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    PCCB: Loss of brake pressure after spirited drivin

    I posted the same topic on the 6 Speed forum, I was wondering if anybody could help me out here.

    Original Thread:

    I am at odds here...
    I took my car out on the back mountain roads yesterday to get a feel of what it could do. Anyways, half way through the drive, I suddenly felt a loss of brake pressure. I immediately parked it and let my brake cool off for a bit. I returned driving after 2 mins of cooling off and the brake pressure was a little bit better, but not 100%. I took it to the dealer the very same day asking them to check my braking system and nothing wrong could be found with my car (on the way to the dealer, which consisted of 20mins of highway driving, the brake pressure returned back to 100%). They bled my brake fluid just in case and returned the car back to me. The car now feels fine.

    This was really surprising because I used to take my 997 C4S on the same road and not once did I feel the loss of brake pressure from the car. I probably did brake harder on the PCCB's, in comparison to the steel unit on my C4S because I was entering the corners quicker with my Turbo. Still, it's very odd because I though PCCBs are suppose to the granddaddy of all braking systems........

    I did a search on the forum and it turns out that some members have experienced similar "loss of brake pressure" after "spirited driving." My question to those who have experienced similar problem is this: First, did I just experience overhearting my brake fluid? If yes then, how can I solve this problem?

    Re: PCCB: Loss of brake pressure after spirited dr

    when fluid boils, it will instead create "fluid vapor." Vapor in the brake fluid, like air, will create an efficiency loss in the braking system.

    When air (or vapor) becomes present within the lines, it creates inefficiencies within the system because, unlike liquid, air can be compressed. So when enough air fills the lines, input at the pedal merely causes the air to compress instead of creating pressure at the brake corners. In other words, when air is present within the system, the efficiency and effectiveness of the braking system is reduced. Usually, a small amount of air within the brake system will contribute to a "mushy" or "soft" pedal.

    If enough air enters the brake system, it can result in complete brake failure.

    So how does air enter the lines in the first place? Sometimes, it can be the result of a service procedure or an upgrade - such as replacing the stock flex lines with stainless steel braided lines. But often it is the result of high temperatures that cause brake fluid components to boil, thus releasing gasses from the boiling fluid into the brake hydraulic system.

    Finally, dedicated race cars should be bled after every track session.

    Re: PCCB: Loss of brake pressure after spirited dr

    Don't our cars have a "brake pre-pressurization" feature (can't remember exact technical nomenclature; I'm not home to check). IOW, when car is driven spiritedly brakes pre pressurize (?) in anticipation of heavy use. Perhaps there's a related malfunction with this system on your car?

    FWIW... .


    Re: PCCB: Loss of brake pressure after spirited dr

    You will need to change your brake fluid for sure. Then... analyze the situation- why did that happen? was it because you had a problem in the brake lines or because you used brakes too much? Yes, there is that possibility. I notice that most inexperienced drivers (they never acknowledge that) are binary operators, i.e., they use both the throttle and the brake pedal as on-off devices, rather than as varying analog controls. That style of driving applies undue stresses on the equipment and is far less desirable than smooth driving. I prefer the latter and my brakes never boil. On an event I got to the end of the road course near the top of the group and my brakes were cool, while many others were smoking...

    Re: PCCB: Loss of brake pressure after spirited dr

    stability control (PSM) in these cars actuates the rear brakes to correct the car's attitude in cornering. On many GT3's drivers have quickly cooked the rear brakes in spirited driving without knowing it. It is possible that you experienced this exactly

    Re: PCCB: Loss of brake pressure after spirited drivin

    How many miles/km do you have on your turbo? If the brakes have not been bedded in properly, and this is the first time you are out driving more aggressively, that may happen.

    Re: PCCB: Loss of brake pressure after spirited dr

    Quote:
    ADias said:
    You will need to change your brake fluid for sure. Then... analyze the situation- why did that happen? was it because you had a problem in the brake lines or because you used brakes too much? Yes, there is that possibility. I notice that most inexperienced drivers (they never acknowledge that) are binary operators, i.e., they use both the throttle and the brake pedal as on-off devices, rather than as varying analog controls. That style of driving applies undue stresses on the equipment and is far less desirable than smooth driving. I prefer the latter and my brakes never boil. On an event I got to the end of the road course near the top of the group and my brakes were cool, while many others were smoking...



    Honestly, I don't think that it is possible to take PCCB to its limits on public roads (not even on unrestricted German Autobahnen).

    Therefore, the above experience is likely to result from a technical problem or, more likely, a problem with the brake fluid (which should be replaced in a first step).

    Another idea: a friend had a similar experience with his new 997TT. However, after the brakes were run in properly the problem did not occur again. It seems that new PCCBs need to be broken in (i.e.: heavily used once) before they develop their full potential.

