1AS

On the 996tt board, a new Rennlister posted that his brother crashed a new (3,600 miles) 996tt Cab Tip on a track when the brakes totally and without warning failed. He notes that pumping was without effect. This occurred after 5 or 6 laps with a driver who has some but not extensive experience.
Later, when the car was examined, the brake fluid resevoir was full.
There is an assertion that tt brakes can fail suddenly and without warning after relatively few laps.
My questions are:
Is this the experience of others?
Would the resevoir be expected to be full if sudden boiling resulted in complete brake failure?
Does 5 laps sound like very few for this type of failure?
While I have a lot of track experience, it isn't with my ttX50. I'd love to be wrong, but the story doesn't hold together for me, so I'm seeking wisdom. AS

mrbill_fl

hmmmm.

I had a student last month in a modded 996 tt, (green student). we were working on braking, and I had him using the brakes on the 2nd day.

Anyway, after that session, he said the brakes were to the floor... he was able to stop the car, but he had never experienced this before. (I don't think he had felt the abs before that session either.)

well, we cooled the brakes in the paddock, and parked it, by the next session the peddle had come back up... but he was concerened, and we only lighly braked in the last session of the day.


so, I'm not sure if its normal for peddle fade, but it was new for this driver.

(we were hammering the brakes pretty good, on two turns in a row, but only those two turns, after about 5 laps of that, the brakes started to go. *edit: psm was ON.)




( the car had stock brakes and street pads, on a 600+hp tt.... green student, and english was his 2nd language) -or, just your typical so. fla p-car driver.... ;-)

JCP911S

You absolutely need racing fluid iand performance pads n these cars on the track..

That said, we had some very wierd experinces with TTs this weekend. With the PSM off the brakes do strange things and lock up suddenly.... there was much speculation, but we re-produced the symptoms in two different cars with two different and pretty experiences drivers....

sooo...

Alan C.

If I was out in a car that had the brakes go to the floor I don't think I'd step back in until I saw someone bleed the brakes.

I got a soft peddle last weekend after the second session. I had not bled the brakes for this event as I had done it before the last event. I was using ATE Blue and had no issues with the previous car doing this. It appears that the C2 996 is another story, lesson learned. Also, I had the PSM turned off, I'd rip it out if I could.

Phokaioglaukos

Hope this is not too OT, but when you flush brake fluid, about what volume of fluid do you use? If going from ATE blue to gold or the reverse in a complete flush, do you get some of the old color persisting after driving, and maybe triggering the ABS?

Ed Newman

I have logged about 9,000 track miles. I tried Performance Friction pads during a DE at Summit Point. 3rd lap the brakes overheated, boiled the super blue fluid all over and left me with no brakes at all. Thank god for the gravel trap, the total damage to the car was only $10k. I ruined a set of wheels, broke some suspension parts etc. Another 996 did the same a few laps later. His pads.... PFC also. I switched back to Pagid and no problems ever since. P.S. I change my fluid every 6 mo and bleed every event.

Bill N

Which PF's?

Ed, I hope you meant you bleed the brakes every event! :-)

Lefty's Deceiver

I've had a situation where repeated driving over agressive rumble strips pushed my pads back adn I've had to pump them with my left foot. I've noticed the Speed World Challenge drives on the same track (Road America) pump the brakes on the straights.

Bull

Stock pads and/or stock fluid won't work on the track if you are a serious student. I don't care if it is a TT or not. I had two students completely lose their brakes last year (fortunately both had run-off areras at the end of long straights). One was told that his tech put in "track pads and fluid", which turned out to be a blatent lie, the other was told that "Porsche brakes are great and you will be fine". We didn't go back on the track untile the fluid was FLUSHED and track pads were put in place at the event.

Get the proper pads and fluid in place and change the fluid regularly, particularly if the car isn't driven regularly/tracked often.

1AS

Ed, when you boiled the fluid, did you lose fluid,or was the resevoir still full? When you say, "boiled it all over", it sounds like fluid escaped. That's my point. I wasn't aware that you could completely and suddenly boil your fluid to the point of failure, and still have a full resevoir. AS

Larry Herman

Alex, when you boil fluid, it usually occurs directly behind the piston in the brake caliper. It produces a gas bubble, and when you hit the brakes, the gas bubble compresses and you use up all of you master cylinder travel. Pumping the brakes usually does not help, as the gas bubble just re-expands as you release the pedal. Once the system cools down and the gas is re-absorbed, the pedal becomes hard again.

If the fluid has moisture in it, and it boils, it tends to leave a bubble of moisture that is not re-absorbed and when you bleed your brakes, you will get some "air".

BTW I have found that the Performance Friction pads are the worst for heat transfer back to the caliper, and Pagids are the least conductive of heat.

38D

Pagids + SRF = no brake issues

JPhillips-998

PFCs + SRF = No problem.

996TT. big, heavy, fast doesn't sound like a good combination on the track with stock fluid and pads.