Warped Rotors?
Super Moderator
Joined: May 2004
Posts: 29,380
Likes: 118
From: Central Coast of CA
Like I stated in my above post, I've had brand freaking new rotors straight out of the box that were warped, with zero disk thickness variation. THAT is frustrating as hell.
Stewart
Tuned
Joined: Jan 2009
Posts: 265
Likes: 12
I'm not saying rotors don't warp (I've had sets brand new, out of the box that needed to be turned before they could be used) but I am saying it's not ALWAYS a warped rotor.
From what I've read on the 'net and in talking with my friend who owns a tire and brake shop locally to me, as well as my experience with my Ford trucks, there are many, MANY occasions where disk thickness variation or hot spotting/cementite creation (sometimes called "black spotting") is what is causing the pedal to shimmy.
http://www.powerbrake.co.za/download..._01_judder.pdf
EBC Brakes | Troubleshooting Information | Bedding in new brakes | Brake Noise / Squeal | Brake Vibration
If you Google "brake cementite" you'll get more reading.
Ease up a bit, skunk. We can discuss topics with each other and disagree without getting aggressive or condescending in attitude.
Stewart
From what I've read on the 'net and in talking with my friend who owns a tire and brake shop locally to me, as well as my experience with my Ford trucks, there are many, MANY occasions where disk thickness variation or hot spotting/cementite creation (sometimes called "black spotting") is what is causing the pedal to shimmy.
http://www.powerbrake.co.za/download..._01_judder.pdf
EBC Brakes | Troubleshooting Information | Bedding in new brakes | Brake Noise / Squeal | Brake Vibration
If you Google "brake cementite" you'll get more reading.
Ease up a bit, skunk. We can discuss topics with each other and disagree without getting aggressive or condescending in attitude.
Stewart
Super Moderator
Joined: May 2004
Posts: 29,380
Likes: 118
From: Central Coast of CA
I agree. And I should. But when educated people think they are devouring on you Because they like to use big words instead of common verbs and adjectives I find it funny. Don't worry I'm out on this one I don't wanna have to pull up 2 more pages 1 with the dictionary and 1 with a thesaurus so I can keep up in this conversation about brakes.
And really, you have good info, just when someone disagree's, or has another viewpoint, there's no need to take it personal. Aint nobody here trying to devour anyone.
As for big words, just because someone's vocabulary includes them, doesn't mean they are using words to be pushy on someone.
Ya might be full of **** and vinegar (as I've been accused, over the years), but remember to use honey when communicating on the 'net. You'll educate more people that way and even if someone disagree's with ya, they'll still like conversing with you because you present your info nicely!
It's all good. We're all here to try and help each other, not bap each other on the head.
Stewart
Moderator
Joined: Aug 2002
Posts: 6,100
Likes: 380
From: Southern California
The fact that the trucks became symptom free after changing their practice of cold water on hot brakes makes it likely (obviously) that the cold water was causing the problem. I say "likely" because few things in wrenching are for certain. Vehicles and symptoms can be diabolical and some things are never really figured out.
This scenario depends on whether or not it was real life or just a scenario. In real life this would be pretty surprising. Altho brake rotors can get damned hot, cooling is proportional to delta T so the hotter the rotors get, the faster they cool. The suspension and wheel offer a lot of surface area so once the brakes quit generating heat, the rotor temps would drop from "very" high to "pretty" high in seconds.
Can't be a metalurgical issues. Altho interesting things happen to cast iron at high temps, by the time Joe pulled out the water hose the rotors would have cooled enough that water wouldn't change the structure of the cast iron.
That's "structure" as in annealing and work hardening, not structure as in shape.
Since rotors are made of homogenous cast iron, heat expansion and contraction would be entirely symmetrical. So expansion and contraction alone would not be enough to cause the kind of off-axis rotation that would result in pulsating brakes. The likely culprit would probably be the combo of heat expansion and the exact nature of how the rotor was held in place by hub, studs/lug bolts, and wheels. Those fastening points would resist the rotor's attempts to expand and contract symmetrically. If there was some assymetry in fastenings, then rotor warpage is possible I suppose.
Why are we in this quiz show game? Some childish "stump the newby" thing? Why make this a contest of egos? You'll be 50 some day too. If I had a choice I'd much rather be 20. Man how I would burn thru the chicks if I could be 20 again <muses with a nostalgic grin>.
