boqueron

Need help Please!! In this two last track Days ( Saturday and Monday ) on different tracks I have braked and missed the turns after long straights on four occasions . BTW, it has NEVER happened to me before!

It has happened after a long straight and I have started braking at well known ( at least by me ) references.

The car will start braking normally but, when squeezed harder, it will keep on braking and - suddenly - ( at the limit, when I would expect a possible ABS noise) it "looses" it's bite !! : the car stops braking and goes forward increasing the speed .. and sending me out of the track !!! It has happened after some warming laps. THe ABS did not enter and I did not block the wheels.

This has been witness by a "pro" coaching on my passenger seat.

The pedal didn't feel spongy and did not go down. The brake fluid looks OK with correct levels, the discks look well. The only think is that the front pads ( new pads ) look totally "burned". I have chequed with the computer the ABS which does not show failures..

I am using RS19 f and RS14 Rear ( for the first time). Before I would use - with no problems - R19's F and Rear. NOthing else has been changed in the car, exception made of the tyres, I have shifted to Toyo's R888's and was wearing before MPSC's.

Could it be that the front pads have not been cprrectly beded and that, when they attain a certain temperature, the friction can not keep up ?

It will be great to have a clue of what is happening !!

LVDell

Three possible explanations without actually feeling it.

(1) Cooked your fluid. Just looking at it won't tell you that it is "fine". Bleed if it has air or Flush if it is totally cooked.

(2) If the pads were brand new you might have just experienced green fade.

(3) Your tires can't catch up to the braking power of the pads. If your ABS did NOT kick in then I would probably default to explanation 1.

99firehawk

improeprly seated pads subjected to race conditions, can casue the pads to over heat easily and loose all grip on the rotor, try sandign the pads till they arent glazed and hitting the rototrs with a non direxctional to aide in seating the pads

Carrera GT

It seems like a typical pad problem (old, grooved, glazed rotors roast the pads for lack of transferring pad material to the rotor surface) but you could also now haved boiled (and possibly wet) fluid. The solution is (ouch) to replace the rotors, pads and fluid. Flush it with a good fluid, preferably go to Motul. Break in the new pads on the new rotors according to the conventional approach. And keep the rotor vent slots or holes clear. I suspect that a combination of poor cooling and inadequate maintenance (for frequent track driving) has created a pretty typical syndrome. I've been there. : ) ... And you could just go with bedding in fresh pads and bleed the brakes, but then you might crash when the pedal goes to the floor. Or you could flush the fluid, use non-metal sand paper to clean the pads and rotors (that will take about two hours with a power tool plus the time to R+R the rotors and pads.) But again, it's no sure thing until you've replaced the three major components of the system.

And that brings me to the final observation. Get your brakes checked at the dealer (not an independent unless they're really good) and have them check line pressures and test the ABS (simple OBD codes won't tell you if the ABS is failing at a mechanical level.) I've not heard of even one case of GT3 brakes failing, but you could always be the first and whatever happens will probably happen to someone pushing their street car on the track. Assuming you're still under warranty and you have a friendly dealer (are the dealers friendly in Spain?) then you should be able to get a tech to really "nut and bolt" the brake system to diagnose any mechanical problem. That's a long shot and I don't expect to find trouble because you're describing a typical pad/rotor/fluid failure, but I'd still get it checked and it's only possible to fully flush the system with the factory tool to cycle the ABS pump.

Z06

ABS comes on with out the normal pulse at the pedal, bumps will do it and all checks of brakes as above is a good idea.

boqueron

LV Dell.-

Thanks for your help. I am using Castrol SRF. The brake pedal hasn't shown any fade. It was bleeded two track days ago. The pads were bedded...on the highway. I am not 100% sure of having bedded them properly this time ( my previous set were bedded at the track )

Carrera GT.-

Thank you for your answer !!

This Pagid set is 300 miles old (!). I check the fluid (Castrol SRF) and bleed it regulary as well as the rotors, allways clean and I look for any kind of cracks .. I am putting now metal lines.. I have just spoken to my independent mechanic.( a former chief Porsche mecanic at the Main Porsche importer for Spain) and he swears to be using the same checking system than Porsche. in fact he claims to be using an original POrsche system..

I have read that , when changing different pads compounds, one should change PADS AND ROTORS but am not sure if this is the case when shifting old to new padas of the same manufacturer. My present rotors do not show big grooves...

Z06

I understand that ABS pulse can be there or not, but the pulse can not change (?). The sensor could trigger or not at the right moment (??). In any case, the computer would show it...

LVDell

Mabye glazed rotors???

boqueron

??

LVDell

I guess the best analogy would be that instead of having a nice layer of brake pad material transfer instead you have a "glazed" film of material that has been "cooked" from improper bedding of the pads and thus your pads will not bite against the rotor but rather almost slide across the rotor. Not sure if that made much sense. Sorry.

boqueron

It could make sense..The problem is my little knowledge....!! In case of doubt I will change rotors AND pads ...

LVDell

If your pads are relatively new and your rotors are not anywhere near the end of their effecetive life my guess would be at this point either (a) glazed rotors which can be fized with a proper bedding in of the pads. Also, you can "finely" sand the pads and rotors to effectively start over. .........or (b) a fault in the brake system. Personally I would assume (a) and try to remedy and if that failed I would definitely swing by the dealer for a more diagnostic look.

Rob Mc

I am very interested in your opinion on the Toyo R888 and how they have compared to the Cups during your track day.

boqueron

Rob Mc.- I am very happy with them but.....unfortunately, I have not been able to compare lap times against my previous MPSC's.. They are very proggressive and they behaved very well this weekend. One month ago I tried them in a semi-wet track day ( light rain that leaved dry and wet zones. ) they behaved very well...

Anyhow, it seems that I will shift to 100% slicks. All my Porsche mates are using slicks, and I carry my GT3 to the track on a truck.....

Carrera GT

It sounds like your mechanic is what we call a "master tech" in the USA and he's probably using the PST2, which is the right tool for the job. The right tools combined with a solid tech's years of experience (presuming he's familiar with 996's) should get to the bottom of the situation with the least cost (and waste.)

There are a few other possibilities, but now you're best off to go with him doing a thorough inspection and diagnosis.

I'm curious to understand what's causing the fade without losing pedal feel. I'm guessing that's trapped gases.

From what you mention about putting on fresh pads and developing this problem, I'd say you have chemical problem with the friction material and the rotor surface. If the rotor holes are clogged with pad dust, you might even be having gas build up between the pad and the rotor.

Your tech will get it sorted out. Sounds like you're having fun with your GT3!

99firehawk

pictures of the pads and rotors?