Cracked AP disc :( => solution :)

[tertius]

I really don't think he needs ceramic discs. Hundreds if not thousands of cars run steel discs successfully in similar scenarios.

I think the likeliest scenario is a manufacturing fault or a localised issue with his brakes/setup.

As a side point some people have gone on about the number of 'ring laps his car does, but the 'ring is really not a heavy braking circuit; there are only a handful of big braking zones and they are very widely spaced. Nothing like as hard as a day at Brands Hatch for example.

 

[teamemmenracing]

no question its a product fault .......
I've raced bikes for years and have seen discs glowing red before ...... they are designed for constant rapid extreme heat cycling ....... AP racing discs more so.

I would expect they will send you 2 new discs and ask you to return yours for lab tests.

 

[Lower]

Don't forget that as you get more experienced on track you will get faster and therefore work the brakes harder. What worked last year won't necessarily work this year.

That's true… But even so; this crack is to big to be normal.

Its not good, but not uncommon.

On proper race cars discs are changed regularly and before the small cracks you've got all over your discs appear. The reality is that the disc/pad combination you've got is taking the discs way outside the parameters discs see on normal road cars and failures are going to happen from time to time. Those small cracks you have all over the discs show just how much heat cycling the discs are going through and if iron is heated repeatedly above ~600degrees C it will crack. Unfortunately some of those small cracks have joined up

I doubt you'll get much joy from AP unless its as a goodwill gesture. I doubt they're faulty, just used harder and longer than designed for. I would start looking for a pad with a higher coefficient of friction and a higher initial bite. Brings the disc temperature down considerably.

For reference i've attached a pic of a Spoon disc used on track with Ferodo DS2500 pads on my first S2000.


The DS2500 pads performed very well but overheated the disc. I then tried the DS2500 pads and Dixcel Type Z pads on a disc using heat paint to indicate the peak temperature reached. With the DS2500 pads the discs were exceeding 625 degrees C. With the Dixcel type Z pads the discs were under 530 degrees C.

Different pads seem to perform differently with different cars though.

 

[Ewazix]

Don't forget that as you get more experienced on track you will get faster and therefore work the brakes harder. What worked last year won't necessarily work this year.

That's true… But even so; this crack is to big to be normal.

Its not good, but not uncommon.

On proper race cars discs are changed regularly and before the small cracks you've got all over your discs appear. The reality is that the disc/pad combination you've got is taking the discs way outside the parameters discs see on normal road cars and failures are going to happen from time to time. Those small cracks you have all over the discs show just how much heat cycling the discs are going through and if iron is heated repeatedly above ~600degrees C it will crack. Unfortunately some of those small cracks have joined up

I doubt you'll get much joy from AP unless its as a goodwill gesture. I doubt they're faulty, just used harder and longer than designed for. I would start looking for a pad with a higher coefficient of friction and a higher initial bite. Brings the disc temperature down considerably.

For reference i've attached a pic of a Spoon disc used on track with Ferodo DS2500 pads on my first S2000.


The DS2500 pads performed very well but overheated the disc. I then tried the DS2500 pads and Dixcel Type Z pads on a disc using heat paint to indicate the peak temperature reached. With the DS2500 pads the discs were exceeding 625 degrees C. With the Dixcel type Z pads the discs were under 530 degrees C.

Different pads seem to perform differently with different cars though.

Wot he said

Brilliant picture, the size of the gap in that crack shows how much tensile stress the outer edge of the disc is under trying to split off the centre hub, imagine what pressure it would take to close it again!

 

[Franzino]

Fast heavy cars + proper use = cracked rotors and monster heat.

i would guess your car has done more laps on the ring than any other on this forum, your a quick driver, using a proper racing compound brake pad I'm guessing rd-29 or 14s?. AP may well say under those circumstances, s**t fails, id HOPE they replace them however, these brakes have taken a heavy hike in price recently too, they are serious money. I'm still on your side, they should replace the rotor ring for free imo.

