never ending warping rotor
- Thread starter journeyman291
- Start date
thaywood
Dedicated LVC Member
You lost me here.
I'm sorry. It's just my metallurgy class memories flooding back
Anyhoo, once the metal is warped, the internal moleculecular structure of the metal will hold that shape. Even if the outer surface is milled down perfectly flat, there will still be a warp present inside the metal itself. The best way I can think of to illustrate this is with an illustration:
So after you turn the rotor, you've still got a warped rotor, but it is now a warped rotor with flat outer surfaces and less material to regulate heat.
ford nut
Local nut case
Its cast iron....
slowmkviii
Dedicated LVC Member
Thaywood i think you are somewhat right
Except that you dont know why the rotor warped
So the inside structure may actually be straight
If the metal warped from even heat you probably released
Tension already in the steel but either way the tolerance in cast iron is not very
tight i dont think you will ever notice a thickness difference of. 020-.030.
Except that you dont know why the rotor warped
So the inside structure may actually be straight
If the metal warped from even heat you probably released
Tension already in the steel but either way the tolerance in cast iron is not very
tight i dont think you will ever notice a thickness difference of. 020-.030.
thaywood
Dedicated LVC Member
Yep. Unless you get a stainless steel rotor. But yeah. Most are cast iron. I know all about cast iron. I used to work in a cast iron foundry. We worked with high nickel content nodular iron.
As long as you don't get the rotor overly hot again it may never warp again after turning. I'm just wary of it because I've had issues in the past with turned rotors. I just feel safer replacing them with new ones.
sprocket
Well-Known LVC Member
I'm a machinist by trade and there is a serious flaw with the warped rotor/ stress theory. The flaw is the assumption that the "new" internal structure of the warped rotor (vs. the "old" internal structure of the previously straight rotor) is under stress. It TOOK stress and heat to get it warped but that doesn't mean it is under stress anymore. If it were under stress, then if you left it sit on a table, it would start to straighten out over time.
As an example, imagine a steel bar that is heated up with a torch and then bent to 90 degrees and allowed to cool in its new state. Once it cools and relaxes it has no stress and will stay in its new shape.
I do a lot of precision surface grinding where the whole point is to take a machined part that isn't flat (AKA, warped) and grind it so it is flat, sometimes less than .001". The parts DO stay flat after grinding. The only time there is a risk that they won't stay flat is if they are so warped to begin with that I have to PRESS them flatter on a hydraulic press before grinding. That DOES created internal stress and the part WILL want to move back, but that is NOT the way a rotor is warped.
On top of that, rotors are made from cast iron which has a very stable structure to begin with. Turning the rotor and making it THINNER, would make it warp easier but not by much because there is tolerances on how thin a rotor can be.
As an example, imagine a steel bar that is heated up with a torch and then bent to 90 degrees and allowed to cool in its new state. Once it cools and relaxes it has no stress and will stay in its new shape.
I do a lot of precision surface grinding where the whole point is to take a machined part that isn't flat (AKA, warped) and grind it so it is flat, sometimes less than .001". The parts DO stay flat after grinding. The only time there is a risk that they won't stay flat is if they are so warped to begin with that I have to PRESS them flatter on a hydraulic press before grinding. That DOES created internal stress and the part WILL want to move back, but that is NOT the way a rotor is warped.
On top of that, rotors are made from cast iron which has a very stable structure to begin with. Turning the rotor and making it THINNER, would make it warp easier but not by much because there is tolerances on how thin a rotor can be.
Markviiiedrea
Speed Bump
How many Machinist we got on this ship, anyhow?
