Lost brakes at 100mph

Advice please Oulton park track day. Brakes working really well. New brembo front disks, plenty of pad material front and back. Brake fluid 1 year old. Carrera 4 with PSM. PSM on. About 2 hours in, Car being driven by my mate who holds a MSA A licence - much faster than me and much more aggressive on the brakes. Sudden loss of pedal - ie pedal went nearly to bulkhead!! We had a trace of brakes with pumping pedal but only at full pedal travel. Limped to pits. I've had brakes fade out before and it deffo wasn't like that, they were great on one corner and virtually nil on the next. The pedal just travelled++. In paddock checked the car over, no brake fluid loss on wheels. Brake fluid level at max. Took frunk plastic off. No leaks around master cylinder, ABS pump or PSM block. Calipers were hot but equally so. No disc blueing. Bled the front brakes. No air in fluid. Fluid crystal clear. After 20 mins brakes could be pumped to a decent pedal. After another 10 mins brakes felt normal. Took car for gentle run on the road. Brakes all good. Went back on track, PSM off. Did about 3x 6 lap runs with 15mins cool down inbetween. Same problem re-occurred with me driving. Car cooled for 1h, we didnt bleed anything. brakes returned to normal with a bit of pedal pumping. Drove home. Car feels normal. ?? Master cylinder seals, all advice / ideas welcome.. Guy

Boiled the fluid by the sounds of it.

Boiled brake fluid is my guess, perhaps you have a slightly sticking pad/caliper/ piston. Have not a clue on the ABS/electronictrickery etc.etc. but would bet on fluid boiling... Been there done that and got away with it too.. Hopefully there will be some smarter folks who will provide alternatives for you in time. :thumb:

What you have described is normal in the sense of the fluid boiling. That can be down to several factors including whether you are riding the brakes for too long e.g. drivers who coming to a bend brake far too early and on the brakes for longer instead of braking later for less time. But you need some proper fluid SRF etc in there and also probably some brake ducting to help keep everything cool. As an example a non GT3 Porsche driven well you can loose the pedal within 20km on track without proper cooling and fluid. The other point to mention is that many people think that upgrading brakes in itself is enough - on the road they say how great they are etc, but take on track and all of a sudden brakes getting hot. If you think of it in simple terms, if you have a larger disc in the same wheel housing, without changing the airflow, you are actually going to have more heat. That is why when we upgrade brakes, we also do the air flow at the same time. Ken

My C2 brakes did more or less the same thing during a track day at Bedford. It was obviously boiling fluid. I have brake ducts but they're the standard rather than GT3 ones, and my fluid was old and the longer it's in there, the more water it absorbs from the atmosphere, and the lower its boiling point becomes. If you put on bigger brakes then you're dissipating the same amount of heat energy for the same 'stop' through more mass (via bigger calipers and discs) and radiating out that heat across bigger surface areas. Because of that, bigger brakes will have less of a propensity for boiling fluid if they're bigger. If you don't have several grand lieing around to pay for a big brake upgrade, then buy the highest boilingpoint fluid you can find and then put the larger GT3 brake ducts on. They're cheapest from your OPC, believe it or not.

Boiled fluid. Change brake ducts for GT3 and fluid for something like RBF 600/660 type or SRF if your wallet extends.

I had the brakes go at the end of the extended straight at Bedford, the discs were in poor state and as deMort pointed out, were mounted on the wrong side of the car. I took to the grass and took a lap or two with my tail between my legs. Car had the GT3 ducts. I do accept I probably was sitting on the brakes for too long. Anyways, replaced the discs and pads with Brembo items. Gave the calipers as good as service as I could to try regain lost functionality. Finally had racing fluid put in.... no brake issues when I returned.

I've boiled brake fluid a few times at Oulton and each time it was obvious it was going to do it due to the pedal travel getting longer over a few corners. That's the bit of your experience I don't get, one corner fine then the next gone, seems a bit too quick, also any time I've boiled the fluid everything been seriously hot and smelling strongly of burning brakes and the discs have a fair bit of colour to them? The rest of your experience does match ie the recovery back to normal when allowed to cool? Mac

Thanks everyone for your experience and wisdom. High temp fluid and GT3 ducts on order. Any advice on pads for track day use?

I experienced brake issue on my very first track day in a 911 (996 C2); soft pedal, suspected boiled fluid. It turned out that as I was braking, the outside of my foot was catching the throttle ever so slightly (thus braking with throttle on); this wasn't picked up by myself as it was masked by H&T downchange. Then I had the opportunity to spend some time with an instructor, and he pointed out my problem straight away. The 996 was my first car with floor-hinged pedal hence my issue. Since then no more problem; the humble C2 has superb brakes.

When I had my C2 I used Pagid RS-5 which has since been discontinued. I guess any Pagid RS line would be fine (RS-29 the best but might be overkill and some experienced squealing for road use)

If you can get pads to fit, Ferodo DS2500 are superb pads. Instant bite, no noise & very little fade. For you to loose brakes that quickly, it defo sounds like boiled fluid or the heat affecting the master cylinder seals.

There is always a lot of discussion here about upgrading brakes and there's a number of reasons for doing it. The usual reason on the road is for improved pedal feel - more bite like a typical modern road car. The standard brakes have plenty of stopping power for road use. For track use the major problem is that brakes overheat on repeated use. Not a problem you should ever see on the road unless, perhaps, you descend an alpine pass very quickly in a high gear. There are typically two different symptoms of this depending on the brake setup: 1. Fade is where the pads lose performance at higher temperatures, pads that have good characteristics for road use (bite, friction levels wear rates etc.) are not set up for high temperatures and lose performance when they get hot - fade. This can be terminal for the pads as they can become 'denatured' as some of their core materials can be burned off, permanently damaging the pads. Track pads are designed for high temperature use and often work poorly at low temperatures and are therefore not good on the road. You've probably seen disks glowing red/white hot on formula one cars. 2. Fluid boiling. What it says, too much heat boils the fluid. There can be other heat related issues as well. Disks can get red hot and rubber and plastic parts can be damaged, not good. Disks designed for road use can also become distorted at higher temperatures than they are designed for. On the track, it's a matter of dissipating the heat. Bigger disks can hold more heat but as above, the heat still has to be dissipated. They basically hold more heat and delay the point at which the temperatures become too high but this may not be a solution on the track. They are also heavier, not a good thing on the road or track. Their larger surface area does aid cooling but only if there is enough airflow around them. As Ken says, ventilation is the key. Ventilated disks cool better than solid ones but the answer is to get air across the disks (see formula 1 ducting!) Carbon disks etc are a whole level above this!

When I went underneath my car, I saw the ducting already installed. Didn't know the GT3 had more effective ducting. So it's worth changing to get more air flow. I've seen that some people cut vents in the wheel arch lining to do this too.

Thanks maldren, you answered the question I was just about to ask relative to racing pads for road use, I had wondered if that situation had changed/improved with new pad materials......NOT that I am into that sort of stuff now, just that in my yoof I used to think race ANYTHING was an improvement on my bikes and later cars, it took some time and a fair bit of cash to realise that altering the all important balance of a machine designed for the road by fitting /tuning to pure race spec could be a real disappointment. As you typed cold race spec pads can be a pain in the rear or worse on the road, especially in the wet and cold in stop go traffic...hmm...?