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Old 03-30-2009, 02:43 AM
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bleeding brakes question.

ok i have a physics question ive always wondered about.


how in the heck does bleeding brakes even work when technically air rises and should rise to the high points of the brake system and would seemingly get caught permanently in these points no matter what you do.


yet it does work, always.


i dont understand.

is brake tubing just small enough that air defies common physics laws and will actually travel and get pushed(even downwards) out of the tubing ??

very confused haha.

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Old 03-30-2009, 07:25 AM
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the bubbles are also large enough that the air completely fills the diameter of the tubing and won't allow the fluid to get past it. brake lines are a closed system so the fluid won't budge because it would create a vacuum.

you can see this for yourself with a straw and a soda and some ice. drink the soda until it starts to sputter. cap the straw off with your tongue and you'll see layers of air and soda trapped. same thing in your brake lines.
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Old 03-30-2009, 07:10 PM
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interesting and confusing at the same time

im still confused haha

thanks
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Old 03-30-2009, 08:09 PM
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yes like you said it does work, and the other guys expaination was a very good one, you just have to make sure that you are steadly topping off the resivour (i cant spell, so please excuse me), they do make a system that will actually bleed your brakes from the master cylinder though, and it is said to to a much better job, and there is another system called a vaculla, that is a one person system, that doesn't require that you press the brake pedal, but just hook up the vaccum system to it, i think with that you still have to fill the resivour as you go though
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Old 03-30-2009, 09:40 PM
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yes, not that ive ever had any real trouble bleeing brakes over the years we have bled lots and lots the most recent was a 93 C1500 pickup the other day we replaced a rusted front line on driver side under the firewall and under the floorboard for the resar 1/4" tubing. bled out pretyt easily.

i just always wondered how its even psosible to push air out downwards and how it can possibly work so well when air is supposed to rise, not fall

just crazy it messes with your head,


thanks
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Old 03-31-2009, 01:24 AM
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Well fast68, you are not the only one to ponder this seemingly impossible violation of the laws of physics either....

Like jcoby said, the bubble is big enough that it fills the diameter of the tube..The surface tension of the fluid around the bubble maintains it's size, and the viscosity of the fluid does allow it to rise, but very very slowly.

A better illustration of this phenomenon is to go get some clear vinyl tubing, about 1/8 or 3/16 ID and fill it with brake fluid...leave some air in it, plug one end with a pencil or something and hang it up so the whole tube is vertical...now go get a beer and a copy of the Mcmaster Carr catalog or something to pass the time while you wait for those bubbles to rise through the fluid in the tube....

Also, you need to bleed the brakes because much of the line in a car is horizontal, to and the air would never have anyplace to rise to... and the various altitudes of the line as installed has sections where the air would have to travel downhill to get back to the master cylinder ....

The act of bleeding actually depends on the brake fluid being viscous enough to carry the air bubbles out through the tubes when it is moving at a relatively slow rate.. it only has enough room in a short time span to rise to the top of the column of liquid in the wheel cylinder or disc piston bore...

If you look at the fmvss standards for brake fluid it has a minimum and maximum viscosity test procedure...and timing bubbles as they rise through a specific volume of fluid is one of the tests...

That is also why gravity bleeding works, even with the slow rate of fluid flow, the bubbles still get carried with the fluid...

That is what I have deduced from watching bubbles rise in brake fluid....
Yeah trying to figure out that stuff didn't mess with my head....not one bit....hahahah

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Old 03-31-2009, 11:53 PM
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lmao lmao


good stuff, good stuff

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