2 GTOs

I have DTC 70s on a C6Z06. Stock GM drilled rotors and ATE Blue. The pads have more than 50%. First few laps brakes seem fine. Maybe around the 6th lap, the are fine on initial application, but the car starts to vibrate as I apply the brakes longer or use more pressure. By the last few laps, I get vibration even under light application.

The next session, same thing all over again. Fine for the first few laps, then progressively worse. I find myself trying to be easier on the brakes later in the session.

What usually causes something like this? Is this causing any type of longer term problem?

jaa1992

Improper bedding maybe caused a buildup of pad compound on the rotor?

moespeeds

Dom take a look at the pads to see if they are glazed, and the rotors themselves, do you see any kind of pattern on them? Try changing out all 4 rotors to see if it goes away. If the pads are glazed you can take sandpaper to them, but I usually just scrape them on the concrete to rough them back up.

It's obviously something that is agitated by heat buildup, maybe just a warped rotor that goes back straight when it cools. Also double check those hub bolts!

ktlspider

How did you bed-in the brakes, if at all? The Hawks are a really good brake pad but they may act up if not bedded-in properly. But I recall a friend using these for the first time on his dedicated race car and he didn't put a ton of work into bedding them, other than scuffing the rotors to remove the previous pad material (Performance Friction PF-97)

So I would definitely agree on the deposition comment. Since the problem takes some heat to arise (doesn't do it right away), it is pad transfer-related. Seen it happen alot. I suspect whatever pads you had on there before are not agreeing with the new Hawk material? However you say that you've got 50% pad material. So it sounds like you've had them on the car for a while.

You can burnish the rotors by scuffing them with a rotor hone. It's a rotary disc that goes on the end of your cordless drill and it has a bunch of ball hones on it. You run this around the disc as its rotating and it finely cuts the rotor surface w/out harm. What this does is remove the old pad material and allows new Hawk pad material to transfer onto the rotor. The braking effect works most effectively when the pad material and rotor surface are "seeing" the same material.

The OE rotors are quality pieces, so there should be no issue with warpage. Warping is somewhat of a thing of the past with the high quality metallurgy and pad compounds used in modern brakes. Especially the Z06 equipment.

Here's a good article on some misconceptions about brakes written by the guys at Alcon. They have been making high end brake systems for top tier race teams for a very long time.

Myth of Warped Brake Discs- Alcon Brakes

How are the brakes in terms of temperature? Some think that since they have monster brakes (like the Z06) that cooling isn't needed. Not so. Proper brake temps (meaning, not excessively hot but not stone cold) are key to your pads and rotors performing and lasting. I know from personal experience that even a moderate amount of cooling air makes a big difference. Here's another bit of tech info from the guys at Alcon

Why Use Brake Cooling- Alcon Brakes

AU N EGL

the drilled holes may be scrapping the pads, and depositing pad material on the rotors.

time for some solid side or slotted rotors.