Do we believe in warped rotors?

therotman · 05-10-2008, 01:03 PM

So my front drivers side was making a sound like I had a nail in my tire so I took it off and there was no nail.

The sound is coming from the brake rotor making contact with the brake pad. The disk spins freely until two spots very close to each other on the disk where it rubs and is hard to pass?

What could be causing this?

It's on a 80 sc

peppy · 05-10-2008, 01:12 PM

I believe in warped rotors. I do not believe in turning them, I think as soon as you get them very hot they will be back just like they were. I could very well be wrong about this, just my personal experience with rotors.

therotman · 05-10-2008, 01:38 PM

So just some high speed stops should clear it?

I so wish the speed limit wasn't 55 here!

dad911 · 05-10-2008, 01:45 PM

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

From the article:
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.

vreference · 05-10-2008, 02:42 PM

In general if you cannot feel any pulsating in the pedal you probably do not have an issue with rotors - my understanding is that a small amount of runout is normal and desirable. I've seen some pretty bad rotors but I've never encountered one that would make a sound like a nail in a tire.

Steve@Rennsport · 05-10-2008, 02:56 PM

The ONLY way you know if you warped a rotor is to measure the axial runout with a dial indicator,......everything else is simply conjecture.

Overtightened lug nuts can distort the hubs sufficiently to feel like the same thing as well as uneven pad deposition.

Tyson Schmidt · 05-10-2008, 03:03 PM

What Steve said.

Plus, hot spots, which have a different friction co-efficent than the rest of the rotor. (Think of little heat-treated areas.) Ask me how I know.

Those hot spots probably start out as pad deposit spots that get hotter than the rest of the rotor.

adam912 · 05-10-2008, 03:17 PM

When I first picked up my '66 (in 1972!) It had a bad case of warped front rotors, the pedal pulsed pretty badly. These were solid rotors on a 912, so perhaps more likely to have been overheated. I removed them and had a local shop turn them down for me. I'm still running the same disks, believe it or not! Some 480K miles on them by now, and they've never warped again after that first experience. I've had my share of long downhill runs on Mulholland (brake fade is Nature's way of telling you it's time to slow down) and track time, but never a problem.

I do believe in warped rotors. I do!

Adam912.Out.
'66 912, 480K miles, 2.2L of lightweight T4 fun
Remember what we say in the 912 Registry, a 912 is one better than a 911!!

rnln · 05-11-2008, 01:05 AM

I had both experiences, most of the times turn them, worked for a long time. Once, I turned the rotors on my old MB, the warp cames right back after several days. Turned again, with new pads, warp came back again. New rotors and pads fixed the problem. So it's all depend, on what? I don't know.

rfn026 · 05-11-2008, 03:47 AM

I've actually seen warped rotors - but not very often. Get your dial indicator out and check it. You may be one of the rare cases.

Richard Newton

Wheel and Tire Performance Handbook

Bill Verburg · Bill Verburg's Garage

Quote:

Originally Posted by Steve@Rennsport

The ONLY way you know if you warped a rotor is to measure the axial runout with a dial indicator,......everything else is simply conjecture.

Overtightened lug nuts can distort the hubs sufficiently to feel like the same thing as well as uneven pad deposition.

+1, they do bend, sometimes inelasticly

As Tyson noted hot spots are generated when ever there is rotating friction, the number & position is related to the pad size & composition, rotor speeds, and temperatures. The crystal structure of the hotspots is rearranged to a hardness that will ruin tool steel cutters. The surrounding rotor material being much softer will erode much more quickly, leaving a wavey pattern in the rotor faces.

pad deposition is an entirely different issue which can be felt as a pulsation in the brake pedal, some pad materials can build unevenly, the most notorious here is Pagid Orange which if not carefully bedded will leave deposits unevenly across the rotor faces. Newer pad materials have greatly alleviated this problem.