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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 02-07-2005, 07:35 PM
bmw325 bmw325 is offline
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Question on using Racing Brake pads to cure rotor vibrations

My steering and brake pedal vibrate slightly when I apply the brakes over 60 mph. I'm assuming that this is likely due to uneven pad deposits (I've read enough from reputable sources to believe that there's really no such thing as "rotor warping"). To solve this, I could either buy new rotors and pads, or I could take the rotors to a shop and have them "turned" (not a good idea from what I hear)

I've also read that racing brake pads are much more abrasive than regular street pads. So, I'm wondering if a cheap and easy way to solve this issue might be to buy some racing pads for my front brakes, put them on, and apply the brakes at speed enough to "grind" down the existing deposits (but not enough to heat up the racing pads and allow them to form their own deposits).

Do you think this would work?
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  #2  
Old 02-07-2005, 07:46 PM
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Quote:
Originally Posted by robg
My steering and brake pedal vibrate slightly when I apply the brakes over 60 mph. I'm assuming that this is likely due to uneven pad deposits (I've read enough from reputable sources to believe that there's really no such thing as "rotor warping"). To solve this, I could either buy new rotors and pads, or I could take the rotors to a shop and have them "turned" (not a good idea from what I hear)

I've also read that racing brake pads are much more abrasive than regular street pads. So, I'm wondering if a cheap and easy way to solve this issue might be to buy some racing pads for my front brakes, put them on, and apply the brakes at speed enough to "grind" down the existing deposits (but not enough to heat up the racing pads and allow them to form their own deposits).

Do you think this would work?

You need to re-bed the pads to the rotors. This always works for me unless the rotors have been scorched.
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  #3  
Old 02-07-2005, 09:10 PM
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I run Pagid Orange pads and they too can leave deposits. It's changing your braking style that matters most. You're either keeping too much pressure at stop signs/lights or initially applying too much pressure when braking thus transfering pad material to the rotor's surface.
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  #4  
Old 02-07-2005, 09:37 PM
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Quote:
Originally Posted by robg
(I've read enough from reputable sources to believe that there's really no such thing as "rotor warping").
Rotors CAN and DO "warp"! They don't actually bend, but they can become wavy. We measure this all the time during development of vehicles. It is refered to as rotor thickness variation, and rotor runout. Brake rotors are a bit unstable from a materials standpoint, and can reshape slightly if too much heat is applied to them. Some of the best brakes I have tested were rotors that got hot and "warped", then we had them turned and they were great for a long time after that(Presumably because the internal stress of the material was relieved).
Quote:
Originally Posted by robg
To solve this, I could either buy new rotors and pads, or I could take the rotors to a shop and have them "turned" (not a good idea from what I hear)
It all depends on how much material is left on the rotor, and how bad the problem is. If it is fairly new and has a slight thickness variation, you only need to take off very little material, and they will be as good as new.
Quote:
Originally Posted by robg
I've also read that racing brake pads are much more abrasive than regular street pads. So, I'm wondering if a cheap and easy way to solve this issue might be to buy some racing pads for my front brakes, put them on, and apply the brakes at speed enough to "grind" down the existing deposits (but not enough to heat up the racing pads and allow them to form their own deposits).
Do you think this would work?
NO, I don't think this will work. YES, race pads are more abrasive, But not cheap. If your problem is in fact pad material transfer to the rotor, then a race pad will only add to the problem. Your theory on getting the pad just hot enough will never work, because a race pad needs to be HOT to work. When the pad is not hot, it is not effective and it's brittle, and when cold is actually is usually worse than a street pad.

Your best bet is new pads, and turn the rotors! If the rotors are too far gone, new rotors as well. I just don't understand why people always want the cheap route when it comes to brakes. Brakes are the #1 safety device a vehicle has... don't get cheap on them. Buy the parts, and do it yourself to save some money. A brake job is about one of the easiest do-it-yourself jobs that people never want to try themselves.
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  #5  
Old 02-07-2005, 10:06 PM
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Quote:
Originally Posted by Test_Engineer
Rotors CAN and DO "warp"!
According to Carroll Smith, they don't.
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  #6  
Old 02-07-2005, 10:35 PM
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Quote:
Originally Posted by SergioK
According to Carroll Smith, they don't.
Rotor Thickness variation is a "warped" rotor.

These little marks """""" means that I didn't actually say warp, just using it to keep consistant what the general public refers to as RTV or RO. Trust me, I have read the Carroll's article before, and completely agree. I am a mechanical engineer with a materials backround, now working as a development engineer on chassis and brake componets for an OEM. I deal with this everyday.

