alan-g-w
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Location: Glasgow
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quote:
Originally posted by AK
quote:
Originally posted by alan-g-w
Why would these pad deposits not be rubbed off by the pads when you clap them on at 100mph though AK? If I'm correct, you're saying they leave deposits if the disc gets so hot that it melts the pad onto it. Say you were braking from 100mph, surely the pad material would then be heated up and rubbed off the surface of the disc?
And for anyone that's saying it's all about heating them up until they're pliable - who says they need to be pliable to bend them? If I was to take a disc off my car and whack it with a ball pein hammer it'd dent it wouldn't it? Obviously your pads in the caliper's not really the same but just because a disc isn't at 1200degrees doesn't mean it can't change shape.
HEAT SPOTS....
the pad deposits create different surfaces so certain spots get hotter and build up more deposits
You've clearly missed my whole point.
You say you get pad deposits on the disc from the disc being so hot they 'melt' onto it. How in the name of fuck can you claim that these bits of pad then become the same hardness as the metal of the disc? If it happens by sitting at the lights with your foot on the brake, surely the next time you went on a spirited drive, heated up the discs but USED the brakes at the same time the fact that these pad deposits are getting heated up to their 'melting point' (ie - the same temp they were when you were sitting at the lights with the pads clamped creating them) would mean that the pads would wipe the disc clean? How would the pad deposits be so hard that they could stand up to that?
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Steve
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Registered: 30th Mar 02
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quote:
Originally posted by Graham88
quote:
Originally posted by Steve
how can you argue that you are confident, yet a place that actually builds brake systems are saying its a myth? do you not feel they are more in a position of confidence? or do you have evidence to suggest otherwise?
Yes. The brake discs attached to my car.
and how are they proof to backup your theory? as far as i know they were juddering and you assumed it was warping. Have you had them checked for warping?
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Steve
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Registered: 30th Mar 02
Location: Worcestershire Drives: Defender
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quote:
Originally posted by alan-g-w
quote:
Originally posted by AK
quote:
Originally posted by alan-g-w
Why would these pad deposits not be rubbed off by the pads when you clap them on at 100mph though AK? If I'm correct, you're saying they leave deposits if the disc gets so hot that it melts the pad onto it. Say you were braking from 100mph, surely the pad material would then be heated up and rubbed off the surface of the disc?
And for anyone that's saying it's all about heating them up until they're pliable - who says they need to be pliable to bend them? If I was to take a disc off my car and whack it with a ball pein hammer it'd dent it wouldn't it? Obviously your pads in the caliper's not really the same but just because a disc isn't at 1200degrees doesn't mean it can't change shape.
HEAT SPOTS....
the pad deposits create different surfaces so certain spots get hotter and build up more deposits
You've clearly missed my whole point.
You say you get pad deposits on the disc from the disc being so hot they 'melt' onto it. How in the name of fuck can you claim that these bits of pad then become the same hardness as the metal of the disc? If it happens by sitting at the lights with your foot on the brake, surely the next time you went on a spirited drive, heated up the discs but USED the brakes at the same time the fact that these pad deposits are getting heated up to their 'melting point' (ie - the same temp they were when you were sitting at the lights with the pads clamped creating them) would mean that the pads would wipe the disc clean? How would the pad deposits be so hard that they could stand up to that?
and you're missing his point hes not saying bits of pad are left on the disk are causing the juddering, hes saying the bits of pad stamped onto the disk alter the properties of the disk at the point they were pressed on.
as far as your point stands you are semi correct, because you can get rid of heat spots on the disks by regrinding them. However using your brakes hard wont achieve it
either new disks, or regrind, usually the cost of new disks is similar to a regrind so most people do that
[Edited on 08-02-2011 by Steve]
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Steve
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read that article i posted, its from someone that knows a hell of a lot more then anyone on here, so that is the advice that i am going to take and believe. Not from a bunch of people with made up theories based on nothing more then logic in there own heads
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Steve
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Registered: 30th Mar 02
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Heres some more reading for you
http://www.examiner.com/auto-in-orlando/there-s-no-such-thing-as-warped-brake-rotors
There's no such thing as 'warped' brake rotorsJuly 10th, 2009 1:11 am ET
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Red-hot brakes/courtesy of siemens.com For as long as the disc brake setup has existed, drivers who report a brake vibration or pulsation during high-speed braking (such as exiting a highway) have brought their vehicles into a service station and been told the rotors are 'warped.' The consensus is that if the brakes get hot enough during service, the rotors warp under the heat and variations in their thickness occur. The belief is that as the pads ride over these undulations, the braking power rapidly increases and decreases, causing a vibrating or pulsating sensation.
