GMC 1976 ZEO 6083 Maintenance Manual page 189

SHOCK ABSORBERS
See Section 3A "FRONT SUSPENSION" for
trouble diagnosis of shock absorbers .
HEIGHT CONTROL VALVE AIR
LEAKAGE CHECK
NOTE : Air leakage check can be performed for
air line connections, only when valve is installed
on vehicle . The following instructions explain
procedure for performing air leakage check on
valve when removed from vehicle .
1 . Clean exterior of valve assembly .
2 . Connect air pressure line to air inlet port, then
open the air pressure (90-120 psi) .
3 . Submerge valve assembly in a container of
water, then watch for air bubbles when the valve arm
is in center (neutral) position . No air should escape
from any point of valve assembly .
REAR SUSPENSION 4- 5
4 . If bubbles appear from the bellows port, this
is an indication the air inlet valve assembly is defec-
tive and must be replaced .
5 . Remove air pressure line from air inlet fitting
and connect it to the bellows port . If bubbles appear
at the air inlet check valve port, this is an indication
that check valve unit is defective and must be re-
placed .
6 . If bubbles appear at the exhaust port it is an
indication the exhaust valve assembly is defective
and must be replaced .
7 . If bubbles appear around edge of valve cover
plate, the cover plate gasket must be replaced .
8 . If no leaks are detected, remove valve assembly
from water, then with air pressure still connected to
bellows port, actuate valve arm to expel any water
which may have entered exhaust valve chamber .
Remove air line and connect it to air inlet port and
repeat operation to remove water from air inlet valve
chamber.
REAR SUSPENSION TROUBLE DIGNOSIS CHART
Problem Possible Cause Correction
No air pressure in air 1 . Open circuit breaker .
1 . Find cause of circuit breaker
reservoir-unit not
being "OPEN" and correct it .
Aerating .
Circuit breaker is located behind
the glove box door .
. Faulty wiring. 2 . Check to see that wiring is
intact .
. Low battery . 3 . The compressor runs off the
automotive battery, check its
condition and correct as
necessary .
. Faulty or pitted contacts
4 . Replace pressure switch .
n pressure switch .
. Motor has developed an
5 . Motor brushes or commutator
pen circuit .
worn out. Replace motor .