seveneleven

The DBA 4000 Rotors was running with:
Original Caliper with Thermlock-Pistons, DOT5.1, Air Ducts.
4x20min Hawk DTC70
1x30min Carbotech XP12
1x30min Carbotech XP12 (wet cond.)
cooling down the break after each session

i had no problem when i finished the sesion, i park the car and one hour later they look like that!

DBA 4000 Brakedisc working just on the paper

http://www.flickr.com/photos/6673058...in/photostream
http://www.flickr.com/photos/6673058...in/photostream
http://www.flickr.com/photos/6673058...in/photostream

DBAsteve

Hello seveneleven,

We are keen to have this rotor returned so we can do a full failure analysis report on the rotor in question.

Can you please email dbasteve@dba.com.au so we can organise for the rotor in question to be returned and have replacements arranged.

Thankyou

DBASteve
dbasteve@dba.com.au

Adam@Amp'dAutosport.com

RicK T

I'd be interested to hear the outcome of that invest.

AORoads

me, too.

el es tu

Wow I didnt know we had a rep from dba here.

I was wondering, are your solid 4000 series rotors vented so they properly exhaust the the heat (the factory units suck air in on one side of the car and push it on the other because of their vane shape and the fact that the left and right side rotors are the same - I want to avoid any rotors that pull air into the wheelwell).

Also are the solid 4000's sold in the US? I have only seen the slotted units and drilled units for sale even though the dba website advertises solid 4000's.

Thanks!

DBAsteve

As a follow up to this. We are yet to have any contact from Seveneleven.

We have sent him an email but no response as of yet.

El es tu, we do have a small quantity of plain faced 4000 series rotors for the C6 Z06 in our US warehouse. They aren’t all that popular and we don’t sell many but we do have them available, all you have to do is ask your retailer.

Our Corvette 4000 series rotors are vented in our "Kangaroo Paw" or pillar vent pattern. The venting works on centrifugal force which draws the air already in the rotor to the outside, this in essence 'sucks' in more air from the inside of the disc to replace the air it is moving to the outside of the rotor.

The reason Kangaroo paw is more effective over other vent patterns is the amount of surface area. There is a relationship between heat dissipation and surface area and to put it simply so I'm not writing an essay it basically works out that, the more surface area the faster heat will dissipate. However there is a point where too much surface area becomes ineffective because there is not enough air movement over the surface area to remove the dissipated heat.

Our Corvette discs are not reverse vented, i.e. they don't draw new air from the wheel side of the disc, they draw air from around the hub. So things like air ducts help greatly in forcing new cold air into the rotor to keep it cooler.

If you want to know anymore just shoot an email to dbasteve@dba.com.au

Cheers,

DBASteve
dbasteve@dba.com.au

el es tu

thanks for the info!

I plan to do a z06 brake upgrade within a year and dont want the factory rotors but wanted a factory look. These look like the best bet with some 1 piece racing pads.

seveneleven

i'm really the first with a cracking DBA Disc, because the Skyline Guys crack them in the last years by dozen

the question for me, is a 1pc Disc overloaded at the track regardles of manufacturer? may be is the thermical stress on a big 1pc Disc because type of construction to mutch



@DBAsteve
1. i`m surpride, for 8 weeks i had no reply of my mail to DBA Australia

2. replacements, no thanks, i`m not interested to to this experience again with me (and my Z06) the next time i am no so lucky and she crack at the track and we talk not about 150bugs, and my pitch, i have again two new ones at stock

3. analysis report: when i can ship the Disc for free, I will send the Parcel also to the other side of the world (are the Disc they crack some years ago all analyzed?)

4. is the "Kangaroo Paw" really so god an the Disc runs measurable cooler than actually my Coleman-Disc (i`m very surprised about the last mesurements of the QUANTUM Competition Brake Cooling Kit)

AORoads

8 weeks to Australia, and then you posted here and VOILA! answers, the same day from DBA!

