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Discussion Starter #41
Just a quick update:

Porsche Bahrain has provided me with an initial repair estimate, total of 30 k USD !!! (23 k for the parts and 7 k for the labor work).

they told me they can't check the car log to see if there was a technical issue with the break until all the repairs are done.

I took the car to Porsche dealer in Saudi (where I purchased the car originally ) and they offer 20% discount in all parts and 10% in labor work, when they check the car they told me they can fix most of the damaged parts without replacing, so they will repair and paint the damaged exterior body parts except the fender and maybe the front front bumper, they still have to decide. At Porsche Bahrain they were changing everything and took them almost a week to prepare the estimate.

you can see the list of the parts needs to replace, painted and repaired (attached). when I took a close look at the car I found most of the parts can be repaired, mostly scratches thanks to the XPEL Ultimate PLUS PPF, expect the mechanical parts, left head lamp and LHS fended were they were completely damaged. The most expensive part is the LHS LED head lamp around 4 k USD alone !!!
 

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How much are they quoting you for the repair in Saudi? Just curious as a comparison to the Bahrain quote.
 

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However, I still believe that in general the thoughts are correct. In order to lose the brakes due to air in the lines requires one to heat the brake fluid above it's boiling point. That is how compressible bubbles are introduced into the system. If you have a non high-temp brake fluid, either brake compound can cause boiling. If you have high-temp brake fluid that is impervious to boiling, neither brake compound will cause boiling outside of exceptional circumstances.
Ah. I hadn't considered that you meant a gas from having boiled the brake fluid! Gack. (I wonder how closely boiled break fluid adheres to Ideal Gas Law.) Of course once the fluid is gaseous it will keep pressure on the pads against the disk and not let everythng cool so well. Again, the dominant behavior of heat loss would be that a sudden spike intemperature for a short time causes more heat loss, so if the total heat loss per lap is the same as you alternately get on and off the brakes, blowing off a lot of heat at once is better.

Also again, whether the pads matter depends more on ow well they conduct heat from the rotor surface to the caliper. I wouldn't think there is much difference. On the other hand, pads which lose friction earlier may make the driver spend more time on the brakes and lower the maximum temperature the disk reaches, thereby raising the average around the track.

I'm sure you in the right of it about brake fluid boiling point. The lower it is the sooner it will boiol under severe braking. Once you boil it you start flying a brakeless missle.

In a British cars mailing list long ago one member accidentally typed fluif. That became the accepted term. So now we discuss brake fluif.
 

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Ah. I hadn't considered that you meant a gas from having boiled the brake fluid! Gack. (I wonder how closely boiled break fluid adheres to Ideal Gas Law.) Of course once the fluid is gaseous it will keep pressure on the pads against the disk and not let everythng cool so well. Again, the dominant behavior of heat loss would be that a sudden spike intemperature for a short time causes more heat loss, so if the total heat loss per lap is the same as you alternately get on and off the brakes, blowing off a lot of heat at once is better.

Also again, whether the pads matter depends more on ow well they conduct heat from the rotor surface to the caliper. I wouldn't think there is much difference. On the other hand, pads which lose friction earlier may make the driver spend more time on the brakes and lower the maximum temperature the disk reaches, thereby raising the average around the track.

I'm sure you in the right of it about brake fluid boiling point. The lower it is the sooner it will boiol under severe braking. Once you boil it you start flying a brakeless missle.

In a British cars mailing list long ago one member accidentally typed fluif. That became the accepted term. So now we discuss brake fluif.
Jim:
I'd love to say that I was talking gas pressure but it was just a brain fart. But it is an interesting thought that after the brake fluif is boiled into a gas that there is now a constant gas pressure against the piston/pads. I can't imagine it would be enough to make any difference though.

This is an interesting conversation. Maybe any real brake system engineers on this forum could chime in, if there are any here.
 

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I am not sure that there is any pressure on the piston if the fluid has boiled and turned into a gas bubble in the line. In theory, if the pressure at the caliper piston side is nearly atmospheric (with the brake pedal at rest) then the pressure in the bubble would be nearly atmospheric.

Now you hit the brake sending a volume of brake fluid to be added in the brake line. The bubble will be compressed increasing its internal pressure some but there will be little movement at the other side of the bubble where the caliper piston is. So, the pedal will go all the way to the floor, without any appreciable increase in pressure at the caliper piston.

That's what happens when you pump the pedal while trying to bleed the line, purging any air bubbles.
 

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Discussion Starter #47
Just a quick update:

Finally my car is back and repaired at my local Porsche dealer, total cost around $ 15,000, original estimate was 30,000. The dealer offered 20 % on parts and 10 % on labor work.

Regarding the issue from the brake, no warning messages were found, brake pads and discs in good condition, Porsche technicians were not able to find any reasons why the brake failed !!

