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

[GreekGod]

By Carroll Smith:

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml#

[Richy04]

The last line gets me about not topping off brake fluid, I dont know about any of you but I always replace the rotors along with the pads and always preferred a 4 wheel disc system over disc/drum combos (if I can avoid them during my vehicle purchase). So the point is moot in my book about topping off fluid. As we all know, the rotor/pads to watch is on the front right wheel. Its always the first to grind..

I never cut rotors on the newer cars anyway... I throw them out, Raybestos or Bendix all around and a set of cheapo NAPA chinese rotors on the beaters (FWD) and I squeeze an easy 50k with that combo out of cars that usually get 15k with OEM's before the rotors warp.

I once bought a set of Stillen rotors and pads for my Saturn, they lasted 13k before they started making noise and disintegrated within 20k miles, total garbage and they dont back up their product.

They drill the holes in the rotors and they dont heat treat them so the Rockwell hardness around these drilled holes is higher than the rotor surface from some type of unintentional annealing or tempering. The cause is the generated heat of the rotating drill bit as it cuts thru the metal surface. Since the metal is harder around the drilled holes, the metal wears slower causing little volcano shaped impressions on the rotor as the actual "untreated" flat surface wears a bit faster, which in essence cheese grates your pads in no time.

Never buy cross drilled rotors unless they have been heat treated or nitrogen dipped and machined to spec.. Hi end vehicles rotors usually get this treatment but not the lower end of the spectrum unless you pay for this service. The Panther platform is used in rough service/Police service so there are probably plenty of sources for new and high quality rotors for these cars.

[ahess77]

I thought this article had excellent information and emphsis on "good" brakes. Correct break-in of new pads/rotors is critically important, and why even brand new cars have sucky brakes (those get driven by idiots before they get to the dealers lots. In fact, I drive vehicles to troubleshoot windnoise, water leaks, etc. before we put them on the car hauler at the plant and I can tell you we are NOT wearing-in the brakes properly. Wait, does that make me an idiot too?)

I'm happy with my Command rotors & Napa pads so far.

[finster101]

I have been an ASE Master Tech. for twenty years and I have NEVER seen a rotor cracked like that one. As for "Warped Rotors" they do indeed exist. In fact there are many factory TSBs out on how to treat them including how to measure runout. Most warpage is driver induced. I can go 30,000 mi. on them my wife might get 10,000. till one day I noticed she was standing on the pedal at lights. Hot rotor, lots of pressure. I brought this to her attention and the problem has almost vanished as she is trying to change her habits. Same vehicle, same pads, just resufaced the rotors. Everyone has there opinion but since most of us drive our cars on the street, the larger rotor and Wildwood caliper is more than sufficient for most needs




'

[whd507]

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.


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uh, thickness variation, and run out would be the dictionary definition of a warped rotor...


if you ever re-surfaced a rotor, (or thousands in my case)you will often see a high spot on one side of the rotor, with a matching low spot on the other side. seems warped to me.

[GreekGod]

He mentioned "cupping", which sounded like warping to me, but it might, technically be different. I was told that Mercedes Benz auto, and some other rotors, are not to be "turned".

[Richy04]

That transferance of material is hogwash, I recently bought a set of rotors from one of the big chains when the local Napa couldnt get them for me. Under heavy braking you can actually feel the rotor surface change as they heat and the cast metal vents create little ripples in the rotor surface. When they cool off they brake like normal so I cant complain, its just a noise and slight ripple effect that you feel in the pedal. I wont use those rotors again. But the issue is not brake pad material, its the materials and how they are cast/machined.

The one thing they touched upon was steel vs iron. Iron is a far superior material to make rotors out of. Back in the old days, you could stand on a Typical GM brake pedal and never warp or overheat any of those big old rotors that took a set of D-52's. In fact you can change the pads 3-5 times before you had to cut or replace them as they were bulletproof.. Its these new sissy FWD cars and imports that led the way for substandard brake materials and shoddy engineering.

[finster101]

Those rotors were very heavy and included the bearing races with the wheel studs being installed into the rotor. Less prone to warping. Modern rotors are of "Top Hat" design with the center where it fit over the hub and wheel studs being very thin, they are significantly lighter and serviced much easier allowing for sealed bearings whitch is why they are used. Lug nut torque is very important on this style of rotor and should be tightend in a star pattern. without even torque they will warp. This does not happen immediatly but with repeated use heating and cooling.

[whd507]

putting a heat-transferring grease (tune up grease) behind the disk at the hub, I'm told will transfer heat away better.

yes most new rotors are meant to be replaced every time, not enough material for even one turn. thank CAFE standards, and auto companies run by accountants, not car people.

[Stranger in the Black Sedan]

heavy braking you can actually feel the rotor surface change as they heat and the cast metal vents create little ripples in the rotor surface. When they cool off they brake like normal so I cant complain, its just a noise and slight ripple effect that you feel in the pedal. I wont use those rotors again. But the issue is not brake pad material, its the materials and how they are cast/machined.