I don't know, but if it were me I might give DBA a chance to see the rotors and give you new ones. maybe????

of course, your concerns about breaking on the track under racing conditions and going off track...hmmm, that might make me think twice, too.

BEZ06

I've cracked a number of rotors - OE and this one which is a DBA 4000:




I've just always accepted the fact that if I'm running a one piece rotor that I'll get cracks. I think it's just the nature of the way the one piece rotor/hub works - the way the rotor connects to the hub, both sides of the rotor just can't expand and contract at the same rate, hence the rotor will "cone" and this makes it very susceptible to cracking.

A two piece floating rotor, where the rotor ring and hub are not cast in one piece, allows rotor ring to expand and contract without flexing due to being part of the hub. With the rotor ring bolted to the hat, when the rotor is no longer serviceable you just unbolt it from the hat and bolt on a new rotor ring.

So.....I just take it for granted that a one piece rotor is likely to crack.

Butt.....Steve, I'll take some new DBA 4000's if you're sending them out to those of us that have cracked some!!!!

Bob

DBAsteve

Seveneleven,

In all seriousness, the 'Skyline guys' crack a lot of discs from a lot of different manufacturers because the brake package is not adequate for the weight and performance of the vehicle once it has been modified and put on a race track.

To give a comparison an R34 GTR weighs 1550kg (3420lbs), a Corvette Z06 weighs 1430kg (3150lbs). They will both do similar speeds on a track but the R34 GTR will have more inertia because of the increased weight. The extra inertia requires alot more brake effort to stop the car, this extra effort generates significantly more heat from the prolonged friction and hence the rotors fail sooner. Subaru WRX & WRX STI's also suffer from similar problems due to the inadequate size of the brakes for track use.

To back that up lets compare the brake packages between the 2 cars. An R34 GTR uses a Brembo system (4 pot front, 2 pot rear opposed piston calipers) with 324mm x 30mm (with 8mm friction cheeks) up front & 300mm x 22mm (with 6.5mm friction cheeks) rear rotors. While the lighter Z06 uses a PBR brake system (6 pot front & 4 pot rear opposed piston calipers) with 355mm x 32mm (with 10mm friction cheeks) front & 340mm x 26mm (with 7.5mm friction cheeks). From that we determine that the Z06 has a 10% larger front rotor with over 30% more cast iron on the friction faces which means the rotor has a substantially higher thermal capacity than that of the R34 GTR front rotor.

So not only does the R34 weigh more but it also has substantially less thermal capacity in its rotors and hence a less suitable brake package for track work than that of the Z06. Really you cannot compare the rotor consumption of an R34 GTR to that of a Z06.

Now back to your questions.
1/ can you please provide the email address you emailed at DBA so I can find out where the email went.
2/ before you reject replacements you might want to know what we were going to send you first. Please email dbasteve@dba.com.au and I will let you know what we were going to send as replacements.
3/ As I asked in the email I sent to the address I believe is yours, please let us know an address that the rotors can be picked up from and DBA will arrange shipping for them to Australia.
4/ If your asking whether 'Kangaroo Paw' venting is better than curved vane then yes it is but a 1pc disc will not run as cool as a 2pc disc. So making a comparison between a 1pc DBA 4000 series disc and a 2pc Colman disc is like asking whether your Hawk HPS pads are better than Hawk DTC70 for serious motorsport use. Asking whether our 2-piece 5000 series is better than another competitors 2-piece is a better comparison, however I have never seen in the flesh a Coleman 2-piece disc so cannot comment on them.


BEZ06,
Sorry mate but we don't cover normal wear and tear, only manufacturing defaults. Those rotors have seen some high temperatures, the significant crazing on the face shows that. There are some things you can do to help reduce crazing and if you care to email dbasteve@dba.com.au I'll be more than happy to run through somethings which if you don't already do might help prolong the life of your discs.

Cheers,

DBASteve
dbasteve@dba.com.au

Dan Wendling

for DBA

My experience is that they are a great organization that takes care of their customers. Not many of those left in today's economy.

DBAsteve

Thanks Dan.

