Need help curing Repetitive Brake Vibration Syndrome

[SoundGuyDave]

Okay, assuming fresh rotors and pads, here's how I break them in... Go out first session, ducts sealed, take a few relatively easy laps, around 60% or so, then step it up to around 85%, until you feel the first HINT of pad fade (rock hard pedal, but reduced stopping force), then park the car, rolling it 5-6' every few minutes. After approximately 30 minutes, unseal the ducts, then go out and drive like a maniac until your brakes are shot. If it's cool out, at BHF, I would seal HALF of each duct inlet. Blackhawk is THE most brutal track that I've seen on brakes! If you have (or have access to) a pyrometer, keep shooting brake rotor temps. Most race pads have a "sweet zone" for temp where they work the best. Too cool, and you scrape off the transfer layer and can get uneven deposits. Too hot, and you get pad fade. If you suspect you're not getting enough heat in them, either left-foot-brake to drag them for and extra 100' or so before you go to your braking point, or just start braking a little earlier, and reduce your total pedal effort. All the extra friction will raise brake temps pretty dramatically. Remember that proper threshold braking will put the minimum amount of heat into the rotors!

If you're flushing, then the sequence is pretty important, to avoid cross-contamination. You flush the longest line first, and that way if you siphon any fluid from line to line, it'll be fresh... Bleeding, it's not so critical, but it's a decent habit to get into.

 

[DUFUS]

Thanks, I'll try to be more conscious of building the proper amount of heat in the pads/rotors before I try for any record lap times (for me at least) with major threshold braking.

Speaking of brake bleeding, is an ABS activation "event" recommended prior to, or after, bleeding the system? Or not needed at all?

 

[SoundGuyDave]

In an ideal world, you would use the high-dollar factory ABS tool as part of the bleeding procedure, but in practice, don't sweat it. If you're bleeding fairly regularly (lunch and the end of each day), you'll eventually cycle it all through.

 

[roboworm]

I had the very same problem with the brake shudder. I just put on my second set of PowerSlot rotors and PFC01 pads (first set was awesome), did a street break-in and everything seemed fine. Went for a weekend to Laguna Seca, and massive brake shudder after a few laps. It only happens when the brakes get really, really hot. Ruined an expensive track day.

When I got home, runout was .003 and .007 left/right front. I had the rotors turned (runouts under .003) and everything seemed fine testing on the street, until another track day, same problem only not quite as bad, barely driveable. I tried to reproduce the problem on the street. It is really hard to get your brakes up to track temps on the street! I had to do over 25 80-20mph hard stops repeatedly to get the shudder to occur. Once it started it wouldn't stop until a full cooldown.

Everyone was telling me something different as to what it could be, mainly hubs and/or pad deposits. I finally decided to by a new set of cheap $90 NAPA rotors, using the same pads, the problem has dissapeared! Went to brake busting Buttonwillow yesterday, 100 degrees out and no problems whatsoever! Obviously a bad rotor, even after resurfacing. I met a guy who said about 10% of one-piece rotors can't handle track temps and I just got unlucky. Anyways I believe him and it makes sense for a cast hunk of iron not to be perfect all the time.

BTW, I became a runnout measuring freak now, and I'm pretty sure that it's not as important as you think. Rotors are extremely flexible and you can test this be pushing on it with your hand while measuring. My last set measured .005 runout and works fine. Indexing the rotors over to another lug will change the runout a lot, so I wouldn't worry about runout as much as thickness variations. And yes, my hubs are fine.

If what I have said is true, there is a 1% chance of having two sets of bad rotors. I guess you never know, hope this helps...

 

[DUFUS]

Thanks for the input. I may have had the best luck (most sessions) with the original Brembo rotors. Although it wasn't by much, because the shudder developed with them as well. So I don't know whether I'll go back there, especially considering the cost vs. marginal "performance" gain. I'd like to get the ST43 pad and Raybestos rotor combo to work, but that may be my wallet talking and not in the cards. I'm not averse to spending the money where needed when I know it will cure the problem, so maybe 2-pc rotors eventually. But I won't do that until I'm satisfied I understand what's gone wrong (or what I've DONE wrong) in the past, when others have gotten similar eqpt to work fine.
We'll see what happens this weekend with prepping by the book and using suggestions/responses to this thread. Thanks all.

 

[DUFUS]

OP update after a track day with meticulous prep and operational suggestions posted herein...
Still developed a shudder/vibration, although not as quickly or as bad as in the past. So, I'm getting around to measuring the runout on all the used rotors I have lying around. I know that's not the end-all, but I have this gauge and might as well use it, visually they all look OK. Looks like the Raybestos rotors fared the worst, anywhere from 006 - 010. Centric slotted was .004. One Brembo was 001, the other 004. So, for what all that is worth, I guess one can somewhat conclude that you get what you pay for. I have some new Centric blank rotors coming, but I'll probably (re)mount these Brembos, using a .003 adapter plate thingey for the one out of spec, and see what happens at Road America in a couple of weeks. I'll bring the new ones as standby. I might go back to the Hawk DTC60 vs. Raybestos ST43 just to see if I can stumble upon a winning combination. Depending what transpires I may install new hubs and/or 2-pc rotors over the winter.
Oh.. one other thing, I will adjust my "homemade" (using stock backing plates) brake duct mountings/adapters. I crafted these fine pieces back when I know even less than I do now, and wasn't diligent in making sure the air would be directed ONLY at the center where it would be dispersed through the vanes and not blowing on the inside friction surface itself. Perhaps uneven cooling inside-outside? Who knows, but it can't hurt to get it a little more in line with the theory.
It's too much fun when things are going right to not keep trying.

 

[SoundGuyDave]

Sorry to hear you're still getting judder... Look me up at RA (I'll be in the Silver #50 S197), and let's compare notes.

Your brake duct may actually have contributed to the issue. The differential cooling (inboard face running cooler than the outboard due to airflow) can cause the rotor to "bell" as it gets enough heat in it, and I seriously doubt it will do so evenly! Good catch!