Maybe my cars had done more laps on the ring then any other car here. But the fact is that the ring is not so hard on brakes, the crack on the side appeared after my first track day of Spa this year. My previous set of AP racing front discs had a much harder life and always performed as expected (3 trackdays @ Spa, 1 track day @ Zolder, 1 track day @ Ecuyers, 17 visits to the Nurburgring). It's true that when you use the brake very intense on a racetrack that in time you will get really thin superficial hairline cracks on the front discs. But this is normal and I have seen this on every AP BBK which sees regular track time. Nothing to worry about!

 

[Franzino]

It looks like you've got it all covered, but get the cheque book you may need ceramic discs :evil:

Carbon-Ceramic brakes is something I personally would not want and would never buy (when the are so expensive). There are even people who change the ceramic brakes of their Scuderia into steel brakes (for trackdays). Ceramic brakes last really long on the street, but not on track… Is perfect for real race cars…not so for track day cars. My ideal track day car is a GT3 RS without ceramic brakes. Ceramic brakes are only good for people with an unlimited budget…on track they are worn out faster then ice in the sun :wink:

 

[Franzino]

I doubt you'll get much joy from AP unless its as a goodwill gesture. I doubt they're faulty, just used harder and longer than designed for.

IMO I did not use them harder or longer then designed for. They are designed for trackdays and for the use I give them. This set of discs had hardly any track time in comparison with the previous set. Personally I think I had bad luck with one disc and there was a weak spot in the metal. This can happen and that's why I had a crack like this. Ok, the discs is useless and not safe to use on trackdays again, but it was only a crack..the disc did not explode and was not separated in two. When driving home I did feel something was wrong and when I checked the brakes it was clear what was going on.

I would start looking for a pad with a higher coefficient of friction and a higher initial bite. Brings the disc temperature down considerably.

I use Pagig RS-14; this is a pad that already has a real high initial bite (higher then the commonly used RS-29). RS-14 offer very low heat conductivity which allows less thermal transfer from disc through pad, thus resulting in lower caliper and brake fluid temperatures which can have a critical effect on ultimate brake performance.

Friction Level RS-14
Cold 0.44
At 100°C 0.47
At 300°C 0.49
Max at (@ 600°C) 0.54
Constant working temperature 400 – 700°C
Max temperature for short period only: 800°C

Friction Level RS-29
Cold 0.40
At 100°C 0.43
At 300°C 0.47
Max at (@ 550°C) 0.49
Constant working temperature: 400 – 700°C
Max temperature for short period only: 750°C

For reference i've attached a pic of a Spoon disc used on track with Ferodo DS2500 pads on my first S2000.


The DS2500 pads performed very well but overheated the disc. I then tried the DS2500 pads and Dixcel Type Z pads on a disc using heat paint to indicate the peak temperature reached. With the DS2500 pads the discs were exceeding 625 degrees C. With the Dixcel type Z pads the discs were under 530 degrees C.

Different pads seem to perform differently with different cars though.

Ferodo DS2500 is a fast road pad, NOT a intensive track day pad. When using DS2500 intensively on trackdays then it's asking for trouble (I have heard this many times from other people)… Great for fast road driving..not so great on track!

 

[Franzino]

Good news! After sending some emails with AP racing UK and telling them about my experience and the problem...there is a solution. As a gesture of goodwill; AP racing UK is going to ask my Belgium AP dealer to send me 2 new front discs. AP also wants my old discs to investigate the damage and try to find out what happened with it.

I did not expect this and it is a very nice gesture from AP! Their customer support is A-class! I can only hope this cracking of the AP disc was a occasional event...the future will tell if this is the case. But for now I'm happy that I did contact AP first before trying other brands of discs.

 

[Beedub]

Good news! After sending some emails with AP racing UK and telling them about my experience and the problem...there is a solution. As a gesture of goodwill; AP racing UK is going to ask my Belgium AP dealer to send me 2 new front discs. AP also wants my old discs to investigate the damage and try to find out what happened with it.

I did not expect this and it is a very nice gesture from AP! Their customer support is A-class! I can only hope this cracking of the AP disc was a occasional event...the future will tell if this is the case. But for now I'm happy that I did contact AP first before trying other brands of discs.

respect AP....

