GMC 1976 ZEO 6083 Maintenance Manual page 208

4- 24 REAR SUSPENSION
0.100" for each revolution of indicator needle,
then proceed with valve lever gap adjustments
following:
AIR INTAKE AND EXHAUST VALVE
LEVER ADJUSTMENTS
IMPORTANT : Before making these adjustments
the overtravel lever must be centered as ex-
plained previously.
Two methods of adjustment are available:
1 . Using Both Air Pressure and Vacuum .
NOTE : If vacuum source is available, this
method will take less time to perform adjust-
ment . Vacuum source is used to make the ex-
haust valve lever gap check only .
2. Using Air Pressure Only .
NOTE : When this method is used, it will take
longer to perform adjustments as the valve cover
must be in place each time air pressure is applied
and then removed to permit adjustment of ex-
haust valve lever.
Method Using Air Pressure and Vacuum
1 . If air supply and vacuum lines were not con-
nected to control valve assembly as directed previ-
ously when centering valve overtravel lever, connect
lines.
2. Apply air pressure and regulate it to 80 to 110
psi . Apply vacuum and regulate it at approximately
15 incbes .
3 . Move overtravel lever fore and aft several
times and then back to true center position .
4. Starting at true center position, slowly move
lever to where air intake valve just begins to open .
Listen for escaping air. Note reading on dial at this
point. Reading should be 0.025" to 0.027" from lever
center position . Bend lever to correct setting. Refer
to Figure 53 .
5 . Return overtravel lever to center position .
Slowly move lever to exhaust side find at same time
note the vacuum gauge reading. When vacuum just
begins to fall off, the exhaust valve has opened . Valve
should open when overtravel lever is moved 0.035"
to 0.037" from center position . On both front and
rear control valves, bend lever to correct setting .
Refer to`Figure 53 .
From Center Position
0 .025"-0 .027" Intake
0 .035"-0 .037" Exhaust
Figure 53-Method of Adjusting Air Valve Lever Gaps
6. Recheck intake and exhaust valve lever gaps,
then proceed with "TIME DELAY CHECK" ex-
plained later.
Method Using Air Pressure Only
ure 53 .
NOTE : This method may be performed when a
vacuum source is not available.
1 . Connect air supply hose (80 to 110 psi) to air
inlet port (figure 50).
2. To adjust air intake valve lever gap:
a. Move the overtravel lever slowly from true
center position to point where intake valve just be-
gins to open. Listen for escaping air. Note reading to
dial at this point which should register 0.025" to
0.027" .
b. Bend lever to correct setting. Refer to Fig-
3. To adjust air exhaust valve lever gap:
a. Install valve cover on the valve using the
rubber gasket and four attaching screws .