Brake failure

[testdrv321]

We had a very concerning pair of incidents at Summit today. Two cars had brake failures one lap appart. Both 996's. We both experienced the same problem at the same time. Basically, just the pedal going soft and to the stop with no braking effect. Both of us were able to drive the cars off with minimal damage. The question is what happened? I am going to strat diagnosing tomorrow, but I have a few thoughts and wanted to get some feedback from those of you racing 996's. We were both running high temp fluid, but nothing fancy. Different pads, both recently bled and/or changed. The brakes came back after cooling, but the fluid in the resivoir was to the top and some actually leaked out the cap onto the top. These cars are driven hard and fast. I asked around and quickly heard of a similiar problem with one of the other instructors Boxster S. The problem has been a balloning of the factory rubber brake lines. Another non Porsche friend had a similiar problem in his track car. Any thoughts on upgrading to teflon/braided stainless lines? Also what about fluid? I've heard that Castrol SRF is the way to go. I am starting club racing this fall and need to have my confidence in the braking of the car restored? Any thoughts or suggestions for braking on a race 996? Also, are ducts necessary? Anyone bought or made them for this car?

[KarlS]

I ran a 996 for three years in DE and never had a soft brake pedal. I ran Summit many times, VIR, Watkins Glen, Mid-Ohio, and Road Atlanta. My set-up was as follows:

GT3 calipers and rotors (not necessary and they will bump you into B Stock in Club Racing)

Pagid Orange pads

SRF brake fluid

Cargraphic front cooling kit

I ran with the stock brake lines and never had a problem. My Cup car has the stock rubber lines as well, so I doubt that brake lines are the problem. Especially since you say the fluid level is up, which indicates that you have air in the system somewhere.

Since this is certainly a heat related issue. There are several potential causes/remedies you can think about.

Upgraded race pads, such as Pagid or Hawk, typically handle the heat better and dissipate the heat faster than OEM. However, once the pads are past half their original thickness, they become less effective at handling the heat. So always make sure your pads are fresh, don't let them get down too far before swapping them out. Pads are pretty cheap in the overall scheme of things, so no reason to scrimp.

Different fluids have different hot boiling points as well as water absorbtion characteristics. SRF is good stuff, high hot boiling point and low propensity to absorb water. However, other brands, such as AP 600 are almost as good and much cheaper. With fluid the issue is to 1) keep it fairly fresh. Anything more than 6 months old should be totally flushed, more frequently if you are doing a lot of track work. 2) proper bleeding after each event. This is not as necessary with SRF but it's a good practice. Make sure you bleed correctly to get the air out of the system. There are several good DIYs available that explain the process if you aren't certain.

Brake cooling can definitely help keep the system running better by keeping the rotors and calipers cooled down. The Cargraphic kit was effective on my car but pro racers I have talked to say the size of the hoses on the Cargraphic kit are too small to really be effective. Most of them recommend the GT3 Cup/RS brake cooling ducts which are available through Porsche Motorsports. They mount to the inner fender liner and front A arms and you need to cut a hole in the front fender liner to allow air in from the front radiators.

Lastly is braking style. This can have a big effect on heat generation. If you brake early and stay on the brakes longer prior to your turn in, this will generate more heat than braking later and harder but being on the brakes for a shorter period of time. So at Summit, you should be able to carry full throttle until at least the 4-5 marker before braking hard, rather than beginning braking at the 6 marker and staying on them until you enter turn 1. Summit is not known as a track that is hard on brakes, since there are really only 2 places where you brake hard and plenty of time in between to cool things down. So there is definitely a problem in your brake system.

Definitely flush the system and replace the fluid, there is surely air in it now. Check your pads and if they are more than half gone, replace them before your next track event. Use a race compound from Pagid or Hawk. Consider adding a brake cooling kit, especially since we are getting in to the hot part of the year now.

The brakes are one of the strongest features on the 996 and with proper materials, maintenance, and technique, you should never have any brake problems on the track or on the street.

Karl

[clord]

I agree with everything that Karl has said above. I would only add the fact that many racing pads like the Pagids have a thin ceramic layer between the backing plate and the friction material to slow down heat transfer/soak from the pad material into the caliper pistons and on to the fluid.

The new GT3 has significantly upgraded brakes in the areas of size, and cooling, and also claims: "The calipers themselves are equipped with zirconia ceramic inserts to prevent the transfer of heat from pistons to fluid."

[Nevada996]

I've never had problems on the track with the brakes in my Boxster or 996, but have heard of problems like you describe caused by warped roters. The variation in the rotors creates a vibration that pushes the pads back into the caliper, so that when you hit the brakes it takes a couple pumps to bring the pads back into contact with the rotor. But If your rotors were warped that bad I guess you have other signs...

[RJFabCab]

Nice discussion, guys... which brings me to my question. Is it really that imperative to change your brake fluid every 6 months? This whole brake failure thing has got me to thinking... hmmm...

I've been to 4-5 DEs, all on the same brake fluid. I have had my car for 18 months. No brake failure issues at all. Am I lucky? Or am I due for a failure event???!!! :o

[Mike in CA]

RJ, brake fluid absorbs moisture from the atmosphere. Over time, as the moisture content of the brake fluid increases, the boiling point decreases, which can lead to brake fade or failure. Maybe you haven't overheated your brakes to the point where this has occured (yet), but the older your fluid the better the chance this could happen. Also consider that old fluid is more likely to become contaminated with dirt and other particulate matter, which can lead to damage of delicate seals and other parts of the brake system. Finally, brake fluid contains anti-scuff and anti-corrosion compounds which become less effective over time. For a car driven normally only on the street, once every two years is OK for changing fluid. Cars that see heavier duty, lots of mountain driving for example, should change once a year. And for cars driven in occasional competitive events, 6 months is probably a maximum interval. It's cheap insurance to bleed the brakes. Get yourself a Motive Power Bleeder (about $45) and it's an easy one person job.