This is what I was talking about***********:

Last edited by Test_Engineer; 02-07-2005 at 10:37 PM.
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  #7  
Old 02-07-2005, 11:04 PM
Mr Paddle.Shift Mr Paddle.Shift is offline
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Quote:
Originally Posted by Test_Engineer
I am a mechanical engineer with a materials backround, now working as a development engineer on chassis and brake componets for an OEM. I deal with this everyday.


I think the street notion of warpage of a disc-like object is a deformation from it's side profile centerline axis. For a rotor that thick, I am not even sure what it takes to "warp" it by that notion, unless maybe with the rotor rotating, unidirectional braking forces are applied at, say, 3 and 9 positions and in the same direction.

The surface thickness variation is probably the standard measure of warpage. Believe it or not, a similar total thickness variation is a common measure of silicon wafers. ASTM even standardized the latter!
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  #8  
Old 02-08-2005, 04:21 AM
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Racing brake pads cost 2-3 times as much as new rotors.

http://www.eap4parts.com has the brembo front rotors for $38.90 each.
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  #9  
Old 02-08-2005, 05:01 AM
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Quote:
Originally Posted by robg
My steering and brake pedal vibrate slightly when I apply the brakes over 60 mph. I'm assuming that this is likely due to uneven pad deposits (I've read enough from reputable sources to believe that there's really no such thing as "rotor warping"). To solve this, I could either buy new rotors and pads, or I could take the rotors to a shop and have them "turned" (not a good idea from what I hear)

I've also read that racing brake pads are much more abrasive than regular street pads. So, I'm wondering if a cheap and easy way to solve this issue might be to buy some racing pads for my front brakes, put them on, and apply the brakes at speed enough to "grind" down the existing deposits (but not enough to heat up the racing pads and allow them to form their own deposits).

Do you think this would work?
No such thing as warped rotor? OK, how about getting rid of those concentric scratches first? Trying to cure a problem using abrasive brake pads? Are you serious? If you are willing to finagle a problem, I would try turning the rotors to eliminate the scratches which I think is causing the vibration. Go with softer pads too.
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Last edited by Dave 330i; 02-08-2005 at 05:05 AM.
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  #10  
Old 02-08-2005, 06:28 AM
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I "warped" my front Brembo rotors a few thousand miles after I installed Hawk HPS pads. I replaced the rotors with another set of Brembos and promply "warped" those within a few thousand miles. So I replaced the pads with Axxis Ultimates (same rotors) and by the time I finished the pad bedding procedure, most of the "warp" vibration was already gone. Within a few hundred more miles, it was entirely gone.

Fortuantely I saved the first set of "warped" rotors and they'll go back on the car when this set of rotors is finally worn.

So, yes this works and you don't need to go to full-blown race pads to accomplish it.

Plus, the Ultimates are great pads. Excellent stopping power and they don't need to warm up to work properly (like the Hawk HPS and all racing pads do).
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  #11  
Old 02-08-2005, 08:23 AM
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Try re-bedding your current pads first. Most times that will "cure" the deposit problem. If not, or if the build-up is really bad (moderate vibration) then have your rotors "skimmed". This involves taking a very small fraction of material off, usually its just the surface variation and doesn't get further into the rotor than that.

The theory behind using race pads to remove deposits comes from the difference between adherent friction and abrasive friction. Adherent friction is where a uniform layer of pad material is laid down on the rotor so friction comes from the making and breaking of the pad material (pad) and pad material (on rotor) at a molecular level. In other words, they both try to adhere to one another at temp. Generally this is the best type of friction for a braking system. Abrasive friction is just like its name sounds. Its where the friction is caused by the pad "grinding" on the rotor. This usually happens where an inappropriate pad (ie:racing) is used on a street application OR where regular pads weren't bedded in. There is no pad material transfer (bedding in) or the pad nevers gets to operating temperature (wrong type pad), thus just producing friction by abrading. While this works, its just not the best that it can be.

