Jake951

Since late last year I've been experiencing problems with the brake pedal going soft on the track after a few minutes. My shop and I have not been able to figure out yet why this is happening. The stopping power is still there but the pedal sinks about halfway down before the brakes start to bite. Once the car cools down overnight, the pedal firms right up and it bites near the top of the pedal travel until I go back out on the track. On the street the pedal is always firm. It has to be heat related.

I tried multiple kinds of brake fluid, most recently Motul RBF600 and Stop Tech STR-660. The brakes have been flushed and bled many times. None of this makes any difference.

Other things that have been done:
Replaced master cylinder
Rebuilt front and rear brake calipers with new piston seals and dust caps
Replaced rubber brake lines with stainless

Rotors are Stop Tech 2-piece slotted in front and OEM drilled in the rear. Pads are PFC08 both front and rear.

Next thing we are going to try is brake caliper temperature strips to see how hot the calipers are really getting on the track. I have an IR pyrometer but by the time you get to take a reading off the track, the rotors are already cooling down a lot.

Any other suggestions on what to try or look for?

YearOne

Mine has been doing this and I believe its due to the metal brackets on top of the pads that wear and bow and hold the pads apart, I was having to left foot pump the brakes on the straights to get the pedal back. Hopefully yours is this simple solution.

etchhead

I had the same thing with a set of new PFC08s I installed earlier this year and tracked. First few sessions it had same effect but then improved throughout the day (after cooling). Next few track days were better, but still have a bit of that after a 25min session and after cooling between its fine again. I'm using drilled in back and Cayenne slotted up front. Similar on my old turbo with PFC01s as well.

aero997c2s

On a very hot day in July last year I boiled the OEM fluid. Flushed system when I got back into Paddock, but the pedal never felt the same after, except when driving normal on the street, like you said. Really hindered any confidence I had and I couldn't find a solution either. Were not OEM pads btw.

AudiOn19s

are the rotors full floaters or solid mount 2 piece rotors?

oldskews4

Not enough stimulation? Sorry, couldn't resist.

Tacet-Conundrum

First thing I think of in this situation is always the Fluid. Across differrent makes of cars it always seems to be the fluid heating up after some time of fast driving.

audipwr1

When you flushed the fluid did you cycle the ABS pump? Often forgotten step if you fluid has overheated

Spyerx

This is highly possible part of issue. Watch any video of the feet of a pro cup car driver. They tap the brakes before any hard braking zone. On some floaters they can wobble and push out pads. They do this to set the pads and ensure the brakes are there (this is the explanation I got from my shop).

I have brembo floaters and have not experienced this, but supposedly full race rotors float more. My pedal grabs right at top and stays there. Brembo/pfc setup,with endless fluid.

Also agree that if there are any spacers between pads and pistons take them out.

Maybe try an Oem front rotor if you have access to a set?

Mvez

+1. When I switched from my 2-piece AP rotors, to the PFC full floating race set (even with the shim set installed), I noticed that under high load situation very slight knockback would occur, which made the pedal travel just a bit more.

Also, tired wheel bearings cause some pad/pistion knockback.

I personally hated Motul RBF600, and the pedal feel it gives. I would highly recommend something like Prospeed 683 or Endless RF650. Both are extremely low compressibility fluids, which give a much firmer pedal.

rickg87

Try castrol SRF. That's what the top race shops use in our club racing caymans and 911's. I'm getting a .1 RS soon. Street and some track. Will prob use the same.

F1CrazyDriver

Something sounds off.

IMO it is not rotors
Not brake calipers
I highly doubt brake lines.
I really doubt brake fluid

I believe it is master cylinder or not bleeding abs pump/ air gaps there. If anyone here has had a master cylinder fail-- sounds like starting stages of how mine have failed in past....

tcsracing1

I Run SRF and Pagids. Stock Callipers. 40k miles. No issues to date.

Something must be going on.....dosnt seem right?

kyrocks

I have StopTechs and do not have this issue.

TraqGear

Exactly. Make it a habit to left foot tap after exit on any big straight. You shouldn't see the problem anymore unless there is a fluid/air bubble problem. One tap should do it though. If you pumping them to get pressure then something else is wrong. I try to use up all the track and almost always track out on the rumbles. So, I notice it when I don't tap right away..I have no brakes!