brake fluid ?

[socialDK]

a guy at work asked me about brake fluids boiling point. i didnt even know it had one or 2.  another guy couldnt really explain it to us so can some one out there explain what is the difference between wet and dry boiling point is? which is more important? does boiling occur because you ride the brake to much? what are the effects of it?

[GeeP]

Silicone brake fluid is hygroscopic, it absorbs water vapor out of the air.  Water in the fluid modifies the boiling point significantly downwards.  Ensuring your fluid has a high boiling point is one of the main reasons for changing it every so often.  The other reason is to prevent corrosion of the brake system components from wet fluid.

Your brakes bleed off mechanical energy by converting it to heat energy.  In the process everything gets hot.  If you use the brakes enough, the caliper and piston will get hot.  If the temperature of the caliper and piston exceeds the boiling point of the brake fluid, the fluid will boil.  When the fluid boils and it's vapors expand it increases the the at-rest pressure of the braking system, the pressure the system "sees" with your fingers off the lever.  The at-rest pressure in the system should be 0, but when the at-rest pressure rises, that's the same as squeezing the lever.  The result is dragging brakes, which heat the caliper further, which boils more fluid, which increases the at-rest pressure even more, which clamps the brakes even tighter on the rotor.  NOT a good thing leaned over in a corner!   

[The Buddha]

Stop stop ... somebody make him stop ...

Silicone brake fluid is non hygroscopic. The others are.

OK all the rest was correct.

These posts need to be in general discussion.

Conventional brake fluid actually more than temperature will boil due to pressure ... or lack there of. Top of pikes peak the fluid will boil in summer. It lead to the development of better brake fluid over the years.
Cool.
Buddha.

[GeeP]

Stop stop ... somebody make him stop ...

Silicone brake fluid is non hygroscopic. The others are.

OK all the rest was correct.

These posts need to be in general discussion.

Conventional brake fluid actually more than temperature will boil due to pressure ... or lack there of. Top of pikes peak the fluid will boil in summer. It lead to the development of better brake fluid over the years.
Cool.
Buddha.

The others just absorb MORE water.  Even the silicone fluid absorbs water.

[The Buddha]

Negative Geepo ...

Silicone fluid will absorb very very little water. Its got the ability to disperse water in fact. Kinda like wd40.

From - http://auto.howstuffworks.com/question451.htm

The three main types of brake fluid now available are DOT3, DOT4 and DOT5. DOT3 and DOT4 are glycol-based fluids, and DOT5 is silicon-based. The main difference is that DOT3 and DOT4 absorb water, while DOT5 doesn't.
One of the important characteristics of brake fluid is its boiling point. Hydraulic systems rely on an incompressible fluid to transmit force. Liquids are generally incompressible while gases are compressible. If the brake fluid boils (becomes a gas), it will lose most of its ability to transmit force. This may partially or completely disable the brakes. To make matters worse, the only time you are likely to boil your brake fluid is during a period of prolonged braking, such a drive down a mountain -- certainly not the best time for brake failure!

As a DOT3 or DOT4 brake fluid absorbs water, its boiling point decreases. It can absorb water from the air, which is why you should avoid opening your car's brake fluid reservoir. For the same reason, you should always keep containers of brake fluid tightly sealed.

DOT5 fluid does not absorb water. This means the boiling point will remain relatively stable, but it also means that any water that does get into your brake system will tend to form pure water pockets, which could cause brake corrosion.

Cool.
Buddha.

[Roadstergal]

Don't forget to metion that DOT 5 sucks.

And that DOT 5.1 is not silicon-based.  It's regular hygroscopic fluid.

[The Buddha]

5.1 is synthetic.
and
Why 5 sucks ?

Cool.
Buddha.

[sledge]

DOT5/5.1?

I wouldnt touch the stuff with a shi*y stick.

http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html

[The Buddha]

Oh yea lets try this unsubstantiated BS ...

Summary
Over the years, the debate has continued as to which is the best fluid. Racers and custom builders have traditionally promoted silicone fluid, and many street riders have assumed this meant it was good for them also. However, silicone is the highest-maintenence of all brake fluids, one that demands frequent attention.

And what he offers as proof is ...
Silicone Brake Fluids
In years past, all brake fluids were glycol. Then D.O.T. 5, a silicone fluid having a higher temperature rating, emerged, initially to meet the higher boiling point requirements of racing use. (Race car brake systems include oil-cooler-like heat exchangers and ceramic pads.) Silicone fluid was able to withstand the most heat of any brake fluid, so it earned a reputation as a racing brake fluid. However, silicone brake fluid has properties very different from glycol fluid, and has its own pros and cons. On the advantage side, silicone fluid will not harm paint or plastic, and does not aggressively attract additional moisture as glycol fluid does. On the disadvantage side however, silicone fluid aerates easily. Harley-Davison, one of the sole current OEM users of silicone fluid, warns buyers to let the fluid sit at least an hour before using it. The trip home in the saddlebag is enough to aerate silicone brake fluid until it looks like a freshly poured soft drink. Silicone fluid is also slightly more compressible than glycol fluid, does not change color to tip the user to its moisture content, and worst of all, neither accepts or disperses moisture, making systems using it more corrosion prone, and requiring much more frequent fluid changes. Silicone brake fluid also lacks glycol fluid's naturally occuring lubricity, making it incompatible with the mechanical valving in some antilock braking systems.



