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8-12
SERVICE-ADJUSTMENTS
BRAKES
(
256)
Air will be int r oduced into the hydraulic sys-
tem if the brake pedal is
operated
when the
fluid is too low in master cylinder reservoir,
Air will also enter the
system
whenever any
part of
hydraulic
system is disconnected.
It
will be necessary to bleed the hydraulic
system at all four
wheel
cylinders if air has
been introduced through low fluid level or by
disconnecting brake pipe at master
cylinder.
If
brake pipe is disconnected at any wheel cylin-
der, then that wheel cylinder only need be bled.
If
pipes
are
disconnected at any fitting located
between master cylinder and wheel cylinders,
then all wheel cylinders served by the discon-
nected pipe must he bled
.
See figure 8-2.
The following bleeding operation is performed
at one wheel cylinder at a time, to avoid get-
ting fluid level in reservoir dangerously low.
CAUTION: Do not perform bleeding
operation
while any brake drum is
removed.
1. Fill master cylinder reservoir with speci-
fied fluid
,
using Filler J 713 and Adapter J
713-2 (par. 8-8). Leave Filler J 713 in place
during all bleeding operations as it automati-
cally maintains the proper level in reservoir as
fluid is pumped out of master
cylinder.
Figure S-7-Bleeding Wheel Cylinder
2.
Remove screw and attach Bleeder Drain
Assembly J 628-A to
wheel
cylinder bleeder
valve.
Place
lower
end of
dra in
t
ube
in a clean
glass jar. Unscrew
bleeder va
lve three-quart er s
of a turn, using Bleeder Wrench J 627. See
figure 8-7.
3. Depress brake pedal a full stroke, then
allow pedal to return slowly to released posi-
tion. Allowing pedal to return quickly my dra~
air into
system.
Continue operating pedal in
this manner until fluid flows from drain tube
into glass jar in a solid stream
t
hat
is free
of
air bubbles.
4.
If
Filler J 713 is not used to
maintain
proper fluid level in master cylinder reservoir,
fill reservoir after each five
strokes
of brake
pedal. Approximately one-half pint of fluid is
required to bleed each wheel cylinder. Allowing
reservoir to be emptied will cause air to
be
drawn into hydraulic
system.
5. When bleeding operation is
completed,
close the bleeder valve
securely.
Remove
bleeder drain and install screw in valve.
6. When bleeding operation is completed at
all wheel
cylinders
where
needed, make
sure
that fluid level is
1J2"
to I
"
below top of master
cylinder filler opening then install filler plug
and
gasket.
See figure
8-5.
7.
Discard the brake fluid deposited in glass
jar during bleeding operation.
It
is poor
econ-
omy to attempt to clean fluid that has once
been used.
8. Test brakes
(par.
8-5 and 8-6).
8-10 FLUSHING BRAKE HYDRAULIC
SYSTEM
It
is recommended that the entire hydraulic
system be thoroughly flushed and cleaned ever y
15,000 miles, or whenever new parts
are
in
-
stalled in the hydraulic system, or new shoes
or linings are
installed.
Flushing is
also
r
ecom-
mended if there is any doubt as to
the
grade
of fluid in the system or if fluid has been used
which contains the
slightest
trace of mineral
oil.
G.
M.
Declene Flushing
Fluid,
Group
4.683,
is recommended as the most
satisfactory
flush-
ing and cleaning fluid.
If
Declene is not avail-
able, G. M. Super
No.9
Hydraulic Brake Fluid
or a good grade of alcohol may be used for
flushing.
Gasoline, ke
rosene,
or any other fluid
containing even a 'trace of mineral oil must
not be used as such fluids will cause
serious
damage to rubber parts.
One quart of fluid is required t
o
flush the
hydraulic system, and the
followin g
procedure
should be used:
1. Remove screws and attach Bleeder Drain
Ass
emblies
J
628A to bleeder
valves of
a
ll four
wheel cylinders. Place lower end of drain tubes
in clean glass jars. Unscrew bleeder valves
three-quarter of a turn, using Bleeder Wrench
J 627. See figure 8-7.
2.
Operate brake pedal full strokes to force
all fluid from system, then fill master cylinder
reservoir with Declene or other approved flush-
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