[David in VA]

I have the exact same thing happen on mine at the track under heaving braking. I always assumed it was pad deposits, I'm using Zimmerman drilled rotors and Hawk HP Plus pads. Other than the shaking I never noticed any other detrimental effect to braking and it always goes back to being fine once it cools down.

[Jase007]

Michael et al.

"The "Warped" Brake Disc and Other Myths of the Braking System"

by Carroll Smith

xcellent article and 99% of the time is " ...pad material transferred unevenly to rotor surface".*

*caveat - rotor to hub mounting surfaces clean, rotor installed flush, caliper and wheels mounted and torqued in correct sequence per mfg. instructions.

[Mackpipes]

Originally Posted by michael lang

Okay, excellent. Thank you. Now after you did that, did the problem ever return? And did you go through the same procedure or had you gotten rid of your 911 so you really don't know if it ever came back? Thanks again Ted.

The problem never did return. I did continue to use the pads until they were gone. I believe the problem occured in the first place because I did not follow the break in proceedures. I should add that I was using stock rotors.

[michael lang]

Thanks for the article Jase. I really don't have time to read it all right now but just skimming through it, looks like it may be on the right track. I am going to go through what Ted did as well. Good news is I don't have to worry about it right away as track season is pretty much done until spring.

[Hunter]

Michael:

FWIW, I had that happen to me twice. The first was pad material build up and the second time was a bad pistion in my front caliper. It is alot more uncommon than pad build up but I went through pads really quick since the pads where wearing unevenly. I have stock rotors and at the time Pagid Blues. I now have a new caliper and Pagid Yellows and they are great. I would getprogressively more shimmy/shake under hard braking. My steering wheel would jump +/- 1" at the approach to turn 1 at Summit.

Good luck.

[William Miller]

The article mentions:

"If only a small amount of material has been transferred i.e. if the vibration is just starting, vigorous scrubbing with garnet paper may remove the deposit. As many deposits are not visible, scrub the entire friction surfaces thoroughly. Do not use regular sand paper or emery cloth as the aluminum oxide abrasive material will permeate the cast iron surface and make the condition worse. Do not bead blast or sand blast the discs for the same reason."

Where to get "garnet paper" What Grit?


He also mentions to have the rotors "Blanchard Ground"
What's that?

I had this problem really bad on the upgrade to the 928 4 piston calipers.
I though the rotors were bad.
Tony Kelly took me on the back roads near SP and heated them up smokin hot for a while and it did get rid of most of it. This was on stock type pads.
They squeeled bad after that until I sanded the pads down some and re-bedded them.
Now there's just about 1/10 of the shuddering.
I'd love to get rid of this once and for all!

[michael lang]

Originally Posted by Ken Weiss

Michael:

FWIW, I had that happen to me twice. The first was pad material build up and the second time was a bad pistion in my front caliper. It is alot more uncommon than pad build up but I went through pads really quick since the pads where wearing unevenly. I have stock rotors and at the time Pagid Blues. I now have a new caliper and Pagid Yellows and they are great. I would getprogressively more shimmy/shake under hard braking. My steering wheel would jump +/- 1" at the approach to turn 1 at Summit.

Good luck.

Ken, what I forgot to also mention was that the front brake calipers were also replaced with brand new from Porsche at the same time I did the front & rear pads/rotors and installed steel braided brake lines. I'll be doing what Mackpipes had suggested on Sunday afternoon but I won't be able to know if it did anything to improve until next spring. Thanks for the suggestion.