    Re: PCCB: Loss of brake pressure after spirited dr

    neosky have the dealer check your rear pads. I bet they are alot more worn than the fronts - that is what happened to the other cars who experienced this PSM related rear brake issue. The fluid boils from the excessive heat in the rear brake and then returns some as it cools. It has nothing to do with bedding in the brakes or "green fade"

    Re: PCCB: Loss of brake pressure after spirited dr

    That's interesting because I don't think the PSM on my car engaged when I was driving because the car didn't slide at all. And regarding the previous comments on drivers who are inexperienced and overcook their brakes, that might be possible, but considering that I have taken my C4S on the very same road for over 100 times and not once did I experience this loss of brake pressure, I'm pretty sure I didn't overpower my brakes. It is true that on certain corners (ie. longer straights), my arriving speed is much higher with the Turbo, in comparison with my C4S because of the extra horsepower, but I don't know if that would have such a significant impact in terms of brake wear. Considering I have the PCCB system on my car, I expected more from it.

    My car currently has 2900 km. Would that be considered as "broken in" yet?

    Re: PCCB: Loss of brake pressure after spirited dr

    In response to Mose55's comment:

    Yes, it is my first time taking my car out and driving it aggressively, but I thought brake system takes approximately 500-1000km to break it in properly?

    Re: PCCB: Loss of brake pressure after spirited dr

    Quote:
    MKSGR said:Honestly, I don't think that it is possible to take PCCB to its limits on public roads (not even on unrestricted German Autobahnen).



    Have you tried spending a day driving HARD on some really twisty tight back roads?

    Do it long enough and you'll definitely find the limits like I did a couple times.

    Re: PCCB: Loss of brake pressure after spirited dr

    Quote:
    neosky said:
    My car currently has 2900 km. Would that be considered as "broken in" yet?



    Sure is it broken in then. Based on your summary above I would recommend exchanging the brake fluid. That should (hopefully) resolve all issues

    Re: PCCB: Loss of brake pressure after spirited dr

    Quote:
    atomic80 said:
    Quote:
    MKSGR said:Honestly, I don't think that it is possible to take PCCB to its limits on public roads (not even on unrestricted German Autobahnen).



    Have you tried spending a day driving HARD on some really twisty tight back roads?

    Do it long enough and you'll definitely find the limits like I did a couple times.



    No way can you take PCCB to its limits on public roads

    For example: I drove a PCCB equipped car on Porsche's Leipzig track for several hours some weeks ago. You will unlikely be able to use the brakes in a comparable way on any public road (high-speed driving on Autobahn excluded). The brakes did not show any fading or other weakness

    Re: PCCB: Loss of brake pressure after spirited dr

    Something to consider. I was told this by a Porsche technician and he said, if the brake fluid exceeds it's maximum temperature for the utmost efficiency then the very next time the fluid heats up the threshold will be lower, meaning that you will lose 100% efficiency sooner. Usually some higher grade (is able to achieve a higher heat level) brake fluid will help, so it may be that you have exceeded the specification of the fluid also.

    Re: PCCB: Loss of brake pressure after spirited dr

    Quote:
    MKSGR said:
    Quote:
    atomic80 said:
    Quote:
    MKSGR said:Honestly, I don't think that it is possible to take PCCB to its limits on public roads (not even on unrestricted German Autobahnen).



    Have you tried spending a day driving HARD on some really twisty tight back roads?

    Do it long enough and you'll definitely find the limits like I did a couple times.



    No way can you take PCCB to its limits on public roads

    For example: I drove a PCCB equipped car on Porsche's Leipzig track for several hours some weeks ago. You will unlikely be able to use the brakes in a comparable way on any public road (high-speed driving on Autobahn excluded). The brakes did not show any fading or other weakness



    Agree....in my expce, 997TT PCCB was robust vs mtn twisties driving ...but have my doubts re: PCCB response in rain driving, esp w/o periodic application....

    Would be interesting to stress-test 599 CCM vs 997TT PCCB in aggressive track/AB/twisties driving and wet response...and understand the decay curves of latest-tech brakes/tires vs mileage/heavy use

    Doubt we'll ever obtain hard comparo data to draw conclusions; so, based upon my suspicions re: the shape of those decay curves and pace of quiet/publicized tech advances/debugging, I trade-in any F/P/AMG by about 5K mis to maximize active safety....

    Re: PCCB: Loss of brake pressure after spirited dr

    Sounds like you had a bit of the dreaded "Vapor Lock" or "Hydrostatic Lock"
    It's what happens when brake fluid boils or has too much water that boils.

