PA safety inspection...failed!!

[stentech1]

The cracking that is present on the rotors is from expansion and contraction when subjected to the extreme thermal stresses created by the energy conversion process we call braking. The outer surface is  expanding and contracting at such extreme rates rated compared to the body or core of the rotor that these cracks develop.  Often these cracks are on the surface but only extend into the sub service a few thousandths of an inch. This happens to fly wheels as well with extreme clutch slippage. I have machined the rotors on my 996 tt that looked very bad with thermal stress cracks. After they were cut they looked almost like new. It is very difficult to evaluate the depth of these cracks with out resurfacing them. But any time a rotor is machined you are decreasing its thermal mass. Because there is less material thickness for heat to transfer to the rotor may warp easier (likely not a problem with a gt3 rotor). I did not need to take much off the rotors. Just make sure to be above the required thickness spec. Still have them on the car and they are fine.  Lots of shops are just unaware of whats taking place when a rotor has these cracks and wrongfully assume they fail. It is a judgement call and many just don't have enough experience to do it properly so they often error on the side of caution which is not always a bad thing. If you need a place that will inspect it call me.
SM