Warped Brake Discs and other Myths - A Brake Primer

[Steve04SE]

Warped rotors has been a hot topic on the Corvette Forum and this link surfaced (no pun intended ) a while ago creating much controversy. A Vette buddy of mine (who I find to be very knowledgable) has proven, to himself at least, the article has merit. He was given some supposedly warped Eradispeed rotors and after removing (I'll confirm his method) the brake pad deposits, the brake pedal pulsing ceased - so now I think the article has merit. Anyway, each can make up his own mind on the subject; afterall, it is good, informative reading.

http://www.stoptech.com/whitepapers/...otors_myth.htm

The term "warped brake disc" has been in common use in motor racing for decades. When a driver reports a vibration under hard braking, inexperienced crews, after checking for (and not finding) cracks often attribute the vibration to "warped discs". They then measure the disc thickness in various places, find significant variation and the diagnosis is cast in stone.

When disc brakes for high performance cars arrived on the scene we began to hear of "warped brake discs" on road going cars, with the same analyses and diagnoses. Typically, the discs are resurfaced to cure the problem and, equally typically, after a relatively short time the roughness or vibration comes back. Brake roughness has caused a significant number of cars to be bought back by their manufacturers under the "lemon laws". This has been going on for decades now - and, like most things that we have cast in stone, the diagnoses are wrong.

With one qualifier, presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification, 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. I have seen lots of cracked discs...

PREVENTION

There is only one way to prevent this sort of thing - following proper break in procedures for both pad and disc and use the correct pad for your driving style and conditions. All high performance after market discs and pads should come with both installation and break in instructions. The procedures are very similar between manufacturers. With respect to the pads, the bonding resins must be burned off relatively slowly to avoid both fade and uneven deposits. The procedure is several stops of increasing severity with a brief cooling period between them. After the last stop, the system should be allowed to cool to ambient temperature. Typically, a series of ten increasingly hard stops from 60mph to 5 mph with normal acceleration in between should get the job done for a high performance street pad. During pad or disc break-in, do not come to a complete stop, so plan where and when you do this procedure with care and concern for yourself and the safety of others. If you come to a complete stop before the break-in process is completed there is the chance for non-uniform pad material transfer or pad imprinting to take place and the results will be what the whole process is trying to avoid. Game over.

[Memphis4x4]

Good article Steve.

I have always heard that warped rotors could be 'fixed' by turning them.
I am not a big proponent of turning rotors......I feel that it is the Service Departments way of getting more money out of us by removing rotor mass and thus requiring the rotor to be replaced after two turnings. I have almost 200k on a Toyota 4Runner and have never replaced the rotors. During the first 50k miles, I got severe vibrating and shudder through the braking system. I thought, "Great, my Toyota is exactly like my old Honda Prelude with cheap brakes that warp easily." I replaced the factory pads with a metallic/dustless pad and drove with those. Over time, the shudder/vibration went away.....I thought that the harder pad material had 'turned' my rotors for me. When I read your article, I think that what really happened was that the harder pads removed the brake pad deposits on the rotors thus 'fixing' the problem.

Thanks again for the article

[Half Shovel]

Hmm. I'm no expert, so I'm not going to come out and disagree with this article, but I did work as a mechanic for a couple of years, and I turned my share of "warped" rotors. You could see 'em shimmy on the lathe, and they were pretty obviously NOT straight. Can you comment on this? Also, it seems that once a rotor is "warped", turning it is almost always only a temporary fix - they re-warp at some point.

HS

[1Titan]

Yes. that is an excellent article I came across as well while researching other sites,there are many good sites re: factors that cause warped rotors. Notice the way pads are broken in as described in the article? I seriously doubt that is ever done properly. Even on new vehicles from the factory. And the TSB out right now by Nissan describes the burnishing similar to the article above. Thanks for sharing that.

[Steve04SE]

Originally Posted by Half Shovel

Hmm. I'm no expert, so I'm not going to come out and disagree with this article, but I did work as a mechanic for a couple of years, and I turned my share of "warped" rotors. You could see 'em shimmy on the lathe, and they were pretty obviously NOT straight. Can you comment on this? Also, it seems that once a rotor is "warped", turning it is almost always only a temporary fix - they re-warp at some point.
HS

IMHO, they will re-warp even quicker because there is less metal thickness after being turned. Also, the rotors of today are significantly thinner from the factory than those of 20-30 years ago which had enough thickness so that being turned would NOT create accelerated warpage like today's rotors.
My .02