Mark in Baltimore

My stock rotors have a number of small hairline cracks that I understand are common under heavy track use. I have done a search on the archives regarding rotor cracks and have reached the following conclusions (please let me know if I am off-base on any of these points):

1) Rotor cracks originate from the vent holes and are caused by high heat generated from hard brake application.

2) The cracks need to be watched and the discs replaced when the fractures meet or migrate to the outer edge of the disc.

3) Cleaning brake pad material from the vent holes may or may not help this problem.

4) Cryogenically frozen rotors are less prone to cracking but will eventually experience the same problem. Some say frozen rotors make little difference in terms of warping or cracks or disc life.

4) Solid rotors do not have this problem. Also, modern brake pads do not create gases upon heavy application as they once did many years ago. Thus, the vent holes are unnecessary in relieving these gases and are designed more for dissipating water when running in the rain. I have read conflicting opinions on the true purpose of the vent holes.

So, can anyone recommend a solid disc, stout enough for racing or DE's, to prevent this from happening? I have seen some discs with lines cut into the rotor but I'm not sure what effect these slots have, especially in light of the gases vs. no gases debate. If there are no solid, race-worthy discs out there, what are people doing to prevent or slow this problem, other than replacing the discs every year?

I've done some extensive searching but if I missed something, please include a link. Thanks for your help.

chris walrod

Slotted rotors would be my first choice. Let us know if you find someone who makes them for the 993...

fluid15

Cracks will originate from the holes since stresses are much more around the hole edge than throughout the solid planar surface (you engineers reading this will understand the 3x formula ).

Steve Weiner-Rennsport Systems

Hi Mark:

Good information posted by Fluid15,....he is right on target.

Drilled brake rotors crack from the heat and the expansion range they endure. Its almost impossible to prevent this.

AFAIK, nobody makes a 299x28mm plain or slotted rotor that fits these cars. I certainly can make you an Alcon racing rotor/hat combo but those will cost almost as much as a Big Red kit with no better thermal reserves,...

Although you might not want to hear this,.....the real answer and solution is to increase the mass of the "heat sink" and do the Big Red TT brake conversion. This will pay dividends by reducing your current rotor & pad temperatures and therefore reducing the frequency of replacement.

maurice97C2S

Hi Steve

Having just replaced front rotors and pads, I was struck by the incongruity of taking the trouble to cast hollow spoke wheels, and then attaching them to 8.5Kg rotors (and that's not the big ones!) supported by aluminium wishbones.

Do the racing ones have significant unsprung weight advantages?

Cheers, Maurice

993944S2

Hi Steve;

I have a similar question to Maurice. In your opinion, most things being equal, do the advantages you mention in going to Big Red's, outweigh the disadvantages of additional weight?

Thanks;

Don Ehinger

swftiii

Mark - great topic! I will be needing to replace my rotors this winter too and was wondering if there was an alternative.

Steve and everyone else. Thanks for the advise. I already have the Big Reds and am interpreting that the only solution is the cross drilled rotors in replacement. Is there a brand that makes better rotors, or should I just stick with OEM?

Thanks

Flying Finn

I'm having cracking problems also (I don't have big reds)...

I have brake cooling ducts but I think for cracking that might not help since your brakes are cooler before you come to the braking zone, so when you suddenly aplly hard braking (lot of heat), that's even worse?

Mark in Baltimore

Gentlemen - Thanks so much for your reponses, although they weren't what I wanted to hear. Can anyone elaborate or clarify on the efficacy of frozen rotors?

Skip - looks like we're going to be old pros at changing out the rotors.

Steve - I guess all roads (tracks) lead to Big Reds, yes? Dammit.

swftiii

Mark - yup. We'll plan on doing both cars at our DIY weekend! Sam is interested as well.

All others - We'll let you all know when we are doing the DIY weekend. Right now it includes the following: Skip's brake rotors, Mark's brake rotors, Mark's Catz HID install. We are considering Nov/Dec time frame (once the DE season is over...)

-Skip

Rezal

Steve,

My mechanic expressed concerns upgrading the C2/C4 with Big Reds specifically around the F/R bias and the smaller C2/C4 master cylinder.

There's been a lot of discussion around here re: the proportioning valve. Someone even posted the part number for it (it had a 964 prefix). Others have said to remove the valve altogether. What's your take on this?

Also, with the small master cylinder, will I get a spongier brake feel or longer brake travel due to the larger volume of fluid to move with the larger Big Red pistons?

Finally, are the front Big Reds actual floating rotors? They appear to be of a 2 piece design (i.e. rotor connected to hub with bolts). My understanding is that floating rotors have less warpage and provide better heat dissipation.

Todd B

Mark & Skip,
I just replaced my front rotors a couple of weeks ago before going to VIR. Also put on Pagid Orange pads, boy do those suckers stop, now I just need to brake later . Replacing the rotors was real easy, it helps if you have the brake line modification on your front shocks, that way you don't need to disconnect the brake line from the caliper.

Also get the factory rotors, that way you don't need to paint the hubs. I bought the OEM rotors and needed to paint/bake them.

My oranges were squealing like mad at VIR, I have been told that I'm not braking hard enough and letting the pads get hot.

Let me know when you guys are planning to do the DIY weekend.

Todd

Mark in Baltimore

Todd,

Thanks for the info. I have Pagid Oranges on, too, and love how they stop. Like you, one person told me my pads squeal on the track because my pads aren't warm enough but I'm skeptical. At turn one at Summit, I'm braking at the second line. I suppose I can try going one line deeper to make my brakes *really* hot. And everywhere else, I'm darn near hitting the ABS on the bumps in braking zones such as Wagon Bend and Turn 5.

I ran into Manny a couple of days ago and he said you and he had a ball chasing people at VIR. I think he said you dropped 10 seconds from your time. Nice!

Are you going to the First Settlers DE at VIR next weekend? Manny, Tim and I will be there.

JC in NY

Factory Cup rotors are the same as what you have. They are the Big Reds.

swftiii

Todd - I believe you are referring to the modification to the brake line holder using the dremmel tool. I don't think mine are modified, but I just got a dremmel, so it should be fun. Is it easy to do without screwing up the brake line?

We'll let you know about the DIY and with the post, you can be the rotor replacement instructor...

-Skip