The remedy for 'warped' rotors is to grind them down and resurface them to restore a uniform surface and smooth out the brakes.
However, badly 'warped' rotors frequently repeat their vibrating in a short period of time, and are then completely replaced to eliminate the problem for good.
Well, the truth is, brake rotors do not warp at all, and a simple recommendation can save you a lot of money at your next brake services and the future ones to follow.
According to this magnificent article from StopTech, the cause of brake vibrations or shimmies is the result of uneven transfer of brake pad material to the rotor, thus causing the variations in the rotor surface.
Standard road cars use brakes that function mostly by abrasion, or the breaking down of the bonds between the pad material molecules by the friction generated by pushing the pads against the rotors. Under normal city conditions, the worn-away pad material is simply carried away as brake dust (the black dust commonly seen on wheels). However, under heavier braking, such as an emergency stop or slowing down from a highway exit, the brakes become much hotter, and that material can actually 'cook' to the brake rotors.
The best way to aid in this 'cooking' process is to keep the pads in constant pressurized contact with the rotors... by remaining firmly on the brakes after the vehicle has come to a complete stop.
As the pad material bonds to the rotor, the surface of the rotor then becomes uneven, and the brakes begin to vibrate at high speeds. The brake rotors do not warp, however. Even the most extreme braking conditions on public roads do not generate enough heat to cause the brake rotors to warp.
In reading the StopTech article and following its advice, I have safely avoided ever 'warping' rotors or experiencing any brake vibrations in over 100,000 miles of driving in many different vehicles.
To euphemize this as best as possible... I'm not exactly the slowest driver in the world. As a result of my driving style, I wear out two automotive components far more quickly than the average driver: tires and brake pads.
For example, a vehicle I used to drive a few years ago once needed brake pads at only 18,000 miles. However, that vehicle's rotors were in pristine condition at the time of the brake service, having no inconsistencies in thickness or braking surfaces, thus requiring no resurfacing.
On another occasion, I wore down a different vehicle's brake rotors to the point where a ¼-inch deep valley was formed in the rotor by several sets of brake pads. The rotors of course had served their purpose and needed replacement, but the brakes never shimmied or pulsated at any time.
I've also done numerous premature brake jobs on my personal vehicles, not just as a result of my lead foot, but because of a few autocrosses and rallycrosses along the way. But not once have I needed to replace or resurface rotors.
I follow this one simple rule to avoid brake vibrations: when I come to a hard stop, I immediately release the brakes completely as soon as the car is stopped. I even go so far as to take the vehicle out of gear to ensure that it does not move when I release the brakes. This disallows the brake pads to transfer the worn material onto the rotor.
Now, as the StopTech article points out, rotors that are already heavily embedded with pad material, and thus full of vibrations, are likely ruined. The 'cooked'-on pad material is called cementite, and it is pretty much permanent, where no amount of resurfacing can remove it.
So, if you're currently driving a vehicle with excessive brake vibrations, simply have the rotors replaced at your next brake service, and follow the rule of releasing the brakes completely after a hard stop from then on.
By doing so, only your brake pads will require replacing at your next brake service, thus saving you time and a lot of money.
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Steve
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Registered: 30th Mar 02
Location: Worcestershire Drives: Defender
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Soembody heres who investigated stop techs claims
They do not cause the pulsating brakes everyone complains about. That is from cementite inclusions in the cast iron.
http://www.stoptech.com/tech_info/w...brakedisk.shtml
I've personally confirmed their claims with a scanning electron microscope. Perks of being a BioChem major back in college.