OK so it gets aerated ... so you have to let it sit till aeration goes away ... great ... then it wont show you hom much moisture there is ... maybe there isn't any ...
Ergo, once you let it sit and get it all filled and bled after completely evacuating the system ... it essentially will perform forever ...
BTW fluid vac pumps use silicone based lubricant ... so that fluid getting into it wont hurt it ... and even better it wont eat paint when spilled.
A completely BS statement is right at the begining ...
Try this ...

Air? From Where?
Let's begin at the beginning. A brake system is not a sealed system. A physics principle known as Boyle's Law in a round-about way establishes that a fluid cannot leave a container unless air can follow it. If the vent in your gas tank plugs up, for example, fuel will eventually stop flowing. Similarly, a brake system is, like a fuel tank, vented to atmosphere, usually at its highest point, the reservoir. (Ever notice that little notch?) Thus a brake system has continuous access to air.


Oh really ... I can pretty much guarantee you ... there isn't ... OK maybe there is like 3 molecules ... literally ...
The brake reservoir gasket is a rubber accordion. That can be soaked in brake fluid if its silicone ... cos spilling it wont hurt ... Then, you fill and bleed the system ... yea watch out for the aeration BS ... OK ... all done ... no air ... OK ... after you fill your reservoir to the top, put it on and screw in ... OK you'd spill some fluid ... again, its not harmful to nothing so spill away.
Now as you pump the fluid into the piston during the course of your braking and as the pads wear and piston pushes out more and more ... Yea fluid comes out of the reservoir ... correct, so air takes its place ... nope ... wrong ... The accordion type top cap sinks to the level of the fluid due to its accordionated nature. Booya ... no air.

I know, I have used this crap for years on bikes ... 97-98 was when I switched to it full time. From there on I put 25K on that 89 of mine, plus maybe 50-60K on 30 others. Been through 1 round of pads on the virago so far, and running synthetic in it ... never a problem. I filled it back up 8 months ago ... it doesn;t indicate water content ... cos there isn't any ...
3, 4, and 5.1 are pure garbage if you ask me ...
I will give you 1 concession though ... 4 is the best for brake lever feel ... no question, never tried 5.1, and 4 is the fluid my friend put and bled my 89 with in 96, fresh new clean 4 and a ss line will give you brake lever feel nirvana ... 5 does have a spongy touch ... only discernible when tested back to back with identical 4 system.
I'd say, 5 is the best for commuters, 4 is for short distance racers and guess 5.1 for endurance racers.
Also I have heard some old brit and american bikes ... 50's though 70's need the petro fluids for keeping their seals soft ... our vintage jap bikes, dont care.
Cool.
Buddha.

[Roadstergal]

DOT 5 is mushy *giggles at censor of perfectly reasonable description*, and I'd be shocked if you can find a racer that uses it, car or bike.  No pros do.

DOT 5.1 isn't silicone, so I think it would be at least as good as 4.  I use 4 because I can find it, and it works great for my needs.  I used ATE SuperBlue in WA because I could get it for cheap at a local place.

I bleed reasonably frequently - no less frequently than once a year on my streetbikes, and about once every other outing or so on my dirt/track bikes.

[The Buddha]

If you bleed often yea 4 ... if you dont want to and can manage the little mushy feel ... 5.
All I am saying is ... the water entering all systems constantly aspect is BS, and there for dot 5 is worst is double BS.

5 is less work overall, spilling is harmless, does not take in water at all, more $ but you can never bleed and still be OK so you use less, and its a wee bit mushy ... you'd never know that with the stock rubber lines though.

4 is better brake feel but need SS lines, regular replacement is a must (yearly atleast) will eat paint and take in water, but in effect will give you better brakes, if you have the lines to make it happen.

That article has a lot of 1/2 truths. Racing is 4 or 5.1, street almost always is 5 if you are looking for the optimal.

Cool.
Buddha.

[Roadstergal]

I have steel on my bikes, and I don't mind the bleeding - on a bike, it's quick 'n easy (and doesn't take much fluid).  I like a firm, progressive feel on my brakes.

I remember, when I started tracking and racing, I was told by a certain helpful mentor that the weak parts on most people's riding are line-of-sight and braking, and I've found that to be the case; they really sucked for me.  I've become a lot less lousy at both through practicing and drilling, and both have done a lot to help my speed around a track.  Improving my braking has also made me much more sensitive to how brakes feel, but I think on balance that's a good thing.

[ohgood]

I have steel on my bikes, and I don't mind the bleeding - on a bike, it's quick 'n easy (and doesn't take much fluid).  I like a firm, progressive feel on my brakes.

I remember, when I started tracking and racing, I was told by a certain helpful mentor that the weak parts on most people's riding are line-of-sight and braking, and I've found that to be the case; they really sucked for me.  I've become a lot less lousy at both through practicing and drilling, and both have done a lot to help my speed around a track.  Improving my braking has also made me much more sensitive to how brakes feel, but I think on balance that's a good thing.

sorry, but i had to.

that was just childish, rg's insight to the world of motorcycling is cool, funny at times, and always leaning on experience.

brake fluid is crap. i shouldn't have to change it ever, but alas, i do, monthly. a little bleed does so much good !

[The Buddha]

but alas, i do, monthly. a little bleed does so much good !

Monthly bleeding are we even talking about the same thing ... 

Cool.
Buddha.

[Roadstergal]

I prefer to think of it as not pleasant, but necessary, and quickly over with.

[socialDK]

ok? so what im taking from this is change as recommended and ill get a fluid with a high wet temp.