[NXS]

Do rotors really warp? that's the main question. I've turned a few in my life, how about you?

[techinspector1]

Yes they do and when you turn them, you remove metal, reducing the mass and making them even easier to warp.

[pepi]

is this the same as run out

[Rob Keller]

Uh wwats a rohter?

Yea rotors warp. a lot of stop & go "city traffic then add a problem like a sticking slide on a caliper making one side work harder then the other side of the caliper .
Or a sticking caliper creating excessive heat {its can get cherry red } then when it stops moving the heat inside the caliper / rotor will dissipated slower then the rest

Thus the cause for drilling heat vents/ports

R

[1931 steve]

Most certainly they warp. I have cut thousands of brake rotors in my life. The real question is why do they warp?

Steve

[curtis73]

Yes rotors warp, but they do not cause the pulsating brakes everyone complains about. That is from cementite inclusions in the cast iron.

http://www.stoptech.com/tech_info/wp...rakedisk.shtml

I've personally confirmed their claims with a scanning electron microscope. Perks of being a BioChem major back in college.

If you think about it, calipers (floating and fixed) are designed to put equal pressure on both sides of the rotor. If the rotor is warped, either the caliper moves (floating caliper) or the caliper transfers fluid. Even if it didn't, when the warped part comes around, it would add friction to one side and remove it from the other, keeping mean friction similar throughout the rotation.

machining rotors removes cementite inclusions, but if you don't properly bed in new pads, you'll be back at square one in a week or less. Its happened to me many times with my track pads. within a week there was little or no runout, but the pulsing was unbearable. I've also had rotors with lots of runout and no pulsing at all.

[NXS]

Originally Posted by curtis73

Yes rotors warp, but they do not cause the pulsating brakes everyone complains about. That is from cementite inclusions in the cast iron.

http://www.stoptech.com/tech_info/wp...rakedisk.shtml

I've personally confirmed their claims with a scanning electron microscope. Perks of being a BioChem major back in college.
.

That link is exactly what started this thread.

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.

================================================== =
Why they warp.Steve, I can tell you....if nobody else does.

[yesgo]

I cant vote due to the options.
I cant say that rotors cant warp. They are metal after all, and go through heat cycling.

I can say that I've turned thousands at least, and seen multiple thousands turned by others.


The majority of problems I have seen regarding pulsations are from turned rotors,
though close to half are factory, unmachined discs. Many discs on a first brake job, or new, installing shop machined discs, are machined with excessive runout, which eventually becomes a thickness variation, which becomes a pulsation. For the discs with less than .003" run out which have a pulsation, I tend to wholeheartedly agree with stoptech on the material transfer. For the rest, I still agree with stoptech.

I have seen freshly turned rotors with up to .040" runout cause no pulsation. I have also seen such rotors with +.020" cause low speed braking surge on fixed caliper applications.
I've seen a truck with ZERO rear brakes for hundreds, if not thousands of miles, have zero front rotor problems.

I've read TSBs regarding improper material and/or bonding adhesive transfer causing brake vibration or pulsation. On car lathe turning + new approved pads is the only fix for those, and even then, the transfer of material can run deep into the metal.

My biggest problem is techs who use the "scratch" method. Many techs who use this continually find boxed rotors or used rotors with "excessive" runout, but never inspect it on the hub. A bench-lathe is far from perfect, esp in a dirty brake shop with multiple techs.

[redsdad]

I think I am going to get flamed, but here goes. Impact gun instead of a torque wrench. I have seen it many times.

[1931 steve]

Originally Posted by redsdad

I think I am going to get flamed, but here goes. Impact gun instead of a torque wrench. I have seen it many times.

I also have seen this many times,

Why they warp.Steve, I can tell you....if nobody else does.

I do know most of the reasons that brake rotors warp.

Yes rotors warp, but they do not cause the pulsating brakes everyone complains about. That is from cementite inclusions in the cast iron.

Call it what you will, but when a customer steps on his or her brake pedal and the car shakes so hard that a tooth comes loose, they are looking for for an answer on why its doing what its doing. try explaining that its from cementite inclusions in the cast iron and they look at you like your crazy. Regardless of what caused the high or low spot in the metal, a high or low spot is still a warp in the metal.

Steve

[fitzwell]

Originally Posted by redsdad

I think I am going to get flamed, but here goes. Impact gun instead of a torque wrench. I have seen it many times.

yep.....torque wrench only !!

Rotors on my t-bird are bad about it, however, my lovely girlfriend is the cause of this. She has two feet and the car has two pedals...ergo, one pedal & one foot should be on the floor at all times

[Hippie]

When I was a pup I was an Inspector for Bear Mfg., you older guys remember the little yellow Bear signs right? We built brake lathes among other things and local garages would give us old rotors to use to test the lathes. I don't know what anybody else would call it but when you see regular alternating high and low spots I call that "warped".

[johnsongrass1]

Those who ride thier brakes in rain storms. Or those who are all brake or gas or both and drive thru water puddles.

Or your hard on the brakes and hit a 6 foot high concrete wall at 100mph.

[curtis73]

I think I see a discrepancy that should be cleared up. Some of us are discussing the same argument but different sides of the coin.

Warped describes a disc with UNIFORM thickness, but with runout. Like a vinyl record that gets hot. A warped disc doesn't cause brake pulse because the calipers are designed to let the pads follow the surface.

A rotor with bulges or depositions that change its THICKNESS will cause brake pulse, but that is not caused by heat, dragging brakes, or water puddles. That is caused from deposition of material.

I just wanted to maybe get us on the same page. A WARPED rotor doesn't change thickness, it only alters from flat. Its no longer a flat surface. A distorted rotor or one with depositions/inclusions on it has different THICKNESSES and will cause brake pulse. The spinning rotor is trying to squeeze thicker parts through the pads that you are applying pressure to. If its warped, the pads just alter their position to follow the rotor, but it doesn't necessarily alter the friction being applied to the rotor.

I think that's the difference. Die-hard techs call any rotor that needs to be turned a "warped" disc. Nothing has changed, its just a greater understanding which has caused us to apply a more accurate terminology.

[curtis73]

A photo to help explain what I was trying to say...

If you view rotors from the edge, here is what I'm saying. I may not be right, but at least it may identify how we're on different pages. This is obviously an exaggeration, but hopefully its demonstrative.



The rotor on the left is warped by the textbook definition and would not necessarily cause pulsing brakes. The rotor on the right is not warped, rather you could call it distorted, swelled, or maybe augmented. I don't see how the alteration on the right could be caused by anything but pad deposition, given the expansion properties of cast iron, but I've been wrong before. Under heat, the rotor would swell uniformly and contract uniformly at rest. I could understand that the heat cycling could cause warping like on the left, but it can't cause the distortion like on the right.