Re: [ST] Brake Fluid Explained (Long)

[John Ulizzi <jaulizzi@xxxxxxxxxxxxx>]

Thanks for sharing , Brett. That clears up a couple
questions for me....

John

--- brettwilson21@xxxxxxx wrote:

> I grabbed this off www.bikersoracle.com interesting
> reading if you're wondering whats really going on
> with brake fluid.
>  
> Enjoy,
> Brett.
>  
> Brake Fluid Facts 
> by Steve Wall
> 
> As a former materials engineering supervisor at a
> major automotive brake system supplier, I feel both
> qualified and obligated to inject some material
> science facts into the murky debate about DOT 5
> verses DOT 3-4 brake fluids. The important technical
> issues governing the use of a particular
> specification brake fluid are as follows:
> 
> Fluid compatibility with the brake system rubber,
> plastic and metal components. 
> Water absorption and corrosion. 
> Fluid boiling point and other physical
> characteristics. 
> Brake system contamination and sludging.
> Additionally, some technical comments will be made
> about the new brake fluid formulations appearing on
> the scene. 
> 
> First of all, it's important to understand the
> chemical nature of brake fluid. DOT 3 brake fluids
> are mixtures of glycols and glycol ethers. DOT 4
> contains borate esters in addition to what is
> contained in DOT 3. These brake fluids are somewhat
> similar to automotive anti-freeze (ethylene glycol)
> and are not, as Dr. Curve implies, a petroleum
> fluid. DOT 5 is silicone chemistry. 
> 
> Fluid Compatibility
> 
> Brake system materials must be compatible with the
> system fluid. Compatibility is determined by
> chemistry, and no amount of advertising, wishful
> thinking or rationalizing can change the science of
> chemical compatibility. Both DOT 3-4 and DOT 5
> fluids are compatible with most brake system
> materials except in the case some silicone rubber
> external components such as caliper piston boots,
> which are attacked by silicon fluids and greases. 
> 
> Water absorption and corrosion
> 
> The big bugaboo with DOT 3-4 fluids always cited by
> silicone fluid advocates is water absorption. DOT
> 3-4 glycol based fluids, just like ethylene glycol
> antifreezes, are readily miscible with water. Long
> term brake system water content tends to reach a
> maximum of about 3%, which is readily handled by the
> corrosion inhibitors in the brake fluid formulation.
> Since the inhibitors are gradually depleted as they
> do their job, glycol brake fluid, just like
> anti-freeze, needs to be changed periodically.
> Follow BMW's recommendations. DOT 5 fluids, not
> being water miscible, must rely on the silicone
> (with some corrosion inhibitors) as a barrier film
> to control corrosion. Water is not absorbed by
> silicone as in the case of DOT 3-4 fluids, and will
> remain as a separate globule sinking to the lowest
> point in the brake system, since it is more dense. 
> 
> Fluid boiling point
> 
> DOT 4 glycol based fluid has a higher boiling point
> (446F) than DOT 3 (401F), and both fluids will
> exhibit a reduced boiling point as water content
> increases. DOT 5 in its pure state offers a higher
> boiling point (500F) however if water got into the
> system, and a big globule found its way into a
> caliper, the water would start to boil at 212F
> causing a vapor lock condition [possible brake
> failure -ed.]. By contrast, DOT 3 fluid with 3%
> water content would still exhibit a boiling point of
> 300F. Silicone fluids also exhibit a 3 times greater
> propensity to dissolve air and other gasses which
> can lead to a "spongy pedal" and reduced braking at
> high altitudes. 
> 
> DOT 3 and DOT 4 fluids are mutually compatible, the
> major disadvantage of such a mix being a lowered
> boiling point. In an emergency, it'll do. Silicone
> fluid will not mix, but will float on top. From a
> lubricity standpoint, neither fluids are
> outstanding, though silicones will exhibit a more
> stable viscosity index in extreme temperatures,
> which is why the US Army likes silicone fluids.
> Since few of us ride at temperatures very much below
> freezing, let alone at 40 below zero, silicone's low
> temperature advantage won't be apparent. Neither
> fluids will reduce stopping distances. 
> 
> With the advent of ABS systems, the limitations of
> existing brake fluids have been recognized and the
> brake fluid manufacturers have been working on
> formulations with enhanced properties. However, the
> chosen direction has not been silicone. The only
> major user of silicone is the US Army. It has
> recently asked the SAE about a procedure for
> converting from silicon back to DOT 3-4. If they
> ever decide to switch, silicone brake fluid will go
> the way of leaded gas. 
> 
> Brake system contamination
> 
> The single most common brake system failure caused
> by a contaminant is swelling of the rubber
> components (piston seals etc.) due to the
> introduction of petroleum based products (motor oil,
> power steering fluid, mineral oil etc.) A small
> amount is enough to do major damage. Flushing with
> mineral spirits is enough to cause a complete system
> failure in a short time. I suspect this is what has
> happened when some BMW owners changed to DOT 5 (and
> then assumed that silicone caused the problem).
> Flushing with alcohol also causes problems. BMW
> brake systems should be flushed only with DOT 3 or
> 4. 
> 
> If silicone is introduced into an older brake
> system, the silicone will latch unto the sludge
> generated by gradual component deterioration and
> create a gelatin like goop which will attract more
> crud and eventually plug up metering orifices or
> cause pistons to stick. If you have already changed
> to DOT 5, don't compound your initial mistake and
> change back. Silicone is very tenacious stuff and
> you will never get it all out of your system. Just
> change the fluid regularly. For those who race using
> silicone fluid, I recommend that you crack the bleed
> screws before each racing session to insure that
> there is no water in the calipers. 
> 
> New developments
> 
> Since DOT 4 fluids were developed, it was recognized
> that borate ester based fluids offered the potential
> for boiling points beyond the 446F requirement, thus
> came the Super DOT 4 fluids - some covered by the
> DOT 5.1 designation - which exhibit a minimum dry
> boiling point of 500F (same as silicone, but
> different chemistry). 
> 
> Additionally, a new fluid type based on silicon
> ester chemistry (not the same as silicon) has been
> developed that exhibits a minimum dry boiling point
> of 590F. It is miscible with DOT 3-4 fluids but has
> yet to see commercial usage. 
>  
> _______________________________________________
> Triumph Sprint ST/RS mailing list
> Send list posts to ST@xxxxxxxxxxxxxx
> Change your list options at www.Triumphnet.com
> 

_______________________________________________
Triumph Sprint ST/RS mailing list
Send list posts to ST@xxxxxxxxxxxxxx
Change your list options at www.Triumphnet.com