From: Bjorn Brandstedt (super_deuce@hotmail.com)
Date: Fri Aug 15 2003 - 18:16:43 PDT
Make sure that you bleed the air hydraulic cylinder. There are two, un upper
and a lower. Check your manual for exact locations. TM 9-2320-260-20 (July
1972, page 2-250)./Bjorn
>From: "Wayne Harris" <papercu@hotmail.com>
>To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
>Subject: Re: [MV] M817 soft brakes have me stumped.
>Date: Fri, 15 Aug 2003 21:26:49 +0000
>
>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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