Now, where its good and cost effective is if you participate in track days or autocross and want to use a "racing" pad. Install the "race" pads before you drive to the track. Drive normally and don't get them hot. Obviously, only do this if its safe for you to do so. This will keep them in abrasive mode and clean off any "street" pad material. When you get to the track and have the opportunity, you should bed your "race" pads in. After your session, and you're on your way home, just keep the track pads in (AFTER they have cooled down). Use them gently, plan your stops, and don't get them hot. This will keep them in abrasive friction mode again and "take off" the pad material on the rotor that was laid down at the track. Again, don't do this if you can't get home safely. When you get home and after the pads have cooled, pop them out and put in your street pads. Bed these back in and you should be good to go until you next track day. More info here www.zeckhausen.com

Last edited by shortyb; 02-08-2005 at 08:36 AM.
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  #12  
Old 02-08-2005, 08:46 AM
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OK, I have a question.

So it seems important to properly bed-in a new set of pads. All the theories make sense here. But you're depositing a layer of friction material to the surface of the rotor. But that surface wears away continuously. Yet you pretty much never hear about re-bedding every 500 miles or whatever in order to re-bed the newly exposed surface. Does this automagically happen as you drive normally? It shouldn't, given the conditions under which it needs to happen during a traditional bed-in. Is the whole process just a crock? What gives?
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  #13  
Old 02-08-2005, 09:42 AM
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Quote:
Originally Posted by Kaz
OK, I have a question.

So it seems important to properly bed-in a new set of pads. All the theories make sense here. But you're depositing a layer of friction material to the surface of the rotor. But that surface wears away continuously. Yet you pretty much never hear about re-bedding every 500 miles or whatever in order to re-bed the newly exposed surface. Does this automagically happen as you drive normally? It shouldn't, given the conditions under which it needs to happen during a traditional bed-in. Is the whole process just a crock? What gives?
I'm no expert by far, but what I've read here http://www.stoptech.com/whitepapers/...otors_myth.htm it seems that the material layer gets regenerated by use. This is because the bonds are transient and can cross the interface of material between pad and rotor, and this is what can reform the material back onto the rotor. Unless the temperature exceeds the pad limit, the material is constantly kept fresh and uniform, thus eliminating the need to re-bed at given intervals.
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  #14  
Old 02-08-2005, 09:51 AM
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The point of bedding in the pads is that you start with an EVEN SURFACE. Once you've got that even surface, they'll wear and grip evenly, but if you don't do that, then you can have braking issues.

Does that make sense?
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Old 02-08-2005, 09:59 AM
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Originally Posted by Nick325xiT 5spd
The point of bedding in the pads is that you start with an EVEN SURFACE. Once you've got that even surface, they'll wear and grip evenly, but if you don't do that, then you can have braking issues.

Does that make sense?
This part makes sense. The 'depositing of material' is the part that doesn't.
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Old 02-08-2005, 10:20 AM
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Originally Posted by Kaz
This part makes sense. The 'depositing of material' is the part that doesn't.
Are you talking about the initial transfer (deposit) of material to the rotor?
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  #17  
Old 02-08-2005, 10:29 AM
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Interesting. I've read some seemingly conflicting opinions here from some very knowledgable people. "Rotor warping", "pad deposits" and "brake bedding" issues still seem murky. I would think that by now there would be a common understanding shared by automotive experts. I guess I don't see any harm in attempting to "re-bed" my current brakes to see if that solves the problem--worst case I buy new pads and rotors which I would've done anyway. While the process of initially "bedding" new rotors makes some sense to me, I don't really understand how "re-bedding" existing brakes could solve a problem of "baked on" uneven pad deposits. Unless the theory is that the rebedding process will also scrub away these existing deposits?
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Old 02-08-2005, 10:33 AM
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Quote:
Originally Posted by Kaz
This part makes sense. The 'depositing of material' is the part that doesn't.
The pad material on the surface is part of what the pads grip. When this isn't evenly distributed, you get wear in some areas and not so much in others.

That's one reason why new pads on new rotors have trouble.
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Old 02-08-2005, 10:34 AM
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Quote:
Originally Posted by robg
Interesting. I've read some seemingly conflicting opinions here from some very knowledgable people. "Rotor warping", "pad deposits" and "brake bedding" issues still seem murky. I would think that by now there would be a common understanding shared by automotive experts. I guess I don't see any harm in attempting to "re-bed" my current brakes to see if that solves the problem--worst case I buy new pads and rotors which I would've done anyway. While the process of initially "bedding" new rotors makes some sense to me, I don't really understand how "re-bedding" existing brakes could solve a problem of "baked on" uneven pad deposits. Unless the theory is that the rebedding process will also scrub away these existing deposits?
Yes, that's the idea. I've persnally never been able to do that successfully, but when I get pad deposits, I get them BAD.

