Section 16: SUSPENSION
PA1562
36
Neutral Position
When vehicle body reaches the normal ride
height, the height control valve overtravel lever
reaches the "neutral" position and keeps both
the supply and exhaust ports closed to ensure
normal ride height is maintained. This condition
remains static until the vehicle load is altered.
Unloading Position
As the load decreases and raises the vehicle
body, the overtravel lever commands the height
control valve to release air from air springs.
6.1 MAINTENANCE
The height control valve requires no periodic
maintenance. Height control valve linkage
operates on rubber bushings and no lubrication
should be attempted at this location. Inspect the
valve for loose joints, air leaks and worn
bushings.
6.1.1 Removal and Installation
Before disconnecting a height control valve air
line, securely support the vehicle by its jacking
points on the body, and place safety supports
underneath body. Refer to paragraph "16.
Vehicle Jacking Points" in Section 18, "Body".
1. Exhaust air from air system by opening all
air tank drain cocks. Remove height control
valves.
2. Disconnect overtravel lever from link and
pull down lever to exhaust remaining air
from air springs.
3. Disconnect air supply and delivery lines
from the height control valve. Cover line
ends with tape to prevent entry of foreign
matter.
4. Remove the nuts retaining the height control
valve to the mounting bracket, then remove
valve assembly.
Reverse removal procedure to replace height
control valve. After installation, check for
leakage using a soap and water solution.
7. AIR SYSTEM
The basic air system consists of an air
compressor, tanks, valves, filters and
interconnecting lines and hoses (refer to Section
12, "Brake and Air System" for complete
information). It provides a means for braking,
operating controls and accessories, and
suspension. An air system schematic diagram is
annexed at the end of this section for better
understanding of the system.
The air coming from the air dryer is first directed
to the wet air tank, then to the primary (for the
primary brake system), secondary (for the
secondary brake system), and accessory (for
the pneumatic accessories) air tanks (Fig. 49
and 50).
In addition, an expansion air tank may be
installed in series with each air spring.
7.1 AIR TANK MAINTENANCE
Ensure that the accessories air tank is purged
during pre-starting inspection. A good practice is
to purge this tank at the end of every driving day
by the remote air tank drain valve located in the
steering compartment (Fig. 52).
Moreover, purge all tanks by their bottom drain
valves at specified intervals.
7.1.1 Wet Air Tank
This tank is installed above the drive axle on the
L.H. side, and is provided with a bottom drain
valve. It is recommended to purge the wet air
tank by its bottom drain valve every 12,500
miles (20 000 km), or once a year, whichever
comes first.
A remote valve located in engine compartment
and accessible through engine R.H. side door is
used to drain the air dryer (Fig. 51).
7.1.2 Primary Air Tank
The primary air tank is located above the drive
axle on the R.H. side.
This tank is provided with a bottom drain valve
(Fig. 49 and 50). It is recommended to purge the
primary air tank by its bottom drain valve every
12,500 miles (20 000 km) or once a year,
whichever comes first.
7.1.3 Secondary Air Tank
This tank is located in front wheelhousing,
between air springs. The tank may be installed
vertically depending on type of front suspension
and is provided with a bottom drain valve (Fig.
49 and 50).
It is recommended to purge the tank by its
bottom drain valve, every 12,500 miles (20 000
km) or once a year, whichever comes first.
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