getting discourged

[funky technician]

the brakes get bled every 2 years to keep water out

Not to throw salt on the wound...but...bleeding is to get the air out, not the water....if you have water coming out, your seals are destined to fail from steam boiling out or the internal rust being pushed through.

I guess I should have rephrased that a bit, I bleed the brakes to keep the fluid fresh, brake fluid is hygroscopic and will attract water through time just because of its nature, so flushing is actually a good preventive maintence habit, but your right , once I get this all figure out I hope it will be good for a while (at least till the summer :roll: ), its gonna start getting really cold hear soon (like -10C isn't cold enough :cry: )

[funky technician]

Also...bleeding is not considered nornmal brake maintenance...it should only be performed when the circuit has be breeched or if symptons indicate (spongey) such.

????

Actually, most manufacturers recommend that your brake fluid be changed/flushed once every two years or 30k miles. Brake fluid is hydroscopic (absorbs moisture), and will become laden with excess water content fairly rapidly. The heat genereated by normal braking helps to dry the fluid, but is only so effective. Also, as the calipers/wheel cylinders/master cyinder exercise, small particles of the seals do separate, and float around in the fluid. To prevent corrosion from moisture and scoring from floating debris, the fluid should be exchanged at a regular interval. This becomes even more critical with modern anti-lock brakes, traction control, stability control, electronic brake force distribution, and hybrid vehicle braking systems (very subseptible to moistue contamination since the friction brakes are used less aggressively).

HA HA I didn't even see this post! LOL

[kzbill]

Thats just it, you work on it for a while then drive it for a while. all in all cheaper than payments on a new one.
And every time you fix it you get a little better at it. once all the trouble spots are fixed it stays that way for a long while.

[jglutz]

Brake fluid is hydroscopic (absorbs moisture),

I beg to differ.....that's why it's brake fluid and not water...if what you said is accurate alot of airplanes would fall out of the sky. At 30,000 feet their hydraulic circuits would freeze. I know alot of manufactures want the circuits to be flushed...not bled...but if the fluid had an infinity for H2O, it would not work .................................................. .................................................. .................................................. ..........................................(period)

The circuit (components/carbon steel/ductile iron) may have an infinity for H20...but the fluid..no (insert universal...ing) way!

[collegeboi]

i agree haha

[FB71]

Sorry, but yes. DOT 3 and DOT 4 are alcohol based. Read the bottle. It specifically says not to leave exposed to moisture. Aircraft don't use this type of fluid (I worked on C-130's in the AF). They use a mineral oil based fluid. And Dot 5 is silicone based, a whole different critter.

Flushing and bleeding are a matter of semantics. Bleeding is specifically to remove air from the system. Flushing replaces the fluid in the system, and requires bleeding afterwards.

[jglutz]

^^ I agree, my point/problem is the word hydroscopic.
The stuff in an aircraft (skydrol) is ester based (alcohol and acid) not mineral oil based.
Your mis-understanding is how alcohol works...many believe alchohol can be used to mix water and oil....not true...alchohol thin water so that it is suspended in oil...the proper word is surfactant or flux or soap.
Brake fluid will conceal or suspend water...no doubt...that's what it's suposed to do... water distributed thru out the circuit prevents the boiling point of the fluid from being lowered to a dangerous level.
But not hydroscopic. The difference...brake fluid can absorb water and distribute it with minimal consequense to either the boiling point or freezing point....Hydorscopic means it's searching for water...there is a big difference. Think about it...if brake fluid was hydroscopic...why would they let the cap on the brake fluid reservoir breath?

[FB71]

ok, they don't let the cap breath. The resivour (sp) is sealed from the atmosphere. I do understand how alcohol works, but glycol esters aren't the only thing in brake fluid. I don't believe alcohol can mix water and oil. The two substances do not solubilize, I know that. They can, however, emulsify (sp?), but we'll save that for a different discussion. Oh, and yes, the boiling point of DOT3 and DOT4 lowers quite dangerously when saturated with water. Read this quote;

POLYGLYCOL ETHER BASED FLUIDS
Fluids containing Poly glycol ethers are regarded as DOT 3, 4, and DOT 5.1. These type fluids are hydroscopic meaning they have an ability to mix with water and still perform adequately. However, water will drastically reduce the boiling point of fluid. In a passenger car this is not an issue. In a racecar it is a major issue because as the boiling point decreases the performance ability of the fluid also decreases.

Poly glycol type fluids are 2 times less compressible than silicone type fluids, even when heated. Less compressibility of brake fluid will increase pedal feel. Changing fluid on a regular basis will greatly increase the performance of the brake system.

FLUID SPECIFICATIONS All brake fluids must meet federal standard #116. Under this standard is three Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1 (for fluids based with Polyalkylene Glycol Ether) and DOT 5 (for Silicone based fluids).

MINIMAL boiling points for these specifications are as follows:


from this web page; http://www.afcoracing.com/tech_pages/fluid.shtml

And, anything water soluble is hydroscopic. Check this MSDS; http://www.thecloroxcompany.com/prod...otmsds8-04.pdf

And yes, C-130's used a mineral oil based fluid. Not sure about commercial aircraft.

[FB71]

Also, check Federal Motor Vehicle Safety Standard 571.116, specifically S5.1.9

http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.asp?section=571.116

[jglutz]

^^good stuff...
Question: If the res cap does not breath...as the level drops...does the volume between the top of the fluid and the cap bcome a vacuum?
Comment: Most fluids are nominally non compressable...that's why they're fluids. When the compresability doubles...this typically means from 0.02% to 0.01%. something negligible to the driver.

[FB71]

correct on the compressability...

no, the space is not under vacuum. Did you ever notice that the cap seal is a pleated accordian deal? As the level drops, the cap allows atmospheric pressure to push the seal down into the space previously occupied by the fluid.

[skeeters_keeper]

from my understanding dot 3/4 becomes saturated at 3% water, is that really enough water to cause rusting in the lines? I can see if it was sitting for a while perhaps, but under normal driving i don't think that 3% of water would really be able to do much... correct me if i'm wrong!

[festivaWES]

If the brakes work they're good enough for me.... I'm not into this whole glyco, water, acohol based dot 3,4,5 BS. Too much knowledge on brake fluid for me!

[FB71]

yes, 3% water is plenty enough to cause rust. Remember, it's not water by itself that causes corrosion. Its water and free oxygen in a catalytic reaction that cause oxidation. Again, its best to flush the system once every two years for optimum corrosion protection.

[packrat427]

I know that Dot 5 will not take the paint off , that is why I run that in my S-10