From: Wayne Harris (papercu@hotmail.com)
Date: Fri Aug 15 2003 - 14:26:49 PDT
Are you still using the silicone type brake fluid? Take a look at the link
for other reasons. Wayne
http://www.babcox.com/editorial/bf/bf109954.htm
All from the web:
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 and
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/water/fluid situation. Because water boils at approximately
212º F, 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. Therefore
silicone brake fluid lacks the ability to deal with moisture and will
dramatically decrease a brake systems performance.
Plain old air is a big problem with DOT 5 fluids. While DOT 3/4 fluids hold
a maximum of say 5% dissolved air by volume, DOT 5 holds 2 or 3 times that
much. This creates the problem that I experienced -- no matter how many
times you bleed the brakes you never get a good, firm pedal. I tried and
tried and tried but the pedal always felt spongy. When I bled the brakes, I
couldn't find any air.
Drawbacks
1. ) Very hard to pour without entraining air bubbles - hence an
application will generally have a softer, spongier pedal feel.
Maybe a Fix:
The ability of silicone brake fluid to retain air was taken care of by
slowly heating the silicone brake fluid on my stove to release the air
before putting it into the system. (make sure your wife or girlfriend is not
around) My brake pedal is high and firm.
Also found with DOT 5 that pressure bleeding works better than manual
bleeding (if you manual bleed it has to been done s-l-o-w-l-y) but have had
lousy results with vacuum bleeding.
>From: "Jim" <jehill@cabinetdoors.com>
>To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
>Subject: [MV] M817 soft brakes have me stumped.
>Date: Fri, 15 Aug 2003 07:43:31 -0700
>
>My M817 5-ton dump truck has developed a problem with the brakes which has
>me stumped.
>The brakes are soft. Push the brake peddle the first time and it has some
>resistance. It goes all the way to the floor, but has some resistance.
>Push the peddle a second time and it goes to the floor with little or no
>resistance.
>I've followed the procedure (from the manual) to bleed the brakes, and I
>got
>air, but now all lines are air free.
>Still the soft brakes.
>I hate to start replacing things without knowing the replacement (master
>cylinder???) will really fix the problem.
>The master cylinder seems to get added boost from the "Air Hydraulic Unit",
>but I don't have any documentation on this hydraulic unit.
>The trucks air pressure is strong and doesn't leak.
>I'm stumped. Anybody have any experience on this type of problem?
>What can cause these soft brakes, besides air in the lines?
>If my master cylinder is bad, where can I get a new one?
>Jim
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