General thought aimed at no one in particular. Forums are anonymous. Some folks react to that anonyminity(sp?) by treating others poorly and looking for opportunities to declare how cool they are. Heck with that. Go spend your whole adult life as a Marine and Army Ranger. You'll get over the need to prove how cool you are each day, I promise. React to that anonyminity by being courteous and helping others where you can. That is the real measure of your worth.
This scenario depends on whether or not it was real life or just a scenario. In real life this would be pretty surprising. Altho brake rotors can get damned hot, cooling is proportional to delta T so the hotter the rotors get, the faster they cool. The suspension and wheel offer a lot of surface area so once the brakes quit generating heat, the rotor temps would drop from "very" high to "pretty" high in seconds.
Can't be a metalurgical issues. Altho interesting things happen to cast iron at high temps, by the time Joe pulled out the water hose the rotors would have cooled enough that water wouldn't change the structure of the cast iron.
That's "structure" as in annealing and work hardening, not structure as in shape.
Since rotors are made of homogenous cast iron, heat expansion and contraction would be entirely symmetrical. So expansion and contraction alone would not be enough to cause the kind of off-axis rotation that would result in pulsating brakes. The likely culprit would probably be the combo of heat expansion and the exact nature of how the rotor was held in place by hub, studs/lug bolts, and wheels. Those fastening points would resist the rotor's attempts to expand and contract symmetrically. If there was some assymetry in fastenings, then rotor warpage is possible I suppose.
Why are we in this quiz show game? Some childish "stump the newby" thing? Why make this a contest of egos? You'll be 50 some day too. If I had a choice I'd much rather be 20. Man how I would burn thru the chicks if I could be 20 again <muses with a nostalgic grin>.
General thought aimed at no one in particular. Forums are anonymous. Some folks react to that anonyminity(sp?) by treating others poorly and looking for opportunities to declare how cool they are. Heck with that. Go spend your whole adult life as a Marine and Army Ranger. You'll get over the need to prove how cool you are each day, I promise. React to that anonyminity by being courteous and helping others where you can. That is the real measure of your worth.
FYI- I had a MSE at a Ford dealer who simply didn't agree that this could happen, so I took the rotor into him, he mic'd it, agreed with the cold spec, but still disagreed that it could get worse and could "return" to its further deformed state when heat is applied....I told em go ahead, heat the rotor, they did with a torch while it was on the lathe, now I'm not saying that this is scientific in any way, because it is not, but, the rotor "warped" .008 after less than 1 minute of heat.
New User
Joined: Apr 2010
Posts: 16
Likes: 0
From: Savannah, GA
Also stated that we don't normally mic rotors once they've cracked. Why bother? But when we have brake shudder problems we just go out and do some hard laps ensuring that we brake hard as heck. And that fixes the problems pretty much every time. The exception is the rare occasion where there is some underlying problem that is forcing the rotor out of true.
Re. citing marketing materials. Big thumbs up for doing some research, that's really a big deal and I salute you. But you have to check a lot of sources and you have to be wary of "marketing".
Go back and check out who wrote the StopTech article. It was Carroll Smith, one of the premier race car engineers in the country. Note that there is certainly some overlap between what he said and the other sources cited.
In the end tho, this is a silly argument. If you've made up your mind, you're done. If you're not sure, do your own research, but just be wary of marketing materials. The racing community has a heck of a lot less tolerance than the DD community for exaggerated claims and shoddy physics, so that's something to think about.
Consider how the popular magazines tell us how one car has better brakes than another because of shorter stopping distances. Don't let people play you for a rube, the physics of racing is not rocket science. If people can't explain their assertions, don't buy it. If the test wasn't rigorous, don't buy it. No butt dynos, no CAI= 20hp, and no "these brakes stop you faster". Don't be trusting, do the research and demand explanations.
Tuned
Joined: Jan 2009
Posts: 265
Likes: 12
Not sure what you are waiting for. I discussed some of the failure modes of overheated DD pads. So far that's the only scenario I've read here that provided a possible explanation for different hot vs. cold behavior.
Also stated that we don't normally mic rotors once they've cracked. Why bother? But when we have brake shudder problems we just go out and do some hard laps ensuring that we brake hard as heck. And that fixes the problems pretty much every time. The exception is the rare occasion where there is some underlying problem that is forcing the rotor out of true.
