Brake Fade

[Craig-o]

I took my car out on a great road-course about 2 weeks ago. Having done this only 1 time before, I was aware of the significant stress such an activity can have on the braking system. With 60,000 miles on my '01 I decided to change brake pads (with AC Delco Dura-stop), and as long as I was at it, I flushed the brake system and replaced the fluid with a high-temp brake fluid.

What I experienced was, to me, a bit odd. After the second 30-minute session of the day, and for most all of the sessions thereafter, I experienced a strange phenomenon. The first time I applied the brakes going into a sharp turn, the brake pedal seemed a bit spongy, and didn't grip when I expected it to. However, all that seemed to go away after the first time I used the brakes on that session. In other words, it seemed that my brakes faded the first time I used them, then seemed to tighten up.

I throroughly flushed the system and used a blue fluid for the replacement, so I could tell when all the old was flushed out of the lines. I also bled each caliper and was satisfied that there weren't any air bubbles in the line. I used a pressure bleeder, and had extra fluid left in the bleeder reservoir, so I'm sure the master cylinger never ran dry.

Aside from the Dura Stop pads and blue fluid (from a German manufacturer who's name escapes me), the braking system is stock; no braided flex hoses, stock calipers and rotors -cut once as a result of the tire-store over-torquing the lug nuts, but still well within thickness spec.

Any ideas on what caused this, or what I can do to remedy it? I have to add that I have not experienced this same phenomenon since having the car on the track. So whatever it is (was), it must be related to the extreme conditions experienced with track driving in the northern Central Valley in California, where air temps were in the mid-90's.

Any thoughts?

Craig-o

 

[Bioscache2]

I'm no expert but it seems that this is actually not that strange as I think its just the fact that the brakes are settling. When you install new brakes it takes a few uses and drives for everything to settle back in, especially if you changed the pads and flushed the system. Even if you drove it between the change and the track it may not have settled cause the heat and the extra pressure applied may push the brakes to settle more then they would under normal driving conditions. Unless you plan on returning to the tracks very soon it should be all fine by the time you drive it again. You might want to get a second opinion just in case though as I'm no mechanic.

 

[atmmac]

i believe he is right. This could however be the TSB that is mentioned for 2001 corvettes. If your car is in warranty i would have it done.

 

[Hib Halverson]

There is no such thing as "settling", ie: a situation where there is a normal decrease in brake pedal height and/or feel shortly after a bleed, flush and pad replacement.

My guess is one of several things is happening.

1) The Dura Stop pads are most likely a less costly replacement for OE and are probably a poor choice for race track use. You need at minimum the pads off a Z06 and a better choice are the pads Baer sells for street/track use

2) The Dura Stops, as poor a choice as they are for race track use, were probably not bedded properly for that duty cycle.

3) It is possible the bleeding process may have been faulty or you make need to perform the autobleed procedure to your ABS.

The only TSB for Corvette in MY01 is for a problem with dragging brakes and/or stop lights "stuck" on and solution is to change the brake booster.

 

[DkBG]

Hib , could you please explain your number two possibility a little more . Specifically , bedding . Thanks . Cliff

 

[Craig-o]

The AC Delco Dura Stop pads were supposedly an upgrade over the stock pads, so I'm curious, Hib, if your comment was speculation or did the dealer steer me wrong? They were about 20% costlier than the stock pads.

As for the bleeding process, I made sure to have the car turned on, so that the ABS wouldn't interfere, but that's the only precaution I took. As I said, I used a power bleeder, with a blue fluid, so I knew by the color change when the new fluid had made it from the reservoir to each caliper. Can you elaborate on the "autobleed procedure" to the ABS?

The bedding process I used was one that I'd used previously on passenger cars. Drive for about 3 miles at 35-40 MPH with slight brake pressure to heat the pads and rotors, then perform some (3-4?) failrly hard 50-0 stops; not hard enough to activate the ABS, but hard enough to lock up the seat belt.

I'm not sure I know what an appropriate bedding procedure would be for track driving, anyone have some insights?

I haven't experienced any problems with the brakes since the day at the track, but I would like to get this addressed (if there's somehting I can do) before I head out there again.

Thanks for the help.

Craig

 

[vettepilot]

I think Hib's #3 suggestion may be the culprit. Because of the anti-lock system there is a special procedure, which, I believe requires a computer/controller when bleeding the systems. Does your car also have active handling? I think it was an option in 2001. That system is tied into the anti-lock system also.

Re. The brake pads, the 2002 and later Z06 front pads are very good pads.


vettepilot