HPDE Brake Heat Issues - Boiled Fluid?
 

Hello All,

I'm a relatively new 911 owner, 2006 C2S. Love the car! Of course, right after purchasing it in early August, I scheduled some track time in order to see what it was really capable of at the limits. Having had brake heat issues in the past with my previous car on track, I did some research on what brake setups people typically use. I ended up deciding to go with Performance Friction (PFC) 08 compound pads, with the stock rotors and calipers. I was right at the 60k mile service, and so I had my indy throw in the pads along with the new spark plugs, and fully flush the fluid in the brake and clutch system. I had them put Motul RBF600 in it as well, and remove the brake pad dampers and zip-tie away the pad wear sensors. The pads bedded in fine and felt great, although they are way too loud to be streetable. This was 2 days before the HPDE.

At the track, however, after about 10 laps in my first session, I lost braking pressure. The pedal didn't go all the way to the floor like a blown line, but I had to pump the brakes at 120mph to get the car slowed down in order to make a turn. Not a great experience! After that, I pitted, and after cooling down the brakes seemed fine, so I went back out for the second session. After about 5 laps, the same issue happened. Loss of pressure, had to pump the brakes to slow down the car. Again, I pitted. I didn't bring all of the equipment with me to the track to do a brake fluid flush or even burp the system, and even if I had I just wasn't confident in my ability to fix the issue and not end up in the grass.

It definitely felt like boiling fluid to me, as the only issues with the brake system were heat induced. There was no softness in the pedal before the track day.

I called my indy in a bit of a rage the next morning, assuming the only explanation could be junk fluid, and they said they would try to make it right. I assumed that they had screwed something up, but having talked to the technician for a while and watching him work on the car (not to mention the 4 or 5 dedicated track cars sitting around the shop) I'm reluctant to blame them. The technician said he drained the old fluid out of the system, then put 1.5 pints of Motul through it with a pressure bleeder, and also checked the pedal pressure during the flush, used both bleed screws in the correct order, etc. Seemed like they knew what they were doing.

I know some guys swear by Castrol SRF, but I really can't believe that I boiled RBF600. I talked to multiple people at the track event that were driving WAY harder than me and running ATE or another less hardcore fluid, with no issues.

When the technician bled the system, we did not see anything indicative of major brake issues, like white goop from a degraded ABS pump or dark, discolored fluid, black chunks, etc. It was the normal look of Motul fluid, but it's hard to tell. Even if it was "normal" fluid, I still find it hard to believe that I boiled it if It was dry!

What gives? The brake system seems fine now, but I can't see myself getting enough heat in it on street to test whether the issue is resolved, and I'm reluctant to burn more money on track time when I may have to sit most of the sessions out.

Any thoughts or previous experiences that could help? I'm not sure what to try, replacing the master cylinder, rebuilding the ABS pump, etc are all options but it seems silly to do that without a proper diagnosis. Thanks in advance!

Self bump.

The technician tested the fluid that came out and it was <2% water content, so the fluid wasn't terrible. Still hunting for a diagnosis.

I assume fluid level did not change (go down from leaky system)?
that's all I can think of.
comparing your driving to another is not useful as they may use less brakes but with that fluid it should be fine. what was ambient temperature and was there any pad transfer to discs?

That's correct, the fluid level was fine at the reservoir, and no brake fluid drips in the garage.

It was a hot day, ambient temps around 80-90 degrees, but the track doesn't have crazy elevation change or many aggressive corners (Putnam Park in Indiana). No pad transfer to rotors, they were nice and clean.

are you a heavy braker? The only way I can see this happening is if you are overbraking badly. Do you have the gt3 brake ducts?

I do not have the GT3 ducting.

I wouldn't consider myself a heavy braker, I run in the green group -- my instructor specifically said that i'm not particularly hard on the brakes -- straight line only, no trail braking, and short, hard braking zones where possible.

I can check the video and see if I have some examples.

Here's a video of some of the laps I did in the second session, the angle isn't great but you can see what's going on for the most part.


The failure occurred at around 4:50. Initially I thought the pads had just separated from the rotors but in later corners the brakes didn't have pressure. This was after a total of probably 5-10 laps.

have you checked the ceramic brake pucks that sit between your caliper pistons and pad back plates? They are notorious for braking, cracking, etc which will introduce a ton of heat into the fluid. Some replace the ceramics with titanium.

"We have found that the majority of enthusiastically driven/tracked GT4's and 991 GT3/RS's coming through our shop have failing or failed factory ceramic caliper piston pucks. Regardless of whether the brakes are factory Steel or PCCB calipers, there are factory ceramic pucks screwed to the face of the pistons that serve as a thermal barrier between the pads and the pistons, lessening the heat transfer to the fluid. Due to the intense heat and heat cycles from hard/extended braking, the ceramic pucks are becoming brittle and disintegrating. Early signs of this are cracking or chipping. Broken or lack of ceramic puck material may cause reduced braking effect and additional heat transfer through the pistons and into the fluid. If a large number of the ceramic pucks were to fail this could lead to significant braking issues. This problem is often overlooked during pad replacement, as technicians are not aware of the issue and are not checking for it. Unfortunately replacement ceramic pucks are not available, Porsche only offers complete replacement calipers. They will only replace the calipers under warranty if the car is running OE pads and rotors. Even if replacement calipers are installed, the issue will ultimately happen again. To prevent spending thousands on new calipers and to solve the issue once and for all....we developed a solution."

titanium replacements

https://cimg1.ibsrv.net/gimg/rennlis...693ef9c1e3.jpg

https://cimg4.ibsrv.net/gimg/rennlis...69a62720aa.jpg

I'm planning on swapping back to the stock pads this weekend, I will check out the pucks when I do, and update if there are any signs of cracking or chipping.

I read here that the OEM lines are good for about 10 yrs and on a 12 yr old car, I think they are due. Sounds like your lines are swelling and might be a good time to upgrade to SS lines.

Interesting. I'd buy a set of the ducts, they should be under $15 for the set.

lines are not the problem unless they have been damaged in some way.

Long shot - check that the front rotors are not swapped left to right. The internal vanes should be pointing towards the rear of the car when moving forward (looking at the 12:00 position). If swapped the brakes will heat more than normal.

Just checked, here's a picture of the passenger side rotor, looks like they're pointed in the correct direction.
https://cimg6.ibsrv.net/gimg/rennlis...027669dbba.jpg


Thanks for the tip, just picked up a set. Couldn't hurt!

They can swell internally w/out any indication on the exterior. Especially for a HPDE why would you overlook the lines, especially since they are such an inexpensive yet effective upgrade. $155/pair of Goodridge lines at Suncoast.

https://i.ytimg.com/vi/bqNkWlyIDLM/maxresdefault.jpg

The estimated life of a typical 'rubber' brake hose is 6 years, according to BrakeQuip, the manufacturer of aftermarket rubber and high-performance stainless steel braided brake hoses. The actual wear of your brake hoses depends on weather conditions where you drive and store your vehicle, your driving style, etc. Here are some factors influencing the rate of deterioration of your brake hoses:

• Moisture absorption into the brake fluid through the hose.
• Contaminants in brake fluid are abrasive on the inner walls.
• Hoses deteriorate from inside as well as outside.
• Hose reinforcing fabric weakens from expansion and moisture.
• High brake operating temperatures.
• Constant flexing from steering and suspension weakens hoses.
• Brake hoses swell with age which causes restricted flow.

I've cut 20 year old rubber lines and they were just fine. i'd put big money on the lines not being the issue.

Also, standard 997s don't have ceramic pucks as far as i know.