GMC 1976 ZEO 6083 Maintenance Manual page 186

4- 2 REAR SUSPENSION
Figure 2-Air Compressor Location (Brown)
AIR BELLOWS
The air bellows are mounted between the control
arms, for the tandem rear wheels . On each side of the
air bellows is a piston which is connected directly to
the control arm.
AIR COMPRESSOR
Compressed air for the system is supplied by an
electric compressor which operates when the ignition
key is in the "ON" or "ACCESSORY" position . It
is a demand-type compressor which will start com-
pressing air when the pressure in the system drops
below 100 psi, and will shut off when the pressure
reaches 120 psi. Air compressor for the system is
located behind the left-front access door . There are
two models used, a single piston Brown Compressor,
(figure 2) and a double piston Dana (figure 3) .
AIR RESERVOIR
.
The purpose of the air reservoir is to provide a
place to store compressed air for the-rear suspension .
The reservoir is located behind the left front access
door . The reservoir allows the rear suspension to
adjust without the air compressor operating.
Another purpose of the reservoir is to provide a
place where the air, heated during compression, can
cool and the water vapor can condense . Drain .reser-
voir monthly.
AIR BELLOWS
The air bellows serve as a flexible connection
between the two control arms on each side of suspen-
sion bracket. The flexing of the air bellows allows the
control arms to move up and down in relation to the
frame . This action absorbs road shocks in the same
manner as an inflated rubber tire cushions shock
caused by road roughness.
SHOCK ABSORBERS
A double acting shock absorber is used at each
wheel on the rear suspension . The shocks are
mounted to the top of the control arms and to the
frame at the bottom .
The shock absorbers are gas filled cell type
shocks . They are filled with a calibrated amount of
fluid and sealed during production . They are non
adjustable, non-refillable and cannot be disassem-
bled . The only service they require is replacement if
they have lost their resistance, are damaged or leak-
ing fluid.
HEIGHT CONTROL VALVE
(FIGURE 4)
Height control valve automatically maintains a
constant vehicle height by controlling the flow of
compressed air into or out of suspension system air
bellows. A delay piston in each valve provides a mo-
mentary delay in intake and exhaust valve action .
Therefore, air in bellows is exhausted only during
load changes and not during intermittent road
bumps.
Figure 3-Air Compressor Location (Dana)