TROUBLESHOOTING THE HMMWV - OD1616 - LESSON 1/TASK 1
Hydraulic brake fluid is the liquid medium in the brake system used
to transmit fluid motion and pressure to the wheel brake components.
The hydraulic brake fluid used in today's modern vehicles must have
some important properties; the most important are discussed in this
paragraph.
The fluid must remain a liquid during all operating
temperatures. The boiling point of the fluid must be well above the
temperatures encountered during the most severe brake applications on
the hottest day, and also maintain an even viscosity at extreme cold
temperatures.
The brake fluid must be able to absorb and hold
moisture and also act as a lubricant.
There are several types of
hydraulic brake fluids in use today.
Silicone Brake Fluid. After 40 years of research and development, a
brake fluid that was acceptable under extreme operating conditions
was developed.
This fluid achieved low water pickup and good
corrosion protection.
The fluid also provides good lubrication
qualities and rubber compatibility.
Silicone brake fluid has been
used in all military vehicles since the end of 1982.
This is the
only brake fluid used in the HMMWV.
(4) Combination Valve.
The combination valve consists of a one-
piece housing containing a rear brake proportioning valve section and
a differential valve and switch. The proportioning section provides
balanced front-to-rear braking action.
The pressure differential
valve sections activates the brake warning lamp, should a pressure
loss in the front or rear hydraulic system occur.
The combination
valve is just that, a combination of two different valves often found
in brake systems.
These two valves are the proportioning valve and
the limiting valve. The operational characteristics of each of these
two valves will be discussed in the paragraphs that follow.
(5) Hydro-boost.
The hydro-boost is a hydraulically operated
power assist mechanism that is used to increase fluid pressure in the
brake system while at the same time decreasing the pedal effort. The
hydro-boost is also a component of the steering system.
This unit
does the same job as a vacuum booster and is connected in the brake
system in much the same way. The major difference between the two is
that the hydro-boost unit uses pressurized power steering fluid to
obtain its
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