I've sort of resorted to replacing rotors on my own cars instead of turning them (we have a nice Bendix at work) for longer rotor life. On my 94 Crown Vics with turned rotors I could only get 5k miles before I start to notice it slightly. With new rotors I can stand it for up to 30k miles. My son made it 30k on his 93 Mark Viii before we replaced the turned rotors. On my 2000 Explorer that I bought at 100k miles I turned the front rotors after owning it a few yrs but when I turned the rear rotors it made all the difference in the world and they are holding their own. Funny thing is, on my 96 Mark Viii I have gone 40k miles and the previous owner replaced all the pads and 2 rotors. I don't remember which rotors but it doesn't exhibit noticable pulsating unless extreme braking. The front pads are wearing into the rotors fairly deeply and will need replaced when the pads do (another 10k miles). I don't know what quality of pads he used but the fronts do exhibit black dust easily. My theory is that turning rotors will not dissipate heat as good and lead to earlier pulsating compared to new thicker rotors. The bigger the rotor on the car is to begin with the less problem hince my crown vic rotor problems over the yrs compared to the Mark Viii and Explorer.
Sprocket, my son works for a tool and die maker in the summers (he's a mechanical engineering student) and he deals with warpage in big, heavy, heat treated dies.
Sprocket, my son works for a tool and die maker in the summers (he's a mechanical engineering student) and he deals with warpage in big, heavy, heat treated dies.
slowmkviii
Dedicated LVC Member
Cool sprocket i am also a precision grinder
Sapperfire
Dedicated LVC Member
I wouldn't call myself a "machinist" but I've resurfaced 10s of 1000s of rotors and drums
As Optmanf said, people drive their cars on brakes that are embedded into the rotor deeply. If you machine a rotor and run it deep again, you run a chance of running it into the fins eventually... just not the most brilliant idea
As Optmanf said, people drive their cars on brakes that are embedded into the rotor deeply. If you machine a rotor and run it deep again, you run a chance of running it into the fins eventually... just not the most brilliant idea
Spree
Dedicated LVC Member
Why turn a rotor? There so cheap to buy new! I haven't turned a rotor since the 70's. Through them away and buy new!
Sapperfire
Dedicated LVC Member
Cuz was only "99.88" lol to machine the metal and replace the pads. Which is how some people get the huge misconception that this "fixes" brakes
slowmkviii
Dedicated LVC Member
Spree
Dedicated LVC Member
Dam! My cheap 13" rotors are original tho. I guess if they ever go bad (which they probably won't if they haven't by now) I'll just buy some more cheap 13" and call it a day!
I don't see any reason to put bigger rotors and bakes on when it doesn't stop you any faster!
Sapperfire
Dedicated LVC Member
Yes it does
Jacksun
Dedicated LVC Member
I don't understand people who constantly break accelerate. People need to learn to coast.
ford nut
Local nut case
To save money, material cost, rotors are cast thin now.
Resurfacing will not always give the desired results because of this.
They heat up fast and warp again..
It has little or nothing to do with the structure of the cast, unless you pay more from the start and buy a better cast rotor.
A turned rotor will be more inclined to warp again because of thickness and the disbursement of heat, not because the structure of the cast has changed.
Resurfacing will not always give the desired results because of this.
They heat up fast and warp again..
It has little or nothing to do with the structure of the cast, unless you pay more from the start and buy a better cast rotor.
A turned rotor will be more inclined to warp again because of thickness and the disbursement of heat, not because the structure of the cast has changed.
sprocket
Well-Known LVC Member
The more I think about it, the more trouble I have figuring out how a cast iron rotor can warp even with heat. I've never seen cast iron warp. When surface ground using coolant it is like mud coming off from it. Like sand.
I tend to not automatically accept things as true even when it has been said over and over. Warping cast iron just doesn't ring true to me. I could see how pad material could get stuck to the rotor in uneven distribution, causing brake pulse. That makes more sense to me.
I tend to not automatically accept things as true even when it has been said over and over. Warping cast iron just doesn't ring true to me. I could see how pad material could get stuck to the rotor in uneven distribution, causing brake pulse. That makes more sense to me.
Perhaps it is something to do with material from the pad embedding in the rotor. I'm extremely easy on braking and have had problems on my Vics and with my 83 Ranger in the past. Never wore out the pads, only had to turn rotors to get good pulse free braking.
thaywood
Dedicated LVC Member
Oh they warp
It's easy to see if you check with a micrometer. I haven't used one in years, but a plunger-style dial gauge micrometer can tell you exactly how much warpage is present in your rotor. Just mount the micrometer so that the tip is touching the rotor and rotate the rotor under it and watch the dial go back and forth. It's fun for the whole family!
slowmkviii
Dedicated LVC Member
Just to clarify so not to confuse newbies if they choose to go buy said tools.
