Carnerd

No LS days, just 3 days at TH. Two days were put on by the first owner some where in Florida and the cracks were half that size before my 3 days...

fc-racer

I have the Porsche document on evaluating cracks, here is what it says:

Evaluating the cracks on the grey cast iron brake discs
• The brake discs must be replaced (as a precautionary measure), if the perforation crack
length is over 5 mm (as there is no mileage reserve in the event of further extreme load)
and/or the friction plate rim is torn (less smooth braking and an increase in the likelihood
that a disc will break)!
• In the evaluation of damage, the following drawings must be used!

A. Corresponds to a disc exposed to above-average load.
• Need not be taken out of the vehicle!

B. In parts, perforation starter cracks are over 7 mm long.
Conditions after shock braking 1,200 times (minimum desired: shock braking 200 times).
• Brake disc can no longer be used!

C. Brake disc with torn friction plate rim -arrow- .
• Brake disc can no longer be used!

Picture A has a rotor with slight cracks. Picture B has a rotor with long cracks. Picture C has a rotor with cracks that extend to the outer edge.

Carnerd

Is that referring to total crack lengths or the lengths of each of the two individual cracks per cross drill?

fc-racer

The document is kinda tough to understand without the pics, so I'll put it up for your reference: www.fcracer.com/gt3/porsche-rotor-cracks.pdf

todinlaw

I have this document and that is what prompted my thread. I do not have cracks connecting holes but some of my cracks are getting rather long. I am going to bed by new brakes and keep a close eye on the rotors. I am going to bring my back up set with me to the track. I bought the protosport slotted rotors.

Does anyone know where I can just by a rotor that is solid no slots no drilled holes. that will be my next rotor.

todinlaw

Most of my track days are at mid-Ohio only one long straight with heavy braking. So brakes are somewhat track dependent. It took me awhile to learn to go in slow to come out fast, for awhile I was not using enough brake and consequently not going vary fast either. Either that you you are just way faster than me.
I will say that they have not gotten much worse over the last 6 track days since the weather has been warmer and I don't think I shock the rotor as much with cold air.

KOAN

Frank,

I would use them until the cracks extend from hole to hole, or extend to inner or outer edge of the disc. These look like they have about 1 more weekend at Mid Ohio on them. If you are really concerned, then change them and take that lingering doubt out of your mind. If you figure out the cost per weekend, relative to all of the other costs, you will be throwing away very little. If mine looked like this, and I had a long time before the next event, I might just change them anyway. And as you probably know, rotor failure can be catastrophic. You also don't know what the cracks on the inside look like, unless you have been under there.
Will you be at the NORPCA , ARPCA or MVRPCA events at MO? I'll be going to those.

todinlaw

Thanks Chuck, I will be at NORPCA and MVRPCA I am undecided on ARPCA, I can do lapping days with MO school and may do that mid sept. instead of ARPCA. Did you get that ground hog damage repaired?

Kevinlpl

for what it's worth, My front rotors looked like that after one day at Laguna seca. They looked the same after two days at Buttonwillow, with no changes in crack length or depth. I switched to PFC direct drive rotors in front with PFC 97 pads front and rear. Not a cheap option but they work excellent.

On the "shocking the rotor" piece I have noticed that you can over cool rotors and they do seem to crack more (very fine hair line cracks) when it is cold out. In fact on my M3 I need to cover my Cooling ducts on all but 90+ degree days. The GT3 does look to have a very efficient system of getting air to the Rotor. I wonder has any one experimented with covering the holes in the air dam? I think there is a Dam available with no holes. Cracks did initially arrive on a cool day. It may not matter any way, just a thought. I have seen guys crack and explode a rotor at the track that look fine at the beginning of the day. In the case of the car I saw his rotor just destroyed the pads on that wheel.

mooty

i would go with slotted rotors: Deman motorsport or protosport

if you must use non slotted and no drilled, i THINK cayenne S rotors are solid and SHOULD fit your car (front)

BlackRain

Having Preformance Friction Slotted front rotors and pads installed this weekend. Putting new oem rotors back in the box.

todinlaw

I agree with you on the "Shocking" part, I showed my rotors to a metallurgists and he said it was not from heat build up but per se, but from quick changes in temp "shocking" he felt that over cooling is just as much a problem as heating them up and suggested tape over the ducts on cool mornings. I will start doing that in the morning runs.

Mooty I have the protosports now which will be installed when the current ones are shot, we will see how long they last.

Carnerd

The track i run isnt very hard on brakes either but i'm a very late braker. It's something i'm still working on. Funny you should mention slow in fast out, as thats what my instructors keep yelling into my ear. lol. But i think for a beginner like me, its definitely easier to come in fast and go out slow, hence the need for lots of work

I highly doubt it.

Are the 996 and 997 rotors essentially the same?

todinlaw

I think the the 996 rotors and calipers are smaller, but not for sure, I know I have 6 pistons up front big suckers.

As one of my fav instructors likes to tell me. at first when you are leaning to drive you are having so much fun and driving with you foot to the floor is way fun, it takes awhile to figure out that its even "more fun" to blast out of the corner at WOT

ze_shark

I just came back from 4 days at the Ring and the fronts look marginally worse than the pics on this thread. My rear pads are wearing twice faster than fronts, a Porsche tech on site told me it's because of TC being active even if there's no visible sign of intervention.

What are the merits of Cup steel rotors compared to OEM compared to slotted discs like Girodisc ? My independent specialist will only fiddle with Cup parts ...