Edit: The notion of spending $200 on pads to fix $80 of rotors is pretty laughable, though.
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Old 02-08-2005, 10:44 AM
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Quote:
Originally Posted by Nick325xiT 5spd
Yes, that's the idea. I've persnally never been able to do that successfully, but when I get pad deposits, I get them BAD.

Edit: The notion of spending $200 on pads to fix $80 of rotors is pretty laughable, though.
Guess that was oversite on my part-- I hadn't looked at the price for racing pads. Clearly, that was a bad idea. I will never think of it again.

I'll give re-bedding a shot- although I have a feeling that it probably won't solve my problem and that i'll end up buying new rotors and pads.
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Old 02-08-2005, 10:44 AM
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Originally Posted by robg
Guess that was oversite on my part-- I hadn't looked at the price for racing pads. Clearly, that was a bad idea. I will never think of it again.
Good job.

<--in asshole mode these days.
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Old 02-08-2005, 12:51 PM
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Quote:
Originally Posted by robg
Interesting. I've read some seemingly conflicting opinions here from some very knowledgable people. "Rotor warping", "pad deposits" and "brake bedding" issues still seem murky. I would think that by now there would be a common understanding shared by automotive experts. I guess I don't see any harm in attempting to "re-bed" my current brakes to see if that solves the problem--worst case I buy new pads and rotors which I would've done anyway. While the process of initially "bedding" new rotors makes some sense to me, I don't really understand how "re-bedding" existing brakes could solve a problem of "baked on" uneven pad deposits. Unless the theory is that the rebedding process will also scrub away these existing deposits?
Re-bedding with existing pads will work because, as the Stoptech papers say, no pad/rotor operates in purely adherent or abrasive mode. There are just different thresholds where these modes exist and that is a result of pad compounds, ie: race pads, street/OEM pads etc. Now its harder for a street/OEM pad to operate with a bias towards abrasive mode (given the pads were bedded in properly) because they are designed to operate well at lower temps. You CAN "fool" the pads somewhat by doing 2-3 quicks stops (25mph-10mph) when the pads are dead cold and they should operate in mostly abrasive mode. After that, they are usually at temp and biasing more 50/50 (again, if pads were bedded in correctly). Doing this a few times prior to a re-bed should help with some of the heavier deposits.
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Old 02-09-2005, 05:52 PM
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Quote:
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Plus, the Ultimates are great pads. Excellent stopping power and they don't need to warm up to work properly (like the Hawk HPS and all racing pads do).
The HPS are strictly street pads. They are a step down from the HP Plus pads, which are street/light duty track pads. Neither is a race pad and they do not require heating up. The Ultimates are about the same level as the HPS pads. Don't go anywhere near a fast racetrack with the Ultimates - they are only good on the street.
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Old 02-09-2005, 07:41 PM
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Originally Posted by Test_Engineer
Rotors CAN and DO "warp"! They don't actually bend, but they can become wavy. We measure this all the time during development of vehicles. It is refered to as rotor thickness variation, and rotor runout. Brake rotors are a bit unstable from a materials standpoint, and can reshape slightly if too much heat is applied to them. Some of the best brakes I have tested were rotors that got hot and "warped", then we had them turned and they were great for a long time after that(Presumably because the internal stress of the material was relieved).
so i am not quite sure what you are saying here, "they don't actually bend, but they become wavy..." and you also say that the rotors can reshape? so how does your explanation coincede with the idea that the "warping" is actually uneven pad deposits on the rotor surface?

and from the diagram that you posted later, it shows the rotor surface as wavy...is this local elastic deformation only due to heat, or is it plastic deformation that permanently changes the surface?
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Old 02-09-2005, 09:05 PM
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Quote:
Originally Posted by Ace
so i am not quite sure what you are saying here, "they don't actually bend, but they become wavy..." and you also say that the rotors can reshape? so how does your explanation coincede with the idea that the "warping" is actually uneven pad deposits on the rotor surface?

and from the diagram that you posted later, it shows the rotor surface as wavy...is this local elastic deformation only due to heat, or is it plastic deformation that permanently changes the surface?
Rotors and pads are a whole bag of problems waiting to happen, let it be deformation OR pad deposits. Heat is usually a local elastic deformation(in extreme cases can become plastic deformation), while pad deposits I would guess have some local plastic deformation. I've never had the chance to mount a cross section of a pad deposit, so I can't say for sure, but you can measure thickness variation and runout do to heat damage.
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