Chevrolet 70 Series 1970, Service Manual

Page: 268 / 841

REAR SUSPENSION 4-55
position without causing valve action. T his com pen­
sa te s fo r sm a ll ro ad bum ps. The bum ps a r e ab­
so rb ed by tir e s and bellow s without causing m ove­
m ent of co m p ressed a i r e ith e r into o r out of s u s ­
pension system .
H ydraulic Delaying Action
O peration of delay piston (fig. 7) in height
contro l valve p re v en ts change of bellows a ir p r e s ­
s u re a s a re s u lt of m om entary road shocks, con­
s e rv e s a ir supply, and adds life to valve. The nylon
piston moves inside cylinder containing a silicone
type fluid. A flap p er valve on eith er end of piston
allow s displacem ent of fluid o r a c ts a s a check
valve, depending on direction piston m oves. Delay
p iston is moved by p isto n pin (fig. 7), that is th re a d ­
ed into o v e rtra v e l shaft. A 2 to 9 second delay r e ­
su lts from the closing of one valve to the opening
of o th er valve.
O v e rtrav e l pisto n (re fe r to fig. 7) is held
again st flat side of o v e rtra v e l shaft by two sp rin g s
inside piston. P isto n keeps o v e rtra v e l shaft in
p ro p e r position re la tiv e to o v e rtra v e l le v e r. P isto n
a lso allow s o v e rtra v e l le v e r to ro ta te through a
com plete c irc le , if n e c e ssa ry , without damaging
p a r ts inside valve.
HEIGHT CONTROL VALVE REMOVAL
B efore disconnecting any height control valve
a i r lin e s, sec u rely support fra m e by placing blocks
between fra m e and ax les. Exhaust a i r fro m a ir
supply sy stem by opening d rain cock on a i r tank.
A fter the above p re cau tio n s have been taken, r e ­
move height control valve a s follows:
1. D isconnect height control valve o v e rtra v e l
le v e r fro m valve link. P u ll le v e r downward and hold
s e v e ra l seconds to overcom e tim e delay feature;
th is w ill re le a s e co m p re ssed a ir fro m bellow s.
2. D isconnect a i r supply line and bellow s a ir
line from height control valve. Tape ends of lin es
to prev en t foreign m a te ria l entering.
3. Remove two bolts, nuts, and flat w a sh ers
attaching height control valve to mounting b rack et
and rem ove valve assem b ly .
HEIGHT CONTROL VALVE
INSTALLATION
B efore in stallin g height control valve a s s e m ­
bly, se e that a ir line fittings a r e clean and undam ­
aged. R eplace line connector ru b b er s e a ls if de­
te rio ra te d o r damaged.
NOTE: DO NOT USE SEALING COMPOUND
ON THREADS. S ealer is u n n ecessary , and if used,
may cause valves to stick . Absolute clean lin ess is
e sse n tial when in stallin g height control valves.
D irt and sealing compound m ust be kept out of
valves. Even m inute p a rtic le s of foreign m a tte r
may becom e lodged in valve c o re s o r flapp er
valves and may se rio u sly affect operation of s u s ­
pension system .
1. P ositio n height control valve at mounting
b ra c k e t. A ttach with two bo lts, nuts, and flat w ash­
e r s and tighten to to rq u e lis te d in "S pecifications”
at end of th is sectio n.
2. Connect a ir supply line to intake check
valve ad a p te r. Connect bellows a i r line to outlet
a d a p te r. Tighten a i r line connector nuts firm ly .
3. Connect height control valve o v e rtra v e l
le v e r to valve link. B uild u p a i r p r e s s u r e i n sy stem
and te s t for leak s. Check rid e height dim ension
and adjust if n e c e ssa ry .
HEIGHT CONTROL VALVE
AIR LEAKAGE CHECK
NOTE: A ir leakage check can be pefform ed
fo r bellows mountings and a i r line connections only,
when valve is in stalle d on vehicle. The following
in stru ctio n s explain p ro c ed u re fo r p erfo rm in g a ir
leakage check when valve assem bly is rem oved
fro m vehicle.
1. Clean e x te rio r of valve assem b ly .
2. Connect a ir p r e s s u r e line to a ir inlet p o rt
(fig. 8), then open the a ir p re s s u r e (80-110 psi).
3. Subm erge valve assem bly in a co ntainer of
w a te r, then watch fo r a ir bubbles when the o v e r­
tra v e l le v e r is in ce n te r (neutral) position. No a ir
should escape fro m any point of valve assem bly.
4. If bubbles ap p ear from the bellow s p o rt,
th is is an indication the a i r in let valve assem bly
is defective and m ust be rep laced .
5. Rem ove a ir p re s s u r e line from a ir inlet
fitting and connect it to the bellow s p o rt (fig. 8). If
bubbles ap p ear at the a ir inlet check valve p o rt, th is
is an indication that check valve unit is defective
and m ust be rep laced .
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL