Hot brakes , how do they feel?Is this a symptom?

[motoadve]

Drove long and fast twisties pushing it.No traffic at all 30 minutes, turn after turn mostly downhill and pushing it .
The brake pedal felt a bit softer and I got a squaling noise.

Is that a symptom of hot brakes?

Will brakes fail completely if too hot?

[racer_d]

Well, tell us more about yor car?

How old is it?
What kind of brake pads are in it?
When was the last time you changed brake fluid?
What kind of brake fluid are you using?

Hot brakes tend to get a soft, mushy feeling as the heat from the rotor and brake pad heat up the brake fluid, most often causing it to boil, thus diminishing braking ability.

You don't mention how fast you were going and how much air was able to get to the brakes, but it sounds like you were experiencing some fade. The "squeal" well, not usually related to brake fade per se, more often a symptom of brake dust accumulating on the pad/rotor and causing noise during light application of the brakes.

[MNBoxster]

Hi,

Sounds like Boiling Fluid to me. Someone traveling through the twisties with no Traffic isn't likely to encounter Heat Fade.

The SAE did a study of 1,000 two year old cars and found the average moisture content in the Brake Fluid at 4% with a high of 7%. At 4% moisture content, the Boiling Point of DOT4 Fluid will drop to about 240°-260° F - not much better than using straight water in the system...

Happy Motoring!... Jim'99

[motoadve]

Its a Base Boxster Tritpronic 2005
8,000 miles.
Stock brakes, and tires.
Stock fluid, never changed or touched

Speed was between redline 2nd and 3rd gear all the time.

[limoncello]

the "squaling" (squealing?") - might want to check the rotors to be on the safe side, to be sure that the sound is not worn pads scoring them.

If it's all OEM, the wear sensors should be in tact, but maybe worth a look. Visually check for any grooves in the rotors.

Agree with the others, mushy pedal sounds like fluid. Try ATE Super Blue, or if you want the same golden color to look like OEM for warranty purposes, try ATE 200 (I think the correct number) has the same characteristics without the telltale blue color.

Or you can simply flush & replace with OEM fluid. That will get rid of moisture and air, but the boiling point is still lower than ATE. Keeps the dealer & warranty happy, though.

[z12358]

Originally Posted by MNBoxster

Hi,

Sounds like Boiling Fluid to me. Someone traveling through the twisties with no Traffic isn't likely to encounter Heat Fade.

The SAE did a study of 1,000 two year old cars and found the average moisture content in the Brake Fluid at 4% with a high of 7%. At 4% moisture content, the Boiling Point of DOT4 Fluid will drop to about 240°-260° F - not much better than using straight water in the system...

Happy Motoring!... Jim'99

Jim, thanks for the info. Moto, sorry to hijack the thread but I feel this is related. At my last brake fluid change, I requested Super Blue after reading how it's the standard track fluid (highest boiling point). However, the mechanic (The shop preps most track Porsches in the Limerock area) recommended Gold for street cars (with occasional track day). He said that Super Blue -- though more heat resistant -- is also more hydroscopic (?, meaning absorbs water easier) than Gold, and I'd have to change it more often than Gold (which, btw, has only 20 deg lower boiling point). Does, this make sense?

He also said that switching to Super Blue would have taken a few minutes longer, which I didn't quite understand why. Is it because they'd have to do a more thorough flush when switching to a different fluid? The price was the same for both fluids. I listened and went with Gold.

Z.

[986 Girl]

At my last (and first) track day, I was advised not to bother going with Super Blue, because chances are at my first event I wont be driving hard enough for it to matter.

Wrong advice. For street driving I highly doubt you need Blue, but if you are going to be doing any sort of track days, you WILL want it.

