3 - 1
Safety
Brakes
There are two brake systems on your vehicle, the
service brakes, and the combination emergency
and parking brakes, both of which are described
below.
Your vehicle is also supplied with ABS brakes
(antilock braking system) and can be equipped
with 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
Jacobs
Engine Brake
, page 4-3, or
Transmission Re-
tarder
, page 4-4.
Service Brakes
The service brakes use air pressure from a
footpedal-operated brake valve to actuate cham-
bers which apply the brakes at each wheel. The
air system is divided into two independent circuits
to isolate front brakes from rear brakes, thus
providing safe braking if one circuit fails. Front
axle brakes operate from the secondary air
system, while brakes on both the drive axle and
tag axle operate from primary air system.
Note:
The tag axle service brakes operate only
when the axle is in normal ride position (down).
Furthermore, the brake application sequence,
which starts with rear brakes and then front
brakes, provides uniform braking on slippery
surfaces.
For brake effectiveness, vehicle air system pres-
sure should reach at least 95 psi (655 kPa) in
both primary and secondary air circuits. Refer to
items #31 & #32 on page 2-9.
A warning light turns on (see items #4 & #5, page
2-7) and a buzzer sounds when air pressure in
one of the primary or secondary circuits drops
below 60 psi (415 kPa). Vehicle must then be
stopped and cause of pressure loss must be cor-
rected before further operation.
Warning:
"Fanning" or "Pumping" brake pedal
is not recommended on a vehicle with an air-
operated brake system. 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, pos-
sible 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
(275 kPa), spring-loaded emergency brakes will
immediately be applied at full capacity on drive
and tag axles wheels to stop vehicle. In an ex-
treme condition, the emergency brakes might be
applied quite rapidly. Vehicle must then be
stopped and cause of pressure loss must be cor-
rected before resuming operation.
Parking Brakes
Spring-loaded parking brakes are manually ap-
plied by pulling up the control valve knob, located
on L.H. side control panel.
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 consid-
erably longer than with a normal brake application.
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).