Re. citing marketing materials. Big thumbs up for doing some research, that's really a big deal and I salute you. But you have to check a lot of sources and you have to be wary of "marketing".
Go back and check out who wrote the StopTech article. It was Carroll Smith, one of the premier race car engineers in the country. Note that there is certainly some overlap between what he said and the other sources cited.
In the end tho, this is a silly argument. If you've made up your mind, you're done. If you're not sure, do your own research, but just be wary of marketing materials. The racing community has a heck of a lot less tolerance than the DD community for exaggerated claims and shoddy physics, so that's something to think about.
Consider how the popular magazines tell us how one car has better brakes than another because of shorter stopping distances. Don't let people play you for a rube, the physics of racing is not rocket science. If people can't explain their assertions, don't buy it. If the test wasn't rigorous, don't buy it. No butt dynos, no CAI= 20hp, and no "these brakes stop you faster". Don't be trusting, do the research and demand explanations.
Also stated that we don't normally mic rotors once they've cracked. Why bother? But when we have brake shudder problems we just go out and do some hard laps ensuring that we brake hard as heck. And that fixes the problems pretty much every time. The exception is the rare occasion where there is some underlying problem that is forcing the rotor out of true.
Re. citing marketing materials. Big thumbs up for doing some research, that's really a big deal and I salute you. But you have to check a lot of sources and you have to be wary of "marketing".
Go back and check out who wrote the StopTech article. It was Carroll Smith, one of the premier race car engineers in the country. Note that there is certainly some overlap between what he said and the other sources cited.
In the end tho, this is a silly argument. If you've made up your mind, you're done. If you're not sure, do your own research, but just be wary of marketing materials. The racing community has a heck of a lot less tolerance than the DD community for exaggerated claims and shoddy physics, so that's something to think about.
Consider how the popular magazines tell us how one car has better brakes than another because of shorter stopping distances. Don't let people play you for a rube, the physics of racing is not rocket science. If people can't explain their assertions, don't buy it. If the test wasn't rigorous, don't buy it. No butt dynos, no CAI= 20hp, and no "these brakes stop you faster". Don't be trusting, do the research and demand explanations.
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Tuned
Joined: Jan 2009
Posts: 265
Likes: 12
LOL, you won't have to with those pages. They are pretty easy to read.
And really, you have good info, just when someone disagree's, or has another viewpoint, there's no need to take it personal. Aint nobody here trying to devour anyone.
As for big words, just because someone's vocabulary includes them, doesn't mean they are using words to be pushy on someone.
Ya might be full of **** and vinegar (as I've been accused, over the years), but remember to use honey when communicating on the 'net. You'll educate more people that way and even if someone disagree's with ya, they'll still like conversing with you because you present your info nicely!
It's all good. We're all here to try and help each other, not bap each other on the head.
Stewart
And really, you have good info, just when someone disagree's, or has another viewpoint, there's no need to take it personal. Aint nobody here trying to devour anyone.
As for big words, just because someone's vocabulary includes them, doesn't mean they are using words to be pushy on someone.
Ya might be full of **** and vinegar (as I've been accused, over the years), but remember to use honey when communicating on the 'net. You'll educate more people that way and even if someone disagree's with ya, they'll still like conversing with you because you present your info nicely!
It's all good. We're all here to try and help each other, not bap each other on the head.
Stewart
Tuned
Joined: Jan 2009
Posts: 265
Likes: 12
This guy has the right idea. It's almost always pad deposit. I race a BMW. Racers go thru more rotors in a year than most folks will go thru in a lifetime. Pad deposit problems are common. Less common is a rotor that is not on "square" and therefore causes pulsations. Warped rotors are quite rare.
.
.
Super Moderator
Joined: May 2004
Posts: 29,380
Likes: 118
From: Central Coast of CA
Well, no offense bro, but he truly qualified his post. It almost always is uneven pad material transfer.
I've found you can buy crappy rotors, but more commonly, problems are due to crappy pads.
Brake pedal shimmy is more often than not, cause by problems other than warped rotors. A warped rotor is just not as common as before.
That's NOT to say it doesn't happen, it's just not the first reason anymore.
Stewart
I've found you can buy crappy rotors, but more commonly, problems are due to crappy pads.
Brake pedal shimmy is more often than not, cause by problems other than warped rotors. A warped rotor is just not as common as before.
That's NOT to say it doesn't happen, it's just not the first reason anymore.
Stewart
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