TT Surgeon

Does anybody make a good track pad for the pccb's?
What are the cup and grand am guys doing to cool their rears?

MJones

There is NO computer controlled rear brake bias.(who makes this stuff up????)

The brake distribution between front and rear has been readjusted. The rear axle has relatively higher braking power. (for more info see Technik Introduction)

PCCB Pads
F 997.351.948.01
R no p/n in PET at I have

eclou

There may not be a computer controlled brake proportioning valve, but I have ordered the exclusive option TSA "Technik Stamm-Affe" aka Trunk Monkey

JasonAndreas

If you look in PET there doesn't appear to be a proportioning valve attached to the hydraulic unit (996GT3 or 997GT3) but there is a pressure sensor that was used on the other (996+PSM/996TT/GT2) models that used Elektronische Bremskraft Verteilung (EBV).

MJones

The sensor that you mention would be for the anti-lock (ABS) control unit.

krC2S

i think people are referring to ABD (automatic brake differential) which is the "apply brakes" if needed part of TC just as ASR cuts power

it doesn't change "the bias" but has a similar effect

mitch236

Let me get this straight. I though TC on these cars ONLY cut power to the wheels and did NOT touch the brakes. If this is not true, I guess I will have to run with it off. Also, if it is true that TC uses the brakes, that would explain the rear pad wear over the fronts and probably the higher temps being seen. I wonder if anyone has tested rear rotor temps on these cars with the TC off?

BTW, is there a tool for spreading the pads on the rear calipers? My old method doesn't work since I have to remove the caliper.

NJ-GT

Why are experienced drivers running with TC On at the track? I know is a DE, but TC On is like removing the E from DE.

stout

You speak with so much certainty, yet did not know that the new GT3's traction control system combines Automatic Brake Differential, Automatic Slip Control, and Engine Drag Control?

Yes, the GT3's TC system can and does apply braking force as needed. However, I do not see the need to turn it off unless big sideways is your game. Talk to most racers and they will tell you that running "naked" on a road course makes very little difference to lap times (even with the far more obtrusive early PSM systems) -- if you are smooth. And the risk factor goes up exponentially...

As for your concerns about "active" brake bias, I looked back to the June, 2006 997 GT3 in-depth preview in Excellence Magazine to check my memory.

In the section about the braking system, based on documentation provided by Porsche's PR (which is certainly not always totally accurate; the problem seems to stem from translations of engineer-speak-to-PR-speak + German to English along with good old-fashioned human error), the article states:

"Brake bias has been retuned to apply more braking force to the rear axle initially, taking advantage of the GT3's wide rear tires to reduce stopping distances."

I'll need to research this further, but on the one hand I see your point in that the first part of the sentence implies bias HAS been retuned (static). On the other hand, the "initially" in the sentence implies that bias is altered (actively).

Moreover, if TC can apply rear braking only (and, as can PSM, individual wheel braking) why wouldn't it be possible for the system to alter bias electronically? All these systems are tied together. They have to be.

The braking system in the new GT3 is a complex animal, with the ability to "prime" the pads, bringing them closer to the rotor to reduce response time when you hit the pedal.

In the case of the 997 PCCB soft pedal I recently experienced after just 10-15 minutes to spirited driving on Highway 1 -- which resembled the to-the-floor-pedal one might get after flogging a Kia with five people on board down the Stelvio Pass (repeatedly) -- the dealership couldn't a) replicate the problem as its test loop was insufficient to build enough heat, or, b) offer an explanation. A bit of time on the PWIS and a full flush *seemed* to fix it, and the car exhibited no more bad behavior after it was returned to me.

In talking with a good friend, ex-factory BMW M engineer, and current BMW area service rep after experiencing what I did (the ONLY time I have EVER experienced serious fade in a modern Porsche and the only time I've experienced ANY fade in a PCCB car), he rolled his eyes and said that fixing the electronic aids in relation to ESP/PSM/TC/ABS systems is a nightmare, and often results in "hopeful" component replacement.

Clearly, the questions raised here by the initial poster should be posed to an engineer within Weissach. Otherwise, I suspect it's a subject that would take some research and careful consideration to figure out. Dismissing data points out of hand, however, probably won't help find the answer.

