warped rotors? - Page 2
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This is a discussion on warped rotors? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I didn't have the time before to find this link, but here it is: http://www.surrealmirage.com/subaru/brakes.html And here's a thread from ...

  1. #16
    Registered User thechickencow's Avatar
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    I didn't have the time before to find this link, but here it is:

    http://www.surrealmirage.com/subaru/brakes.html

    And here's a thread from altimas.net that has some good info mixed in with a bunch of BS. Pay attention to the posts by "Cobra" which are on the 3rd page. He exhibits some SERIOUS OWNAGE of the people that act like they know what they're talking about. This should take you to the page, just scroll down to his post to get an explaination.

    http://www.altimas.net/forum/showthr...5&pagenumber=3


    tcc

    Screw it...here's his post...

    Post by Cobra on altimas.net

    quote:
    --------------------------------------------------------------------------------
    I am going to be opinionated here for a bit, just like in the other post (the DZ coilover post). I am kinda tired of unqualified answers, so I speak from a personal and professional experience with brakes.
    Here we go.
    --------------------------------------------------------------------------------

    My advice - pick a new profession. Something simple. Perhaps - a Wal-Mart greeter. Your qualifications are almost adequate for that.

    quote:
    --------------------------------------------------------------------------------
    Crossdrilled rotors-by design, crossdrilled rotors were designed for track use. Why? Because, when you drill holes in your rotors, they are designed to dissipate heat (not to rid of brake dust as most people think).
    --------------------------------------------------------------------------------

    I found the root of your problem. It is right here. You don't know the definition of "dissipate". You also don't understand the interaction between a rotor and the pads. Here is how it works. The friction between the pad and rotor is what causes you to stop. This friction converts your forward energy into heat (remember Einstein: Energy is neither created nor destroyed, it is converted). Now that heat is a bad thing. Yes it is bad for the rotors but it is a lot worse for the pads. A warped rotor will still stop the car - it will just feel like ****. Overheated pads however WILL NOT stop the car. It is here where the rotors secondary responsibility comes in. Its job now is to DISSIPATE the heat away from the pads and DISPERSE it through itself. Notice that DISSIPATE and DISPERSE are interchangeable? Once the heat is removed from the pad/surface area it is then removed. Notice where the removal falls on the list of duties? That's right - number 3. Here is the list again. Memorize it because I will be using it a lot in this post:

    #1 Maintains a coefficient of friction with the pad to slow the forward inertia of the vehicle

    #2 DISSIPATE the heat

    #3 REMOVE the heat from the brake system

    Let's look more in-depth at each step now shall we? No? Too bad assclown we are doing it anyway.

    #1 Maintains a coefficient of friction with the pad to slow the forward inertia of the vehicle:
    This one is pretty simple and self-explanatory. The rotor's surface is where the pads contact and generate friction to slow the vehicle down. Since it is this friction that causes the conversion of forward acceleration into deceleration (negative acceleration if you want) you ideally want as much as possible right? The more friction you have the better your stopping will be. This is reason #1 why BIGGER brakes are the best way to improve a vehicle's stopping ability. More surface area on the pad and the rotor = more friction = better stopping. Does that make sense Ace? Good. Let's move on.

    #2 DISSIPATE The Heat:
    Let's assume for a second that the vehicle in question is running with Hawk Blue pads on it. The brand doesn't really matter but that is what I am using as my example. They have an operating range of 400 degrees to 1100 degrees. Once they exceed that 1100 degree mark they fade from overheating. The pad material gets too soft to work effectively - glazing occurs. This means that a layer of crude glass forms on the surface of the pad. As we all know glass is very smooth and very hard. It doesn't have a very high coefficient of friction. This is bad - especially when I am coming down the back straight at VIR at 125MPH. Lucky for us the rotor has a job to do here as well. The rotor, by way of thermal tranfer DISSIPATES the heat throughout itself. This DISSIPATION lessens the amount of heat at the contact area because it is diluted throughout the whole rotor. The bigger the rotor the better here as well. The more metal it has the more metal the heat can be diluted into. Make sense? This isn't rocket science here d00d.

