Brembo vibration?

[NSXRguy]

I bought a used set brembo gran turismo for the nsx. Previous owner said around 10k on them.

Anyways, when driving speeds hit like 30+ and i press slightly on the brakes, the steering wheel will start shaking. If i press harder and harder, it doesnt vibrate.

Is this normal for a bbk? Would an improper break in cause this?

 

[swerve2007]

most likely the rotors are warped. if the deviation is not extreme, they can be resurfaced on the lathe while trying to remove as little material as possible (which means- take it to someone that cares).

 

[docjohn]

before you go resurfacing(turning) go to the hardware store and get some abrasive sandpaper or other abrasive instrument and just hand buff the rotors,of course taking the wheels off ect....you may just have uneven pad deposits that will cause this...In fact I have to do the same after my recent track event.

 

[CL65 Captain]

most likely the rotors are warped. if the deviation is not extreme, they can be resurfaced on the lathe while trying to remove as little material as possible (which means- take it to someone that cares).

Warped rotors are a myth. It is possible, but not very likely. Most people chaulk up brake judder to a warped rotor when it's actually uneven pad deposits. Sandpaper doesn't work - have tried that. Same with steel wool.

You have two choices. Buy a set of Hawk Blue pads and put them on. Hawk Blues are VERY abrasive when cold. Go out and give a few hard stops, but make sure to let the rotors cool in between. The goal is NOT the same as bedding in the pads. You don't want the Hawks to get hot enough to transfer material to the rotors. You are just using the cold abrasive nature of the pads to scrub off the rotors. You can also just leave the Blues on for a few days with normal driving. When you begin to hear them squeal when coming to a stop and/or the rotor looks shiny then you are good to go. Second choice is to go have the rotors turned to give you a fresh surface and re-bed in the pads.

I have a set of Hawk Blues that I use just for this. I use them when switching between street and track pads. You don't want street pad material on the rotor because it will overheat and begin to smear and create bad judder. PFC01 pads are very finicky about this.... they need a fresh rotor surface or they judder so bad that you think you broke something in the suspension.

BTW: Hawk Blues for the Brembo are $150. Turning the rotor is $20-30. If you are just going to do this once, the choice is easy. If you plan on switching back and forth between pads or plan on using the brakes hard (like at the track where the temps go 600+) then get a set of Hawk Blues to keep in the garage for periodic cleaning duties.

 

[docjohn]

A good sanding has worked for me in the past and peter Mills as well...so maybe the capt needs to rub harder

 

[NSXRguy]

how should i sand the rotors? what grit? direction for sanding?

 

[swerve2007]

Warped rotors are a myth. It is possible, but not very likely.

frankly i am puzzled here- i've seen it more than few times, including 2 sets of warped OEM rotors that came off my nsx. while resurfacing them it was very obvious they were warped and not just by a little bit but about .040 in (1mm) in runout- much more than any uneven pad deposit.

 

[docjohn]

how should i sand the rotors? what grit? direction for sanding?

I use a metal scotchbright pad followed by 100 grit aluminum oxide sandpaper,and rub like hell Only hurts for awhile but ohh the chaffing:redface: Anyway give it a shot.If that dos'nt work your local dealer/race shop might be able to lathe(turn) them on the car.

 

[nsxtasy]

frankly i am puzzled here- i've seen it more than few times, including 2 sets of warped OEM rotors that came off my nsx. while resurfacing them it was very obvious they were warped and not just by a little bit but about .040 in (1mm) in runout- much more than any uneven pad deposit.

The shudder typically starts with an uneven layer of brake pad deposits on the surface of the rotor. You may be able to remove it simply by re-bedding the pads/rotors; if not, the techniques of sanding or using an abrasive pad like the Hawk blues will work. You then need to re-bed the pads (with a series of progressively harder stops, and then NOT using the brakes at all and letting the brakes cool overnight). However, if you don't do something to remove the uneven deposits, then they can then cause the rotors to actually warp due to heat differences across the surface of the rotor.

You can read more about this phenomenon in these technical white papers on the Stoptech website:

The "Warped" Brake Disc and Other Myths of the Braking System
Pad and Rotor Bed-In Theory, Definitions and Procedures

This is not specific to the Brembo setup and can occur in any braking setup. FWIW I have never experienced any shudder in the rear brakes at all; it has only occurred in the front, and I have successfully avoided it by going through a proper bedding procedure any time I change rotors or pad compounds (not when replacing pads with the same type).

