3 - 1
Safety
Brakes
There are two (2) brake systems on your
vehicle, the service brakes and the combination
emergency & parking brakes, both of which are
described below.
Your vehicle may also be supplied with ABS
brakes (antilock braking system) and an
additional retardation system. ABS brakes
system information is available in this section on
page 3-2; for information regarding both optional
retardation systems, see "ENGINE RETARDER
SYSTEM (JACOBS)" on page 4-3 and
"AUTOMATIC TRANSMISSION OUTPUT
RETARDER" on page 4-5.
Service Brakes
The service brakes use air pressure from a
footpedal-operated brake valve to actuate
chambers which apply the brakes at each
wheel. The air system is divided into two (2)
independent circuits to isolate front brakes from
rear brakes, thus providing safe braking if one
(1) circuit fails. Front axle brakes operate from
the secondary air system, while brakes on both
the drive axle and tag axle operate from the
primary air system.
Note: The tag axle service brakes operate only
when the axle is in normal ride position (loaded
& down).
Furthermore, the brake application sequence,
which starts with rear brakes and then front
brakes, provides uniform braking on slippery
surfaces.
For safe brake effectiveness, vehicle air system
pressure should reach at least 95 psi (655 kPa)
in both primary and secondary air circuits. (see
items #14 & 15 on page 2-10)
A warning light turns on (see Dashboard items
#7 & 8, page 2-10) and a buzzer sounds when
air pressure in one of the primary or secondary
circuits drops below 60 psi (413 kPa). Vehicle
must then be stopped and cause of pressure
loss must be corrected before further operation.
Warning: "FANNING" or "PUMPING" brake
pedal is not recommended. This practice will
not increase brake system effectiveness, but will
instead waste air and thereby reduce brake
effectiveness.
"RIDING" the brake by resting foot on brake
pedal when not braking can cause abnormally
high brake temperatures, excessive lining wear,
possible damage to the brake drums, and loss
of brake efficiency.
Combination Emergency and Parking
Brakes
Emergency brakes
In normal operation, if air pressure in both brake
circuits drops below approximately 40 psi (276
kPa), spring-loaded emergency parking brakes
will immediately be applied at full capacity on
drive and tag axle wheels to stop vehicle. In an
extreme condition, the emergency brakes might
be applied quite rapidly. Vehicle must then be
stopped and cause of pressure loss must be
corrected before resuming operation.
Parking brakes
Spring-loaded parking brakes are manually
applied by pulling up the control valve knob,
located on L.H. lateral console (see page 2-4).
They are not designed to be used as service
brakes. In normal driving conditions, control
valve knob must be pushed all the way down.
Note: Parking brakes can supplement service
brakes to stop the vehicle in an emergency con-
dition only. The stopping distance will be con-
siderably longer than with a normal brake appli-
cation.
Before releasing parking brakes by pushing
down control valve knob, pressure gauges
should be checked to ensure that brake system
air pressure has built up to a minimum of 95 psi
(655 kPa).
Warning: Always apply parking brake before
leaving driver's seat.
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