Shimmy?

Okay so last weekend I washed the car and put it away. This morning I pulled it out to come to work and noticed that the pads were slightly fused to the rotors since they were obviously wet when I pulled it in to the garage. So a few miles down the road and the rusted crap was worn off. Cool. But I have a shimmy/shake under braking that I suppose that I didn't notice before. The road surface that I am on is asphalt and is brand new so it is smooth as silk. I notice the shimmy while moving alone at 45mph and also noticed the same pulsing pattern when slowly coming to a stop. For the longest time I was going in to have the wheels re-balanced because I thought that this was the problem and then cursing the dude for not doing it right. Now I am thinking that it is my rotors! Can it be? The reason I am now leaning towards the rotors is that on my truck they are warped and I know it. This causing some serious wobble while driving and under braking in a bad way but the truck is old and frankly I just don't give a damn. But my car...my pride and joy...she is acting the same way. Could it be braking issues? She is only 31,000 miles young. For the last year I have been so pleased with the brakes compared to anything else that I have owned thus far and here I am faced with them possibly being no different that (gasp) a standard car???

Hot rotors can warp if they are rapidly quenched from driving through water puddles. Do you recall braking hard, then passing through a puddle?

Rotors warping under normal driving conditions would be extremely unlikely. Have you had the rotor's/brake pads changed? Might be a tire balancing issue - have you had your tires speed balanced? Did you hit a bump that would push the car out of alignment?

It may be coincidence with the car washing/brake rust etc..., but I would go along with Riad and think more along the line of tire problem. (Unless the brake pedal is pulsing up and down when braking and that would point towards needing the rotors turned)

I have the same problem whenever I wash my car. If I don't take a 10 minute drive to properly dry the rotors right after washing, the next morning I will actually have to "break" the rotors loose as the car won't move. I will then get a vibration from the rear under braking for about 10 -15 miles, until all the rust/crud wears off. My solution is to drive the car after the body is dried for about 10 minutes, making sure the brakes get nice and warm. Before I put the car away, I'll clean the wheel interior of the rust and crud from the rotors. Stefan

Do another break in of the brakes to clean the pad and rotors. Common problem with many cars washed and put away with wet brakes. A few hard long braking applications, both forward and backwards should clean them right up. Rotors do not warp, but pad material can adhere to them.

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'99 - I heard you make this statement before. I have seen rotors cut and it looked to me that the parent material of the rotor was being shaved off, not pad material. As the rotor spins, the high sides would turn a bright silver and the low sides would be a low luster silver indicating that the rotors are indeed warped until flatness was achieved. Also, can you explain how a hot, very hot rotor when quenched in a water puddle doesnt warp? I have experienced it myself several times on inferior non-slotted or cross-drilled rotors. I know this is not pad material bonding to the rotor causing the out of flatness condition.

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It is possible for a rotor to warp, but only under extreme and exceptional conditions and I have seen it very seldom. What the lathe is removing is one of things. Either a soft spot on the rotor that has swelled or, most often material from the pads that have bonded to the rotor. This often happens when rotors are extremely hot and pads are tight against them.

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Brake pad material is softer than a rotor. If the cutter of the resurfacer hit brake material that is supposedly bonded to the rotor, it would make less of a cutting sound. Or possibly, no sound at all. On comparison, a screwdriver can easily damage a brake pad. On softness of the rotor material in places. Arent rotors cast? If they are, the metal is in a liquid state before pouring into the mold, you would think it is pretty "mixed" and uniform.

FYI....it is damn near impossible to "warp" a rotor. Uneven pad material build-up almost always mistakenly called a "warped" rotor. Spray em down with water. Let some rust form and then do do some high speed bedding in of the pads. Should clear it right up.

As best that I can read from the original owner's paperwork and services, these are the original rotors and pads. While we have had a great deal of rain, I haven't gone through any standing pools of water.

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Pad material is constantly being transfered to the disc. If the pads are not bedded properly or are held against a non moving disc under certain cirrcumstances, you then get an uneven transfer of pad material. Aggressive braking often removes this buildup, depending on the type of pad material that was transferred. High content metal and carbon pads form a harder buildup on the disc..

Search "brake rotor warpage" and it is commonly accepted as a fact. It is simply from rapid expansion and contraction, all the metal I know of and work around, warps. Can brake material transfer, sure. Is it the biggest cause of "shimmy", I doubt it. Yes indeed, Porsche rotors are hard to warp because of their design, but they will. Not the same for the rest of the commuter vehicles.

Cory, you're running into an argument you can't win. Does uneven pad material create a feeling of shimmy/vibration under braking? YES. Do rotors warp? Damn near impossible. And no it is not commonly accepted as "fact" but rather it is anecdotal evidence accepted what we like to call a myth.

