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

[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.

[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.

[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

[CJ_Boxster]

interesting, I had no idea that some abs systems were vented. Thanks.

[edevlin]

This is somewhat off topic, but does relate to braking. I was wondering if one should push in the clutch when doing hard braking from higher RMP's. It seems like if you dont, you are applying breaks to not only the wheels but the engine as well.

Ed