If you think about it, calipers (floating and fixed) are designed to put equal pressure on both sides of the rotor. If the rotor is warped, either the caliper moves (floating caliper) or the caliper transfers fluid. Even if it didn't, when the warped part comes around, it would add friction to one side and remove it from the other, keeping mean friction similar throughout the rotation.
machining rotors removes cementite inclusions, but if you don't properly bed in new pads, you'll be back at square one in a week or less. Its happened to me many times with my track pads. within a week there was little or no runout, but the pulsing was unbearable. I've also had rotors with lots of runout and no pulsing at all.
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Steve
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Registered: 30th Mar 02
Location: Worcestershire Drives: Defender
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More
http://www.cleanmpg.com/forums/archive/index.php/t-13246.html
i could go on
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chrisritch
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Registered: 2nd Sep 08
Location: Northants Drives: V40
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someone in here going to have a fight?
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Ben J
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Registered: 31st Jan 05
Location: Cheshire
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I think.....I couldn't give a shit.
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AK
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Registered: 5th Jul 00
Location: Aberdeen City
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quote:
Originally posted by alan-g-w
quote:
Originally posted by AK
quote:
Originally posted by alan-g-w
Why would these pad deposits not be rubbed off by the pads when you clap them on at 100mph though AK? If I'm correct, you're saying they leave deposits if the disc gets so hot that it melts the pad onto it. Say you were braking from 100mph, surely the pad material would then be heated up and rubbed off the surface of the disc?
And for anyone that's saying it's all about heating them up until they're pliable - who says they need to be pliable to bend them? If I was to take a disc off my car and whack it with a ball pein hammer it'd dent it wouldn't it? Obviously your pads in the caliper's not really the same but just because a disc isn't at 1200degrees doesn't mean it can't change shape.
HEAT SPOTS....
the pad deposits create different surfaces so certain spots get hotter and build up more deposits
You've clearly missed my whole point.
You say you get pad deposits on the disc from the disc being so hot they 'melt' onto it. How in the name of fuck can you claim that these bits of pad then become the same hardness as the metal of the disc? If it happens by sitting at the lights with your foot on the brake, surely the next time you went on a spirited drive, heated up the discs but USED the brakes at the same time the fact that these pad deposits are getting heated up to their 'melting point' (ie - the same temp they were when you were sitting at the lights with the pads clamped creating them) would mean that the pads would wipe the disc clean? How would the pad deposits be so hard that they could stand up to that?
No - you're missing the point!
I'm not saying pads are melting at all.
Go out do some VERY hard braking, then come to a full stop and leave your foot planted on the brakes. Leave for 10 mins then let them cool. Remove the disc and have a look at it. You will see a pad shaped mark on the discs. This area will generate more heat in the future (aswell as creating an uneven surface) that will create a different friction surface / 'use' a differing amount of pad material in the future. Simply USING your brakes doesnt clean the discs of pad material. Discs NEED pad material on them to make them work properly.
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AK
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Location: Aberdeen City
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see here - http://www.trackscotland.co.uk/forums/viewtopic.php?t=3&postdays=0&postorder=asc&start=105
my warped disc with a pad shaped mark... funny that eh!
funny how the pad shape is nearly always at the same point.... different friction properties, causing uneven depositing of pad material... MAKING JUDDER WORSE
[Edited on 08-02-2011 by AK]
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alan-g-w
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Location: Glasgow
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If the pads aren't melting onto the discs what is causing the uneven surface?
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AK
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Registered: 5th Jul 00
Location: Aberdeen City
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PAD MATERIAL ON THE DISC.
Do you know what melting means?
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alan-g-w
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Location: Glasgow
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How is that pad material getting to be stuck to the disc?
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AK
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Location: Aberdeen City
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quote:
Melting, or fusion, is a physical process that results in the phase change of a substance from a solid to a liquid. The internal energy of a substance is increased, typically by the application of heat or pressure, resulting in a rise of its temperature to the melting point, at which the rigid ordering of molecular entities in the solid breaks down to a less-ordered state and the solid liquefies. An object that has melted completely is molten.
