On Fri, 27 May 2005 06:33:23 +0200, "Poul Dam" <pouldamadslhome>
wrote:
>men på bane duede det ikke.
Nej - det gør det ikke, lad os tage den lange version :
Brake Fluid Tech
The two most common brake fluids used in the automotive industry are
fluids that contain polyalkylene glycol ether and fluid that contains
silicone or silicium-based polymer. Both fluids are common but very
different in regards to the manner in which they perform. Fluids
containing polyalkylene glycol ether are more widely used and are the
only fluids that should be used in racing brake systems. Because brake
systems may reach extreme temperatures brake fluid must have the
ability to withstand these temperatures and not degrade rapidly.
SILICONE BASED FLUID
Fluids containing silicone are generally used in military type
vehicles and because silicone based fluids will not damage painted
surfaces they are also somewhat common in show cars. Silicone-based
fluids are regarded as DOT 5 fluids. They are highly compressible and
can give the driver a feeling of a spongy pedal. The higher the brake
system temperature the more the compressibility of the fluid. This
increases the feeling of a spongy pedal.
Silicone based fluids are non-hydroscopic meaning that they will not
absorb or mix with water. When water is present in the brake system it
will create a water/fluid situation. Because water boils at
approximately 212¾F, the ability of the brake system to operate
correctly decreases, and the steam created from boiling water adds air
to the system. It is important to remember that water may be present
in any brake system. Silicone brake fluid lacks the ability to deal
with this moisture and will dramatically decrease a brake system's
performance.
POLY GLYCOL ETHER BASED FLUIDS
Fluids containing polyglycol ether 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 the 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 of the fluid also decreases.
Polyglycol type fluids are two times less compressible than silicone
type fluids, even when heated. Less compressibility of the brake fluid
will increase pedal feel. Changing fluid on a regular basis will
greatly increase the performance of the brake system.
All brake fluids must meet federal standard #116. Three Department of
Transportation (DOT) minimal specifications for brake fluid are
defined in this standard. 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:
Type Wet Boiling Point Dry Boiling Point
DOT 3 284¾F 401¾F
DOT 4 311¾F 446¾F
DOT 5 356¾F 500¾F
DOT 5.1 375¾F 518¾F
DOT 3 VS. DOT 4 and 5.1
U.S. Brake 570 Gold is a DOT 3 type fluid. However, it has a dry
boiling point that is 52¾ higher than DOT 5.1 specifications, 124¾
higher than DOT 4 specifications and 169¾ higher than DOT 3
specifications. U.S.
Brake's 570 Gold fluid meets or exceeds all DOT 3, 4, and 5.1
lubrication, corrosion protection and viscosity specifications. U.S
Brake's 570 Gold racing fluid meets but does not exceed federal
standards for wet boiling point specification; therefore, its
classification is DOT 3.
U.S Brake's Ultra HTX brake fluid dramatically exceeds all DOT 3, 4,
and 5.1 standards for wet and dry boiling points, lubrication,
corrosion protection, and viscosity specifications.
WET VS. DRY BOILING POINT
The term boiling point when used regarding brake fluid means the
temperatures that brake fluid will begin to boil.
WET BOILING POINT
The minimum temperatures that brake fluids will begin to boil when the
brake system contains 3% water by volume of the system.
DRY BOILING POINT
The temperatures that brake fluid will boil with no water present in
the system.
MOISTURE IN THE BRAKE SYSTEM
Water/moisture can be found in nearly all brake systems. Moisture
enters the brake system in several ways. One of the more common ways
is from using old or pre-opened fluid. Keep in mind that brake fluid
draws in moisture from the surrounding air. Tightly sealing brake
fluid bottles and not storing them for long periods of time will help
keep moisture out. When changing or bleeding brake fluid always
replace master cylinder caps as soon as possible to prevent moisture
from entering the system. Condensation (small moisture droplets) can
form in lines and calipers. As caliper and line temperatures heat up
and cool repeatedly, condensation forms, leaving behind an increase in
moisture/water. Over time the moisture becomes trapped in the internal
sections of calipers, lines, master cylinders, etc. When this water
reaches 212¾F the water turns to steam. Many times air in the brake
system is a result of water that has turned to steam. The build up of
steam will create air pressure in the system, sometimes to the point
that enough pressure is created to push caliper pistons into the brake
pad. This will create brake drag as the rotor and pads make contact
and can also create more heat in the system.
Another way that moisture may enter the system is through diffusion.
Diffusion occurs when moisture enters through rubber brake hoses.
Using hoses made from EPDM materials
(Ethlene-Propylene-Diene-Materials) OR steel braided brake hose with a
non-rubber sleeve (usually Teflon) will greatly reduce the diffusion
process.
THINGS TO REMEMBER
• A brake fluid's dry boiling point is more important then wet boiling
point when used in a racing brake system.
• Racing brake system fluid should be changed often. A system with
fresh fluid will have a lower moisture content and therefore perform
best.
• Never use silicone-based fluids in racing brake systems.
• Never re-use fluid. Never mix types or brands of brake fluid.
• Purge the system (completely drain) and replace the brake fluid
often for maximum performance.
--
-Michael
No. 74 riding shotgun...