x-drilled rotors cracking photo - 986 Forum - The Community for Porsche Boxster & Cayman Owners

ekam · 06-10-2009, 02:45 AM

I think this was brought up by Kirk, he said he has never noticed it before. Well...

It's from a 996TT after 6 DEs.

http://www.6speedonline.com/forums/2383623-post36.html

Lucky · 06-10-2009, 04:47 AM

This is common with cross-drilled rotors on all cars that are tracked. The prevailing wisdom (and one I trust) is it is a non-issue until you have a "significant" crack that connects one hole to another.

The rotor in your picture has insignificant surface cracking and nothing connecting the cross-drilled holes to each other. It isn't a concern at this point in the rotor's service life.

On a car I tracked often, I would not use cross-drilled rotors. Gas-slotted rotors perform just as well with less risk of failure due to cracking. That's what I used for many years on my 911 track car.

ekam · 06-10-2009, 05:28 AM

Regardless, I just don't like the idea that the rotors need to be replaced before they reach minimum thickness.

I am reluctant to order the rear stock S OEM rotors since they only come in x-drilled unlike the base model rears which come in plain or x-drilled.

jmatta · 06-10-2009, 06:01 AM

A 996TT is a very heavy car and will generate a lot of heat under braking, especially if the driver is not highly experienced in using brakes for short periods of time (may or may not be the case here).

I agree with Lucky's comment that those aren't throw-aways just yet, but I'd certainly keep an eye on them for further cracking. Slotted is a better way to go for track cars with plenty of air ducting. I've been tracking 911s for years and have always considered rotors throw-away items and would purchase fronts by the half dozen.

944boy · 06-10-2009, 07:28 AM

I saw a 944 S2 at the last DE that actually cracked the rotor so bad it was 'clicking' when the crack hit the pad.

jmatta · 06-10-2009, 10:58 AM

Quote:

Originally Posted by 944boy

I saw a 944 S2 at the last DE that actually cracked the rotor so bad it was 'clicking' when the crack hit the pad.

That is not good. We had a 911 cup car lose it's front end at a very high speed braking point and crashed, when the front rotor exploded, due to what I could only assume was a crack that went unnoticed.

eightsandaces · 06-10-2009, 12:37 PM

Who is the manufacturer of those rotors? They aren't Zimmerman because mine are not drilled as many times as those.

Lucky · 06-10-2009, 01:00 PM

Quote:

Originally Posted by eightsandaces

Who is the manufacturer of those rotors? They aren't Zimmerman because mine are not drilled as many times as those.

They are 996tt rotors, not Boxster S.

eightsandaces · 06-10-2009, 03:48 PM

Quote:

Originally Posted by Lucky

They are 996tt rotors, not Boxster S.

Are they OEM?

Brad Roberts · 06-11-2009, 08:20 AM

John/Lucky nailed it.

This is normal, and that rotor is not even close to failing. The *only* difference I go by to John's post? We let the rotor cracks go from one to another, but discard the rotors when the crack's are 3-4mm's from the very edge of the rotor.

B