Brakes Rotors DON'T WARP - Article

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SumpChump

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This article was a good read. I just replace the term "officer" with "wife" when i read the article.

In a nutshell they say that rotors wear unevenly.... They dont warp. And imply further that there are not unknown causes of pulsing pedals... there are just mechanics that can't decode the reason.

The comments at the end disagree. But the way it is written makes sense.

One big thing i took away was doing a runout reading AFTER even NEW rotors are mounted.

LINK
http://www.hendonpub.com/resources/article_archive/results/details?id=1787
 
not that im an expert in rotors but every time i have a pulsating brake pedal i changed the rotors and all was good. I know if you tighten the wheel to much on some vehicles that can cause it also.
 
Originally Posted By: crazyoildude
not that im an expert in rotors but every time i have a pulsating brake pedal i changed the rotors and all was good. I know if you tighten the wheel to much on some vehicles that can cause it also.


Right, replacing them works of course.

The article was aimed at making the case that it is mechanical forces and wear rather than heat that causes runout.
 
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People just say the rotors are warped. They are just not of uniform thickness anymore. Could be wear or pad transfer material. Replacing the rotors almost always fixes the problem (for awhile).

How many shops use a dial gauge on brake rotors?
 
I never had the expirience of a "warped" brake disc with a pulsing feel in my Motorcycle. Difference to cars? The brake discs are mounted "full floated", means they can move freely, and are well cooled.

I only expirience warped dics with a pulsing feel in Cars.

I never have this expirience again since i only unse high-quality heat threated brake discs (ATE) with quality brake pads and allways take care that the caliper guides are greased correctly so the caliper can move freely.

However, every rule has a exception: On the ridicoulus small VW 239x12 mm unventend front "Kindergarten" brake disc nothing helps if you do some hard brakes down from 160 Km/h at the Autobahn, the brakes are gone and start pulsing. Only the upgrade to the beefier 239x20 mm vented disc helps.

Just my personal expirience and obeservation over the last 25 years.
 
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Yup, lots of alleged "warped rotors" are really rotors that wore unevenly because of runout or another cause.

When you put them on the lathe it cuts the high spots first, which is probably what had led people for years to think they're warped, when the real issue is thickness variation.
 
I think a lot are pad deposits on the rotor. I use cheap rotors with high quality pads, always use a torque wrench to make sure he lugs are evenly tight. I don't get warped rotors since using good pads like Hawk , wagner severe duty etc.
 
Is it OK if we just invent a new word for "WARP"? Why not just say the rotors have "foobared" and need to be cut or replaced to make the brake pulsation go away? Does that technically change *anything* ?

There are few internet gurus who get very upset at the word "WARP" and go on tirade to convince the rest of us that rotor don't get "WARPED". OK I get their point but the word itself is irrelevant.
 
Checking the hub surface before mounting the rotor and using a torque wrench is the key to a good installation.
 
They definitely get thinner, especially in GM applications where they were too thin to begin with, and eventually will rust in salt/high humidity areas, and they do get wavy when they get too thin. Remember Raybestos does provide a warranty on their rotors, & they have a VESTED INTEREST in downplaying the warpage issue, especially on Chinese rotors.
 
Some parts of the article are correct but you have to realize it is written or endorsed by a company who sells many millions of imported rotors! With today's rotors you need to be ultra vigilant that torque specs and patterns are observed and runout is minimized. Old rotors were much heavier and newer cars try to minimize material to save gas.

I always run the dial indicator on the hub surface too. I found a hub surface that was like .008 on one sector. The face was was free of rust too. The rotor had a nasty hard black spot on it and the wheel would shake noticeably on braking. If I installed another rotor without measuring and replacing the hub, the same thing would have happened, and I would be going back to advance auto in a warranty loop.
 
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I've read that article before and agree with almost everything in there, but there are cases that will warp rotors.

RWD Volvos will absolutely warp rotors if the front lug nuts are improperly torqued and you get on the brakes hard enough to get them warm. They don't wear unevenly, they warp *then* they start to wear unevenly.
 
before last year I never ever even replaced a rotor. I have never had the pulsing brake pedal I so often hear. Then last year, I did brakes on my 08 RAV4 and was surprised how rusted they were. I can see the benefit if new rotors now.
 
Originally Posted By: stephen9666
Yup, lots of alleged "warped rotors" are really rotors that wore unevenly because of runout or another cause.

When you put them on the lathe it cuts the high spots first, which is probably what had led people for years to think they're warped, when the real issue is thickness variation.


I know a guy who took the brake drums off the rear of his brand new truck and put them on the lathe at his workplace cause they weren't evenly machined at the factory. He still has the original rear brakes at like 200,000 miles with hardly any wear.
 
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The main culprit in "warped rotor wheel wiggle" is non uniform pad imprinting.

Where the heat ranges and metals in the rotors isn't well matched with the makeup of the pad and chunks of pad "weld" themselves to the rotor

Manufacturers get this wrong all the time. My titan was like this - it started wheel wiggling on braking right out of the gate. Kept it up regardless of turning until I replaced the whole rotor and pad set.

Ive seen hundreds of brake rotors on lathes and I've seen uneven thickness but I have yet to see a "warped" one.

I'm sure that happens - but Ive never seen it.

UD
 
Originally Posted By: cat843
How many shops use a dial gauge on brake rotors?

Mine. I start off by cleaning the bearing hub surface, washing the (new) rotor in hot, soapy water with a Scotch Brite and finishing with a rag. Rinse and blow them dry. Then I apply a layer of anti-seize to the inside of the rotor hat and tighten them down using cone washers in between the rotor and lug nut. I typically shoot for .002" or less run out, and it's not uncommon to need to re-index them on the bearing hub to achieve it. Every now and again I'll get one that simply won't go in spec and the bearing hub is to blame. It's not often it happens, so I don't typically check them.

Originally Posted By: ford46guy
Some parts of the article are correct but you have to realize it is written or endorsed by a company who sells many millions of imported rotors! With today's rotors you need to be ultra vigilant that torque specs and patterns are observed and runout is minimized. Old rotors were much heavier and newer cars try to minimize material to save gas.

That's not my experience. Rotors seem to be getting bigger and beefier. Look at a rotor from an 80's or early 90's car of truck and compare it to the same model car or truck from a much later year. BIG difference! Bigger in diameter and thicker braking surfaces too.

Also it's virtually impossible to not buy an imported rotor as a shop (who wants readily available parts, soon), but buying premium parts will typically guaranty all OE dimensions are met.
 
It's a question of terminology.

The rotor itself does not warp, uneven wear on the rotor causes the rotor to have a warped appearance.
 
The main causes for what is commonly referred to as warped is the rotor being initially installed on unclean hubs, sticking pips or pads, not checking the run out and caliper bracket misalignment (seldom).
Cleaning the hubs and checking run out is easy enough and should be done every time. Checking the bracket alignment is simple with feeler gauges, misalignment is not very common but if the car is having constant unresolved pulsation issues this is sometimes cause.

A misalignment bracket generates uneven forces even with new pads and pins and can cause all sorts of problems including soft pedal and pulsation. All these can usually be corrected by cleaning and moving the hat in the case of the rotor but sometimes shims are also needed to bring everything into spec.

Good info..

http://www.classicperform.com/TechBook/BrakeTroubleshoot.htm
 
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