    #3 REMOVE the heat from the brake system:
    Now comes your favorite part of the process. This is what you thought DISSIPATION was. It is ok. I will allow you to be wrong. This is the step where the rotor takes the heat it DISSIPATED from the pads and gets rid of it for good. How does it do this? By radiating it to the surface - either the faces or inside the veins. It is here where cool air interacts with the hot metal to cool it off and remove the heat. Once again there is a reoccuring theme of "the bigger the better" here. The bigger the rotor, the more surface area it will have which means more contact with the cooling air surrounding it. Got it? Good.

    Now let's look at why cross-drilling is a bad idea.

    First - as we have already established, cross-drilling was never done to aid in cooling. Its purpose was to remove the worn away pad material so that the surfaces remained clean. As we all know this doesn't have much of a purpose nowadays.

    Next - In terms of cooling: Yes - x-drilling does create more areas for air to go through but remember - this is step 3 on the list of tasks. Let's look at how this affects steps 1 and 2. The drilling of the rotor removes material from the unit. This removal means less surface area for generating surface friction as well as less material to accept the DISSIPATED heat that was generated by the friction. Now because of this I want to optimize step one and 2 since those are the immediate needs. If it takes longer for the rotor to get rid of the heat it is ok. You will have a straight at some point where you can rest the brakes and let your cooling ducts do their job. My PRIMARY concern is making sure that my car slows down at the end of the straight. This means that the rotor needs to have as much surface as possible to generate as much friction as possible and it needs to DISSIPATE the resulting heat AWAY from the pads as quick as possible so they continue to work. In both cases x-drilling does nothing to help the cause.

    Now let's talk about strength - and how x-drilled rotors lack it. This one is simple. Explain again just how drilling away material/structure from a CAST product DOES NOT weaken it? Since you are obviously a man of great knowledge and experience surely you have seen what can happen to a x-drilled rotor on track right? Yes it can happen to a non-drilled rotor as well but the odds are in your favor when pimpin' bling-bling drilled y0! Since you are also an expert on thermodynamics why not explain to the group what happens to a cast iron molecule when it is overheated. I will give you a little hint - the covalence bonds weaken. These bonds are what hold the molecules together boys and girls. You do the math - it adds up to fractures.

    So why don't race teams use them if they are so much better? Consistency? Hmmmm . . . no. I am gonna go with the real reason her chodeboy. It is because of several factors actually. They are as follows but in no particular order:

    - Less usable surface area for generating friction
    - Less material to DISSIPATE the heat away from the pads
    - Less reliable and they are a safety risk because of fatigue and stress resulting from the reduced material

    And what are the benefits? Removal of particulate matter and enhanced heat removal. I gotta tell ya - it is a tough choice but I think I am going to stick with the safe, reliable, effective-for-my-stopping needs solution Tex.

    Finally let's talk about you. You should be ashamed of yourself. You are obviously regarded as a sort of demigod here. I am not quite sure why but the little toadie sticking up his fingers and saying "don't argue with THE MAN" is evidence that there are quite a few lemmings here just waiting to follow you off the nearest cliff. A vendor should really take knowledge and understanding of the products he recommends and sells a little more seriously. Further - who the fvck quotes Super Street as a reliable source of tech info of any kind? That smut is as useful for auto tech as is Cosmopolitan. Only a fool would EVER use claims made by that publication as facts in an argument. Your bad advice is going to get one of these new guys killed because they think you know your ****, they are going to take your advice, and then they are going to careen head on into a retaining wall at 120MPH because the part YOU recommended them failed at race speeds. Fvck you ****head! You may not care if that blood is on your hands but I will do what I can to make sure it isn't on mine.