I did the 30,000 km service which cost me around $ 1600. they changed oil, oil filter. brake fluid and other minor stuff. Also, I have extend my warranty for 2 years which cost me around $ 2500.

My service advisor suggests to do a pre track inspection at the dealer and one after the track session.

I'm really happy the is back, but I'm worried I will face the same brake issue in the future.
 

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I'm so happy for you!

I can't say with certainty, but based on your description, and having experienced it myself in the past, I'm quite confident that it was caused by the [aged] brake fluid getting too hot, boiling the water vapor inside, which now a steam, compressed instead of allowing the master cylinder to apply the pressure to the calipers. Furthermore, I doubt this would've caused any codes in the ECU.

My advice is to definitely do a tech inspection, and change out the brake fluid often, using a high-temp fluid. In our PCA region, we require fresh fluid within the past 12 months, but strongly suggest 6 months. Especially for a vehicle that is tracked often.
 

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Too many people are getting on tracks with really fast cars that don't understand the basic physics of track day driving.

Brake fluid is hygroscopic. This means that it absorbs water vapor from the atmosphere as it sits. Stock DOT approved flex lines are generally made of rubber covering with fiber reenforcement. These definitely allow water vapor to get in your fluid. You don't need to drive the car for this to happen. It's an age/humidity thing. No matter the boiling point of the brake fluid, the boiling point of water is 100C or 212F. It's very easy to exceed 100C at a track session with stock brakes...in the first lap! When water boils, it's a gas. When it's a gas, it will compress...That means hydraulic action is gone. In case you missed physics...Liquids are not compressible. They are of a fixed volume, so when you press on the pedal, you move brake fluid to from the master cylinder to the cylinders in the individual brakes. It's a direct thing. When there's a gas in the line, that's out the window...pedal goes to the floor. Sometimes, you can pump the brake pedal repeatedly and find some braking...sometimes not. If you don't know this can happen, your reaction time quadruples as you panic and then try to figure out what to do. If you're slamming toward Turn 1 on the main straight, the window for safe braking has probably closed by the time you find any brakes.

1st mistake: Stock brake fluid. It doesn't have a high enough boiling point for heavy track use even when fresh. Especially in a high temp environment.
2nd mistake: The brake fluid was OLD. It needs to be fresh with no water in it. See above.
3rd mistake: The stock pads are made to do a couple hard stops from over 100mph on German cars. This is required by TUV in Germany because of autobahn use. This is why German cars have brake dust while cars from other countries often do not. Japan's highways have speed limits of 50 or so MPH. Their brake standards are much different.

My experience is that, in cooler weather, the stock Porsche brakes work OK for a few 20-minute sessions if you don't push braking the to absolute limit every turn and the track is not crazy hard on brakes. They seem to make more heat than my Pagid RS 29s. In general, stock brake pads make more heat.

The reason stock pads not as good for track work, is that they have other qualities that are important for a street car.

1. They need to work when the car and brakes are cold. Anyone who has driven to the track from the motel on morning 2 or 3 of a track weekend, knows what it feels like to use track pads in cold weather...Scary!!!

2. They need to not squeal like a pig at every stop light.

3. They need to not wear out the brake rotors when they're not warmed up (some race compounds are really hard on rotors when cold).

4. They need to not make dust that takes the paint off the car. Yes, there are some very good race compounds that do this, especially if it rains when dust is sitting on the paint.

I don't know if the cause of this problem was boiled fluid or overheated stock pads, but either will put you into a tire wall. LEARN THE BASICS before charging out there!!! I learned about this stuff 30 years ago when I was starting out with a 2002tii at a small BMW CCA event in Wisconsin. I've heard this chalk talk 1000 times in classroom sessions and it's repeated in the printed material in any track day event I've been to.

Car clubs hold pre-techs and tracks ask you "when the last time you changed brake fluid". 3 months is the usual recommendation. They check that your tires are OK and that your lug-nuts are on tight. At the track, they look for leaks,

Perhaps they do things differently in the middle-east but this is really very basic stuff. Tending to brake fluid is actually more important in a street car than a race car because of the increased weight and generally less brake cooling on a street car...ANY street car, not just a Porsche.

😎
 

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Jim:
I'd love to say that I was talking gas pressure but it was just a brain fart. But it is an interesting thought that after the brake fluif is boiled into a gas that there is now a constant gas pressure against the piston/pads. I can't imagine it would be enough to make any difference though.

This is an interesting conversation. Maybe any real brake system engineers on this forum could chime in, if there are any here.
The pressure of boiling fluid or water vapor isn't enough to cause any meaningful change in the braking if the pedal is not pushed. The presence of any gas bubbles in any hydraulic lines will cause the loss of hydraulics. The reason old fluid is bad is because water gets into it. The power of hygroscopic fluids is immense. Water can enter a pressurized containers of hygroscopic gas. I have some work experience with this. Using SS braided teflon lines at all 4 corners helps keep the water out. It's not a guarantee, but it helps.
 
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