At the end of the day, we just want to see this resolved and also determine what caused these rotors to fail. I have my theories but without seeing the rotors i can't come to any conclusions.

AORoads

Steve, I'd appreciate a definition of "crazing" since I don't know what it is relevant to brake rotors. Maybe you could show a pic of one, too (pic worth a thousand words and all that jazz). Thanks.

DBAsteve

Will do, just give me a moment and I'll go photograph some good and bad examples.

taken19

Could you also list what causes it and how to avoid it (or reduce it)? I'm just getting into tracking my vette and want to understand brake systems better.

Thanks in advance,
Sean

BEZ06

Hi Steve

Like I said, I just plan on occasionally having a one-piece rotor crack. But I am interested in your "crazing" comment and your thoughts on how to run the rotors to max life possible.

In the case of my rotors they were used on my 2006 Z06. The cracked one is a front rotor, and as I mentioned I've had the stock drilled rotors crack as well.

After a track session I always do an easy cool-down lap being light as possible on the brakes, and then drive around the paddock area for a couple minutes before parking. After parking I always try to roll the car back and forth a few times every couple minutes to keep the pads/calipers from sitting in one position on the rotors.

The DBA 4000 in my picture cracked after the last session of a 3 day event at Daytona. Each session was 30 minutes, with 4 sessions per day - so the rotors did about 6 hours of hard track time at that event over 3 days. I think they had several track days before that event. I was running either Hawk DTC 70 or Carbotech XP 12 pads that event, I can't remember which, but it was an aggressive high-temp pad.

Below is a video of running at Daytona. You can see that there is a lot of energy dissipated at two main places on the track - on the back straight coming down from more than 160 mph to less than 70 through the chicane, then on the front straight of the tri-oval braking down from about 175 mph to less than 60 to turn into the infield. There is a lot of cooling time while no braking is going on at high speed on the banking, so it probably is the perfect setup for a lot of heating/cooling even while on the track. I don't have spindle ducts, but I do have large ducting attached to the factory ducts that directs the air to the hub area of the rotor for better cooling.

Looking forward to your thoughts!!


Bob

BEZ06

BTW, that crack occurred about 2 years ago - I think it was at the event at Daytona in Dec 2009.

Here's the same picture I posted above. It was right after the track event:




I just went out and took these other 2 pictures - one of the each side of the rotor:







I live here in Daytona, and the rotor has been being used as a paperweight, door stop, and ballast weight over the last couple years around the garage. It might get down into the mid 30 degree range a couple times during the winter, and it regularly gets up into the high 90's in the summer (hotter in the garage).

I guess the temperature fluctuations have caused the crack to continue to widen - you can see that it is now much wider at the outside edge of the rotor and goes all the way down through the hub!!

Bob

DBAsteve

Ok, you asked for it so here it is. Note: this is a simple explanation of it, I'm not a metallurgist and I'm not going to put up here what our metallurgists say about it because unless you are one, it’s hard to understand.

Crazing is typically caused by excessive heat at the friction face, hence it is really only seen in motorsport applications. It happens when the face of the rotor becomes more ductile due to the elevated heat at the friction faces. When the friction face reaches these higher temperatures the tensile stress from the process of braking & differential expansion between the surface of the rotor and the core of the rotor starts to cause the cast iron to form finite fractures at the surface. These finite fractures are the visual signs referred to as crazing. They can progress into deeper cracking and in some circumstances through-cracks if the rotor continues to see elevated temperatures.

Onto some examples, let’s start with a good example of a well used disc that has some light-moderate crazing. It's off an Evo X running the stock size 350mm x 32mm front rotor in a DBA 5000 series design with an Endless 6 pot caliper and Endless endurance pads similar to the N84 compound. The crazing present here is not an issue and this disc had plenty of life left, they just happened to be a sponsored team so we gave them a new one so we could analyse this one. It’s done around 12hrs of actual running around a track across several test sessions/races and seen in excess of 630degrees Celcius (1166 Farenheit). The crazing hasn’t progressed into deeper cracks yet and the disc has minimal wear.





