Brake rotor questions

[A26B]

Originally Posted by Paul Workman

This article is one I can attest to for accuracy by its applicaton to my brakes in several different cars/brake jobs now over several years (since this article came out).

A good read. Check out the article regarding warped rotors and other myths. I've never had a "warped rotor" since studying this article, and neither has my wife since coaching her on braking on especially hard stops.

http://www.stoptech.com/technical-su...nd-other-myths

P.

Admittedly, I am not a brake expert and do not profess to be, but do have some questions about the article. Understandably, the author probably was never able to check the run-out of a hot rotor, i.e. one that was causing pedal pulsation just moments before.

I agree completely with his reference to hot spots and have no arguement with the causes. And, as he states, hot spots do occur for whatever reason. When uneven temperature (hot spots) occurs, thermal expansion/growth will be greater in the hotest areas, which will result in a change in thickness and waviness or irregularity in the flatness of the rotor. Depending on the metalurgy and a host of other characteristics I am unaware of, the irregularity may not be noticable when the rotor cools down, and can be inspected.

I know of no other reason that would cause brakes to work fine, with no pulsation in normal driving, but does occur & progresses as the brakes are used more agressivly, i.e. get hotter. The transference of material and the molecular alteration described in the article is well known, but does not go away when it cools down. If such "buildup is the cause of the pulsating pedal, then I would think it would still be present when much cooler under normal driving conditions.

So, for lack of my complete understanding of the subject or a better term, I call the phenomena "hot warpage," because I think that is what it is. BTW, I do break in according to instructions.

As always, I remain open minded and receptive to productive discussion.

[batchman]

Originally Posted by Paul in SC

I have a very good friend that drives SCCA pro and he goes with custom everything (Coleman Rotors).

I would love to figure out the recipe for Coleman rotors on stock c4 setup. Looking through their catalog once it looked like the stuff was there and not unreasonable, but I've never had a fresh GM rotor to get the measurements off of.

Too bad I just can't afford to buy them from the houses that do know the measurements...

Cheers,
- Jeff

[scottfab]

Originally Posted by A26B

.... snip.....
When uneven temperature (hot spots) occurs, thermal expansion/growth will be greater in the hotest areas, which will result in a change in thickness and waviness or irregularity in the flatness of the rotor.

In the article he says this is not a warped disk. Interesting. I sure would call it warped.

Originally Posted by A26B

Depending on the metalurgy and a host of other characteristics I am unaware of, the irregularity may not be noticable when the rotor cools down, and can be inspected.

I know of no other reason that would cause brakes to work fine, with no pulsation in normal driving, but does occur & progresses as the brakes are used more agressivly, i.e. get hotter. The transference of material and the molecular alteration described in the article is well known, but does not go away when it cools down. If such "buildup is the cause of the pulsating pedal, then I would think it would still be present when much cooler under normal driving conditions.

I know this is counter intuitive but I've experienced it. That is no pulsation after cool down. Upon continued driving after the first say half dozen heating/cooling events the pulsating was permanent. Not sure why the pulsating went away the firs few times.

Originally Posted by A26B

So, for lack of my complete understanding of the subject or a better term, I call the phenomena "hot warpage," because I think that is what it is. BTW, I do break in according to instructions.

As always, I remain open minded and receptive to productive discussion.

I have tried the break in process recommended in the article with mixed results. On my C4 it worked. On a friends Toyota Avalon it failed, not just once but twice with new pads and disks. The solution was to dump the ceramic pads.

In the article it is stated
"Regardless of pad composition, if both disc and pad are not properly broken in, material transfer between the two materials can take place in a random fashion - resulting is uneven deposits and vibration under braking."

Note he states "can take place" not "will take place".
From what I learned on the Toyota when using OEM pads there is NO "material transfer" sufficient enough to cause any pulsation even if no break in process is used.

[4CAM LT5]

Originally Posted by Paul Workman

This article is one I can attest to for accuracy by its applicaton to my brakes in several different cars/brake jobs now over several years (since this article came out).

A good read. Check out the article regarding warped rotors and other myths. I've never had a "warped rotor" since studying this article, and neither has my wife since coaching her on braking on especially hard stops.

http://www.stoptech.com/technical-su...nd-other-myths

P.

Good info....all around. Thanks...!!!