[KarlS]

RJ,

I agree with Mike's comments. In addition, my PCA region requires the brake fluid to be less than 6 months old as part of the pretech inspection process. Our chief tech inspector also has a kit he uses upon request to test brake fluid to ensure it still has the boiling point properties it needs.

Karl

[dj996]

What do you guys think of running stock Textar pads and Super Blue ATE fluid? I ask because the stock pads have given me pretty good service (almost 4 years and 10-12 DEs) and no squealing. I'm planning on new fluid and possibly pads before the next event. This is a street car primarily with occassional track (DE) use. Switching to a racing pad for the track is another option.

[testdrv321]

It looks as if the brake fluid boiled. Summit is a hard track on brakes. Some more details for the discussion...

I was using ATE Type 200 Gold fluid which was change the week before and only had the 2 1/2 days on it.

I was using Performance Friction 01 compound pads for this event. I used Pagid RS-14s in the past and intend to switch back to the Pagids. They seem to stop better.

There is no brake ducting other that stock on the car.

I definitely don't ride the brakes. I brake hard and fast so no worries about draggign the brakes to heat them up.

I am planning the following changes to help with the problem...

Changing to Castrol SRF and I am going to bleed after each track day

Changing to Stop Tech braided stainless / teflon lines - may not help, but can't hurt

I want to put on some brake ducting. Anyone have part numbers for the PM system? Is that off the cup car or the RS? What about homemade ducting? Anyone have pics?

I want to change to big yellows, but to stay in the C stock class, they need to be standard or as an option on the car for that year. I still can't get a straight answer from PCNA if the CRF option will get you the bigger brakes. They keep telling me to call Germany, but not sure who there. Anyone have info on this???

Thanks guys :-)

[testdrv321]

Karl, what kind of times do you run at Summit? I'm running 1:26-1:28. I am not sure if I agree that Summit is not hard on brakes. There are alot of braking zones per lap and some decent changes in MPH. The main straight ends with almost 100 mph of decel, the end of the chute also drops 70 mph. I'd guess there are about 250 mph of decel on each lap. I'd have to think about some of the other tracks to see how this compares.

[Mike in CA]

What do you guys think of running stock Textar pads and Super Blue ATE fluid? I ask because the stock pads have given me pretty good service (almost 4 years and 10-12 DEs) and no squealing. I'm planning on new fluid and possibly pads before the next event. This is a street car primarily with occassional track (DE) use. Switching to a racing pad for the track is another option.

Doug,

Obviously you're pretty easy on brakes as you've had no problems running DE's with the stock pads. Bleeding the system with the Super Blue ATE fluid would be fine. If you want to step up a notch on the pads without going to a racing pad that might be noisier and work less well in street driving you might consider the Pagid Type S sport pad. I have them on my car. They work as well or better than the stock pads for street use, with very minimal squealing, and offer significantly better fade resistance for hard driving or track use. I got mine from TRG for about $275.

[clord]

Doug....I support Mike's suggestion above. With the Pagid's you also get the ceramic heat transfer slow down layer between the backing plate and the friction material. I have those pads on my street Audi with Porsche calipers and agree with Mike's experience.

[KarlS]

Karl, what kind of times do you run at Summit?  I'm running 1:26-1:28.  I am not sure if I agree that Summit is not hard on brakes.  There are alot of braking zones per lap and some decent changes in MPH.  The main straight ends with almost 100 mph of decel, the end of the chute also drops 70 mph.  I'd guess there are about 250 mph of decel on each lap.  I'd have to think about some of the other tracks to see how this compares.

testdrv321,

I ran 1:24s in my 996 at Summit. The two places you mentioned (end of front straight and end of the chute) are the only hard braking areas. They are spaced fairly far apart on the track, so the brakes have a fair amount of time to cool down in between. The rest of corners either have no (2,4,7-9) or moderate (3,6,and 10) braking. A set of pads always lasts a lot longer here than at tight tracks like CMP.

Karl

[RJFabCab]

Truly an excellent forum. Great info... thanks!

[testdrv321]

Interesting thought... my car has the X74 which places it much lower to the ground. This may make the factory brake ducts less effective. The GT3 and Cup car use a different designed duct. Hmmmm.

[testdrv321]

Karl, how would you define moderate verses hard braking zones? Turn 10 at Summit is -40mph, is that moderate? It is compared to Turn 1 at -90 mph. Just another interesting topic.

[KarlS]

To me, hard braking is threshold braking. Where you are getting everything you can out of the brakes without getting into the ABS or locking. At Summit, for me this is the braking zones for turn 1 and 5. Turn 10 is a brief jab on the brakes to scrub some speed, settle the nose, and help the car turn in. Definitely not approaching lock-up here.

Karl

[testdrv321]

I guess there are a few issues for me in turn 10. The X74 is definitely a weakness compared to a full race suspension and as such I can only take this turn at 80-90mph. Typically closer to 80 as I am doing DE's there and not races. I can come out of turn 9 at 80 and accel up to about 120 before braking into 10. With the RS14's the car will ABS after the initial brake stab but usually does not stay in it if the tires are hot and the surface is good. Maybe if I had bigger brakes that would be different. I am running 245-35-18 Hoosier R0S03s up front and 285-30-18's in the rear.