 

[ga41]

That's a very good result mate.

 

[exdos]

It's the right result but I think AP has simply complied with its legal obligations under EC legislation. What you were sold is a product not up to saleable standard which highlights a shortcoming in AP's quality control systems. Hopefully, AP will discover the cause of the problem in its manufacturing process and correct for all future customers.

 

[Lower]

I doubt you'll get much joy from AP unless its as a goodwill gesture. I doubt they're faulty, just used harder and longer than designed for.

IMO I did not use them harder or longer then designed for. They are designed for trackdays and for the use I give them. This set of discs had hardly any track time in comparison with the previous set. Personally I think I had bad luck with one disc and there was a weak spot in the metal. This can happen and that's why I had a crack like this. Ok, the discs is useless and not safe to use on trackdays again, but it was only a crack..the disc did not explode and was not separated in two. When driving home I did feel something was wrong and when I checked the brakes it was clear what was going on.

I would start looking for a pad with a higher coefficient of friction and a higher initial bite. Brings the disc temperature down considerably.

I use Pagig RS-14; this is a pad that already has a real high initial bite (higher then the commonly used RS-29). RS-14 offer very low heat conductivity which allows less thermal transfer from disc through pad, thus resulting in lower caliper and brake fluid temperatures which can have a critical effect on ultimate brake performance.

Friction Level RS-14
Cold 0.44
At 100°C 0.47
At 300°C 0.49
Max at (@ 600°C) 0.54
Constant working temperature 400 – 700°C
Max temperature for short period only: 800°C

Friction Level RS-29
Cold 0.40
At 100°C 0.43
At 300°C 0.47
Max at (@ 550°C) 0.49
Constant working temperature: 400 – 700°C
Max temperature for short period only: 750°C

For reference i've attached a pic of a Spoon disc used on track with Ferodo DS2500 pads on my first S2000.


The DS2500 pads performed very well but overheated the disc. I then tried the DS2500 pads and Dixcel Type Z pads on a disc using heat paint to indicate the peak temperature reached. With the DS2500 pads the discs were exceeding 625 degrees C. With the Dixcel type Z pads the discs were under 530 degrees C.

Different pads seem to perform differently with different cars though.

Ferodo DS2500 is a fast road pad, NOT a intensive track day pad. When using DS2500 intensively on trackdays then it's asking for trouble (I have heard this many times from other people)… Great for fast road driving..not so great on track!

You obviously know you're stuff. The experience i've recited with the DS2500 pads goes back a good few years and was very much a learning experience for me at the time but illustrates the point i was trying to make.

Good result from AP. Will be interesting to see how the long the new set last.

 

[ChawenHalo]

On proper race cars discs are changed regularly and before the small cracks you've got all over your discs appear. The reality is that the disc/pad combination you've got is taking the discs way outside the parameters discs see on normal road cars and failures are going to happen from time to time. Those small cracks you have all over the discs show just how much heat cycling the discs are going through and if iron is heated repeatedly above ~600degrees C it will crack. Unfortunately some of those small cracks have joined up

I doubt you'll get much joy from AP unless its as a goodwill gesture. I doubt they're faulty, just used harder and longer than designed for. I would start looking for a pad with a higher coefficient of friction and a higher initial bite. Brings the disc temperature down considerably.

For reference i've attached a pic of a Spoon disc used on track with Ferodo DS2500 pads on my first S2000.


The DS2500 pads performed very well but overheated the disc. I then tried the DS2500 pads and Dixcel Type Z pads on a disc using heat paint to indicate the peak temperature reached. With the DS2500 pads the discs were exceeding 625 degrees C. With the Dixcel type Z pads the discs were under 530 degrees C.

Different pads seem to perform differently with different cars though.

