WTF is wrong with my brakes?
 

I was at COTA this morning for a track day and during the 3rd session of the day, I had major brake fade 25 minutes in.

The pedal went 80% soft, I still had some brake pressure, so I pulled it into the pits. In the first and second sessions of the day, I did not go hard at all since the track was really cold, my tire pressures were too high, and COTA has a brand new surface in a lot of corners.

COTA is a big, fast track, but isn't what I would consider really hard on brakes. There are 4 corners that you brake hard and deep in, but that is it.

~60 deg. ambient temp
~240-250 deg. oil temp (even w/ vented hood and 25 row oil cooler)

2014 Sport w/ Akebonos (obviously)
Z1 2-piece front rotors, slotted
Z1 1-piece rear rotors, slotted
Z1 SS Lines
Z1 Front brake duct cooling kit
Titanium shims in the front
Carbotech XP10 in front / XP8 in rear
RBF600 fluid, about 3 months old, 1 previous track weekend with this fluid.

I saw some brake fluid was leaking out of 3 of 4 of the caliper bleeder screws on the outside nipple, other threads on this forum say that is common and not that big of a deal and wasn't associated with brake fade.

The ONLY thing I think of that could have any sort of impact is that the pads were brand new, and I used the recon session (1st session) to bed them in. It's possible I didn't bed them in well enough, but I don't know if that would cause the brakes to feel great for a few sessions, then fade to nothing.

Getting really frustrated with the brakes on this Z. Does anyone know what the culprit could be?

Is my expectation to be able to run a full weekend without any fade unreasonable with my setup?

Carbotech pads and z1 piece rotors don’t work too well in my experience. Could not make it past one track day without hint of fade and vibration after the track day. I gave up and bought stoptech 6 piston trophy kit for the front and never had any issues after. Was worried about brake balance but the rear stock akebonos are keeping up no problem. It seems many members to have had issues with carbotech/z1 on the track.

Yeah, you got them hot. Change your driving style or upgrade your brakes.

They do? I must have missed those threads -- I went with this setup because both the 2-piece rotors and the XPs were recommended as the upgrades to get.

If a $3,800 brake kit is needed just to make the Z get through a full track day, I'm about to buy a Miata...

This was the upgrade...

I'm a novice. Still have a lot to learn, but not sure if there's a whole you can do to keep things cool braking after a .62 mile straightaway into a 90-degree corner.

Bleed your brakes. And try a different pad. Z1 rotors are not high on my list of rotors. If you want 2 piece rotors for the track. You have to step up.

99% of people who recommended it are not tracking their cars. For the street they’re good but they are the cheapest 2 piece rotors around for a reason. Some run racing brake with good results but they’re 2x price of z1. You could try these before going proper BBK.
Building a track car and getting faster by starting to push limits turns into never ending money pit especially with 370z.

Brake temps are the issue - have you fitted ducted cooling air from the front fascia to the centre/back of the rotors ?
Tracking for 25minutes even with modest skill is about the same as driving hard down a mountain ..........
You do need to look after your brakes and that starts with managing temps for rotors, pads and calipers/fluid

And to answer your question, there is nothing wrong with your brakes, they've just got too hot.

Yes, I installed the brake ducts specifically for this weekend. 2.5" air inlet and ducting.

So -- riddle me this. What actually happened to cause the fade?
Did the fluid boil? Did the rotor or pad temperature get too hot to be effective?
Would the brakes have been fine for another session after they cooled?

Sound like you boiled the fluid.

Pedal going soggy says you've boiled the fluid.

You would need to bleed the brakes before the next session.

I regularly track my Z (and race an historic V8 MG) and baseline brake fettling was to remove the backing plate, install 3" ducting from the front fascia (mine is an '09 model and there is a neat hole in the fascia to use) and I use a variety of "club-spec" pads - I do not use a full race pad in the Z because they are too aggressive - the Z is not my race car after all.

Track day fettling is to install the track pads, bleed the brakes, stiffen up the shocks and go have fun in 20-minute blocks.

I had brake fade problems too, for brake fluid I went with RBF660 fluid,
I also have the Titanium shims in the front, and brake cooling.
I did do a track day at mid-ohio and one at Road Atlanta did not have any problems..
1 piece front and rear discs...
just my experience

What's been your preference in track pads for the Z?

Your pads are fine, I used the same brake pad and rotor combination with no problem. Gloc, Winn and Hawk are few that people use. COTA is hard on brakes because it is high high speed course that requires long hard braking into several turns. I would change out your rotors as some have suggested and see if that makes a difference. If you don't want to go all out with a quality two pieces rotor like Racing Brake, the get a good solid rotor such as Frozen or Stop Tech.

The other issue you may experience, is ice mode. Many of experience it and it is way worse than brake fade. Some of us have swapped out the Nissan ABS system for the BMW MK60 ABS system.

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This page collects some data on performance brake fluid:
https://parsbrorc.com/?page_id=33

Looks like you can bump up to Endless RF650, Torque RT700, or Castrol SRF

Also, as others suggested, try either solid rotors with the cryo treatment or the racing brake 2pc rotors, which are thicker than Z1’s. I believe it’s 32mm vs 28mm