During one of my 30-minute sets, we got a red flag because of a car that had broken on course. After it was cleared, they had us proceed back to the start line to start off at 30 second intervals (this was a beginner group, so we were just getting seat time). I stopped at the start line and let my instructor-passenger out to do some runs on my own (this was my now ex-boyfriend, so it wasn't a professional by any means). I noticed that my brakes were making a squeaking noise, even when at a stop, whenever I pushed the pedal in. I called to my ex and asked him what that was, and he said that it was probably just the brakes getting hot, but not to worry about it.... "you aren't pushing it THAT hard."

Okay, no biggie... but it still felt weird. My turn came to start out, and around turn 2, when I tried to brake... I got nothing. Brake went straight to the floor with no response. Thankfully I wasn't at full speed because of the restart, but it was still NOT fun... I held it through the turn and pulled off to the side where we got another red flag.

I really can't imagine, in non-track driving, getting my brakes to that point... but I guess it's not impossible. My first, and only warning, was the brake pedal squeaking, so I would be very carefuly. I can't say for certain this is what you should be looking for, but this was my experience.

Hope it helps a little!

[MNBoxster]

Hi,

There's a lot of misinformation about Brake Fluid floating around out there. All Brake Fluid is Hygroscopic, except DOT 5 (which is Silicone Fluid - Race Application only), meaning that it readily absorbs moisture from the air.

All Brake systems are vented at the Reservoir (or you'd create a vacuum and no fluid would be supplied to the system from the Reservoir). Normal Humidity, especially on rainy days, and believe it or not, when you wash your car is where this moisture comes from.

You do not want to use DOT 5 (Silicone), because unlike DOT 1, 2, 3 and 4 which mix with water, the Silicone won't.

Water is heavier than Brake Fluid and if DOT 5 is used, all the water will migrate to the lowest point in the system - the Calipers where it will readily boil as well as corrode the Piston/Bore, better to have the water in solution as it isn't so highly concentrated in the Caliper. Dot 5 has the highest Dry Boiling Point which is why it's used in Racing - they swap fluid every race. It was initially spec'd for the US Military because it had good sub-freezing performance, but due to the accelerated wear to the Brake components and consequent expense, the Military has dropped this specification and reverted back to Polyglycol-based fluid - DOT 4.

ATE Super Blue Fluid and ATE Gold (properly known as Typ 200) are exactly the same Fluid - same Dry Boiling Point, same Wet Boiling Point. The only difference is the color to make flushing the system easier because of the Visual check available to know that the entire system has been flushed - look for the color change in the Catch Bottle. So, you should alternate between Super Blue and Typ 200 (Gold) every Fluid change.

Your Mechanic and AX Instructor are incorrect. Don't believe me? Look at the attached picture of a Can of each and compare their labels. Hope this helps...

Happy Motoring!... Jim'99

[FrayAdjacent]

Jim gives good advice!!

It's recommended that your brake fluid be flushed every 3 years or so. Given my car is 6 years old, and I have no idea if it's been done before, I plan on flushing my brake system within the next few months. I still have good brake response for daily driving, so I'm not too worried.... but if/when I do decide to do an autocross, I'll need better fluid in there!

Should be easy to do with some speed bleeders, and Super Blue. The current fluid in there is the normal off white/clear stuff. Flushing should be uber easy with the blue stuff!

(Another bonus, I know a shop that will take every used fluid except coolant, so I can recycle used fluid!)

[z12358]

Jim, again thanks for the info. I knew it was hyGroscopic and not hyDroscopic but 'hyDro' always made more sense since it's water related. Anyway...

The mechanic actually said that there isn't much difference between the two fluids (price was the same too). Looks like he was wrong, as they seem to have the same boiling points. Good to know. On hygroscopy... Once the water gets into the system, seems like a more hygroscopic fluid is actually better since it will dillute the water into itself better, spread it around, and not allow it to concentrate around the calipers. Is hygroscopic ability measurable, quantifiable? Are Blue and Gold equal here, too?

Finally, if the Blue and Gold are the same across all dimensions (except color?!) why produce/sell both or only two? Why not Pink?
Z.

