Rob, I didn't do anything special with my new 97s, though the rotors had already been broken in with other track pads. I didn't do 100% braking on the first couple of laps, but I normally don't anyway.

No problems whatsoever. I really like the 97s.

97s Good enough for pro-racing in piggy Audi S4s, and good for DE in piggy 951s as well. Good grip, long life (for a track pad), and good heat management.

Regarding shudering when hot and not when cold this makes sense based on the way brakes work.

WHen your brakes are cold the main stopping power comes from friction. The pad material working against the brake disc. Once the brakes heat up, friction is not as much of a factor. Instead the braking force comes from the molecular bonding between the pad material in the pad, and the pad material deposited into the brake disc.

If you have uneven deposition of pad material in the brake disc (caused by improper bedding among other things), then when the braking switches from friction to bonding, you will get shudder because of uneven braking force across the "length" of the stopping surface.

To combat this, burnish the brake disc with an abrasive pad (like scotchbrite) really well then seat the pads again to redeposit material evenly.

Chris,

Interesting. Do you think that I can revive these rotors? Have you had luck doing this?

I was planning to replace them anyway, just because they're very old, but now I'm sort of interested in using them to test this theory. Would Scotch Brite really be aggressive enough to get to the bottom of the (uneven) deposition of material on the rotors? I thought I'd read that even turning the rotors may not bring them back.

Maybe it's a matter of degree. It's my understanding that the uneven deposits can cause shuddering, and stick-slip-stick friction cycling causes damage to the rotors through localized overheating and formation of cementite at the locations on the rotor where friction is highest. In short: shuddering begets more shuddering. But perhaps I haven't run them long enough in this condition to cause such damage. Any thoughts on that?

Also, if I just drive it around on the street for a while, using the brakes but keeping them cool where the frictional mode is abrasion more than adherence, might I just "clean" the brake rotors through normal use? And then I could go through the bedding in process properly? Problem is, I use the car on the street once in a while, and I certainly drive it to the track. I'd hate to think that the bedding in process has to be redone every time. And how would I know when I have to re-bed the brakes? It's not likely that I can tell by looking at them or by the way they feel when I drive the car on the street.

I'd guess this is a dilemma for many people like me who track their cars once in a while and drive them to and from the track on the street. It's not a simple problem. Even changing pads at the track may not fix the problem, because the street pads may have wiped off the deposits necessary for the track pads to work properly, requiring bedding in at every event.

Ah, the life of a dual purpose car...

You certainly can revive the rotors....


Couple of ways.

1) Use an abrasive pad on a drill.... You've probably seen them in brake shops on the small air-gun used for cleaning off rust. You can do the same thing with the scotch-brite ones that will go on a drill for paint stripping.

2) have them skimmed on a brake lathe...

3) What I used to do was put on some SUPER aggressive and abrasive pads for a few laps, then switch back when this happened at the track.

The first option ends up working best... A few sessions with the uneven deposition didn't seem to hurt the discs at all, so you should be okay.

:( that is not recommended by any race shops that I know of

That's kind of a broad statement, which of the three I mentioned? Which race shops?

I'd be interested to hear your reasoning behind that statement. All three methods will successfully clean off the uneven deposition from the discs and allow for a successful re-bedding of the original pads without reducing the life of the disc appreciably.

Well, I'm specifically talking about any of the shops I've worked in, and a few others that I know well.

It has nothing to do with acceptable methods for resurfacing brake rotors... I guess it's a general policy that most people might think is just an excuse to charge a customer for a set of rotors, but the general philosophy I've always been taught is that if rotors need to be resurfaced, rotors need to be thrown away, no exceptions. It's a safety and a liability issue. I want my rotors to last as long as the next guy, in fact longer, but once they reach a point where there's any chatter, or shudder under braking, or they're wearing badly, they've had it, it's time to get new ones. It's not cheap with Big reds, but I'd prefer to live through the next DE or race.

Besides, why does he need to re-bed the pads?, or even switch them?, it's not like he's switching between Ceramic and Metallic pads, where you really can't run them with the previous pad deposits... heck, the PFC-97s are a damn good street pad anyway, they last forever, and are easy on rotors... sure they make noise, especially the rears for some reason, but you don't really need to change them out if you don't want to. Changing pads constantly is what leads to rotor problems requiring them to be resurfaced, etc... I think rob's getting scared over nothing. Put some new rotors on the car, leave the 97s in and forget about it. Drive and be happy.

Andrew,

So here's my experiences in this area...

