Charley Hoyt

I can't believe that I cracked a brand new set of DB4000s in one track day at California Speedway. The stock disks are half the price and lasted a lot longer. I am not sure if I am doing something wrong...but, everything I have read said that these should last a lot longer then stock. I ran a total of 5 sessions. After each session i took a calm "cool down" lap. Then I drove right through the garage area and drove up and down the access road for 15 - 20 minutes to allow them to cool further before I parked. I didn't notice the surface cracks until the next day. And it seems like it is getting worse. I didn't notice any vibration while stopping on the track (although as i mentioned in another post I was having vibration over 135 mph), or on the way home. But now when I stop my car vibrates like a truck.

95jersey

2 things

1) stock rotors are excellent quality and last a long time for me
2) did you put them on new right before your event? (meaning no street time).

If you answer yes to number 2, you basically thermo-shocked them to fast. All rotors should see some light duty to season (meaning heat cycles) them before track duty if possible. I get the longest wear out of my oldest street used rotors.

RDnomorecobra

was the track event the first time you drove with them? or did they heat and cool several times on the street bedding in pads, etc?

Charley Hoyt

I put them on the car about a week before the event. I bedded them in...and drove the car every day. Maybe that wasn't enough time or heat cycles??

SIK02SS

Do you have any cooling ducts? What pads were you using? Are they actual cracks, Can you feel them with your finger, finger nail, or does a cloth snag on it? Just making sure try aren't heat checks..

Charley Hoyt

My car is a C6 (Z51 brakes) with Z06 body/ wheels / tires. The brake ducts are the stock Z06...but, I don't have spindle ducts. The pads are a new set of GM Z51 pads. Heat checking is probably a good description. Tonight I will check to see if I can feel them with my nail. But, it is bad enough that it is now causing a very noticeable vibration when I hit the brakes.

95jersey

also, when you say cracks, do you mean hairline or cracks through the entire rotor face.

You will get many cracks on the rotor before it is trash

sothpaw2

No it's not enough. Reading up here, typically folks drive the car for at least 2 weeks. I'm sourcing mine now and will try & subject them to 3 weeks of stop& go traffic with purposeful higher speed stops before VIR.

This is a good reason why I don't like to space events close together--need time to season another set of rotors.

SIK02SS

a week before is plenty if he did a proper bed-in. I know people who don't do "proper" bed-ins and get decent wear out of them.

I think the OP is getting heat checking in the rotors (which is normal), and should inspect his hubs

RX-Ben

what is "heat checking?"

thehammer69

ever see rotors where they have a bunch of Bluish spots on them? Well those are heat checks and it causes the hardness of the rotors to be diifferent in those spots compared to the non blued spots.

Charley Hoyt

I took my wheels off this evening and took a closer look at the disks. The complete face on the inboard and outboard sides have small cracks over the complete surface. There are also spots on the disk that look like the are getting more wear then others. The DBA rotors have three stripes of color change paint. The first color has changed which means that the disks saw more than 850 degrees F but less then 1020 degrees F. Here are a few pictures...but they don't show the issues very well.

brkntrxn

In the first and second picture, all I see are small cracks which are perfectly normal.

In the first pic, that "spot" looks like what I would call pad smear. A build-up of material from the pad -- if that is what I am thinking. Kinda hard to tell.

The vibration you are describing under braking sounds almost like you need to rebed the pads. You hit some decent temps on the track, but your extended cool down periods and as well as the drive home may have "undone" your bedding and put more uneven amounts of material on the rotor.

Last Fall, I put on a new set of pads and rotors and went out to bed them in. Despite the late hour, there was traffic on the country road and with the cool weather I was unable to get a proper bed. The car vibrated under braking pretty significantly. A week or so later at Road Atlanta, I gave it a couple of good hard laps and the vibration went away as I laid down an even amount of material. Effectively doing a proper bed in.

Try going out and bedding them in again with some good 40-10, 60-10 and 100-20 stops.


YMMV,

-Kevin

stano

Charlie, the small cracks you are seeing are normal. I sent pics to DBA when I thought I had a problem and they assured me they were normal. Mine looked worse than yours.

SIK02SS

i agree. 1st pic is tough to tell...but the "cracks" are normal You should see my rotors right now, they look way worse

bobmoore2

Your problem is uneven pad deposits on the rotor. I can see it in the uneven shine on the whole rotor face in the first picture. Picture # 2 is a close up of some of the pad deposits.

Read this article by StopTech. Start from the top and stop at "Myth # 2". It describes your problem exactly.
http://www.stoptech.com/tech_info/wp...rakedisk.shtml

For example, Here is a sentence from the article. LOOK AT YOUR PICTURE # 2 again, and you'll see that it is a "pad imprint".
"if, when they are very hot or following a single long stop from high speed, the brakes are kept applied after the vehicle comes to a complete stop it is possible to leave a telltale deposit behind that looks like the outline of a pad. This kind of deposit is called pad imprinting and looks like the pad was inked for printing like a stamp and then set on the disc face. It is possible to see the perfect outline of the pad on the disc. "


I think part of the cause of your problem is the GM Z51 pads. The stock pads are not able to tolerate the high temperatures for a long time, so they are breaking down chemically and putting a lot of pad material onto your rotors. You need to get some high performance brake pads.

More importantly, you need to change the way you stop your car when you are parking it in the paddock. When you come off the track your pads and rotors are very hot, and they will stay hot for several minutes. If you make that last stop before parking, by applying the brakes, then the pads will be left sitting against the rotor surface. As some of the heat of the rotor dissipates into the pad, the pad will leave a pad imprint. As the Stoptech article states, uneven pad deposits cause brake juddering like you are feeling.

Here is how you should stop the car when parking in the paddock after a track session. As you get close to your parking place, slow the car down to 2 or 3 mph using the brakes. Release the brake, depress the clutch, and let the car coast into the parking spot. Momentarily release the clutch a little, if necessary to keep it rolling. As you get into the parking spot, the car should be rolling at less than 1 foot per second. Turn off the engine, wait a moment for the engine to stop rotating, and release the clutch, letting the engine braking stop the car. If your car has an Automatic transmission, slide it into neutral to coast and into park for the final stop. The point of this sequence is to not touch the brake pedal for the last several feet of rolling. This sequence takes a little practice to get correct, but it greatly protects your brakes from heat-soaking a pad imprint onto the rotor. It also helps protect your rotors from destructive cracking (not the micro-cracks we always get), because when the rotor face is directly in contact with the pad, that part of the rotor cools at a much different rate than the rest of the rotor. Uneven cooling causes thermal stress, which causes big cracks in rotors.

froggy47

Checking normal, you need a pad with a higher temp rating to eliminate the pad deposits. I had much worse pad deposits but was able to sand them out (garnet paper only).

Olitho

I agree. You need race pads. Some sponsors on the forum here, like Carbotech, have what you need.

Locally I source my pads from Porterfield Brakes in Costa Mesa. I get the Raybestos ST43's or ST47's.

ACS is the only local track we have that is brutal on brakes. You need the best there.

DarkMastyr

Cracked? I call that just getting started

bobmoore2

You may be able to wear off the pad deposits, by doing a bedding sequence again. If not, then sanding them out may be needed. If you use the wrong kind of sand paper, it will leave carbon particles ground into the metal and that will cause the cementite crystals that the StopTech article warned about. Like froggy47 said, "garnet paper only".