Chevrolet 70 Series 1970, Service Manual

Page: 265 / 841

REAR SUSPENSION 4-52
connections with a soap and w ater solution for leak s.
No leakage is p e rm issib le .
PRESSURE REGULATING VALVE
P r e s s u r e regulating valve (fig. 5) is mounted
on fra m e n e a r a ir tank. T his valve se rv e s two p u r ­
p o se s. One p u rpose is to p revent a ir p re s s u r e
fro m entering a ir suspension sy stem until p r e s ­
su re in the a i r sy ste m re ach e s 65 p s i. T his p r o ­
vides a rap id build-up of a ir p re s s u r e fo r o p e r­
ation of b ra k e sy stem . When b rake sy stem a ir
p re s s u r e exceeds 65 p si, the p re s s u r e regulating
valve opens and allow s p re s s u r e to build up in a i r
suspension sy stem . The second purpose of the
valve is to p re v en t lo ss of b ra k e sy stem a ir p r e s ­
su re below 65 p si due to leakage in a i r suspension
sy stem .
SERVICEABILITY TESTS
O perating T est
1. Exhaust p re s s u r e from sy stem by opening
dra in cock at a ir tank. C lose d ra in cock when a ir
is expelled.
2. Connect a te s t a ir p re s s u r e gauge in brake
sy ste m , p re fe ra b ly in the line leading from a ir
tank to p re s s u r e regulating valve.
3. D isconnect the a ir line that leads to height
control valve.
4. Build up p re s s u r e in sy stem and note p r e s ­
s u re on te s t gauge at the sam e tim e valve opens
and discharge a i r through open line.
5. A djust valve if p r e s s u r e v a rie s 5 p si from
the o rig in al setting (65 p si).
Leakage T est
R efer to fig u re 5 fo r a detailed c ro s s section
of valve.
With a i r line s till disconnected that lead s to
height control valve, build up a ir p re s s u r e to a
point ju st below valve setting (65 p si). Coat open­
ing of disconnected fitting on valve with soap and
w ater solution to check fo r leakage. Also apply
soap solution to vent opening in valve cover.
No leakage is p e rm issa b le at vent opening in
valve cover. Leakage at th is point indicates worn
o r d irty in tern a l p a r ts and should be disassem b led
and overhauled a s d escrib ed la te r in th is section.
ADJUSTING PRESSURE SETTING
NOTE: Key num bers in following text r e fe r to
fig u re 5. The adjusting cap (9) controls the p r e s ­
s u re a t which the valve is unseated. Setting may be
in c re a se d o r d e c re a se d by turning cap.
1. Back off lock nut (10).
2. T urn cap (9) clockw ise to in c re a s e p re s s u r e ,
o r counterclockw ise to d ec rea se p r e s s u r e .
3. Tighten lock nut (10) when c o rre c t a d ju st­
m ent is obtained.
DISASSEMBLY
NOTE: Key num b ers in following text r e f e r to
fig ure 5.
Rem ove cap (9), sp rin g (11), p isto n (1), then
rem ov e O -rin g (8) fro m valve body (5). Holding
p isto n assem b ly (1), push valve stem (4) upw ard
to rem ove piston plug (2) from p isto n (1). Com ­
p r e s s valve sp rin g (12) to rem ove valve guide (7)
by p rying off valve (6) fro m valve stem (4).
INSPECTION
NOTE: Key n um b ers in following text r e f e r to
fig u re 5.
C lean a ll p a r ts thoroughly, using a su itab le
cleaning solvent. Exam ine pisto n (1) fo r c ra c k s o r
w e ar. Inspect valve se a t in valve body (5). If sea t
is p itted, sc ra tc h e d , o r chipped, re p la c e the body.
If O -rin g s a r e worn o r hardened fro m age, re p la ce
them .
ASSEMBLY
NOTE: Key n um b ers in following tex t r e f e r to
fig u re 5.
In s e rt O -rin g (8) into valve body (5). In s e rt
valve ste m (4) into pisto n (1). B a c k u p valve stem
w ith a sm all tool so sufficient fo rce can be ex erted
to co m p re ss valve sp rin g (12) and po sitio n valve
guide (7). P u sh end valve (6) onto knob of valve
stem which w ill se rv e to re ta in th ese p a r ts a s an
asse m b ly . L u b ricate insid e of valve body with a
sm all am ount of bariu m b ase lu b rican t and in sta ll
p isto n assem b ly into b o re of valve body. In stall
p isto n plug (2) followed by sp rin g (11). T h re ad ad­
justing cap down until sp rin g can be fe lt c o m p re s s ­
ing. Set valve adjustm ent a s d irec ted previously
un der "Adjusting P r e s s u r e S etting.”
HEIGHT CONTROL VALVES
DESCRIPTION
Height control valve autom atically m aintains
a constant vehicle height by controlling the flow of
c o m p re ssed a i r into o r out of suspension sy stem
a i r bellow s. One height control valve is u sed at
fo rw ard r e a r axle of the tandem s e r ie s . A delay
pisto n contained in each valve p rov id es a m om en­
ta ry delay in intake and exhaust valve action; th e re ­
fo re , a i r in bellow s is supplied o r exhausted only
during load changes and not during in te rm itte n t
ro ad bum ps.
The height control valve contains an intake
valve, a i r bellow s outlet, exhaust valve, delay p is ­
ton, and o v e rtra v e l con trol body. The o v e rtra v e l
co ntro l body contains a sp rin g -lo ad e d nylon piston
which p ro te c ts valve p a r ts if o v e rtra v e l le v e r is
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL