Chevrolet 10 Series 1970 Service Manual page 282

BRAKES 5-44
requ ired with the conventional (nonpower) hydraulic brake
system . The unit is mounted on the engine side of the
Inspection
1. Check vacuum line and vacuum line connections as
w ell as vacuum check v a lv e in front shell of pow er
unit fo r p ossib le vacuum loss.
2. Inspect a ll hydraulic lin es and connections at the
wheel cylin d ers and
hydraulic leaks.
3. Check brake assem b lies fo r scored drums, grease or
brake fluid on linings, worn o r glazed linings, and
make n ecessa ry adjustments.
4. Check the brake fluid le v e l in the hydraulic r e s e r ­
v o ir. The r e s e r v o ir should be fille d to within 1/2"
o f the top o f the f i lle r
r e s e r v o ir c o v e r fo r fluid leaks at gasket.
5. Check fo r loose mounting bolts at main cylin d er and
at pow er section.
7. Check brake pedal fo r bending and m isalignm ent
between pedal and push rod.
6. Check a ir clea n er f ilt e r located in the pow er piston
ex te n s io n --re p la c e filt e r i f n ecessary.
Vacuum pow er cylin d ers are used as standard equip­
ment o r are available as optional equipment on a ll 40-50-
60 s e r ie s ve h icle s with hydraulic brakes.
The tandem diaphragm unit is used with sin gle main
cylin der applications and in crea ses p ressu re to a ll wheel
brakes. Single diaphragm units are used on veh icles
with the dual brake system .
BLEEDING THE SYSTEM
Pressure Bleeding
Stop engine and d estroy
startin g bleeding operations.
1. Check brake fluid in m aster cylin der and fill.
2. Open pow er cylin d er b le e d e r scew and allow fluid to
run until c le a r o r fr e e fro m a ir bubbles.
3. Bleed a ll wheel cylin d ers until fr e e o f a ir bubbles
starting at the cylin d er n earest the pow er cylin der.
IM P O R T A N T : DO N O T
W H ILE ENGINE IS RUNNING, W ITH PRESSURE
B LE E D E R C ONNECTED OR POW ER U N IT M A Y
BE DAM AGED.
4. Disconnect p ressu re b leed er.
5. Apply brakes and check a ll lin es fo r leaks.
MAINTENANCE AND ADJUSTMENT
main cylin d er fo r possible
cap opening. Inspect the
VACUUM POWER BRAKE UNITS
(4 0 -5 0 -6 0 SERIES)
GENERAL DESCRIPTION
Two units are used on the
MAINTENANCE AND ADJUSTMENT
vacuum in system b efore
A P P L Y B R A K E S
fir e w all and connected to the brake pedal through an
au xilia ry le v e r and rod.
Lubrication
The M a ster-V a c pow er brake unit is lubricated at a s ­
sem bly and needs no further lubrication other than m ain­
taining norm al r e s e r v o ir
should be fille d as d escrib ed in this section, using only
recom m ended brake fluid.
Bleeding Instructions
The pow er system m ay be bled manually o r with a
p ressu re b leed er as outlined in this section.
Use only recom m ended brake fluid. Do not use pow er
a ssist while bleeding. The engine should not be running
and the vacuum r e s e r v e should be reduced to zero , by
applying the brake s e v e r a l tim es b efore
bleeding procedure.
A ir Cleaner Service
The a ir clea n er filt e r used with the p ow er brake unit
should be cleaned at lea st twice a yea r.
m ove a ir clean er elem ent and wash thoroughly in cleaning
s o lven t— allow elem ent to dry b efore rein stallin g.
veh icle, each one boosting the p ressu re in h alf o f the
sp lit system .
A m anifold check va lve is installed in the vacuum line
running fro m the engine intake m anifold to the front
cham ber of the booster unit.
F igu res 78 to 82 show the vacuum booster system and
parts. See the Overhaul Manual fo r
NOTE: If fir m pedal is not obtained - - start
engine - - apply brakes ligh tly and reb leed vacu­
um pow er brake unit.
M an u al Bleeding
Manual bleeding is s im ila r to pressu re bleeding except
that the brake fluid is fo rced through the lines by pumping
the brake pedal. An assistant is req u ired to pump the
brake pedal.
1. Start engine and pump brake pedal th ree tim es o r
until grea test pedal height is obtained--m aintain foot
pedal pressu re.
2. Slow ly open b leed er va lve on pow er cylin d er allow ing
pedal to tra v e l only 3/4 strok e. C lose pow er c y l­
inder valve.
fluid lev e l. The r e s e r v o ir
starting the
To clean, r e ­
s e rv ic e details.
CHEVROLET TRUCK SERVICE MANUAL