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Old 12-02-2007, 12:18 PM   #1
MtEric S
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Warped rotors again

I not afraid to spend the money and buy OEM parts for my cars. I do notice though that even when buying OEM rotors and pads I have a problem with the rotors warping after a few months. This has happened on most of my recent cars regardless of make and model.
I'm looking for a way to remedy this.
Do I stop buying the stock pads and get aftermarket pads that are softer-which ones?
Is there a better aftermarket Rotor company? I did buy Brembo rotors that were cross drilled a few years ago and they lasted a long time.
Is there something else to look for?
I'm not driving like an idiot, just commuting and doing what I think is fairly normal driving.
Thanks in advance, Eric S
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Old 12-02-2007, 02:32 PM   #2
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Re: Warped rotors again

Welcome to AF, posting the year and make would help here as many brake system designs lend themselves to this issue. Improper wheel torque procedure, over size tires and wheels, driving habits, failure to clean the mounting surfaces, worn hardware, loose wheel hubs and/or bearings, improperly adjusted or poor rear brake performance, to name a few generic issues.
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Old 12-03-2007, 12:17 PM   #3
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Re: Warped rotors again

if you have warped rotors consistantly on multiple cars, assuming there's not a caliper issue with all of the cars in question, which seems unlikely, that only leaves the driving style

If you are a two-footer (one foot on the gas and one foot on the brake at all times), I wouldn't be surprised at all personally
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Old 12-03-2007, 06:08 PM   #4
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Re: Warped rotors again

Another issue could be the fact that the rear brakes are not doing their job and putting more load on the front brakes and creating heat to warp the rotors. Make sure the rear brakes are functioning, the cylinders are moving and not stuck and the adjusters are working, and are adjusted up.

Some cars rear brakes are adjusted when the car is backed up and the brakes are applied. I believe that other vehicals rely on the parking brake being applied to adjust the rear shoes up.

Regards

Dan
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Old 12-03-2007, 09:41 PM   #5
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Re: Warped rotors again

Rotors don't warp unless you have uneven torque distribution on the hub. If you can rule that out then you have a buildup of pad material usually caused by improper break-in. You can usually have them turned.

If you want good OEM replacement then try Raybestos. They aren't expensive and they do a great job. Get the Quiet Stops for pads and PG Plus for rotors.
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Old 12-03-2007, 10:23 PM   #6
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Re: Warped rotors again

Big old myth.

Warped rotors don't cause brake pulsation. They can't because of the design of the brakes. The floating calipers will put even pressure on the rotor, and float along with the warp. Fixed calipers will transfer fluid to the other side if the rotor is warped, but either way, you are still applying the same pressure to the pads, the pads are providing the same pressure to the rotors, so the problem HAS to be an uneven coefficient of friction over the surface of the rotor.

What causes brake pulsation is deposits on the rotor. You probably can't even see them, but the extreme heat burns pad material into the cast iron rotor. It has a vastly different coefficient of friction and therefore causes brake pulsation. In extreme cases, the deposition can be great enough that it alters the thickness of the rotor. In those situtaions, you typically feel it kicking back through the pedal in addition to pulsating brake torque.

The single most important factor in not getting brake pulsation is to properly bed in your pads when they're new. Not doing this step will almost always eventually lead to trouble.

Do a search for "warped rotor myth" and you'll turn up tons of tech on it.
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Old 12-04-2007, 06:57 PM   #7
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Re: Warped rotors again

Quote:
Originally Posted by curtis73
Big old myth.

Warped rotors don't cause brake pulsation. They can't because of the design of the brakes. The floating calipers will put even pressure on the rotor, and float along with the warp.
curtis, you usually give great advice, but this is so wrong I'm speachless.

Just because a caliper is floating doesn't mean it can compensate for warped rotors.

Simple experiment, purposely chuck a rotor in a lathe and cut a .010" runout into the rotor then go drive it. You'll be quite surprised, I assume, to find it will pulsate like crazy with *any* caliper setup
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Old 12-05-2007, 11:28 AM   #8
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Re: Warped rotors again

Using "warped" in a sense that the rotor is of uniform thickness and merely bent may slightly cause a pulsing feel.

If the rotor is "warped" in the sense of varying thickness as it goes around has no choice but to cause a bad pulsing.

The floating caliper may follow a bent rotor ok , but still isn't good. A caliper that runs on a rotor with much variance of thickness must push and pull fluid.
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Old 12-05-2007, 05:47 PM   #9
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Re: Warped rotors again

Quote:
Originally Posted by UncleBob
curtis, you usually give great advice, but this is so wrong I'm speachless.

Just because a caliper is floating doesn't mean it can compensate for warped rotors.

Simple experiment, purposely chuck a rotor in a lathe and cut a .010" runout into the rotor then go drive it. You'll be quite surprised, I assume, to find it will pulsate like crazy with *any* caliper setup
Flawed experiment... by cutting a .010" runout, you aren't adding .010" to the other side, therefore you are artificially creating inconsistent thickness. That WILL cause pulsation, but I've measured as much as .025" runout with no pulsation, provided its consistent thickness.

