Tinnit

A little over a month ago, I was preparing for my first HPDE event by replacing all my brake fluid with Motul 600 and thoroughly bleeding the brakes. I've been bleeding brakes for decades and had no concerns about that procedure. The track day went well - no braking issues whatsoever. When using the car for daily driving since then, zero problems. The pedal feels great and the car will stop hard enough to suck your eyeballs out.

Since that first HPDE event, I have attended two autocross events and the brakes felt….strange. I had attended several autocross events prior to the brake fluid swap and didn't notice this behavior. It feels like the tires are slipping very early. Way before they should. I press on the brakes hard and the car just doesn't stop. I don't hear tire squeal, nor do I feel ABS pulsing (although it may be doing that - the ABS pulsing is pretty subtle compared to many ABS systems I've encountered). The brakes are relatively cold at this point, having only slowed down for one or two turns on the short course. It's definitely not fade. The pedal is not soft. I would have expected a much softer pedal if it were a problem with air in the lines. And, as I mentioned, I can take it out to the street right after the event and stop much, much harder.

What's going on? I can only think of two possibilities: 1) the tires are sliding like on grease. I'm running Michelin PSS tires and I've had really great luck with their grip so far. I can't imagine they're giving up so quickly on braking when they do so much better on acceleration and turning. 2) I messed up the bleeding somehow. The timing seems to point to the bleeding, because it didn't seem like it was doing this prior to the bleeding. It just doesn't feel like poorly bled brakes. The pedal is firm the entire time.

It does seem like it gets better as the event goes on. Or maybe I just become accustomed to the strange behavior. For what it's worth, I've had two different codrivers in the past two events and they both complained about the poor braking behavior as well. These are much more experienced guys, but I don't know that either of them had raced Corvettes before. In case it matters, this is a base C6 with the Z51 package. Stock pads and rotors, 6 speed, nannies turned off.

Any help would be greatly appreciated!

argonaut

What pads you running?
Could your pads be glazed over/cooked? If the pads were overheated on the track they can get all glazed over and wont' stop worth a shiiiit.
Or perhaps you just can't get them into their proper operarating range on an AX course.

froggy47

Tapered pads, bleed after the event, tires/pads not up to heat on early runs.

Try warming up the brakes before the first run. Drive carefully away from the event & drag them, do a few stops & then immediately get in grid.

brkntrxn

Sounds like the pads are glazed or tapered like mentioned above. Glazed is my guess.

TRACKMAN2

kinda need the pad type to give you an accurate answer ..did you break in the pads properly??..most race brakes need a "material transfer" to the rotor to work right. pads like hawk hp plus just dont work when cold..

Tinnit

Thanks to all for the advice! I really appreciate it!

I don't know for sure what pads they are. I bought the car 6 months ago and, as far as I know, everything on the car is bone stock. However, it has 45k on the odometer. I'd consider it fairly likely that the pads have been replaced at least once. Since the PO never mentioned anything about performance pads, I think it's safe to assume they're either the original factory pads, GM replacement pads, or routine auto parts store pads.

I was associating the weird behavior with the day that I bled the brakes, which was the night before I hit the track for the first time ever. I was not being gentle with the brakes whatsoever on the track. Sure sounds like I did indeed glaze the pads on that track day.

As luck would have it, I already ordered a separate set of pads and rotors (XP12s/XP10s and Centric non-cross drilled rotors) that I had intended to swap in just for track days. Can you guys help me not glaze these? How do I prevent that? Just a proper break-in procedure and that's it? Or is there a cooldown procedure that I messed up on?

And lastly, can anyone recommend a good dual duty pad to replace my glazed street set? I do a lot of autocrossing, but I don't intend to swap rotors/pads for autocross events. I'd like a pad that will do well on the street, yet perform as well as or better in autocrossing than the stock pads (let's assume that's what they are) I currently have. A set of Carbotech XP8s front and rear, maybe? Hawk HP+? I don't care about the noise and I'm fine with lots of brake dust.

Thanks again, all! You guys rock!



edit: Oops, one more question. If the pads are glazed, whcih sure sounds right from what I'm researching now, should I replace just the pads? Or do the rotors become glazed as well? If I pick up some decent replacement pads, will they work well with my stock crossdrilled rotors?

Adam@Amp'dAutosport.com

You need to pull the pads and look at them if they are real shinny on the pad surface they are glazed and they need to have a layer of material removed. Best bet is to get new ones since they did not work for you. For a street pad you can use the AX6 or XP8 since you are already going to use our XP12 & 10 you will not need to change rotors because all our compounds are compatible with each other. I would not use a HAWK pad as our compounds and HAWK are not compatible. Give me a call at 216-780-8825 I will be happy to help you out.

Carbotech™ AX6™

The AX6™ is specifically engineered for Autocross applications. A high torque brake compound delivering reliable and consistent performance over a very wide operating temperature range of 50°F to 1100°F + (10°C to 593°C+). The advanced compound matrix provides an excellent initial bite, high coefficient of friction at lower temperatures along with very progressive brake modulation and release characteristics. AX6™ offers high fade resistance, rotor friendliness at all temperatures and excellent cold stopping power. As a result, AX6™ is an excellent choice for Autocross and has gained tremendous popularity with SCCA Prosolo/Solo2 competitors for its outstanding all around performance. Many drivers use the AX6™ for street driving as well, even though Carbotech™ doesn't recommend street driving with AX6™ due to possible elevated levels of dust and noise. AX6™ is NOT recommended as race compounds in most applications.


Carbotech™ XP8™

A high torque brake compound with a wide operating temperature range of 200°F-1350°F+ (93°C to 732°C+). Carbotech™ XP8™ is the first of our racing compounds. Good initial bite at race temperatures, high coefficient of friction, excellent modulation and release characteristics. Extremely high fade resistance and very rotor friendly. Excellent as a front brake pad for lighter applications weighing around 2,400lbs or less. Perfect for track day use with any tire and can still be driven safely to and from the track. Carbotech™ does NOT recommended XP8™ as a daily driven street pad due to elevated levels of dust and noise. Carbotech™ XP8™ is a great compound on the front & rear of most open wheel and sports racers.

Tinnit

Just wanted to follow up on this.

I swapped in my XP12/XP10 combo and Centric rotors for the track. Everything worked fantastic. Having incredible, confidence-inspiring brakes bailed me out of a number of too-hot turns.

Per Adam's recommendations, I picked up a set of AX6s for the street/autocross. I haven't put 'em on yet, but based on the fact that my disappearing brake problem never occurred after swapping my old pads and rotors out, I'm sure I've got it licked.

Thanks to all for your help!

Adam@Amp'dAutosport.com