[z12358]

986 girl, I don't think squealing is a sign that brakes are about to give up on you. That's only a sign that there's something (dust, debris, metal particles, etc) rubbing against your rotors. One very important advice that my first instructor gave me was to minimize compressing hot pads onto hot rotors (and never keep them plastered there without ventilation) after hard driving. Did you sit on your brakes after the first red flag, and before getting out back on the track? That will boil the fluid much faster.

I use every cool-down lap religiously to cool down everything on the car -- keep the rpms well under 4k, and try not to use any brakes at all right until I park the car into my parking spot in the paddock (I strategically pick a paddock spot that would allow me to easily park without braking on the way to it -- I just glide in.) During the cool-down lap I also allow enough space between myself and the car in front so that I will avoid braking if the traffic clogs as we all get out of the track. All little things that help prolong the life of the fluid and the brakes.

One other thing to learn is to use momentum while driving. Especially in Green and Yellow you can be very fast (the fastest, even) without much use of brakes at all. I noticed that the more I learned the less I used the brakes and the faster I became.

Z.

[MNBoxster]

Hi,

@z12358 - Yes, there is a measure of Hygroscopy, but it is variable because of the mount of moisture which may be present in the air over time. A fun Mr. Wizard-type experiment is to fill a cup to the brim with Brake Fluid and place it on a saucer outdoors. Come back in an hour and you'll find that the Brake Fluid has overrun the cup. This is because of the moisture it has absorbed...

The best measure is a Fluids Wet Boiling Point which is the Boiling Point of the Fluid when it is fully Hydrated - cannot absorb any more moisture.

ATE Super Blue and Typ200 is Racing Fluid. Race Cars have their Brake Fluid changed before every race. ATE simply makes the Fluid in contrasting colors as a convenience. It could well be made Pink, but I don't think the contrast would be as good between Pink and Gold in all light conditions. Besides, Racers don't usually do Pink...

Happy Motoring!... Jim'99

[986 Girl]

Originally Posted by z12358

986 girl, I don't think squealing is a sign that brakes are about to give up on you. That's only a sign that there's something (dust, debris, metal particles, etc) rubbing against your rotors. One very important advice that my first instructor gave me was to minimize compressing hot pads onto hot rotors (and never keep them plastered there without ventilation) after hard driving. Did you sit on your brakes after the first red flag, and before getting out back on the track? That will boil the fluid much faster.

I use every cool-down lap religiously to cool down everything on the car -- keep the rpms well under 4k, and try not to use any brakes at all right until I park the car into my parking spot in the paddock (I strategically pick a paddock spot that would allow me to easily park without braking on the way to it -- I just glide in.) During the cool-down lap I also allow enough space between myself and the car in front so that I will avoid braking if the traffic clogs as we all get out of the track. All little things that help prolong the life of the fluid and the brakes.

One other thing to learn is to use momentum while driving. Especially in Green and Yellow you can be very fast (the fastest, even) without much use of brakes at all. I noticed that the more I learned the less I used the brakes and the faster I became.

Z.

Sorry, I should have clarified... they were squeaking while stopped. IE, while at a dead stop, if I pushed the brake pedal in and out, there was an audible squeak from the pedal itself. It has never done this before or after the incident.

I don't remember if I sat on them when we came to a stop. I do remember pushing them in and out a few times because of the sound, but I probably DID sit on them once I was told they were fine since I don't typically sit without the brakes on.

I'll definitely take that advice for my next track day (June 15th), thanks!

[FrayAdjacent]

I'd bet the squeaking is from water in the calipers.... after all, water is not a lubricant... the pistons could be squeaking in the cylinders.

Probably a very good sign that you have too much water in your system, and that a flush is overdue!

[986 Girl]

Great info Jim, thanks!

Fray: Definitely. I plan to do it as soon as the weather here gets a little nicer... it was still snowing as of this morning. It's stopped now, but I don't trust it with how overcast it still is.