Wot he said

Brilliant picture, the size of the gap in that crack shows how much tensile stress the outer edge of the disc is under trying to split off the centre hub, imagine what pressure it would take to close it again![/quote]


+1 I was told that I would be better off with Paid RS29 (endurance pads) for that reason. No cracks so far, but they do skweel all the time + they do not have fixing pins for the callipers and so they rattle.

http://www.pagidracing.com/products/pagid-rs/

 

[Franzino]

Last weekend I went to the Nurburgring with my new front AP discs and a new set of Pagid brake pads. The brakes are back to the level of really awesome; the braking power and initial bite was immense. Great to have 100% perfect working brakes again! Love them and love the service of AP

 

[teamemmenracing]

Good news! After sending some emails with AP racing UK and telling them about my experience and the problem...there is a solution. As a gesture of goodwill; AP racing UK is going to ask my Belgium AP dealer to send me 2 new front discs. AP also wants my old discs to investigate the damage and try to find out what happened with it.

I did not expect this and it is a very nice gesture from AP! Their customer support is A-class! I can only hope this cracking of the AP disc was a occasional event...the future will tell if this is the case. But for now I'm happy that I did contact AP first before trying other brands of discs.

As I mentioned before ....... they are designed for extreme heat cycling (imagine severe braking from speed into a corner then driving out through a puddle .....)
They will want them back for lab tests ........
A crack like the one you have could cause a locked wheel at speed, possible rollover with fatal consequences ...... as the info is in the public domain (ie the pics are on here) they would be looking at a criminal negligence case if they were not seen to be investigating the cause. I expect that once tests have been done, you will receive a copy of the report.

 

[Atgani]

The discs supplied in the AP BBK's are not the best quality. They can supply better quality discs, but at a cost.
I ran into this problem with the AP kit on my CSL. That had a similar crack (as a footnote, it didn't stop me using the car, and I continued to drive it on the road (fast) for another 12 months and 6k miles)

When I replaced the discs, I was told the better quality AP disc weren't worth buying as Performance Friction supplied a far better quality replacement disc than the "standard" AP items, but at the same price.

The RS 29 pads tend to be superior to the RS19's in my opinion. As for the comments about them squeaking, my experience of them on both the CSL and a 996 GT2, indicated that it's only the rears that squeak, this as they rarely get up to their correct operating temperature and thus begin to glaze up.

 

[ChawenHalo]

The discs supplied in the AP BBK's are not the best quality. They can supply better quality discs, but at a cost.
I ran into this problem with the AP kit on my CSL. That had a similar crack (as a footnote, it didn't stop me using the car, and I continued to drive it on the road (fast) for another 12 months and 6k miles)

When I replaced the discs, I was told the better quality AP disc weren't worth buying as Performance Friction supplied a far better quality replacement disc than the "standard" AP items, but at the same price.

The RS 29 pads tend to be superior to the RS19's in my opinion. As for the comments about them squeaking, my experience of them on both the CSL and a 996 GT2, indicated that it's only the rears that squeak, this as they rarely get up to their correct operating temperature and thus begin to glaze up.

Makes sense, Deluge told me that I'd be better off running something softer and less grabby at the rear to increase stability when standing on it. I'm running the standard CSL set up with braided lines and DOT 5.1 and they need an overhaul. Horrible pads on the street on my set up. Fab on track, but just noisy as hell off it! Can't be arsed blowing 5K on a A&P BBK though, its seems like overkill aside the huge callipers issue that will retain even more heat and I wondering how far I can upgrade the standard system...

 

[tertius]

I find having 29s all round (on an AP kit) means the rear is over-braked, so I have switched the rear pads to RS4-2. Will find out how that works at Brands in a week or so (I hope - Center Gravity are still waiting on Intrax for some parts).

I'm sure I mentioned it already in this thread, but I too was recommended the PF discs over the AP ones. However, I was told that only the fronts were available from PF so I have standard BMW discs on the rear.

 

[AlanJ]

Franzino - a great result and to AP for responding so well. Goes to show that when you approach a problem with a manufacturer in an appropriate way you normally get a good result!

 

[exdos]

I wondering how far I can upgrade the standard system...

Brake cooling: http://www.z4-forum.com/forum/viewtopic.php?f=24&t=38775

Solid brake bushes: http://www.z4-forum.com/forum/viewtopic.php?f=24&t=45293