 

[swerve2007]

i guess i should have been more descriptive with my 'puzzled' comment (which was an attempt to present 'disagreement' in a nice way) not to convey my lack of understanding of the issue.

to clarify- i am not questioning the pad break-in procedure or what actually starts the 'shudder' in the first place (the aforementioned pad deposits) but was responding to the statement that rotor warping is a myth- i agree it is NOT the only cause of shudder but it is far from a falsehood.
furthermore, we can assume that if you are dealing with a brand new rotor that begins to shudder (or one that is a 'known entity' to you) we can eliminate the 'warping suspicion' and move onto the pad deposits as everyone advocates- no issue here again.
The OP has a set of used rotors so we do not really know what the condition is untill you can check the runout so outright dismissal of possible warping is also a speculation. It might be 'unlikely' on a new-ish part, i agree, but we are dealing with a set of rotors used for 10k miles.
what i am saying is that i think that rotors do warp- it does depend on brands/materials, braking habits, pad type etc. but it still occurs. it may not be the cause of shudder in this case but it is not a myth and we all have seen it happen on different vehicles in the past.
the last 2 sets of my front oem rotors came off the car warped with an indicated run-out of over 1mm and a 'classic' potato-chip profile so i can't dismiss it as myth- that was the point i was making.

 

[CL65 Captain]

From Stoptech's website. Some reading for you....

The "Warped" Brake Disc and Other Myths of the Braking System

"In fact every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc. This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures."

 

[swerve2007]

thanks, i've read it when 'nsxtasy' posted it for me.
just to get this straight, i am not being 'difficult' here and am not trying to prove anyone 'right or wrong'- i'd like to verify this for our own reference as few things do not add-up for me here and i'd like to have a discussion about it and folks' inputs.

the deposition makes sense of course but only if you are using pads with a high-metallic content- that is the only way there would be possibility of 'metal melting' and being transferred onto the rotor.
how were the rotors behaving 20 years ago when most pads were full of asbestos instead of metallic-flake?
how do we explain runout on a smooth, clean used rotor with no visible 'deposits' with the use of non-metallic pads?
are the 'deposits' in that case created from the abraded rotor material itself and not the pad?

Edit:
i have a set of used oem rotors that came off my car (i think the pads were 'organic' because they were producing a ton of dust, much more than i have eber seen in the past)- i will check the runout of the friction surface versus the runout of the internal cavity- if they are the same then the rotor is warped, if they are different then deposition has taken place. i will post results tomorrow and we can discuss.

 

[swerve2007]

well, i got home earlier today so i was able to inspect the oem rotors already.
i used a granite surface plate as a base to ensure perfect flatness and laid the rotors on it with the bolt-up face down on granite. with a height-micrometer and dial-indicator i measured the face of each rotor and the corresponding location in the cast vane cavity in the center. i did it at 8 locations on each rotor and the deviation from centerline for both the face and the cavity is roughly the same (within 0.005in or so) in a range from .035 - .045in of run-out, which does indicate that the rotors i have are indeed warped- the rotors were already vibrating when i bought the car so i could not begin to speculate if improper bed-in, pad choice or driving style are to blame.

now, i don't change the pads often enaugh to have an educated opinion on the pad deposits' appearance (maybe CL65 captain, docjohn or other racers can chime in). are the deposits you came across visible as a discoloration different in appearance from the rotor's base metal or does it look just like a 'regular' worn face with uniform color/groove pattern? if they are not visible how do you determine where the removal is necessary?
to me it would appear dificult to try to remove any significant amount of built-up metal with just a scotch-brite pad. i have tried sanding in the past but it never quite worked to my satisfaction (ie to completely remove the vibration) and i always had to resort to cleaning up the rotors on the lathe.
please do post your experiences in this matter as obviously mine are limited.

EDIT:
i just checked a set of rotors from a vintage car that have never seen a metallic pad in their life (always old-school asbestos) and they are slightly warped as well but not nearly as bad (about .015in runout) as the oem nsx ones i measured.

 

[stuntman]

the deposition makes sense of course but only if you are using pads with a high-metallic content- that is the only way there would be possibility of 'metal melting' and being transferred onto the rotor.
how were the rotors behaving 20 years ago when most pads were full of asbestos instead of metallic-flake?
how do we explain runout on a smooth, clean used rotor with no visible 'deposits' with the use of non-metallic pads?
are the 'deposits' in that case created from the abraded rotor material itself and not the pad?

Not necessarily true. Uneven pad deposits can occur regardless of the pad composition -including asbestos pads. It's not really possible to tell if a rotor has uneven pad deposits visually. Metallic pads are composed of metallic "powder", not really 'flakes' of metal. Runout should be measured when spinning the rotor on a hub and not just on a flat table. If the rotor is 'dished' atall, or corrosion has built up on the outer edge of the rotor, it will not give accurate readings. All pads leave a thin layer of their material on the face of the rotor. This is the whole bedding-in process and how the brake system works. Metal in a metallic pad dosn't really 'melt' and cause uneven buildup and height (or runout) on a rotor but rather leave a really thin layer of the composition of the pad material on the face of the rotor which is interacts with the same material on the pad. Through use, the rotor is worn down through friction as well as the layer of pad material on the rotor being wiped on, and 'wiped off' (but not all the way) every time you use the brakes.


