Brake cooling question - so why don't you see...

[CamB]

This is in the "stupid question" basket.

I know you can duct air to your rotors. I know you can put titanium shields between your pads and the piston or install a water-sprayer. I know you can put bigger, more vented rotors.

And still there can be problems with brake fluid getting too hot.

(begin half assed, lack of knowledge makes me look stupid, bit)

Why can't brake fluid be (more actively) cooled? Like a little baby cooler arrangement? I assume it is a hydraulic thing. Or a safety thing. Or a localised heat thing (fluid doesn't get pumped around, per se).

Can anyone shut me up quickly?

Thanks!

Cam

[emcon5]

Originally posted by CamB
Or a localised heat thing (fluid doesn't get pumped around, per se).

This would be my guess.

Tom

[Jack Olsen]

Bingo. It's not boiling in the master cylinder.

There have actually been schemes to 'circulate' brake fluid, in order to cool it. But having an escape valve -- that's capable of failing -- makes it an impractical choice from a reliability and safety point of view.

I think it's been done for racing applications, but I'm not sure of that.

[911pcars]

There's a device called Cool Brake that does this. A series of check valves work in concert to recirculate the fluid throughout the system every time the brake pedal is depressed.

During braking, most of the heat transferred to the caliper is taken up by the relatively small volume of fluid inside the caliper. Meanwhile, fluid in the rest of the system (lines and master cylinder) stays relatively cool.

No affiliation,
Sherwood Lee
http://members.rennlist.org/911pcars

[Wayne 962]

I don't think that the heat in the brake fluid is the major problem here. It takes a awful lot of heat to vaporize hydraulic fluid, and you can always design one to remain solid.

It is my understanding is that as the pads and rotors heat up, the friction between the two of them dissipates, and loses the ability to break the car. I think you want to cool the pads and the rotors, not the fluid...

-Wayne

[911pcars]

Brake fade appears in different forms. Brake pads can overheat and reduce their frictional characteristics. That's brake pad fade and there are solutions that can mitigate this (ducted air, larger brake components - more mass, better brake pad material, different driving style, etc.)

Brake fluid also boils due to the continued heat of braking. This happens when the heat builds up during braking and the caliper/ rotor assy./brake cooling system can't dissipate the heat faster than it is produced. The critical temperature is the boiling point of whatever fluid you're using. Once the fluid boils, air bubbles form which immediately results in a soft pedal. Extreme cases will result in no pedal as master cylinder travel is taken up compressing the air. Otherwise it wouldn't matter what kind of fluid is in the system.

Here's some more info:
http://www.seinesystems.com/BrakeFade.htm

Regards,
Sherwood Lee
http://members.rennlist.org/911pcars

[Bill Verburg]

There are special calipers available for circulating brake fluid through coolers/cooling reservoirs. AP and Wilwood both supply them, they are expensive and complicated. For our cars there are plenty of cheaper more reliable alternatives.

Sherwood has correctly identified the problem, excessive thermal loads at the rotor pad interface can boil the fluid and melt the pad material.
The solution is better air flow(limited potential), better pads(commensurately poorer when cold), bigger rotors(the best though not optimal solution), light weight materials that work as well at extreme temps as at low temps which will also not transfer heat to the fluid (ceramic rotors/Ti insulators)

[bdonally]

This is an auxilliary cooling gadget.. Doubt if it is needed on a Porsche with half-decently maintained brakes - looks more like a stock car accessory.

http://www.colemanracing.com/section/index.htp?id=430

[911pcars]

911toronto,
You're right. Most of us probably don't need something like this. However, not everyone has the same brake requirements. If you'rve got a track car that's maxed out with big HP/Torque/speed potential with max. brakes/rotors, ducting, etc. and your car stil has brake fade issues, what do you do?

That's right. You try something else (assuming all current systems are okay) to see if it'll contribute to overall braking effectiveness. This could be considered one of those items.

Sherwood Lee
http://members.rennlist.org/911pcars
www.seinesystems.com