Warped brake disks & anal orifice dealer


Howdy all:

At 76K miles, my Subaru dealer told me that all four brake disks on my 1996 Legacy GT were warped, two needing replacement & two could be machined. I had it done. 13K miles later, I was told the same thing, all four disks were warped, two needing replacement & two could be machined. Interestingly, the mechanic diagnosing the problem noted that the pads were in like new condition. I have been driving motor vehicles of all kinds for more than fifty years and am easy on brakes. When I demanded an explanation for the condition, with a straight face the service manager responded that the disks warped because I did not drive the car enough. Later, a service rep at Subaru of America added two more possible causes: living in a warm climate and living in a moist climate. I live in Long Beach, Calif. I admit to not having an automotive engineering degree from MIT, but as a retired lawyer and confirmed skeptic who possesses a basic knowledge of matters scientific and mechanical, I smell a strong odor of equine or taurine excrement. I used to tell juries to withhold forming a decision as to guilt or innocence until having heard all the evidence. Can someone please provide me with some information that might corroborate or buttress the (what seems to me to be to be) pure, unadulerated, genuine taurine offal being offered me as an explanation for my warped disks?

Subaru of America has refused to provide any authority for their diagnosis. Our family’s two other Subarus (a 1996 & 2002 model) have had no such problems. This up-to-now loyal Subaru family is, I fear, about to switch loyalties. Thanks for any help you can offer.


You’d do better to replace your dealer. The one you’re using now is a crook.


It would be useless to deny that you have besmirched the equine world by comparing the odor of it’s processed oats to that of the snippet of verbal diarrea coming from the mouths of your dealer and his fellow Neanderthals.

Overtightening lug nuts with a power impact wrench can warp rotors. Any mechanic worth a shot and a beer after work knows that and not all are.


Disk rotors made of “hard material” tends to produce squeaking noises like Amtrak does, and less efficient than softer rotors. Car manufacturers uses relatively soft rotors for their sporty models like your Legacy GT that might explain as to why your’s were warped at 13K while the pads are still newish. Or, those replacement rotors are just softer than the original.

As for the condition of the pads, some wears out at 50K, some at 100K. It would depend on the material of the pads, your driving style(blasting down the PCH), type of rotors/calipers etc. There might be an issue(matching) with the brakes in Legacy GTs.


My experience with a 99 Subaru Legacy, in 100k miles, replaced pads and rotors twice, used Subaru parts, but not a Subaru dealer, I’m also in Southern Cal. the car is my wifes and she is tough on brakes. It’s my belief that an independant brake shop is a better option for this work than a dealer.


As a lawyer, then you should know all of the facts should be presented before deciding a case.

Were your brakes shuddering originally?

Were your brakes shuddering the second time?

Are you using a different shop the second time?

A few comments. Brake rotors can, and frequently do, warp long before 76k miles. They can even warp within 5k miles, or much less.
Rotors that are machined, especially too thin, will warp more easily the second time around and driving habits influence this.

Sometimes a shudder in the brakes is actually not caused by the brakes. With new or machined rotors the brakes may be smooth, but if you have any looseness at all in a suspension part, wheel bearing, etc. then once those new/machined rotors develop a few thousandths of an inch warp, the looseness in the susp. or wh. bearings will exacerbate the shudder.

Rotors can warp no matter how much material is left on the pads so that is a non-issue.

I would not put a lot of faith into the comments about not driving enough or the temperature/humidity thing, although there is a tiny bit of truth in regards to the humidity part.
At times, some Subarus will develop a very noisy grinding sound after sitting for a few days in humid conditions. This normally does not hurt anything and I’ve seen it a number of times even on brand new Subarus that have not even been sold yet.
I drove a demo to a week long service school (San Antonio, TX) and every morning the first few stops made so much of a grinding noise that one would swear every brake pad on it was metal on metal.


Point well taken, ok4450.
My apologies for my laconism. Suffering from a chronic case of fulminating logorrhea, a.k.a. prolixity, & not knowing how much space would be alotted me here, I was uncharacteristically brief. To answer your questions, my brakes have never shuddered. At about 70K miles I began to notice a pulsing at the brake pedal, most noticable when applying the brakes gently at low speed. At 76K miles it had gotten worse and that’s when the dealer told me that all four disks were warped, and I had the work done there. 13K miles later, much to my surprise, the symptom (pulsing at the brake pedal on braking) returned. That’s when the dealer told me that the disks were again warped. And that’s when, in response to my demand to know what could have caused warpage so soon, I was given the BS story about not having driven the car enough. Not wanting to waste time, I had the same dealership replace all four disks and then took the matter up with the owner and then Subaru of America. And that is when they shoveled more manure in my direction, i.e., that a warm and/or moist climate could cause disk warpage. I have on occasion seen oxidation on the disks, but that only caused a few squeaks during the first few stops, and quickly disappeared. Any further thoughts would be most appreciated. Thanks.