I've had Brand New rotors experience this problem... Sometimes it just happens. Rarely with PFC-97's but often with other brands, particularly Pagids... If I were to replace them every time this happened when I was running Pagid's I'd have spent $4-500 every race weekend on rotors.

I'll NEVER use Pagid's again because of this. The instant I switched to PF97 the problems went away. I went from 3 events on a set of rotors to 2 SEASONS on a set. (20 events per season)

Burnishing the disc with a scotchbrite pad or agressive brake pad certainly doesn't take any material off the disc appreciably. So there's no safety aspect there... And taking off 2 thou with a lathe doesn't either... That's all I'm talking about. You just want to remove that bond at the very surface. It's 2% of the acceptable wear on a disc. (2mm = 80 thousandths)

I think throwing them out, especially on a dual purpose car is overkill.

I run 97's on my 78 SC.

Fronts - 0045.97.15.44
Rears - 0031.97.15.44

EXCELLENT pads, no noise, no weird bedding in ritual, just work great (stock rotors)..

Chris and Andrew,

Interesting exchange. I'm certainly willing and ready to replace the rotors, and I may do that. And I'm glad to hear, Andrew, that the 97s are likely to work fine from that point forward and that you've find they work well on the street. I assume, though, that I'll have to bed them on any new rotors I install.

But I'm intrigued that my rotors might be revivable, per Chris, and I'm interested, as an experiment, to see if that can be done. If it means taking them off to a shop with a brake lathe, that may not happen -- once there's a significant cost and bother involved, I'll lose interest. But the Scotch Brite thing may work. I have one of those Scotch Brite wheels for my die grinder and I can try it.

What concerns me, Andrew, is that per your advice, once a rotor starts shuddering, it need replacing. Is that always true? It seems that if my shuddering was caused by deposits, then that could happen to a new rotor as well as an old one, and if it happens again right away, I'll be a lot less enthusiastic about replacing them.

I understand that it's generally not a good idea to take shortcuts with brakes, and as a shop, I might not want to take on the liability for brake rotor turning or other forms of revival. But in this case, I'm curious about using my old rotors as test mules to see if Chris's theory is true. If so, it may be a valid method to use if this problem occurs with brand new rotors.

I'm still wondering if I just drive it around on the street for a while if the rotors might clean themselves.

Chris,

Some of my above post is redundant with yours. We made the same points. You just typed faster than I did.

Which Pagid pads, specifically, had the rotor deposit issues you refer to?

The idea that the rotors need to be thrown away when they start to shudder stems from the belief that the rotors are warped, and once they are warped and delvelop hot-spots they will immediately warp again when at operating temperature regardless of turning them on a lathe. This is one of those things that has been repeated several times so it is automatically believed to be true, it is very convinient for the shops that are selling you rotors.

According to Carol Smith, rotor don't warp at all, and the vibration are due to pad deposit only (article on Stoptech site). I haven't done any scientific study on it personally and since I properly bed-in my pads and rotors I don't ever really experience the vibrations either.

Assuming the vibrations are due to pad deposits there is no logical reason why turning them (a couple thousandths) or cleaning them with an abrassive set of brake pads wouldn't work, obviously if they are warped this won't do the trick. I don't really like the scotch brite idea because there is no way to control the flatness of the disc, you could just end up making the vibes worse.

I've run PF97's on the street and they are okay, in fact they're on my car now because I've got an event this weekend, you need to be aware that they aren't great for your first couple stops in the morning when cold. Also, the dust will destroy the finish on your wheels pretty quickly, so if you are concerned about that use a different pad on the street and clean your wheels well after track days.

Performance Friction makes great pads, in my opinion they are better (and cheaper) than the Pagids that many people are running. I have run PF97s and Pagid orange back to back and I prefer the PF97s. I maintain a few track cars and buy enough pads that I recently became a dealer for PF, Hawk, and Porterfield.

What is my special Pelican price for a set of PF97's for my 1993 964 C2?
:D

I am definitely not theorizing here...

For those that don't know me, I've been racing 911's for 6 years with a fair degree of success. (3 yr. running MCSCC Champion in GT-2) and do specialty racecar work. (see website below).

Anywho... I used Pagid Orange early in my 'career' and was laboring under the warped rotor delusion the whole time. I had a standing account for brake discs... Untill I did some research and figured out what the problem is. I saved many of those old discs and use them now. I've used all three methods successfully.

I'd start with the scotchbrite method, or better yet use something a bit more abrasive like the pads used in your local shop... If this doesn't work, then take a few thou off with the lathe. I'd avoid cutting them unless necessary, it does take some life off the disc. (though not much)

GaryR,

PM'd you