Chevrolet 70 1969 Series, Shop Manual

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POWER BRAKE 5-20
Clean in g, Inspection, an d Repair
W ash all m etal parts in cleaning solvent. Exam ine body
and cover for cracks or other dam age. Inspect exhaust
valve seat in cover; if seat is necked, chipped, or worn, re­
place cover. Rem ove slight scratches or scores from inner
surface of body with crocus cloth. If any part of the valve
carrier and inlet and exhaust valve assembly is scratched,
nicked, chipped, or worn, the com plete assembly must be
replaced.
ASSEMBLY
2. C oat cam surface and pin with a barium base grease.
Install control lever in body and secure with fulcrum
pin. Stake pin in place.
3. T urn body bottom side up and install valve disc, valve
spring, and cap nut, being sure new O -ring is in place
on cap nut. Tighten cap nut firmly.
4. After installing valve in vehicle, or using a test hook­
up, test valve for proper operation.
AIR VALVE OVERHAUL (Fig. 21)
(TILT CAB MODELS)
1. Install new O-rings in grooves in valve body, then
place valve carrier assembly in body.
2. Place new O-ring on body, then install cover, m aking
sure valve guide enters bore in cover. Install cap
screws and lock washers and tighten firmly.
3. A fter installing valve in vehicle, or using a test hoo k­
up, test valve as previously directed under “ Servicea­
bility Tests.”
TW O-W AY VALVE OVERHAUL (fig. 20)
DISASSEMBLY
1. Using a small drift, drive out fulcrum pin securing
control lever in valve body and remove lever.
2. Remove cap nut, O-ring, valve spring, and valve disc
from bottom of body.
3. Push against bottom of valve plunger to remove plun­
ger from top of body. Remove plunger spring from
body and remove O-ring from plunger.
C le an in g an d Inspection
W ash all m etal parts in cleaning fluid. Carefully ex am ­
ine small end of plunger which contacts valve; if any
roughness or dam age is evident, replace plunger. Inspect
valve seat in body; if seat shows wear or dam age, replace
body. Replace valve disc if any wear or dam age is evident.
Replace valve spring if weakened by rust or corrosion.
ASSEMBLY
1. Install new O-ring in groove in plunger and on cap
nut. C oat plunger with a barium base, place spring on
small end of plunger, and install plunger and spring in
top of body.
DISASSEMBLY
1. Unscrew knob from piston. If necessary, place punch
or rod through the hole in piston to prevent piston
from turning.
2. Rem ove two screw and washer assemblies holding
body end cap to body. S eparate cap and body. Lift
two piston springs fiom end of piston. Rem ove and
discard cap O-ring seal.
3. Push piston out of body. Rem ove and discard O-ring
seals.
Cleaning, Inspection, an d Repair
W ash all m etal parts in cleaning solvent. Exam ine body
and end cover for cracks or other signs of dam age. In­
spect piston surface and bore of body and cap. Inspect
seating surface of body and piston. Remove slight scratch­
es or scores with crocus cloth. Inspect piston spring and
replace if dam aged or broken.
ASSEMBLY
1. Install new O-ring seals in grooves in piston. C oat
p i s t o n a n d b o r e s w ith a m u l t i p u r p o s e g r e a s e
(N .L .G .I. num ber 1 with a rust inhibitor ingredient),
and insert piston, threaded end first, into body bore at
cover opening.
2. Install large and small springs in end of piston. Place
new O-ring seal in body groove. Install end cap and
align screw holes with threaded holes in body. Attach
end cap to body with two screw and washer assem ­
blies. Tighten firmly.
3. Install knob on valve piston. Tighten finger tight.
4. A fter installing valve in vehicle, test valve for proper
operation.
CHEVROLET SERIES 70-80 HEAVY DUTY TRUCK SHOP M ANUA L