I've got a 94 3.6 turbo that has only seen the track once. I drive pretty hard and after 15 minutes of sprited driving around buttonwillow, my brake pedal went completely to the floor with no braking action. (yes, I went off track)

I was OK as was the car, I bled the brakes at the track (super blue again) per the instruction manual and went out again, this time more conservatively. However, on my cool down lap the pedal went to the floor once again.

Under normal/street driving the brakes work fine and there is no apparrent air in the system as the pedal is hard.

Any thoughts on what the problem is?

Thanks,

 

Any moisture in the brake fluid will boil when the system is hot and cause the pedal to go to the floor since the water vapor is compressible.
Flush the fluid out with fresh fluid before every trackday and you should be ok. While you are flushing, inspect the flexible lines for hoses bulging and go over the entire system and look for leaks.

 

Flush down with fresh fluid cured it for me. Since then no problems. Probably water in the system as stated by Metal Guru.

 

Did you start off with new pads? Seems like you are on thin pads= boiling fluid=no pedal.

 

The fluid was freshly bled several times (pressure & vacuum on 2 separte occasions) before heading out to the track as I replaced the auxillary slave cylinder (clutch)/ Also, the pads are at 65-75% so they should be fine.


I'm OK with bleeding it again but I just don't want to take the risk as the only times this happens is when I drive the car at 9/10's and there is no visible warning that the brakes will fail.

So, if there are other theories, please bring them on!

Also, the brake light/computer beeps at me when first starting the car so I'm not sure if this is related. According to Adrian's manual, this is normal and nothing to be concerned about.

 

could your pressure pump be failing, after hard use this kicks in to build system pressure back up, if it is not working you would see the results you have. It is under the bonnet (sorry hood in your neck of the woods) on the front right under your carpet. Not sure how to test it, but it normally makes plenty of noise when operating.

Steve

 

When my pressure pump switch went (luckily not the whole thing) i got the opposite, i.e. very stiff pedal with little or no movement, so i thought if the pressure system failed the pedal wouldn't go down to the floor.

 

I had a pump go bad, and it also leaked. Take a look by the battery, under all the carpet and spare tire. Mine never did leak to the ground, but it did spill into the trunk.

 

Also had pump fail few months back and pedal went rock hard!!

Sounds maybe like leak somewhere or air trapped!

Porsche inspector within UK for Peter Morgan.
http://www.petermorgan.org.uk/inspection.htm
964 turbo-Rebuilt using ARP hardware.Modified heads,SC cams,1 bar,headers,cat bypass,powerflow air intake..bilstein hd's/h&r,carbon strut brace.Working with unwired tools develope pt model digiwur,although been running with unit for over 6 months,awaiting latest version then i will post results.