I do not profess to have the definitive answer to this question -- nor did I -- but only offered one more data point. Things like the PET, Technik papers, and PR info are useful indicators, but rarely provide complete answers with interpretation.

I'll try to go back and find the original documentation that led to the Excellence passage above and see if it sheds any light on the subject.

Now, all that said, I am STILL not satisfied that the kind of rear-pad wear this rennlister is experiencing is a normal byproduct of the new GT3's setup. I find it highly doubtful, in fact.

But I've been surprised before...

Cheers,

pete

nkhalidi

It seems like PCCBs on the track are still an up-in-the-air issue. Just another data point for you guys:

I have a Carrera S with PCCBs that sees about 70/30 track/street time. After about 7 track days on OEM PCCB P50 street pads, my fronts were down to wafers; the pad material was barely thicker than the metal backing plate. The rears were in better shape, a little thicker, but still low enough to warrant changing. Rotors had no lip, looked brand new.

In front, the Pagid P40 (green) race pad fits fine. I'm still trying to work out a rear race pad option for my car (my rear caliper takes a different pad than the GT3 rear caliper), and once that's all straightened out, I'll start a thread with findings.

Carrera GT

The word "computer" appears to have crept in as icon interpreted Pete's post. And the description here, to me, reads as a computer control over rear braking. I don't know that it's actively changing a sort of bias (as you might with mechanical bias valve) but the net effect (every few milliseconds) is the same. ish.

Anyhoot. I've played extensively and I can't find TC to be the culprit for the rear rotor heat. Also, I'm not finding the rear pads or rotors to deteriorate, so while they're running hot (still within the limits of a good fluid) I'm not finding any handling problems (like excess rear bias) or fade.

frayed

Active brake bias. . . I highly doubt it. Let's not confuse ABD, ABS, and PSM etc. with brake bias. Those systems certainly have the capability to individually brake wheels, but against the backdrop of the static brake bias of the car set by the factory (which does not change by computer operation while driving).

To change brake bias, oftentimes people mix and match pads, or unwittingly by a improperly sized big brake kit. Actively changing bias requires a proportioning valve, and a computer controlled active brake bias will require a computer to operate that valve.

More than you ever wanted to know about brake bias:

http://www.stoptech.com/tech_info/wp...g_valves.shtml

Also as an FYI, several 996 GT3 owners have retrofitted increased rear bias with a more aggressive rear pad. It's been found to balance out wear by letting the rear wheels do some more of the work.



Going back to the launch materials, my recollection is that Porsche was able to impart more of a rear brake bias by going to a less aggressive LSD. Could be wrong though.

frayed

GT, every person is different in terms of how hard they are on the brakes. I recall a blurb from Barbers' book, in a section about braking technique, of two pro teamates who were pretty much equals, but one consumed pads about 2x his teamate. So, abnormal temperatures (in real terms or relative to the front temps) leaves me curious, a bit concerned, and in my thinking is the likely culprit of excessive pad wear.

Looks like I'll be buying one of those fancy pyrometers to monitor things. Ugh.

stout

Exactly. It's a complex subject, because we're not dealing with 356s, 911s, and 914s anymore.

In my understanding, static bias is still usually set by engineers via piston sizing, swept area, and/or a proportioning valve. I can't speak to a factory engineer's view on using pad compound as part of that equation.

But, generally speaking, I suspect altering static bias in *any* way should be approached with caution and qualifications. It can have great results: I drove a 993 with Motorsport Brembos and a lot more rear braking and it was absolutely brilliant in the dry. BUT it bordered on treacherous in the wet.

Something that is, for all intents and purposes, active bias change could indeed be made if the braking system uses trace amounts of ABD on decel initially. It all gets back to that word "initial." That, or the PR papers I have are wrong...

Driving style certainly plays a role in brake wear, but I am still having a tough time getting my head around the idea of 3x rear pad wear. I just can't see it as driver-related, unless the parking brake was on...

It almost makes me question that data point itself. Can that really be right? Were they "faulty" pads? Has something else been missed?

Cheers,

pete

krC2S

anyway ABD as ABS and TC only come on when some slip level is reached so if not being braught on
they should not influence bias etc