Thanks, anonymous, for offering a more plausible possible explanation for my warped disks than the scat proffered by the dealer


Thanks, Tree Hugger, for the sage advise.


One thing to always remember is that when you’re at a dealer service dept. is that your conversations are generally with a service advisor or service manager. Very, very few of these people are mechanically inclined. I can count on one hand the number I’ve ever worked with that could actually make a living as a mechanic.
Since their job is to be a “service advisor” professional, they will have a tendency to blab a lot of BS rather than appear to be uniformed.

The original pulsation would more than likely be warped rotors.
Since this has occurred again so soon the likely possibilities are:
Rotors cut too thin, which means heat will warp them again more easily.
Some hard driving/braking habits (See my wife. :slight_smile: )
The previously menitioned loose suspension part or wheel bearing. Generally the first thing on a Subaru to go are the inner tire rods.

Brake rotor warpage is easily verified with a dial indicator and loose inner tie rods are also easily verified by grasping the tire at the 3 and the 9 o’clock position and noting if there is any movement at all while wriggling the tire.

In some isolated cases, even a bad tire can mimic a brake pulsation, especially at slower speeds.

The only way the reasoning behind “not driving the car enough” could be used would possibly be if the car sat for months or years at a time without use, but this does not sound like the case here.
The oxidation on the rotors will hurt nothing and is rubbed off after a few stops.

About all I can suggest is placing a dial indicator on the rotors and verifying that is indeed the problem.
Hope some of that helps anyway. :slight_smile:


First, I doubt that your rotors were ever warped. Warped rotors are a myth. People who are hard on brakes seldom have this problem, its the folks that are easy on the brakes that suffer from this.

Modern brake pads use a lot of resin and binders to hold the semi-metalic, ceramic or carbon fiber materials together. The resins will get hot enough to transfer a residue to the rotors that builds up unevenly. This causes the pulsing.

I have found the quickest cure for pulsing brakes is a couple of hard stops from 60+ mph. Don’t lock up the brakes, but do hard stops so the rotors get good and hot. It burns off the residue and the brakes will be smooth for awhile, just as if you had them turned.

Another thing you could do is when the dealer tells you the rotors are warped, have him put a dial indicator on them and show you how much runout there is. There will be a couple thousands, but that is insignificant as the brake pads will deform the rotor when applied by that much. .020 would be significant. .002 would not be.


I will respectfully disagree with your opinion that rotors do not warp.
The dial indicator does not lie and the lathe does not lie either. The countless ones I’ve machined certainly appeared to be warped.

I can certainly tell when a rotor has .005 of an inch warpage or parallelism problem and with any looseness at all in the wheel bearing or suspension it is going to be magnified. An .020 would shake you right out of the car.

With almost all car makers, .002 is about the limit; anything over that means machining or replacement with about .030 being the maximum that can be removed.

A cast iron engine block can change shape so why would you think a thin cast iron rotor would not?


I have “repaired” this problem on many cars with just one or two hard stops. I would not be surprised if the rotors were .001 out after the first use after being machined. The limit on a Honda is .004 with .84 being the max removal, but Hondas have pretty beefy rotors.

BTW, I have to do this on my wife’s Honda about every 10k because she is too easy on the brakes. It usually takes two stops on hers, but only one on my Saturn, about 15 to 20k. I’ve still got the original brakes on the Saturn and changed the pads once on the Honda. Both have about 135k on them.

On my truck, I haven’t had this problem because I feel the brakes are undersized and work harder than the cars. On the Toyota my son drives, well he’s very hard on brakes so he doesn’t have this problem either.

I think this resin problem must be somewhat recent, like in the past 20 years or so, I don’t remember anyone having “warped rotors” back when the pads were still made from asbestos.


Well, the proper repair (according to the factory, skilled techs, or machine shops) on a customer vehicle when a brake shudder or pulsation complaint is made is to check rotor runout and parallelism followed by machining of or replacement of rotors as needed.

Brake problems like this on Subarus are nothing new. It’s been going on since 1980. Pre-80 they were pretty much trouble free. After 80 the rotors were essentially the same but the calipers and yokes changed and the problems started after this.

