Front Disk Cracks - When Unsafe

[drhildr]

Despite clearing out the holes on the front disks, the cracks that radiate from them are now getting steadily worse after 3000 miles, 3 track days and a Vmax. One crack now reaches the outer edge of the disk. Is this now unsafe or can I risk another track day before switching to EBC floating disks?

[batman69]

I'm no expert but i think accepted wisdom is that when the cracks reach the edge of the disc then it's time to change. I guess its cheaper to replace discs than have the chassis straightened.

[rumplestiltskin]

drhildr - how did you clean the holes out. My discs are OK but several holes blocked. I havn't actually tried yet, but is it easy enough to push out the crud from the holes, or is a special tool needed ?

Cheers

R.

[grant3]

Ask Dazren, I think he has had this issue twice.

[aasc]

I've had cracked disks on my 968 machined down - the guy said he didn't need to take much off - result us no cracks just slightly thinner disks. Appears the cracks are surface only & not full thickness of disk - not sure if this is always the case but worth £15 compared to replacements at nearly £200!

[rumplestiltskin]

Did a search.

www.pistonheads.com/gassing/topic.asp?t=235467&f=48&h=0&hw=holes

R.

[drhildr]

I cleaned the holes out with a straightened out coat hanger - went through both sides no problem. Pressure wash and airlines only tackled the problem from one side.

[rumplestiltskin]

great cheers - mine goes in for a service & I just know they are going to say they need drilling out at silly money, so gonna do it myself before it goes in.

R.

[paulburrell]

Use a thin drill bit, that does the job.

[dazren]

Hi DAVID.

Porsche say the discs are servicable when the cracks are upto 7mm. Some people run them further than this to when they are close to joining together or reaching the edge. Personally I change them once they've hit 7mm. One noticable thing is once the discs start cracking the crack grows at an accellerated rate.

So with your car and the fact you'll be braking harder than the rest of us (a by product of being faster!), I'd go ahead with the change.

If you are not absolutley certain which new discs/pads to go with, I know "AdamT", "rods" and of course GuyR have tried various front brake discs etc. Give them a call.

DAZ

Edited by dazren on Thursday 10th August 15:57

[Homer J]

paulburrell said:

Use a thin drill bit, that does the job.

Agreed

[drhildr]

Thanks Daz!

Can anyone suggest an off the shelf supplier of EBC / Alcon floaters to fit a GT2?

[adamt]

Hi David,

You have succumbed to what we succumbed to with our r turbo, serious brake usage and the need to replace them pretty quickly I have forgotten how many brakes we have been through in 45k miles...

Last year i tried Brembo float GTR brakes which werent drilled but slotted. I bought them from Parr motorsport. They require slightly different caliper and they were deemed to be uncrackable (same brakes used in nring 24hrs etc) Anywho after a vmax and some trackdays they were pretty much buggered, the guys at parr couldnt believe it.

However if i was you i would fit the steel GT3 rotors, they are quite cheap, and really good.

Something i have come to realize is that basically no matter how good ones brakes are, and no matter how well you cool them down ( i was pretty fastidous with cool downs) a vmax and the way we drive our cars (and the extra speed they have) just takes it out of em.

350mm rotors and pagid yellows

Hope all is well,

adam

(edit, also i forgot to mention, i would really recommend parr, they were really helpful and just generally really great in helping us out.)

Edited by adamt on Thursday 10th August 17:39

[drhildr]

Thanks Adam - sounds like good advice as I guess the GT3 rotors go straight onto the existing bells? Do you know of an off the shelf supplier other than an opc?

All well here, working the car hard - Goodwood a few weeks bak killed off a set of rear tyres so switcxhing to Corsa's or the like - any experience on that front?
David

[bluesatin]

3 vmax and still on the same pads and discs with no cracks. Only thing I have changed was the brake fluid to castrol srf but doubt this makes any difference to discs!

[cavanagh]

I have just fitted alcons to my gt2 brilliant bits of kit

www.jzmachtech.com/shells/shop_index.php

Edited by cavanagh on Thursday 10th August 18:58

[adamt]

drhildr said:

Thanks Adam - sounds like good advice as I guess the GT3 rotors go straight onto the existing bells? Do you know of an off the shelf supplier other than an opc?

All well here, working the car hard - Goodwood a few weeks bak killed off a set of rear tyres so switcxhing to Corsa's or the like - any experience on that front?
David

I believe so, however dont hold me to that Guy will be able to confirm.

I would recommend Parr Motorsport, but they are quite away from you.

very best
adam

[klm]

I just replaced the front discs for £135 ea from Euro Car Parts which were genuine Porsche.
The discs on mine were fairly well cracked but the pads were crumbling really bad, I don't think they would have lasted much longer.

[r1_jon]

drhildr said:

Thanks Adam - sounds like good advice as I guess the GT3 rotors go straight onto the existing bells? Do you know of an off the shelf supplier other than an opc?

David

David - have a look on the carnewal website, they do a conversion kit to GT3 steels. The problem with this is you have to change the rear caliper as the rotor is slightly smaller.

I've researched this a fair bit and decided I would go for the alcon conversion from JZ. It's more expensive than the GT3 conversion but they do a rear rotor which is the correct size, so no need to change the rear caliper. The general consensus seems to be that they last a bit longer too.

[wildoliver]

Just a question, its not facetious at all because I genuinely dont know, but has ANYONE ever had a set of cracked disks fail?

From a technical point of view surely if skimming them removes the cracks then they are only surface anyway, so worst case a section of the swept surface will come away, has anyone ever suffered catastrophic failure of a disk?