Cutting (resurfacing) 930 cross drilled rotors?

[NY65912]

Hi to all,

I stopped by my local wrench, a P/F/B car shop (Rudtners) to pick up my son's New Beetle on Sat, we had some suspension & exhaust mods done.

Drove the 911 TL out to him about 20mi. Anyway, I mentioned that I get a slight shimmy in the wheel on braking (towards the end of the stop) and around hard corners.

We jacked up the front of the car and he saw some runout on both front tires, which are brand new Dunlops.

My wrench felt it was due to the brake rotors being just slightly out and suggested cleaning them up on the lathe.

Anyone out there have any experiences with "cutting" cross drilled rotors?

(PS....I did a search and came up almost empty.)

Thanks, MikeČ

[jakermc]

Before deciding to do this use a micrometer and take measurements in sevral areas of the disc. Find out just how warped it is so you know just how much thickness you'll lose on the lathe. You'll then want to compare area with the smallest thickness to spec and see if the rotors are still usable after the work.

You'll also want to investigate how your warped your rotors. Under normal circumstances, this shouldn't happen. Is something else wrong that may have caused this?

[asphaltgambler]

European vehicles engineers design their brake rotor and pads to wear together as a unit to obtain maximum performance with low noise. The trade-off is that the rotors are inherently soft compared to US vehicles are are not really made to be machined after a life cycle use.

If you try to machine them they will look ok, but what happens is that the brake lathe bit actually tears the metal surface rather than cutting it. By reducing the overall thickness after machining you increase the chance of the rotor heat-warping because now it is thinner.

[Bill Verburg]

They can be surface ground but not put on a lathe, I would suspect either suspension settings or components are the culprit for abnormal tire wear.

[NY65912]

Done. New rotors for my baby.

Thanks,
Mike

[Drdogface]

You might take a look at this link which was posted yesterday. I found it very interesting...

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