I’m only saying that warped rotors are a common complaint and are very easily verified. I can’t recall ever seeing any .020 out, but I have seen quite a few at anywhere from .005 to .015 or so. Even a measly .002 or .003 can cause a shudder.

In my basement parts stash, I have about 35-40 Subaru brake rotors of various vintages I keep around. Every single one of them is warped to some degree and if the occassion arises I can pull a pair out and resurface them as needed.

There is no way in the world that I would ever agree that warped rotors are a “myth”. The numbers on the indicator do not lie. Heck, I can probably put one on my lathe this weekend and post a few pics of the dial indicator doing its job if needed.
In a lot of cases, one can actually watch that rotor turning on the lathe and visibly see the warpage.
Once the carbide bit starts cutting the rotor one can readily see the problem as the bit will start off cutting on one side only.

I’ve also been cutting rotors for 30 years to straighten them out so it’s nothing new, asbestos or not.


The OP could also read this for an explanation.
Warping is primarily 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.

Several methods can be used to avoid overheating brake discs. Use of a lower gear when descending steep grades to obtain engine braking will reduce the brake loading. Also, operating the brakes intermittently - braking to slower speed for a brief time then coasting will allow the brake material to cool between applications. Riding the brakes lightly will generate a great amount of heat with little braking effect and should be avoided. High temperature conditions as found in automobile racing can be dealt with by proper pad selection, but at the tradeoff of everyday driveability. Pads that can take high heat usually do best when hot and will have reduced braking force when cold. Also, high heat pads typically have more aggressive compounds and will wear discs down more quickly. Brake ducting that forces air directly onto the brake discs, common in motorsports, is highly effective at preventing brake overheating. This is also useful for cars that are driven both in motorsports and on the street, as it has no negative effect on driveability. A further extension of this method is to install a system which mists the rotors with cool water. Jaguar has reported great reductions in rotor temperatures with such a system.

Warping can also be caused by improperly torquing the lug nuts when putting on a wheel. The manual will indicate the proper pattern for tightening as well as a torque rating for the bolts. The tightening pattern varies little between manufacturers and most mechanics are familiar with them. Lug nuts should never be tightened in a circle. Some vehicles are sensitive to the force the bolts apply and tightening should be done with a torque wrench.

Warping will often lead to a thickness variation of the disc. If it has runout, a thin spot will develop by the repetitive contact of the pad against the high spot as the disc turns. When the thin section of the disc passes under the pads, the pads move together and the brake pedal will drop slightly. When the thicker section of the disc passes between the pads, the pads will move apart and the brake pedal will raise slightly, this is pedal pulsation. The thickness variation can be felt by the driver when it is approximately 0.007 inch (0.017 cm) or greater.

Not all pedal pulsation is due to warped discs. Brake pad material operating outside of its designed temperature range can leave a thicker than normal deposit in one area of the disc surface, creating a “sticky” spot that will grab with every revolution of the disc. Grease or other foreign materials can create a slippery spot on the disc, also creating pulsation.

[edit] Cracking


OK4450… if you follow Keiths’logic then all you would have to do is remove the rotor and clean off the resins with brake cleaner.

I too have been turning rotors for pulsations for over 25 years and this resin transfer garbage is B.S. I’ve never cured a brake pulsation by “hard stopping” a couple of times.

Again, it’s a bunch of B.S.


Overtightening lug nuts with a power impact wrench can warp rotors. Any mechanic worth a shot and a beer after work knows that and not all are.

This is so common…and IMHO the cause of about 90% of all warp rotors. Every time I have my tires rotated I watch them to make sure they use a torque wrench on the lugnuts…If they don’t then when I get home I loose all the lugnuts and do that myself. What a lot of mechanics do is use the air impact wrench to put the nuts on…this causes over tightening…thus the warping. MOST of the big tire chains LOVE doing it this way so they can get people in and out fast to maximize profit.


I have found the quickest cure for pulsing brakes is a couple of hard stops from 60+ mph. Don’t lock up the brakes, but do hard stops so the rotors get good and hot
Sounds like you’re doing it to mate up the new brake pads with the rotors, or vice versa. This method is also effective when you want to eliminate “drag noises”, but not for warped rotors though.


I’m standing by the hard stops, it has always worked for me. Why don’t you try it before you write it off?


Been there, done that… doesn’t work. If anything it makes the pulsation worse. I stand by my extensive experience in this field, the rotors need to be resurfaced or replaced to fix the problem.

You triing a couple of hard stops isn’t conclusive evidence to me. I say this because I have triied it dozens of times and it has never worked.