    Drain the brake system, replace the fluid, and bleed the line.

    You should be good to go. If not that, then you may have a faulty brake booster and in which case it should be replaced under warranty.

    Re: PCCB: Loss of brake pressure after spirited dr

    Quote:
    MKSGR said:No way can you take PCCB to its limits on public roads


    I agree, the difference between agressive street driving on a twisty road and lapping on a track that is tough on brakes has to be about 1,000.00%...

    Re: PCCB: Loss of brake pressure after spirited dr

    Quote:
    Heist said:
    you may have a faulty brake booster



    That's along the lines of what I'm thinking.

    Here's a clue from page 4.9 of Turbo Servic Info Book:

    Re: PCCB: Loss of brake pressure after spirited dr

    more:

    Re: PCCB: Loss of brake pressure after spirited dr

    and:

    Re: PCCB: Loss of brake pressure after spirited dr

    Could the problem be explained by one of the following types of brake fade? Good luck and hope this helps.

    http://www.h-e-l.co.uk/HEL_Performance_Motorcycle_Brake_Lines_Brake_Doctor_Brake_Fade.htm

    There are three kinds of fade commonly encountered in fast riding; pad fade, green fade and fluid fade.
    Brake Doctor - Pad Fade

    Pad fade occurs for several reasons. All friction material (the materials brake pads are made of) has a coefficient of friction curve over temperature. Friction materials have an optimal working temperature where the coefficient of friction is the highest. Sometimes you can use the brakes so hard that you get the temperature over the point of maximum friction to where the coefficient of friction curve starts to decline.

    The mechanics of this decline in the coefficient of friction are varied. At a certain temperature, certain elements of the pad can melt or smear causing a lubrication effect, this is the classic glazed pad. Usually the organic binder resin starts to go first, then even the metallic elements of the friction material can start to melt. At really high temperatures the friction material starts to vaporize and the pad can slide on a layer of vaporized metal and friction material which acts like a lubricant. Pad fade is felt on a bike that still has a firm, 'non spongy' feeling brake lever that won't stop even if you are squeezing as hard as you can. Usually it builds somewhat slowly giving you time to compensate for it but some friction materials have a sudden drop off of friction when the heat is put on them resulting in sudden dangerous fade.
    Brake Doctor - Green Fade

    This is perhaps the most dangerous type of fade. Green fade is a type of fade that manifests itself on brand new brake pads. Brake pads are usually made of different types of heat resistant materials bound together with a phenolic resin binder. These are thermosetting plastic resins with a high heat resistance. On a new brake pad, these resins will cure when used hard on their first few heat cycles. The new pad can hydroplane on this layer of excreted gas. Green fade is dangerous because many people assume that new brakes are perfect and can be used hard right off the bat. Green fade typically will occur much earlier than normal fade so it can catch a rider that is used to a certain bikes characteristics unaware. Typically the onset of green fade is rather sudden, further increasing the danger factor. Some teams have a new pads warning sticker that they place on the top yoke to inform the rider to be careful on the first few laps.

    Green fade can be prevented by bedding in the pads correctly. This is a simple procedure to boil off the resins and break in the pads under controlled conditions which has been explained below - Reducing Green Fade <Top>
    Brake Doctor - Fluid Fade

    Fluid fade is caused by heat induced boiling of the brake fluid in the calipers. This produces bubbles in the brake system. Since bubbles are compressible, this makes for a soft spongy lever. In worse cases, the lever can come all the way back to the grip without slowing the bike.

    The major cause of fluid fade is absorbed atmospheric water in the brake fluid. DOT4 Brake fluid has a tremendous affinity for absorbing water from the atmosphere, especially at high temperatures and under humid conditions. Brake fluid can absorb atmospheric water just by sitting in the brake system of your bike. A container of brake fluid sitting open can literally go bad from water absorption in an hour on a hot humid day. It is important to keep your fluid in a tightly sealed container, keeping the cap on at all times except when pouring fluid out!

    Fluid fade can be avoided by running a higher grade racing type brake fluid and most importantly frequent changes of brake fluid. Regularly changing the fluid is the most important thing you can do to avoid fluid fade - change your brake fluid every 3 months and fit braided brake hoses and you will have superb brakes.

    Fortunately fluid fade usually has a gradual onset, usually enabling you to either slow down or pit before a total loss of brakes occurs.

    The reason we are explaining these forms of fade to you is so that you can identify what kind of fade that you are suffering from and do the proper thing to fix the type of fade that you have with the correct countermeasure. If you are experiencing pad fade, switching brands of brake fluid won't help. If you are getting fluid fade, the trickiest carbon pads won't stop you a bit sooner. If you have the finest brake parts available, you could still fall prey to green fade.

     
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