but you simply can't get rotors hot enough, with normal usage, to metallurgically cause them to warp. But we really didn't bother testing the really cheap crap so I cant disagree with all the experts here!


I'm finding a lot of OEM rotors warping. I also never had a replaced rotor warp at all.


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## HotRodx10 (Aug 24, 2017)

rickwhoo said:


> I'm finding a lot of OEM rotors warping. I also never had a replaced rotor warp at all.


Sure. Replacements are all better than OE. Yeah, right.


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## rickwhoo (Nov 4, 2014)

HotRodx10 said:


> Sure. Replacements are all better than OE. Yeah, right.


I think so... OEM is crap these days


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## Jeekinz (Jan 29, 2007)

Marq1 said:


> I'm guessing 9 years as an OEM brake engineer doesn't count for much compared with all the "experience" posted here but you simply can't get rotors hot enough, with normal usage, to metallurgically cause them to warp. But we really didn't bother testing the really cheap crap so I cant disagree with all the experts here!


"Heat" meaning excessive heat from a bad caliper, line, pins, etc. Will in fact warp a rotor.

I had a problem with the ABS module on a E250 van not letting all the pressure return after braking, warped brand new rotors.


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## LawrenceS (Oct 21, 2020)

Jeekinz said:


> Ive never seen brake pad material (fuse) to rotors or drums. Thats on motorcycles to tractor trailers and everything in between.


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.


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## SPS-1 (Oct 21, 2008)

rickwhoo said:


> 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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## Old Thomas (Nov 28, 2019)

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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## Jeekinz (Jan 29, 2007)

LawrenceS said:


> 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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## LawrenceS (Oct 21, 2020)

Jeekinz said:


> 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.









GLAZED AND CONFUSED


Poor brake performance got you baffled? It could be glazed brake pads and rotors. Top braking performance relies on friction—in other words, the brake pad’s ability to grab onto the metal brake rotor. When that ability is compromised, brake performance can go by the wayside faster than that turn...



sunstar-braking.com




.

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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## FM3 (Aug 12, 2019)

Jeekinz said:


> 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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## HotRodx10 (Aug 24, 2017)

FM3 said:


> Doesn't that happen during "bedding the brakes" and is listed as the proper break-in on practically every website about brakes?


Yep. The key part is doing it so that it's an _even_ layer.


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## Marq1 (May 31, 2021)

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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## HotRodx10 (Aug 24, 2017)

Marq1 said:


> 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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## LawrenceS (Oct 21, 2020)

Jeekinz said:


> 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









Cleaning the deposited material off with a Scotch Brite roloc disc on a mini angle air grinder.









After resurfacing the rotor - you can still see somehow the pad material has effected the rotor metal - not sure exactly what happens.


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## HotRodx10 (Aug 24, 2017)

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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## Nealtw (Jun 22, 2017)

HotRodx10 said:


> 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


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## LawrenceS (Oct 21, 2020)

HotRodx10 said:


> 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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## NewDIY4me (3 mo ago)

Cross drilled are crap.


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## Matt1963 (5 mo ago)

HotRodx10 said:


> 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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## Marq1 (May 31, 2021)

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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## HotRodx10 (Aug 24, 2017)

Marq1 said:


> 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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## Old Thomas (Nov 28, 2019)

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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## Marq1 (May 31, 2021)

> The rotors can warp. Warping and deforming are different from melting.


This post is like politics, full of BIG LIES.

I guess the 8 years as a OEM brake engineer just doesn't mean much to folks that know it all!


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## NewDIY4me (3 mo ago)

HotRodx10 said:


> Of course you're right, but entrenched dogma is apparently difficult, and it seems sometimes impossible, to correct.


Agreed...they rotor are "out of round" via the unequal distribution of pad material.


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## Matt1963 (5 mo ago)

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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