[Oeva-list] Changing brake fluid.

Steve's Account stevel at fern.com
Mon Jul 1 13:16:54 PDT 2013

On Mon, 1 Jul 2013, CraigSchaefer wrote:

> What the hell are we talking about?  Who here has ever heated their brake 
> fluid to the boiling point of water?  (In the brake system, that is)

If you have done any driving in the mountains, I'm pretty sure you
have! And the reason you never knew it was that your brake fluid 
was dry.. if it had water in it, it would boil, displacing the
fluid with a compressable gas.. Steam.. and the next time you
push on the break, the pedal goes right to the floor!

It's why the "dot" standards for brake fluid specify the boiling point
of the "DOT approved" brake fluid.

The heavier the vehicle, the higher the boiling point has to be, because
of the greater risk of long, hard braking sessions.

While "brake fluid" doesn't apply to heavy trucks, because they have
air brakes.. I'm sure you have seen brake drums smoking on heavy trucks
going down long hills.. That's a place where you'd see in very graphic
terms where the "heat" is in a braking system.

In EV's using regen braking, the amount of heat disapated by the brake
system is lower than it would be, without regen.. But.. in a 
normal car, all the energy "expended" from getting your car from 
freeway speeds to "stopped" is expended as heat, largely in the
brake disks or drums.. which also heats the calipers/wheel cylinders.


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