Wow you hit that on the head. I have a garbage pair of made in China Ebay "drilled and slotted" rotors, which I found after some research are worst-available budget rotors that are drilled and slotted to increase bling factor. They are way, way worse than stock.

Anyhow, when they are hot, you can feel the machining of the slots. When they are cooler you can't. They are really horrible and I'm going to have to trash them soon with only a little over 2k miles on them.

[Todd TCE]

A transfer issue is most certainly not "hogwash". It's a very real condition.

Brought about usually by either, A. Improper choice of pad material for the application, B. Hard use followed by stopping and baking, C. Moving from one material to another that don't mix well or D. Plated rotors.

A. can be fixed by matching pads to the use. Street, AutoX, open track use etc. If you expect one size fits all...that's hogwash.

B. this one is a combo of poor driving habits and/or the matter of having an automatic tranny. Keeping ones foot on the brake is just asking for problems.

C. is found when specialized materials such as PFC Carbon Metalics are replaced by other pads and the rotor not prepped. Most if not all pads lay down a transfer layer on the rotor. The CM pads do that and leave a deep carbon build up in the void. Many other pads cannot cut through that and skid over it and eventually pull some up to create high spots as they are spread out.

D. like above zinc plating is a major source of this but it's not the pad it's the zinc that gums up in the pad. Usually some high heat use will burn this off if you run hot for a few minutes. Zinc is also hogwash as it's only value is "box appeal" for the most part, it does nothing for function.

[Richy04]

Sorry Todd,

But in all my years of changing brakes I've never seen any kind of buildup on rotors besides incidental dust and whatnot. I'm not saying it doesnt happen, Im saying it hasnt happened to me (which to me means the same thing). I dont bother with exotic materials, just Raybestos and Bendix. I usually have to play around with rotors to find what works best but lately the cheap chinese NAPA's have been doing the job with no fade.

The Bendix or Raybestos were always good enough for every car I had even when run up over 100 mph and I've never seen any kind of transferrance of materials to the rotor. Like I stated before, I dont cut anything on these newer cars nor will I change pads onto old rotors, I change it all out with new so any buildup either imaginary or real is moot at that point.

Anything more exotic than that for normal street use and casual track use is a waste of money. If you want, I have some Stillen rotors from my Saturn you can have (for the shipping cost) with built in cracks and some chunks missing.

[Stranger in the Black Sedan]

Anything more exotic than that for normal street use and casual track use is a waste of money. I disagree. The bendix rotors, like a lot of aftermarket mid priced and budget rotors, are less-desirable side-split castings, unlike the OEM rotors which are almost always center split castings (like the Marauder OE rotors, which are made by LUK). A side split rotor casting will not transfer heat evenly to both faces.

Also, factory rotors are mill balanced, just like you balance a wheel. The Bendix rotors, like most aftermarket mid grade and budget rotors, are not balanced at all. They assume the material density is constant, the casting is close enough with minimal core shift, and that since most exterior metal is lathed, that it is evenly distributed.

You get what you pay for with brakes. OEM rotors are usually better than most aftermarket when it comes to metallurgy and finish. Some good aftermarket rotors, like Centric Parts' better line of rotors, are mill balanced and are center split castings.

So the Bendix, raybestos, and the like are not truly OE-grade rotors. They are better than the econo junk rotors, but not fully OE spec.

[Richy04]

Personally I find that OEM rotors can go either way, I've found OEMs that cant be beat and others that are junk when compared to even low budget rotors. Its hit or miss and finding out what works is not always rocket science but what actually works in a particular application. This may take several tries to figure out what works on that one vehicle.

Side split, fork split blah blah may mean everything or may mean nothing at all.. Most non vented rotors arent cast like that anyway. They are cast in one shot. Vented rotors are only as good as the materials, graining and how they are treated and machined and the only way you will find out in a performance application is putting them thru their paces. Like I said, my Stillens were claimed to be top notch rotors with all sorts of special enhancements and it boiled down to one thing, they were garbage in a pretty box and thats it. Cadmium plating and crossdrilling etc. Didnt hide the fact that these high end rotors should have been thrown in the garbage from day one.

As far as other factors go, the materials used in the performance pads may be too aggressive also causing grief which is why its best to go with what works individually. You can have pads that come in a fancy box with all sorts of claims that the materials used will increase braking efficiency but do nothing but heat up rotors and decrease stopping ability.

If you have no issues with warping, going to a ceramic or some composite pad may actually create an issue of warping and have the opposite effect than what you are expecting. Its all about balance, too much pad and not enough rotor and vice versa, everything plays a part and no two vehicles are alike. It may take a few changes to find out what works in your application.

Here we use alot of Impalas in rough service, fleet was using rotors that were cut and returned, they didnt last more than 3k miles before they started acting up. The rotors used on 9C1's are pretty beefy unlike the regular Impalas. But they dont like to be cut.

I understand what your saying about heat transferrance and rotor assembly, if the rotor is dissipating heat properly, the point at which the rotors are fused may not be an issue as the heat may be bled off prior to that becoming a factor. The quality of the joined area may in fact be better on one rotor as opposed to another no matter where they are joined.