[z12358]

One more thing, Porsche track experts from the club recommend changing your brake fluid at least once a year if you do more than a couple of track events a year. I plan to do it every year.

Jim, is it better to do brake fluid change before winter storage (just like oil) or after?

Z.

[986 Girl]

Found a pretty helpful site for those of us who have never bled or flushed brakes before...thought someone else might find this handy.

http://www.bombaydigital.com/boxster/projects/brakes/bleed_and_flush/

There are a couple other walkthroughs on there (changing rotors, pads, etc) and most sections have a ton of helpful pictures.

[CJ_Boxster]

Originally Posted by MNBoxster

Hi,



All Brake systems are vented at the Reservoir (or you'd create a vacuum and no fluid would be supplied to the system from the Reservoir).

Happy Motoring!... Jim'99

Vented at the reservoir.... last time i checked, i didnt have a check valve or hole on my brake reservoir cap. Only free air in the system is what air is left between the cap and the surface of the fluid in the reservoir, unless you top it off (not recommended) however, if i fill that gap with more brakefluid, the brakes still work, Have you looked at the internals of a brake master cyclinder?

When the brake pedal is pressed, a rod with a rubber tip will slide snugly through the masters cyclinder, past a hole which leads to the fuild in the reservoir, Once the rubber tip has past the hole... it will create a seal between itself and the rest of the brake system below as it continues to slide through the master cyclinder. This seal will cause brake fluid to be pressed through the distribution block and through the brake lines and down to the calipers causing the pistons to squeeze the brake pads against the rotor/brake disc.

Only a small ammount of vacum is created in the reservoir once the Rod has gone past the hole leading to the reservoir not enough to stop the master cyclinder from doing its job... and if it is, then you need a new master cyclinder.

I probably just didnt understand your point to the sentence i quoted you on.

sorry in advance if my spelling is off par.

[MNBoxster]

Originally Posted by z12358

One more thing, Porsche track experts from the club recommend changing your brake fluid at least once a year if you do more than a couple of track events a year. I plan to do it every year.

Jim, is it better to do brake fluid change before winter storage (just like oil) or after?

Z.

Hi,

It's a toss up - Change it in the Fall to prevent any built up moisture from attacking your Braking System, or change it in the Spring so you have the lowest possible moisture content through the Driving Season.

Personally, I do it in the Spring to gain maximum benefit from the Fluid for driving. Corrosion will shorten your Braking Systems life, but probably not too badly if you habitually change it every year...

Happy Motoring!... Jim'99

[MNBoxster]

Hi,

@CJ_Boxster - Some systems are vented while others are not, with Modern ABS Systems, vented Reservoirs are being seen less and less. But, even the sealed systems can/do allow some air (along with it's moisture) to pass the Cap Seal - it's not a perfect seal.

I am totally familiar with the inner workings of a Master Cylinder and have certainly rebuilt many more than you have racked up years - not dissing you, just making an example, in fact I rebuilt a Girling MC for a friend of mine last weekend.

According to the SAE DOT 4 Brake Fluid absorbs between 1.5-2% moisture by weight annually, even in a sealed system. This is because the primary source of moisture invasion comes from the Flexible Brake Hoses at the Calipers and past the Piston Seals themselves. Fluid cannot pass, but minute amounts of moisture can.

Consequently, every 2 years the average system will contain about 4% moisture by weight and should be changed. This much moisture may not dangerously affect the Wet Boiling Point (though it may for some fluids), but 4% Moisture will attack the system components. Also, the SAE found that the moisture content was not linear throughout the system but was found in higher concentrations in the Calipers (because they are closer to the Flexible Hoses and Piston seals), while the Fluid in the Reservoir may have a lower moisture content. They use a Refractor to determine the Moisture content sampled from different parts of the system.

And, the worst place to experience Fluid Boil is in the Calipers because their effectiveness can be reduced to nothing as some people here have found...

Happy Motoring!... Jim'99