SpeedZ

So this past weekend I had a track day at Thunderhill East, I recently had new rotors installed, Endless RF650 fluid flushed through the system, and Endless ME20 brake pads installed. All were pretty fresh ~500 miles and 4 days before the track day. Car is a 2013 991.1 C2 7MT.

Going into Thunderhill East, at turn 1 going 115mph on my 5th lap, my brake pedal went straight to the floor. I thought I had hit the clutch by accident. The car/brakes fortunately still worked, but the pedal was going to the floor until I gave the car about 15 minutes to cool down. Managed to make the rest of the runs for the day fine, but the pedal did go back to the floor once again in a later session. Every run after that first session was unfortunately at around 6/10ths because I lost confidence in my braking system. The second time the brakes went, I definitely noticed a bit of a burning smell coming from the car.

I'm a bit confused because I would assume the braking system is strong enough to handle that much heat. I have run the car with the stock porsche pads and brake fluid at laguna and thunder hill west with no issues in the past, even after 5 sessions. Any thoughts? I have Girodisc rotors on order for both the front and rear brakes right now and I'm currently still using the stock 4 pot brakes front and rear.

I've read some theories from past threads about how maybe there was old brake fluid in the ABS system? I'm planning on doing a full flush next week and also getting some temperature sensitive paint. Id' rather hold off on installing the giro discs since I just got new rotors.

JSETarga

Did you inspect fluid and pads already? Fluid still clear or look burned up? The one time I boiled fluid, it had a dark burnt color to it and not clear anymore. You can get a water meter for a few bucks at auto store to check water content of fluid as well. How does pad wear look?

SpeedZ

Pad wear looks great, very minimal to be honest. I'm going to take a look at the fluid once I bleed it, but the master reservoir fluid is clear. I have a water meter on order and will check.

wareaglescott

Brakes get properly bleed after the fluid change?

JSETarga

Did you bed your new pads on new rotors?

SpeedZ

Yes I did. Although I'd say they're not new now.



I hope they did! I had a shop do it.

snake eyes

sounds like brakes not bleed properly........

JSETarga

Seems like something wasnt done right somewhere leading up to event possibly air in brake lines. I would pull all the pads, inspect everything, move onto giro discs and redo all the fluid again if it were me. You may have life left in your OEM rotors but you can always put them back on later and get use out of them.

Bxstr

I am guessing air in the lines as well.

SpeedZ

Thanks I will check.

Seems like everyone's leaning towards this. I guess the other question I had, is that the brakes should have lasted at least a single session at Thunderhill with the stock rotors? I found it odd that they failed within a single session, even with heat build up I would have expected a few sessions out of them.

Semitone

I agree with some above that is sounds like a not properly bled brake system. Cheapest and easiest thing you can do is bleed and flush the brakes again. That would be my first step.

Joec500

Agreed, I had this happen on my mtn bike, different vehicle but exactly the same principles. I ended up pushing an air bubble to a place where it would compress in the line. For safety sake you should get your brake system flushed, the shop should do it for free.

SpeedZ

Thanks! I'm going to end up doing it myself since I need to get more comfortable bleeding my own brakes at the track.

ohniner

In all the above scenarios your brakes would not have come back so quickly.
another possibility is play in the rotor or a slightly warped rotor that pushes the pads back on the straightaway so that when you apply the brakes you have to bring the pads back into contact with the rotor so pedal goes to floor.
not an unusual occurrence, many racers will do a left foot brake pump before their braking point on long straightaways to bring pads back into contact and provide a high hard pedal.

groundhog

Something to be aware of - higher mu brake pads as mu implies, have higher coefficients of friction. This imparts more brake torque at a higher rate and thus generates more heat more quickly - basically if you're rookie braking (threshold braking) you can cook the fluid in the callipers in one action. The symptom is loss of or partial loss of pedal - but it will come back on cool down and with pumping. Any doubt tap brake pedal before the braking point to see if its there. Bottom line is pads and rotors are on the small size for the base model. Try trail braking and optimising weight transfer whilst maintaining momentum - you will find you will go quicker, work the brakes less and better preserve the tires.

You may want to ensure your pads have the same friction material front and rear - if the front are higher mu than the rears the brake bias will have moved forward which can have all sorts of unintended consequences. Good luck.