If you have a pulsating rotor that measures no runout, send it to me. I'll put it under the scanning electron microscope here at the college and send you photos. You can't normally see inclusions, but they're there. My research has shown me that a "warped" rotor with consistent thickness almost never causes pulsating brakes. If it does its at very low braking efforts where the brake torque being applied is only a small percentage of the pressure required to overcome the movement of the floating caliper, but if you consider the huge brake torque compared to the resistance to caliper movement, its no contest.

The thing is, you measure runout, hear "brake pulsation" and then you machine the rotors to find that the pulsation has disappeared. The logical conclusion is that the warping caused the problem. The actuality is that the runout accounts for little or none of the problem. The inclusions from the pads alter the friction on the surface of the rotor. Machining removes those inclusions and the friction returns to a consistent coefficient.

I did lots of research on this, including looking at about 45 rotors under a scanning electron microscope. Feel free to disagree all you want, but you won't change my mind You can put a pretty severely warped rotor on and as long as its a consistent thickness and friction surface, I have not noticed any pulsation, even on fixed, 6-piston calipers on a race car.
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Old 12-05-2007, 07:06 PM   #10
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Re: Warped rotors again

. Everytime I have run into this in the field, I have checked the runout or variation with a dial indicator,( I know this is total runout including the hub/bearing and machined mating surfaces) the runout was .005 minimum and spinning the rotor by hand you feel the variation in contact pressure. Many n/c manufacturers now require on car resurfacing to qualify for warranty claim payment., What is the long term prognosis to correct this condition, both GM and Toyota serious issues with this on the Tundra and GM with the Malibu, both redesigned the rotors as a resolution. Are you saying the rotors are not the problem but the end result of uneven friction material deposits?
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Old 12-07-2007, 06:32 PM   #11
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Re: Warped rotors again

Quote:
Originally Posted by curtis73
Flawed experiment... by cutting a .010" runout, you aren't adding .010" to the other side, therefore you are artificially creating inconsistent thickness. That WILL cause pulsation, but I've measured as much as .025" runout with no pulsation, provided its consistent thickness.
you would of course cut both sides. I didn't think that needed saying

Quote:
If you have a pulsating rotor that measures no runout, send it to me. I'll put it under the scanning electron microscope here at the college and send you photos.
can't say I've ever seen a pulsating brake issue that didn't have rotors with runout

Quote:
You can put a pretty severely warped rotor on and as long as its a consistent thickness and friction surface, I have not noticed any pulsation, even on fixed, 6-piston calipers on a race car.
not sure what the 6-piston fact changes....have 12 pistons on the front brakes of my bike, and they are well known for rolling dust seals, causing the pistons not to retract properly, and not too surprisingly, cause pulsation

Most pulsations are do to something similar in my experience. Sticking sliders, sticking pistons, bad master cylinders. Whether you cut the rotor, replace the rotor, doesn't do you much good. the problem will be back until you address the root of the problem

Thats why this conversation is fairly moot. Whatever physical property of the rotor and pad that cause the pulsation, doesn't really matter. Its preventing it from happening again that is the real issue IMO. I assume you would agree, for example, if you have a sticking slider, it should be fixed, or issues will come back
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Old 12-09-2007, 05:16 PM   #12
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Re: Warped rotors again

The rotors warping (from my research) does not cause the pulsation. Uneven friction surfaces OR inconsitent thicknesses cause pulsation. Pad deposition is usually the cause of both.

The proper solution is to properly bed in new pads. I agree, bob, that fixing the problem is the way to go.

The disagreement with this myth is still solved by the same procedure basically... cutting rotors (while not the best solution in all cases) will fix the issue... its just that I don't believe that a rotor with runout will necessarily cause pulsation. Its possible that every pulsing rotor you've measured has had runout, but that doesn't prove that the runout is the cause of the problem. Just my opinion.
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Old 12-09-2007, 07:36 PM   #13
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Re: Warped rotors again

i agree breaking in the pads is the best thing, also i always have see different methods of final preperation don to the rotor, like me I prefer to go with a non directional swirl, some other techs prefer to do no swirl and use this rotor anti squek stuff that you spray onto the rotor, others just turn them and leave the smooth and put them on, what are your opinions on what the best finish should be.
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Old 12-10-2007, 03:24 PM   #14
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Re: Warped rotors again

Always non directional to avoid pad walk issues when the rotors look like a phonograph record.The finish should be very smooth to allow faster pad bedding as the raised machinging marks left on a poorly finished rotor severely diminsh pad to rotor contact till the pad and rotor seat, which could take a while in the most severe case.
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Old 12-13-2007, 11:07 AM   #15
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Re: Warped rotors again

OEM rotors should last a real long time. Some cars are notorious for being tough on front brakes. I had a 4-wheel disc Buick that ATE front pads. I wound up going with regular auto parts store replacement rotors and using the best Bendix pads that I could get. As for my spin on cutting rotors, I don't go for a mirror finish on them. On the Ammco lathes I would cut them on 4 while most everyone else cut them on 2, which is a slower feed.

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