    Most of you lemmings will stick your little fingers up at me but I know a few of you will read my words and the words of the others here who are trying to set the record straight. I don't expect any of you to take any of this advice here as scripture. I urge you all to go and do some research. Talk to more than just the ****head in this thread. Find out what people who ACTUALLY race are doing and why they are doing it. I have news for you all. There is no "better" idea. It has all been done before. If it worked people would do it now.

    Commence the banning since I am not willing to swing from the jock of this fool.

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  3. #17
    Registered User ScoobySteve's Avatar
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    Well, Jay - we're in some danger of highjacking dark_rex's thread here, but here goes:

    1st link - Well-reasoned. I don't think it really contradicts what I posted. Interesting that he states the leading cause of rotor warpage is heat / cool cycles, running it hard so that the heat soak from the pads/calipers will cause warpage in that portion of the rotor. Very plausible but that hardly seems to be dR's situation, given the info he has given us.

    2nd link - The Cobra ? Some rude *sshole posting on an Altima board ? LOL, dude. His opinion is no more credible than yours or mine. What truly expert racer interested in helping others would post something like that ?
    Old, but not slow.

  4. #18
    Registered User thechickencow's Avatar
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    I still think that the post by cobra was well reasoned, and he knows what he's talking about. (read 2 posts down on the altima board post for his credentials)

    Either way, doesn't matter to me. I am in agreement with him, and will probably never put cross drilled rotors on a car I have because even with autox, rallyx, and occasional track days I won't push my brakes hard enough to need to worry about it. Like I said before, I don't doubt that a cross drilled rotor will perform better than stock, I don't think it is ideal for pretty much anybody on this board. If others choose to fine, I personally just think they are more for show than anything else for 99% of the people that put them on their street cars. I wonder what Gary S. puts on his car.

    sorry to continue the hijack.

    tcc

  5. #19
    tan
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    Penguinking : it's turning the rotors. After it's turned on the lathe, the finishing operation is manual sanding in a circular motion, so that pads will bed properly.

    missed reason also: Anyone want to take a gander at what causes "brake fade"? Heat from the rotor and the pads release a gas which reduces the pad to rotor contact (it's like hydroplaning). Slots and holes allows for displacement of that gas, to maintain the pad to rotor contact.

    Yes, many people will encounter still this on day to day driving if caught in situations of long stop-and-go traffic.
    Last edited by tan; 10-10-2002 at 06:32 AM.

  6. #20
    Banned dark_rex's Avatar
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    Originally posted by blackshadow
    My car shakes badly too. It only does it when i brake semi hard (or harder) at speeds above 60... is this what you're experiencing dark_rex? I only have 7000 miles and i don't ride the brakes.
    same exact thing.

    brake fade is caused in part by escaping gasses from the heat transfer, but more oftenly, and almost ALWAYS on the track, from increased heat glazing the pad surface over. cross drilled rotors are designed to dissipate/disperse heat. slotted is for the removal of gasses, heat, and excess material/glazing from the pad.

    if subaru tells me their going to turn my rotors, i'm walking out. i've turned rotors since i was 16 in the back of dad's store. i can do that myself, and not have to worry about the tech taking betty for a joyride (caught them twice doing this)

    i'm a good salesman. they'll be replaced if i have anything at all to do with it.

    that guy like to make himself sound smart (in the nissan thread) i'm sure he's qualified, but braking is NOT that complicated. he just wanted to belittle someone imo.

    dR

  7. #21
    Banned dark_rex's Avatar
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    talked to my service man oscar. they're going to turn the rotors, b/c if i do it, i'll screw my chances of getting them replaced.

    the deal is, they turn them once, and if it starts again, they replace them.

    the wrx uses double planed rotors, so even after they turn them, one plane will still be warped. i imagine it will only take a few HARD brakes to re warp it further ,as the supporting plane will be already weakened.

    i want new rotors, this seems like the path to get them.

    dR

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