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

[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

[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.