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Since when does consensus actually mean fact? MOST people get there "so called" knowledge from what they were told or what they read and NOT from practical experience. Remember, the majority also thought the world was flat and that hormone replacement therapy did not harm woman and that lobotomy was the proper way to treat schizophrenia and that sacrin caused cancer, and most men believe that SIZE DOES NOT MATTER.......an on an on an on. It is also popular belief that Mobil 0W40 will not harm your engine and that humans can actually affect the global climate, and , I don't think we ever found green cheese on the moon. Oh Yeah: and DELL actually thinks statistics matter. Here is a link that does a pretty good job of explaining it the brake disk issue: http://www.stoptech.com/tech_info/wp...rakedisk.shtml

I have read the article in the past. I guess Society of Automotive Engineers have always had this scenario wrong........ Here is an exert from Wikipedia. Before you shoot it down as not being credible, look at the references after the summary. Warping is often caused by excessive heat, which softens the metal and allows it to be reshaped. The main causes of overheating are: undersized/overmachined brake discs, excessive braking (racing, descending hills/mountains), "riding" the brakes, or a "stuck" brake pad (pad touches disc at all times). Another cause of warping is when the disc is overheated and the vehicle is stopped. When keeping the brakes applied, the area where the pads contact the disc will cause uneven cooling and lead to warping. ^ Crosley Firsts. Retrieved on 2006-05-20. ^ WHAT MAKES A CLASSIC CAR?. CLASSIC CAR. Auto Lemon. Retrieved on 2006-05-20. ^ The Avanti - Born in Palm Springs. Retrieved on 2006-05-20. ^ Henry, Alan (1985) "Brabham, the Grand Prix Cars" p. 163 Osprey ISBN 0-905138-36-8 ^ Abdelahamid, M. K. (1997), "Brake judder analysis: Case studies", SAE, Technical Paper Series, no. 972027. ^ de Vries, A. et al. (1992), "The brake judder phenomenon", SAE Technical Paper Series, no. 920554 . ^ a b Engel, G., H. et al. (1994), "System approach to brake judder", SAE Technical Paper Series, no. 945041 . ^ Gassmann, S. et al. (1993), "Excitation and transfer mechanism of brake judder", SAE Technical Paper Series, no. 931880. ^ Jacobsson, H. (1996), "High speed disc brake judder � the influence of passing through critical speed", In EuroMech � 2nd European Nonlinear Ocillation Conference, Prague, no. 2, pp. 75�78. ^ Jacobsson, H. (1997), "Wheel suspension related disc brake judder", ASME, no. DETC97/VIB-4165, pp. 1�10. ^ Jacobsson, H. (1998), "Frequency Sweep Approach to Brake Judder, Licentiate of engineering", Chalmers University of Technology Sweden. ^ Jacobsson, H. (1999), SAE Technical Paper Series, no. 1999-01-1779, pp. 1�14. ^ Stringham, W. et al. (1993), "Brake roughness � disc brake torque variation", rotor distortion and vehicle response, SAE Technical Paper Series, no. 930803 . ^ Thoms, E. (1988), "Disc brakes for heavy vehicles", IMechE, pp. 133�137. ^ Anderson, E., et al. (1990), "Hot spotting in automotive friction systems", Wear, v. 135, pp. 319�337. ^ Barber, R., J. et al. (1985), "Implications of thermoelastic instabilities for the design of brakes", Jnl. Tribology., v. 107, pp. 206�210. ^ Inoue, H. (1986), Analysis of brake judder caused by thermal deformation of brake discs, SAE Technical Paper Series, no. 865131. ^ a b Rhee, K., S. et al. (1989), "Friction�induced noise and vibration of disc brakes", Wear, v. 133, pp. 39�45. ^ Kim, M.-G. et al. (1996), "Sensitivity analysis of chassis system to improve shimmy and brake judder vibration on the steering wheel", SAE Technical Paper Series, no. 960734

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Regardless of what the "wikopinion" says, if you have ever been involved in the process of hardening metals, you would understand that a rotor is much to hard (as evidenced by it's cracking) to warp from the reletively low temperatures you created while braking, unless you can get them to above 2000F. Becoming "out of round" is not warping and can only be caused by improper installation.

Now with some extra thought on this topic, it came to my mind that when I ran club racing with sport bikes that every few races we pulled the rotors off and took them to be bead blasted to remove the pad material build up. I didn't have any judder issues but with the heat induced to the rotors, I had some extra build up of material. Once blasted I was able to bed in new pads and the world was anchored yet again. I wonder if getting new pads and having these rotors blasted would be the short answer cure? Should would be the cheapest.

