Brake fluid, was: Re: cross drilled rotors Scott Williams is WRONG!

[Scirocco-Al" <scirocco-Al@insight.rr.com (Scirocco-Al)]

I remember reading somewhere that after 2 years of use regular brake fluid
absorbed so much moisture that it lost up to 80% of it's capability to
handle heat.  So having said that probably the best way to avoid having
brake fade is simply to flush your brake system out regularly with a quality
fluid and avoid having this whole cross drilled/slotted rotor dicussion.
:-).


----- Original Message -----
From: "Brian McGarvey" <brianm@zbt62.eastnet.gatech.edu>
To: "Brett Van Sprewenburg" <brett@netacc.net>
Cc: <scirocco-l@scirocco.org>
Sent: Saturday, March 23, 2002 6:06 PM
Subject: Re: cross drilled rotors Scott Williams is WRONG!


>
> my two cents here
>
> Engineer (electrical) with LOTS of physics background.
> Brett is 99.99% right
> yes our brakes basically turn KE to heat, but there is alittle additonal
> physics going on too.
>
> (please note this first bit is for ppl on the STREET)
> Most pp here are concerned with upgrading ther current brake system
> because of worn parts etc. A few are concerned because they have
> experienced brake fade.
>
> In our cars and most other cars out there we experience brake fade because
> the fluid in our brake systems becomes very hot. THis inturn heats up the
> rubber elements in our systems. Agruing about which brake master clyn to
> use for what pressure required is pointless at this point.
>
> basically the brake system works like basic hydrolics. The brake fluid is
> a high boiling point incompressable fluid (and you engineers out there
> know that the tiny tiny amoun that it does compress is irrelavent). so you
> have a large volume of fluid occupying some space that space is removed by
> depressing the brake pedal moving the master clyn pistion. THis FORCES the
> fluid out of the master clyn. it has to go somewhere. So it goes to the
> wheel clynders which EXPAND if the is no other expansion in the system.
> Under normal operating conditions and when the rubber hoses connection the
> hard line to the brake caliper are fairly new and you havent bee giving
> your brakes a workout heating the fluid and thereby heating the rubber
> hoses. So in the case where youHAVE been giving the brakes a workout. THe
> rubber hoses going to the calipers in the front ant the two hoses
> connecting the hard lines in the back have now become heated and now ALSO
> provide a point in the system for the fluid FORCED out of the master clyn
> by YOUR FOOT to go. Basic brake fade occurs when the rubber hoses are
> expanding enough so that the wheel clynders do not move as much as
> desire or at all picture a baloon at each wheel. THis is due to HEAT.
> THese tepereatures occur well below the boiling point of the brake fluid
> so the brake fluid is STILL and incompressable fluid.
>
> So now here is when you want to upgrade to Stainless steel braided lines.
> basically all you are doing is removing the baloons at each wheel.
>
> Next now you think you have solved your brake fade problem
> Not true. you have only delayed it. Normal brake fade occurs due to the
> expanding rubbber hoses the effect is usually gradual and tells the driver
> to take it easy until the temp comes down a little. with stainless lines
> you konw move into a more dangerous realm of brake fade liquid
> vaporization. THis is why all the racers use the REALLY hight temp brake
> fluid. because what happens is you go from good brakes to ZERO or near
> zero brakes  as the temp rises enought to boil the brake fluid in the
> calipers. THe fluid goes thru a state change from beingand incompressable
> liquid to a VERY compressable GAS.  good brakes good brakes... shit no
> brakes.
>
> SO as you can see before you upgrade anything else you can see that
> cooling the brake system is of the upmost importance. THis is why on an A2
> GLI the little  holes in the spoiler with the plastic funnel compresses
> the air and directs it at the front disk brakes -- adding some cooling.
>
>
> Nw the little problem of effieciency(sp) comes in.
> For the same amount of work (moved fluid) having a longer lever arm
> provides more torque. DOnt belive me. What about your front wheel axle
> nuts. while brakeing does turn KE into heat there are more effienect ways