Now, onto one with more significant crazing/cracking. This is a 321mm x 32mm 4000 series slotted disc off the front of a Holden Commodore VE V8 (Pontiac G8) used as a race experience car (ie. you pay $400 and get to do 6laps with an instructor sitting in the passenger seat). It was used for around 8days where it would have run 60-80laps a day if not more. This disc is basically at the end of its life, it might get through another track day but you’d want to be keeping an eye on it after each session, because it could easily crack further. You can see that the crazing has developed into more pronounced cracks and are starting to open up. It’s been through a few episodes of thermal shock and has been passed Celcius (1166 Farenheit). It would also not have had much in the way of warm-up/cool-downs during its use.



And lastly this disc is dead; it’s been through some significant abuse. This is a 325mm x 32mm 5000 series disc off a Ford Falcon (the same friction ring with a different hat fits a C5 corvette) that was used as a race experience car. It was used for around 8days where it would have run 60-80laps a day if not more. It’s had a tough life with not a lot of warm-up or cool-downs, it has been through countless episodes of thermal shock and it would have been passed 630degrees Celcius (1166 Farenheit) almost every time it went on the track. It stood up to this abuse quite well but it’s had enough and is in danger of failing. (Note: there are some vice jaw marks and dents were it was handled roughly after being taken off)



For those of you that read the above, you will have made note that I mention 630degrees Celcius (1166 Farenheit).a few times. This is because A) it is the temperature at which cast iron starts to fatigue at a higher rate and also is the starting point of change to the metal matrix and B) it is when the red heat paint on our 4000 & 5000 series rotors permanently changes colour indicating it has seen inexcess of 630degrees Celcius (1166 Farenheit).

So what can you do to prolong the onset of crazing & extend the life of your rotors?

First you need to start with a proper bed-in procedure, see here for our motorsport bed-in guide http://www.dba.com.au/system/files/p...MotorSport.pdf.

Secondly, a good progressive warm-up at the start of every session on track ie. don’t go out onto the track and do a hard brake from 200km/h (124m/h). Combine a good warm-up with as long as possible of a cool-down. The rotor needs to gradually return to normal temperature with air flowing in and around it. If you’re at a track that doesn’t let you do a full cool-down lap then driving the car around the pits for a few minutes without using the brakes and then when you’ve parked the car, roll it forward 5-6 inches every 2minutes or so to avoid one area taken a lot longer to cool than the rest.

Thirdly pad choice, choose appropriately rated pads for the application and type of driving you do. By that I mean don’t run a street pad on the track because it’s going to overheat and in turn overheat the disc face as well as cause a few other issues. Also some pad compounds are more prone to causing crazing because of how much heat or lack thereof they absorb from the face of the disc. Knowing which pads are better in this respect comes from talking to people that have experience in using different pad compounds & your own trial an error. However what works for one person does not always work for someone else because everyone has their own braking ‘style’, so start with experienced people that run similar lap times also ring up the technical departments of your preferred pad brand because they are often a wealth of untapped information that is FREE.

Fourthly, the more cool air you can divert to flow into the centre of the disc the better, this helps keep the internals of the disc cooler and helps reduce the overall temperature of the rotor which will decrease the max temperature of the rotor during braking. Systems that spray a water mist etc can work as well but it’s always best to start with as much cool air as you can, it’s also cheaper…

Lastly, inspect your rotors before and after every track day. This should become part of your preparation and reflection for every track day. Often a potential problem can be identified before it happens by simply looking at the rotor. If the crazing is getting like the second example above then I’d be ringing my parts supplier for new ones. Preventing it is better than having to deal with it after it’s failed.

Here are some other tech bulletins worth a read. http://www.dba.com.au/system/files/p...port%201_0.pdf & http://www.dba.com.au/system/files/p...0General_0.pdf

I hope you all got some good pointers from this.

Cheers,

DBASteve
dbasteve@dba.com.au