6speeders,

I rarely post here since my automotive background kicks in and I can usually hone down a problem, but this one is just new to me in general and I think someone who may have had this happen to comment. I have consulted with multiple other professionals on this who gave a few diff solutions, but are stumped as well, so this may be a tough one:

Vehicle: 996 Turbo
Brake Specs: GiroDisc 2 piece rotors (100 miles currently on them) w/freshly cut Pagid pads (orange/yellows F/R respectively)

Last year, I was already running the pagids fresh and new on some older brembo crossdrilled rotors. The rotors were junk, so we swapped them out with a brand new set of GiroDisc rotors as I have had tons of experience with them on other track cars to be stout. Hitup the track, all went smooth and peachy for multiple sessions and track days. At the end of 2011, the car gets put away in a heated garage under a car cover.

2012, car gets taken out and first time on the track, after a once over, and a brand new bleed with Motul fluid on the brakes, the akward starts to happen:

1. When pads are cold, everything works like a charm
2. The moment pads get hot, the pedal and steering wheel violently shake as if I am running old decrepid rotors.

Confused as heck, I contact GiroDisc and we start to go through the issues. First one, is it run-out? Check that, 100% in spec. Everything is bolted down well, but maybe just maybe the old pads are leaving deposits since they are un-even although they were last year as well and should have bedded in. No deposits, nothing. Everything just looks perfect and sound. After wondering for a while, a brand new set of Rotors (not just rings, entire set) is ordered and QC'd by GiroDisc before sending out just to make sure.

Low and behold, the same exact thing happens again and this time, we even filed down the pads and broke them in 100% to spec. I am honestly lost. Possible issues that i can think of:

1. Something is loose, however, there are only a couple bolts from caliper
2. Caliper may be sticking - however, would show signs when cold as well
3. hub(s) may be bad and causing this, however, with a simple check while cold, hub is in good shape and rare for the 996's to have this issue
4. Fill in the blank??


I am hoping someone can comment on this and maybe has had something similar happen. I will answer any and all things that I could have looked over, however, all surfaces were clean with new rotor placements etc etc. so I was meticulous about everything being installed and torqued down properly.


Edward

 

Did you properly break in the pads? Typically rotors do not warp. Vibrations are often caused by improper break in.

 

Yes I did. As well, with pads that may have uneven wear, you can really scuff them up and see if there are deposits or other issues. We have 0 here.

 

You are focusing on the rotors so it seems. Some questions for you
1/ You are sure it is not the ABS that is kicking in??
2/Are ALL 4 wheels vibrating / shaking or just the front or the back, or????
3/ did you try other pads and or swap front and back? what happens?

 

1. its not ABS 100%
2. I cannot comment, but such force seems like fronts. If it were rears, the butt would shake, it does not really
3. I did not. I can though. I have new stoptech street pads i can test as well.

 

Let me know if anyone else has ideas?

 

sounds like hot judder to me. change your friction material and try again!

 

I PM'd you flavorpacket. Hoping to hear back.

As for hot judder, I assume you meant my friction material is bad. I can only attest that maybe these pagids were old and have gone through too many heat cycles from track abuse and are now just trash and should be thrown away. Luckily, I have Stoptech 309's, but they won't compare, however I would rather run those than nothing. Waiting on PM and will try that out tomorrow night to do the swap out.

Edward

 

Thinking it is your pads, so just run the Stoptech to verify shudder is gone, then decide what pads you want to buy. Should be straight forward. Good luck!

 

Did you double check the suspension hardware....specific the upper strut mount hardware?

 

Guess a good swap out is due tomorrow. I hate last minute things but glad I have spares.

Eddie

 

I have not, can you elaborate on this?

Edward

 

Any vibration at speed when you're not braking? Probably not your issue but I just had both front axles refurbished; there's was a small amount of vibration at speed.

 

Did you check the rotors when hot? They expand when hot and a small highspot will cause vibrations. I had this problem with a Mitsubishi eclipse, normal driving everything was ok but track events and repeated high speed stops on the street and I got vibrations. We beat on it then measured and found a small highspot. We heated with a torch then cut the spot down. Also a wheel bearing could be bad. Another vibration source on the eclipse

 

Had the same problem with used stock rotors and new CoolCarbon pads not properly bed before a big trackday at Laguna.

Hot judders began to happen after a few laps in then got worse and worse. I ended up tossing the rotors and pads and starting new. Prob went away and have worn through several sets of pads without further issue.

For me it was the combo and also making sure I have good matching tires. Good luck-