Pic 1 micrometer
Pic 2 dial indicator
Pic 1 micrometer
Pic 2 dial indicator
Spree
Dedicated LVC Member
How do you know this?? People do mods on there cars and take them to the track and come up with quicker times!
Is it the mods or the reaction time of the driver that do the justice?
How do you know it's the bigger brakes/rotors?
Not trying to start a argument, but...Is it the brakes/rotors that stop a car quicker or the reaction time of the driver?
I have newer cars/and stuff, that have bigger rotors/brakes then this car and this stops faster then any of them in my opinion (with stock)!
I just never had any problems stopping on a (dime) in this car with stock brakes/rotors!
Was just wondering because of the "pole mod" that happened to your car! You had bigger brakes/rotors didn't you? Why couldn't you stop in time with the bigger stuff? Was it the road conditions or driver error? How do you know the "stock" wouldn't have been better or the same?
The main question is....what proof is there? Bigger brakes/rotors or reaction time?
Sapperfire
Dedicated LVC Member
Sapperfire
Dedicated LVC Member
People get what they ask for... everyone wanted better gas mileage.. in order to do that manufacturers had to reduce weight ..
Sapperfire
Dedicated LVC Member
The pole mod wasn't done by me, my wife was driving the car to me after she borrowed it. There was a connection issue with the ProChip I was using. The car shut itself off, she tried to steer it into a parking lot, but without power steering she couldn't turn it. It had stock everything at this time other than the tune
The pig mod was done by me thou, at about 70mph. He was the same color as the road. I didn't see it until he turned his head and I saw the eyes- which was too late
Think of a rotor as a Merry-Go-Round.. where's the best place to stop one.. from the center, or the outter edge where you get more leverage?
The disk size has two items to address: diameter and thickness. The diameter is easier to understand and easier to see. As a simple rule, the larger diameter of the rotor, the more force that is available to stop a wheel, just like using a longer wrench makes it easier to break a frozen bolt loose. If you kept the same caliper and same pads, but installed a larger diameter rotor, you would get greater stopping power. This power can be referenced in Newton-meters of torque. Factory rotors are sized according to many factors: wheel sizes, calipers used, unsprung weight, tires, price, etc. Initially, it would seem that the largest diameter rotor that can be obtained should be used, but those other factors must be kept in mind. Even, a reasonably larger diameter rotor will provide increased stopping power.The brake rotor thickness is more difficult to determine. The thickness of a rotor is proportional to the amount of heat we want to retain and dissipate, two very different properties. A properly designed brake system will take into account the optimal operating temperature of the rotors and the pads. A thin solid rotor will retain more heat than a thicker vented rotor. The key is to choose a rotor that will dissipate the excess heat, but still remain within the working temperature range of the brake pads. Some brake pads operate well while cold, others need some heat before they have any bite. The brake disk thickness must be chosen to match the pads and to match the driving that will be done. A short, tight road course (Las Vegas Speedway, 1.8 mile) may need different pads or possibly rotors. Due to the high demand for braking, more heat will need to be dissipated. We may need to use thicker rotors or higher temperature pads. A long open track (Road America, 4.0 miles) may need lower temperature pads or thinner rotors to order to keep some heat in the system. Different pads again may be needed for street driving. Another approach may to be to use a thick, vented rotor and adjust the amount of cooling air that is available to the rotor.Brake rotor material affects its thermal characteristics and friction and wear properties. I'm often asked about the prices of rotors and why some are more expensive than others. It is a simple matter of quality. Good rotors run truer and last longer. For your everyday car, you can go to the dealer and buy front rotors for $120 each, or you can go to your local discount auto parts store and get "the same part" for $20 each. Simple question: does your life depend upon a $20 rotor? Mine doesn't. Good rotors cost good money and my life is worth it.