Mika911

Loving my 2004 Cup but on my second outing I suffered a brake failure which my team has not been able to explain.

The car had fairly recently revised calipers and before the day had its nipples replaced. Discs were good though pads below 50%. Brand new ferodo brake fluid. After lapping without issues for about two hours at a fairly high pace with lots of breaks, my pedal dropped straight to the floor in a 200kph-80kph brake zone. As I was closely following a friend in a 996cup, I had no chance to let the pedal come up and try again, instead deciding to steer as far away as possible from my friend (the video from his car shows how close we came to colliding, but amazingly we both walked away without real damage). As this has never happened to me in 15 years of tracking and racing, I was very anxious to find the root cause.


The team checked:
*no air in the hoses
*brake fluid new so could not really be cause of brake fade
*RS29 pads were less than half, so perhaps they did overheat
*discs are drilled OEM ones and weren't yet cracking

They reckon I may have run a curb too hard which could have pushed the pads away from the discs.

Has anyone had a similar experience which was subsequently explained? Or advice how to avoid this from happening again?

gordonc

CHANGE THE MASTER CYLINDERS ..HAD SAME PROB I managed to get 2 for around £80 from QUESTMEADE who are the distributors in Uk who Porsche buy from and charge u £420 from PMSport !!!!

Terry L

It sure looks like boiled fluid to me. New fluid isn't immune and after two hours and chasing your friend at close quarters, brakes can get too hot. I assume you couldn't find leaking fluid and the reservoir was still full. I'd be shocked not to find some bubbles in the calipers.

Mika911

Thanks. Did you have the same symptom, where the pedal went to the floor immediately on pushing the brake pedal?

The head mechanic at my local Porsche garage suggested the same, whereas the team that maintain the car dismissed that.

After just fitting new pads I did run a 1h race with the car and it was faultless. Will follow your suggestion though, as I want to rule out a repeat.

Mika911

That was my first assumption too. But there was no leakage or bubbles, according to the mechanic. Since the pads were below 50% that could be a cause for overheating though, so I will from now change them sooner.

Viperbob1

No Ferodo fluid here in states. While not street car, there are still issues with the ABS of Black Ice.

Jim Sullivan

I had a catastrophic brake failure on my Gen2 996 brakes. Pad wear can be grossly uneven so you think you've got lots of pad left but, in my situation, the unseen portion of the pad was excessively worn and the puck fell off the piston and my pedal went to the floor.

Mika911

Thanks for sharing that. Pad wear may have played a role here, so that is definitely something I will keep an eye on.

Stuttgart

I've been racing a 996cup for a while. Here's my feedback:

Worn out pistons, MC, or brake booster typically feel pretty similar. Pedal doesn't go to the floor, just feels soft and gets softer through the brake zone.

With knock back your pistons are merely retracted into the caliper slightly, so the pedal engages just a bit deeper than usual then it feels firm.

Your situation sounds like textbook boiling. I've run PFC 01 down to the backing plate with no boiling using Castrol SRF. Historically that's the only fluid the pro teams use. Lots of companies like to quote dry boiling point, that **** is irrelevant. Once you crack that bottle open and pour it into the reservoir that fluid is absorbing water by the minute, so only look at the wet boiling point. Assuming you're using Ferodo "formula" thats a full 100 degrees F lower wet boiling point than Castrol SRF. Also when you say fresh fluid... we typically bleed the brakes every day of the race.

J richard

This^^^

Bumpy brake zone with low hard pedal and no braking power.

Hard to do in the heat of the moment, but get off the pedal and reapply. Different than pad knock back, and will behave normally after cycled.

Early cups can have this issue.

Mika911

Thanks for all the input!

In my case the pedal went straight to the floor, rather than getting soft or increased travel. So reading through all the comments and advice from others, boiling fluid seems the be absolutely the most likely cause, probably triggered by fairly worn pads. Whilst I am personally not very technical and need advice from experts, it surprises me a little that the team (that have been running the car for the previous owner and now me for three years) are a bit dismissive of that possibility. In any case, not running the pads till the end and using better brake fluid will certainly not do any harm. So that is the route I will follow.

FRP||

Your team is probably on top of this but make sure you do not have any dragging pads.