5
Section 250-0000
SM 1948 4-00
to flow into the air chamber part of rear pressure
converter (13). This applies pressure to the brake
hydraulic fluid to apply the rear service brakes. At the
same time, port 'A' is vented through port 'C', allowing
the spring in parking brake actuator (15) to apply the
parking brake. The air from port 'C' flows to the
emergency port of relay emergency valve (11). For
operation of relay emergency valve, refer to Section
250-0280, RELAY EMERGENCY VALVE. The
'EMERGENCY' position should only be used in an
EMERGENCY. For normal brake operation use the
treadle valve.
With the park/emergency control valve (8) lever in the
'PARK' position, port 'A' continues to vent through port
'C' keeping the parking brake applied. At the same
time, air is exhausted from the rear pressure converter
releasing the rear service brakes.
Automatic Brake Application
The first indication of a loss of air pressure in the
system is that the low air pressure warning light on the
instrument panel will illuminate when the pressure falls
below 4.1 bar (60 lbf/in²
). If the pressure falls below
3.1 bar (45 lbf/in²), relay emergency valve (11) opens
and allows the air in the line from rear brake tank (10)
to flow into the air chamber part of rear pressure
converter (13). This applies pressure to the brake
hydraulic fluid to apply the rear service brakes.
BRAKE SYSTEM SAFETY PRECAUTIONS
When working on or around brake systems and
components, the following precautions, should be
observed:
1. Always block vehicle wheels. Stop engine when
working under a vehicle. Keep hands away from
actuator push rods and slack adjusters; they may
apply as air system pressure drops.
2. Always carry out ALL servicing operations in
conjunction with WARNINGS and procedures outlined
in the individual component sections.
3. Always ensure there is no pressure in the air
system before attempting to replace brake pads or
shoes; the brakes will automatically apply as air
pressure drops.
4. Never connect or disconnect a pipe or line
containing pressure; it may whip. Never remove a
component or pipe plug unless you are certain all
system pressure has been released.
Braking System - Air Braking System Schematic
5. Never exceed recommended pressure and always
wear safety glasses when working.
6. Never attempt to disassemble a component until
you have read and understood recommended
procedures. Some components contain powerful
springs and injury can result if not properly
disassembled. Use only proper tools and observe all
safety precautions pertaining to use of those tools.
7. Use only genuine factory replacement parts and
components.
a) Only components, devices and mounting and
attaching, specifically designed for use in hydraulic
brake systems, should be used.
b) Replacement hardware, tubes, lines, fittings, etc.
should be of equivalent size, type and strength as the
original equipment.
8. Devices with stripped threads or damaged parts
should be replaced. Repairs requiring machining
should not be attempted.
BRAKE FUNCTION CHECKS
WARNING
Make sure the area around the machine is clear
of personnel and obstructions before carrying
out these checks.
Note: The following checks are not intended to
measure maximum brake holding ability. If NEW brake
pads are fitted, they MUST be burnished as per the
manufacturers recommendations before carrying out
the checks.
Service Brake Holding Ability
1. Depress service brake treadle pedal and move
transmission gear shift selector to 1st gear.
2. Move park/emergency control lever to
'EMERGENCY' position, then move to 'RELEASE'
position.
3. Depress accelerator control and accelerate engine
to 1 350 rev/min. The machine should not move.
4. Decelerate engine, shift transmission to 'NEUTRAL'
and apply the parking brake before releasing the
service brake.
Courtesy of Machine.Market
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