clubrcr

I had an problem arise this weekend that never has happened in the past. I wanted to get input from everyone to make sure I can solve it.

I was at Sebring this past weekend. It was hot! During practice and qualifying, my car was great. During the first of two races, I developed a vibration under hard braking. I thought I had warped my rotors. After the race, I bled my brakes, took the air gun and blew out all the brake dust from the holes in the discs.

When I went back out for my second race, the first few laps, no vibration. About halfway into the race, I developed the vibration again.

I am using Orange Pagids and have a air hose from the front coming into the inter fender.

I would like to know if the brake dust had anything to do with this and what is the best way to get air directly to the rotor. I have read past postings on this and have heard the old style AJ racing and OG racing kits might not be available.

Thanks in advance for your help.

Jim Newman
92 US Carrera Cup

TrackJunke

It is very unlikely to be a warped rotor. Perhaps craked, but most likely it would be uneven transfer of brake pad material. Read this article.<a href="http://www.stoptech.com/whitepapers/warped_rotors_myth.htm" target="_blank">Warped rotor myth</a>

JohnM

Hi Jim,

I believe this is purely down to the rotors overheating and some warping happening in them under those temperature extremes, all being well the rotors will be true again when they cool down (using floating rotors can avoid this problem, but that means $$$). I had exactly the same happen on my 993 at a recent track day, last few laps of the 4th and 5th sessions developed worse and worse vibration from the front under braking for the hairpin, but everything was fine once the car had time to cool down (well, except the pads got a touch glazed, but no vibration afterwards). The dust in the cross drillings doesn't help (mine ended up filled as well) but most of the disc cooling is from the central venting rather than the cross drillings. Next mod for my car is a brake cooling kit, I believe you need to get the outlet as close to the disc as possible to get much benefit.

Greg Fishman

Jim,
Your brake cooling set up is, like mine, less than ideal. Best solution is a set up which encapsulates the hub of the rotor and sends air directly into it. Don't know if this was related to your problem or not though. I had a problem with some rotors that had pad build up from some Pagid Orange that were improperly bedded by my previous mechanic. I have heard that the Hawk Blues will remove the old pad material, might try that. I use the Hawk Blues and found them to be better than the P.O. in feel and fade resistance.
Greg

marc 1xx1

Jim:

I have also heard and been told by several very knowledgable people that Pagid Orange pads do have a tendency to leave material on the rotor. If this happens, you will get a stong pulsing feeling like a warped rotor. I an told that this happens when you ride the brake rather than apply and release the pedal.

While I have never experienced this, it has happened to several friends with 911's.

I can tell you that I recently switched to Hawk Blue pads on my RSA. I think they bite better and quicker than the PO pads. They don't seem to need as much heat build up to work effectively.

The Hawk pads produce way MORE dirt and dust than the PO pads...but they cost about a third less.

They are a bit more aggressive on your rotors and will clean off any PO build up as well.

Hope this helped.

marc

joey bagadonuts

The OG Racing brake cooling kit for C2/C4 is still available. Mine goes in this Friday. They also have instructions which may or may not come with the kit.

The intake replaces the stock scoop and there's a plate which replace the backing plate and feeds air directly to the rotor. According to the instructions, you need to reverse the direction of the sway bar drop links for a reasonable fit.

Others have commented on the poor design of this kit, but I will leave it to my mechanic to see if we've got something workable. For $300, it's not cheap but it seems to be the only commercially available option.

clubrcr

I appreciate all the input. I have called to get the air ducts, but it seems everyone is out???

The weird thing about this problem is, the brake pad are 5 races old as well as the rotors. I have heard from a couple of people that the Pagids leave a residue on the rotor, this could be a problem.

What is the best pad to use? I have only used pagids.

Jim

joey bagadonuts

Jim,

Are you looking for just the ducts that replace the fog lights or the full cooling kit? The ducts alone don't really cool the brakes, you need to pipe air right to the rotors. Perhaps you already knew this, but I just wanted to be sure.

As for pads, the two best track versions were mentioned above: Pagid Orange and Hawk Blues. One of the PCA Club Racers who frequents this board uses the Hawks in competition, so maybe you should give them a try?

clubrcr

I wanted a full kit. I will get some feedback on the Hawks. I hate to get rid of the Pagids, they work so well.

Thanks,

Jim

Bill Gregory

[quote]<strong>I have heard from a couple of people that the Pagids leave a residue on the rotor, this could be a problem.</strong><hr></blockquote>

Jim,

Just to post what I mentioned in email, I've used Pagid Oranges for years, and have never had any material clumping issues. I believe this is due to following the recommended break in procedure as well as using slotted rotors on the front.

clubrcr

[quote]Originally posted by Bill Gregory:
<strong>

Jim,

Just to post what I mentioned in email, I've used Pagid Oranges for years, and have never had any material clumping issues. I believe this is due to following the recommended break in procedure as well as using slotted rotors on the front.</strong><hr></blockquote>


Bill,

I appreciate your input, but I thought I broke these in correctly. I never had any problem with these in the last 4 races. I had read on the "Stop Tech" website about the material build up. I also talked to a Porsche Grand Am team manager and he also agreed about the material build up. He went on to say that I needed to take a drill and carefully drive out the excess brake dust build up in holes within the rotors. He said that you will find clumps of hard brake dust inside.

I'm not disagreeing with your take on this, I wouldn't have even thought that be a problem until I read your reply posted 11-05-2001.
--------------------------------------------------------------------------------
Arnold,
Are you using Pagid Orange pads? If yes, there's been some discussion here and on the rennlist email list involving pad deposits on the rotor and brake judder due to the deposits (mimics warped rotor when hot).

If you do have warped rotors (as opposed to material on the rotors):


Jim

Bill Gregory

Jim,

And I'd think your rotors with holes would functionally be the same as mine with slots, as far as the Pagids are concerned. What's odd, as you pointed out, is how this surfaced at Sebring, and not before.