The pads arent turning into liquid!
Rub a rubber on a page. Feel the resistance? Thats friction. Thats your pad on a disc. See the rubber bits left behind? Thats your pad material!
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Ojc
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Registered: 14th Nov 00
Location: Reading: Drives : Clio 197
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This thread has made me angry
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alan-g-w
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Registered: 9th Nov 07
Location: Glasgow
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quote:
Originally posted by AK
quote:
Melting, or fusion, is a physical process that results in the phase change of a substance from a solid to a liquid. The internal energy of a substance is increased, typically by the application of heat or pressure, resulting in a rise of its temperature to the melting point, at which the rigid ordering of molecular entities in the solid breaks down to a less-ordered state and the solid liquefies. An object that has melted completely is molten.
The pads arent turning into liquid!
Rub a rubber on a page. Feel the resistance? Thats friction. Thats your pad on a disc. See the rubber bits left behind? Thats your pad material!
No need to patronise me mate, I ignored that question for a reason.
My point is how does this pad material become stuck fast to the disc? Why does it require to be grinded off, how would the pads not just clean up the discs? Since they're the same material the pads should be abrasive enough against the deposits and get rid of them surely?
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Chris x
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Registered: 11th Sep 08
Location: Bexhill
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I warped my old 1.2 8v discs  
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_Allan_
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Registered: 24th Mar 04
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quote:
Originally posted by alan-g-w
My point is how does this pad material become stuck fast to the disc? Why does it require to be grinded off, how would the pads not just clean up the discs? Since they're the same material the pads should be abrasive enough against the deposits and get rid of them surely?
The material build up will either no longer be effectively swept by the pad surface or the material bonded to the disc with the heat generated, is harder than the pad material trying to scrub it. You are talking fractions of a mm and not always visible to the eye for the driver/rider to feel a judder/vibration.
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AK
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Location: Aberdeen City
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that area of the disc has now changed. It doesnt 'wear' the pad at the same rate as the unheatspotted area of disc.
More and more pad material gets 'stuck' making the judder worse and worse.
I'm not trying to patronise you, simply trying to make you understand (that you arent getting your cast iron hulk of metal hot enough to distort).
You can groove discs easy enough.... run your finger up and top the face and you'll feel grooves (like the lip on the outside). This is just from inconsitant material wear
[Edited on 08-02-2011 by AK]
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alan-g-w
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I just watched that video in the original post for the first time. It's confirmed what I've thought all along as far as I'm concerned, have you actually watched it? it shows you him sticking a DTI on the deck I'm guessing and puts the finger of the clock against the disc. The disc in question on a standard UK Impreza WRX is without a doubt 100% warped by the way that the clock moves in a uniform manner. If it was pad deposits in this case the clock would be all over the place, but instead it goes from 30-85 (anticlockwise) and then 85-30 (clockwise).
The disc on that impreza in that video is warped. That fat cunt Mike complained of a 'shuddering while braking'. It is not down to pad deposits at all, so how can you say that you cannot warp a disc after seeing it with your own eyes?
Apart from the fact that the mechanic on that show clearly knows a thing or two and he's the one making these claims. I'm more inclined to believe him than a bunch of internet links.
[Edited on 08-02-2011 by alan-g-w]
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AK
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rigght....
you keep thinking your distorting the metal through heat!
The runout gauge will do the same for pad deposits too  they tend to be in the same place as I clearly showed in the pic above.
Ignorance is bliss Do you really think a TV program is gospel. Do you believe everything on Top Gear?
exactly....
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alan-g-w
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You've clearly not got a clue, the DTI would not act like that with pad deposits. I'm telling you that disc is warped by the way the clock is acting.
And why would a mechanic that's seemingly pretty experienced to be fitting a new clutch to an impreza not know about pad deposits if that was in fact the cause?
I'm not claiming that pad deposits don't exist. I am sure that you can warp the discs on your car though.
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AK
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Location: Aberdeen City
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you believe what you believe.
I'll believe what i've experienced.
Sorted.
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alan-g-w
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Location: Glasgow
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Ironic that you were just telling me that ignorance is bliss.
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