> to do it so you get less heat. (you thermo ppl can help here). (my
> connection is startign to suck again so typos will start up again). SO if
> you still have the problem of you want to stop quicker and your tires are
> NOT sliding if you are sliding.. get BETTER tires or stop pressing on the
> brakes so hard. as the tire starts to slide your coefficent of friction
> goes waaaay doen its very inefficeint. a sliding stop takes as much as 50%
> longer to stop in as a non sliding stop all things being equal.. thats why
> new cars and some motorcycles have ABS brakes. . increasing diameter adn
> the swept area remaining constant will result in less heat or equal heat
> generated. Increasing the swept area
> will integrate the heat over a larger area overall reducing the average
> temperature.
>
> Holes and slots. <-- in some extreme conditions they may actually help.
> but getting larger dia disks with holes or slots is still better than
> smaller ones. (more swept area lewer temp not less heat).
>
> tired of hearing this argument... rage for days.
> basically slots and drilled rotors unless you are RACING for long periods
> of time or in extreme conditions (mud, snow, rain, desert) it deos do
> shit. So there.
> no vented vs. not vented is an easy one. more Surface area  means more
> convection. means lower temperature NOT lower heat. you basically dOuble
> the surface area and increas the mass of the rotor so yes that is a good
> upgrade. but if you drive like my wife or an old lady ... dont bother.
> unless you wanna look cool.....or they come on the car already installed
> by the PO... <-- my case!
>
> brian
> 2.0L Topless bunny
> Brakes.
> Stock booster -- bad sticky brake pedal syndrome manual return often
> required
> Stock master clyn new
> 10.1's in the front zimmerman xdrills PO of 16v bought them
> drums in the rear
> one new wheel clyn in the rear.
>
>
> On Sat, 23 Mar 2002, Brett Van Sprewenburg wrote:
>
> > >Bigger rotors do give the caliper much more leverage to work against
> > >the spinning wheel. You can easily set up your own experiment with a
> > >spinning bike wheel and see what I mean. What do you think is easier
> > >to grab and stop, near the hub or near the rim? Also the rotor and
> > >pad material used in F1 is so exotic we cant even begin to relate a
> > >tenth of the physics going on there and apply it to our street cars.
> >
> > I'm going to scan the article now, as I just can't stand this
> > anymore..The physics of
> > turning kinetic energy into heat works exactly the same between our
> > cars and an F1 car.  You are of course correct that
> > they can use exotic materials to increase their heat handling and
> > transfer...you are also correct that it's easier to stop
> > something spinning near the rim, then near the center.  Here's how to
> > generate the same effect with a smaller rotor:
> >
> > Press On The Brake Pedal Harder.  No kidding. :)  In other words
> > create higher clamping load, which may generate more
> > heat, but then we're back into the heat issues previous discussed.
> >
> > Once you reach the point of tire lock up (and if you cannot, then you
> > DO need brake work) you will NOT generate any
> > more braking force, no matter how far 'out' your caliper is away from
> > the hub.  Just physics.
> >
> > >
> > >While watching some Tarmac rally last year I remember in a tech
> > >sidebar they were talking about putting the largest brakes they
> > >could fit under the wheel in order to cope with the extra braking
> > >needed. I put more stake in a WRC engineer than a guy racing most
> > >anything in the US let alone a Saturn.
> > >
> > >Jasin
> > >one cents worth
> >
> > That 'guy' racing a Saturn is (as I wrote) an engineer creating
> > braking systems for the Robert
> > Bosch corporation (we've all probably heard of them) and I only threw
> > out the fact he was
> > also a racer as a point to his practical experience.
> >
> > Yes, this is info on how braking actually works can be suprising and
> > offensive, as it upsets
> > several beliefs and notions we (including myself) have had...
> >
> > ==Brett
> >
> >  \/  '84 Scirocco (ITB racer 2B) | "Hot VW's, take two home. They're
small"
> > \/\/ '88 Scirocco 16v (Show), '92 Passat 16v (Winter+) | -
brett@netacc.net
> >
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