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You bet your **** I do! Hence the reason anecdotal evidence like the stuff Cory is subscribing to really throws my panties into a tizzy. AND FOR THE LOVE OF GOD......QUICK CITING WIKI AS A SOURCE!!!! There is a reason we have BANNED it as a reference at the university as well as many across the USA.

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You used to be able to by carbon steel pads for just this purpose, however, many modern pads are hard enough to accomplish the same thing.

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Anecdotal? A Society of Automotive Engineers stating this as fact is anecdotal? My creditibility and the facts supporting me is higher than anyone on my opposition. StopTech, a relatively new company versus 40+ years of brake rotor knowledge? And like I said Dell (knowing you are a Professsor), before you shoot down the reference, consider its references.

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It's not the reference that I am shooting down, it is the source that "holds" the reference. If I wanted to I could march right on over to Wiki and change that entry as I see fit. Stop Tech has a good rep in the industry (brakes) but citing Wiki when you have NO IDEA if the info is 100% accurate or not is a bad habit to get into. Just because the society of some engineers name is used doesn't make it real. But go ahead and believe it. I assume you ahve read this from Stop Tech on their OWN website that there is no instances verified by them of a single warped disc? The term "warped brake disc" has been in common use in motor racing for decades. When a driver reports a vibration under hard braking, inexperienced crews, after checking for (and not finding) cracks often attribute the vibration to "warped discs". They then measure the disc thickness in various places, find significant variation and the diagnosis is cast in stone. When disc brakes for high performance cars arrived on the scene we began to hear of "warped brake discs" on road going cars, with the same analyses and diagnoses. Typically, the discs are resurfaced to cure the problem and, equally typically, after a relatively short time the roughness or vibration comes back. Brake roughness has caused a significant number of cars to be bought back by their manufacturers under the "lemon laws". This has been going on for decades now - and, like most things that we have cast in stone, the diagnoses are wrong. With one qualifier, presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification, in more than 40 years of professional racing, including the Shelby/Ford GT 40s � one of the most intense brake development program in history - I have never seen a warped brake disc.

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Sorry, but referneces are meaningless especially when they can't be verified. Go back and read medical journals from the 50's and you'll find all sorts of witchcraft cures that either proved worthless or even deadly. BUT, they were all sanctioned by the worlds most repsectable people.

Ok, so I have to believe you guys reference but you dont have to believe mine? I give up, there is no need to carry on then. I am reading Engineering papers other than the ones from Wikis site and you guys are reading StopTechs website. Funny, no one respects Ford on this board until it favors them, especially 35 year old info.....................the GT-40 program? Here is another paper on the possiblility of brake shudder: http://www-personal.umich.edu/~jbarber/TEI.html Take it for what its worth, probably nothing here.

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MY reference is actually working with metal, from smelting to softening and hardening. If you want proof, take your "warped" rotors off and give them to a good machine operator. Have him only remove the 80% of the high spot and collect the material. You will not find disc metal in the sample. You can then post your finding on Wikopinion and maybe someday, someone will use your test as a reference. BTW: I did not link you to Shoptech for a reference, but because they pretty much had what I I was too lazy to explain to you. Since I know ALL things knowable, there is never a need for me to post references. .

Time for me to jump ship. Damn, sometimes I wish I was just ignorant so I didn't get into these discussions.

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Funny you mentioned this, I was going to say the same thing. You have to do analysis to check for content. This is the only 100% guaranteed, signed, sealed, and delivered way to determine. But since none of us are going to do this test for the sake of the debate, we are both right, and both wrong. We all are going off of someone elses data. That, no one can deny.

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Been there, done that. Summer of 1975. Testing completed by engineer from Sperry Univac in Danbury, CT. There IS only one correct answer. I will not be so bold as to say that you are wrong, but I am definately right.

[QUOTE=1999Porsche911;4576662]Been there, done that. Summer of 1975. Testing completed by engineer from Sperry Univac in Danbury, CT. You witnessed or read about? If you read about the test, give me the link, I would love to be proved wrong so all I have to do is use glass cleaner and tissue on my rotors to get rid of the current shudder I have. Just kiddin'

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Sorry this is such an inconvenience for you. I was told one thing, you were told another. We have opposite opinions that came from hearsay, neither of us actually tested a rotor. Oh, and by the way, you were the one who said never to turn rotors. If you are not taking away parent metal of the rotor when they are being turned, what is the big deal? Your just removing brake pad material getting back to the rotor.

If someone wants to give me material from the turning process, I will analyze it for you.