Speedah

Went to track for the first time today in my RS. Had to call it a day after only 5 laps because I was getting a totally random solid brake pedal (no brakes at all).

I thought it may have been the ESC/TC doing silly things so I turned everything off and it still did it.

Almost crashed into one of the flag marshal huts. I’ve just come from a 991 GT3 and done 50+ track days in that car and never had this problem.

Any ideas?

usctrojanGT3

Did you change out your brake fluid?

Speedah

I purchased the car with 1200 miles on it. I know the previous owner changed the pads and bled the brakes....not sure if the fluid was changed. Car has PCCB if that makes a difference.

usctrojanGT3

Hmmm, that's weird. Obviously take it in to the dealer and have them check it out.

Alan C.

I had that once. Diagnosed as air in the ABS. The tech used the PIWIS tool to bleed the brakes and the problem went away.

Hope it's that easy for you.

Speedah

Thanks for the advice. Did your problem occur after pads or fluid had been fiddled with?

Car goes to dealer on Monday. I'm really stressed about this because it only happens under extreme/certain conditions on the circuit that can never be replicated on the street to prove it has been fixed.

Alan C.

Yes, after pads and flush. Tried 2 additional bleeds and couldn't get rid of the problem on my own.

skxf430

A stiff pedal and little to no braking power sounds like ice mode.

Were you experiencing this in the same corners?

Kobalt

ABS harness might be damages behind rear wheel.
It is included in the rubbing service action "Wheel clearance for track use".

From the mentioned SA:

Speedah

yes...tell me more about ice mode. Happened 3 times at the same braking point on the track.

Rest of the track was fine.

edit...I've googled ice mode. I think you're right. How can I ever go fast again on the track knowing that this may randomly happen.
Confidence in the car has been totally lost.

Speedah

Will check thank you

kyrocks

Keep us updated. Thanks.

Guest89

I was just thinking yesterday, I haven't read much (anything?) about ice mode in the 9X1 generation; is it still a thing?

Speedah

Thread bump..
Been fighting this problem for 9 months now and yesterday I think I have finally found the cause of this stiff pedal/ice mode/ABS fault…or whatever it may be.
I’ve been back to this track (Wakefield park) several times since and the problem still consistently happens. A week ago I took the car to Sydney Motorsport Park…big high speed circuit with plenty of concrete walls everywhere. I did two easy warm up laps then got on at only about 7/10s pace, braked hard from about 120mph…..solid pedal, no speed reduction…very scary. I still made it through the corner and avoided the concrete wall because I left enough on the table in case.

I called it a day at that point. Fast forward to Thursday this week and my Porsche dealer was hosting a track day at this track. They bring along 4 or 5 Pro drivers/instructors so I took the opportunity to have one of those guys drive the car. Porsche also sent two technicians along with their data logger to see if we could get to the bottom of this.

We went out at lunch time on a totally empty track. The pro driver was driving with me in the passenger seat holding the data logging gear.
I few things to note…
My AIM system lap timer/data logger plugs into the OBD port and measures almost everything going on with the car.
I’m a left foot brake and so is the pro driver.

So we went out, he drove cautious for half a lap then built up speed to a point where we were going full speed/deep into the braking areas for 4 laps without issue. I was actually very worried because if the issue occurred we would have went into a wall hard.

One thing I noticed was that he had a clear distinction between releasing the throttle and applying the brake even though he was a left foot braker.
I went out after lunch and tried right foot braking. Guess what…problem totally gone. Confidence in the car was back and I ran a very good lap time.
I’ve spent hours over the last 9 months studying the data from my logger.

See below my findings.
Black trace = accelerator position
Blue trace = pressure in braking system
Green trace = speed in km/h

First capture is left foot braking. You can see over lap between throttle release and brake application. It looks like a lot of overlap but from start to finish is only about 0.25 second. Before anyone asks..I'm not trying to overlap. The overlap just happens if your feet both move at the same time.

This is enough (for whatever reason) for the brake pedal to go rock solid and speed does not reduce. You can see where I had a second go at the pedal to get some effective braking.






This capture shows right foot braking. You can see the clear division between throttle release and brake application. It’s less than a fifth of a second but ensures you will actually stop.





It’s also worth noting that I did 2 years and about 500 laps in my 991 GT3 on various circuits with the same left foot driving style/over lap and never had an issue with that car.

Seems the RS is sensitive to the overlap.

Couple of pics from what was a great day :-)

Kobalt

Very interesting, thanks a lot for taking the time and sharing your findings!