Warped Rotor Myth (by Beandip)

[TomoHawk]

I think the guy did the rotor the way you suggested, not some kind of shortcut. I will review the FSM on this to be sure, but as it had be said earlier, 'certified' tech guys don't need the customers telling them how to do their job, even if they have the FSM with them.

thxZ

[bjhines]

I have to disagree with the issues of pad material transfer. This is made out to be more of a problem than it is.

I have run damn near every combination of brake parts ever used on S-30s. ON TRACK and on the street. Willwoods with a balance bar are on the current track buildup and the only combo I have not run to the breaking point yet. Gimme a few months...

The most common causes of brake shudder are dirty mounting surfaces and warped rotors. Many rotors come out of the box WARPED!!!

Another common problem is dirty/rusted mounting surfaces... clean them well and the rotors will be less problematic.

The aluminum spacers used to mount the 300ZX rotors are prone to corrosion and may even speed up the process between the dissimilar metals. The aluminum spacers seem to exacerbate the "warped/wobbling" rotors symptoms.

The answer to this issue is to mount the rotors on the hub and turn the entire hub assembly with the rotors bolted to it on a brake lathe. This is a "cure all" for those annoying shuddering brakes.

I always do this with new rotors. I keep a second set of hubs with turned rotors mounted and ready to swap.

As far as overheating rotors... I have had them split radially through the entire radius before they warped. I get thousands of stress cracks in the first 30 minutes of track duty.. they last for many events beyond that initial crack-in time. Overheating is not as much of an issue as it is made out to be. Street driving simply will not stress brakes as hard as track use. I don't have warpage problems on track so there is not a correlation between overheating and warpage.

I am willing to bet that there is a problem with getting the brakes WET while hot. That is a much more plausible cause for warpage than simply overheating the rotors. It may turn out that spirited street driving and then running through a river will cause warpage of the rotors.

Edited August 12, 2008 by bjhines

[Tony D]

All you guys bagging on Mr. Smiths caveats to his 'I've never seen a warped disc' statement.

You are grossly eversimplifiying the statement he made (as someone put it earlier 'in a ham-fisted way')

He said (paraphrased) where the rotor was installed correctly and bolted properly---so those of you jumping up to beat the drum of 'I've seen it on the lathe' have to remember that little phrase.

He didn't say it wasn't possible to not warp a rotor. He said it was not possible for BRAKE APPLICATION to warp the rotor.

That is a BIG difference.

When I took the ASE Certification Tests in 1981 rotor deposition was not taught. But what was pounded into our heads was proper cleaning of the mating surfaces of rotor and hub, proper bolting, proper torquing of any fasteners used to mate hub and rotor, and on those slip-on rotors, the critical nature of lug nut torquing.

"Fastest way to warp a rotor gentlemen, is to act like an idiot and impact-hammer the hell out of each individual nut as you reinstall a tire!"

That little speech was followed by a technical demonstration using two rotors and two hub assemblies where each was assembled correctly, according to the GM Assembly Instructions, and then 'quickly like a flat-rater will do'...

We then dropped the wheel assembly off and indicated off the rotor surface.

Guess which one showed CONSIDERABLE runout/warpage?

The big three sucked at a lot of things in the late 70's, but their contribution to local technical education programs was outstanding. And thanks to GM's Largesse at the time (and to a lesser extent, to Ford's) I got some pretty high-end factory-direct technical education. We had people form AC Spark Plugs come in and give extensive lectures hands-on demonstrations.

I get the feeling now, knowing what I know, they were prospecting for talent for their own technical service departments, but that's a different subject.

Carol Smith didn't say there is NO way to warp a rotor. He simply said that barring the ways TO warp a rotor, brake application is NOT one of the contributing factors!

[jmortensen]

Carol Smith didn't say there is NO way to warp a rotor. He simply said that barring the ways TO warp a rotor, brake application is NOT one of the contributing factors!

I don't know why this thread is coming back from the dead, but I've personally had warped rotors on my 93 Toy P/U 2wd. It's a slip on rotor, and I always torque the lug nuts, and I know how to use a torque wrench. Cut the rotors, they warped again. Cut them again, they warped again. Each time was the same, when put on the lathe the cutter hit one side of the rotor and as the rotor turned around it hit the opposite cutter. They were not thicker in one part of the rotor and then thinner in another. They were tacoed, warped, whatever you want to call it. When I switched from Metal Masters to stock Toyota pads the problem went away. You can try and tell me that my hubs were dirty or that I didn't torque the lug nuts correctly three times in a row but have done so ever since, or that I don't understand what "warped" means, but I'm not buying any of that. Carroll Smith was right about a lot of things. On this issue of brake pad deposits, I think he was wrong. Maybe not absolutely wrong, but certainly I believe his statement that braking doesn't cause warpage was wrong. He was also wrong in Tune to Win when he espoused anti-Ackermann. That doesn't make him any less right when he was right, which was about 99.999% of the time.

[Mike]

Nice job!! Thanks guys...

[TomoHawk]

Like Tony recommends, I usually insist that a service person install the parts & fasteners by hand and hand-torque the fasteners, and then hand torque the wheel nuts before letting the car down. Especially for the wheel & brake parts like the rotors. A good or honest person will do that when requested.

And I will demend it on the work request, and stand there and watch when the fasteners are tightened. Any place that won't comply will immediatetly have me walking out the door.

thxZ