Rotors can warp under extreme cases but it is very rare. Most of the time, the vibration is due to uneven pad deposits from an improper bed-in or mixing incompatible pad materials on the same rotor without turning them.


Billy

 

[angus]

It is true, warped rotors are mostly a myth.

 

[docjohn]

I think swerve is gonna short circuit since it sounds like his rotor is warped but we keep telling him it is not lol...:biggrin:

 

[nsxtasy]

I think we're all saying the same thing. Something along the lines of, shudder is usually due to an uneven layer of brake pad deposits on the surface of the rotor, but sometimes - not always, but occasionally - rotors do indeed warp.

 

[swerve2007]

nobody is blowing a fuse :smile:,
as far as the different measurement method goes, it is more convenient to measure runout while spinning the part but if you have the rotor positioned on a truly flat surface (like granite plate) then the results are virtually the same- at least for quick verification purposes.

i am always interested to learn of new variables but for me this just added a layer of confusion as according to the write-up and your experiences, the pad deposits may not be visually identifiable. that fact 'steered' me towards an assumption that metallic pads may be at the center of this pad deposit 'mystery' as only those kind of pads would enaugh metallic material to coat the entire rotor face with 'deposits' in a manner that would make the rotor appear homogenious.
in reality, i think, the only way to 'true-up' the rotor is reverting to the lathe turning regardless of what caused the rotor's vibration- deposits or heat warping. trying to remove something by manual abrasion only makes sense when you can see what you are removing so you do not affect the areas without the material build-up and perpetuate the condition. just something to think about.
good discussion guys.

EDIT:
has anyone measure the minimal rotor 'deviation' (deposits or warping) that would cause detectable vibration?

 

[nsxtasy]

the only way to 'true-up' the rotor is reverting to the lathe turning regardless of what caused the rotor's vibration- deposits or heat warping. trying to remove something by manual abrasion only makes sense when you can see what you are removing so you do not affect the areas without the material build-up and perpetuate the condition.

Not really. If the rotor is not significantly warped, you can scrub the entire surface (with sandpaper or with 9012 brake pads) and you'll remove any material buildup, so the entire surface is ready for re-bedding. And if the rotor is significantly warped, turning them makes them more susceptible to future warping, so you're probably better off just replacing them with new ones.

 

[swerve2007]

i was trying to stay away from 'fringe' cases where the deposits are either so miniscule that simple sanding takes care of it or the rotor is so obviously 'warped' that replacement is necessary- so looking at a scenario where the owner decides to recondition the part (to whatever extent) this is the part i don't feel comfortable with- if you have significant 'deposits' causing vibrations then it means that those deposits are not uniformly dispersed over the rotor's face and if you can't differentiate between the deposits and virgin rotor material then sanding everywhere will remove both the deposits and the rotor material in places where no deposits exist, right? rotor replacement is always the best but if someone decides to recondition then, i think, one should at leat spin the rotor to verify where it is running-out prior to any material removal or to do so on the lathe, my opinion of course.

 

[stuntman]

i was trying to stay away from 'fringe' cases where the deposits are either so miniscule that simple sanding takes care of it or the rotor is so obviously 'warped' that replacement is necessary- so looking at a scenario where the owner decides to recondition the part (to whatever extent) this is the part i don't feel comfortable with- if you have significant 'deposits' causing vibrations then it means that those deposits are not uniformly dispersed over the rotor's face and if you can't differentiate between the deposits and virgin rotor material then sanding everywhere will remove both the deposits and the rotor material in places where no deposits exist, right?

No. Brakes work by having a layer of the brake pad material embedded in the rotor surface itself. This pad material-on-pad material interface is where most of the "mu" (friction) comes from.

The "Uneven pad deposits" does not mean a visual or probably measurable difference in thickness of the material on the rotor, but rather the degree of penetration and embedding is not uniform and has varying degrees of "mu". While visually it looks homogeneous, and from a thickness standpoint it is the same, the 'uneven deposits' are more of a 'mu' difference -due to improper bedding or incompatable pad materials which is independent of the thickness of the pad material layer (which is extremely thin -less than a thousandth).

 

[swerve2007]

thanks, i wanted to get to the bottom of it because as you recall we had a discussion that rotors rarely warp and the concensus was that any vibration of the rotor is associated with 'pad deposits' only, which in turn made me question certain claims as it seemed impossible to me to have 'deposits' of such large thickness as to cause physical run-out (of course, mu variations will affect heat transfer and be a factor in eventual rotor warping). just wanted to spell it all out as truncated info is confusing to everyone.