p
BRAKES
be either a defective master cylinder or the use of
low grade brake fluid which has expanded because
of heat. Use standard duty brake fluid conforming to
SAE-J1703
specification.
P-7.
Bleeding
Brakes
The
hydraulic
brake system must be bled whenever
a
fluid line has been disconnected or air
gets
into the system. A leak in the system may sometimes
be indicated by the presence of a spongy brake
pedal.
Air trapped in the system is compressible
and
does
not permit the pressure, applied to the
brake
pedal, to be transmitted solidly through to
the brakes. The system must be absolutely free
from
air at all times. When bleeding brakes, bleed
at that wheel with the
longest
line from the master
FIG.
P-5—BLEEDING
BRAKES
1—Bleeder
Screw
cylinder
first, the next
longest
second, etc. During
the bleeding operation the master cylinder must
be kept at least %
full
of hydraulic brake fluid.
To
bleed the brakes, first carefully clean all
dirt
from
around the master cylinder filler plug. If
bleeder tank is used follow the manufacturers in
structions.
Remove the filler plug and
fill
the master
cylinder
to the lower
edge
of filler neck.
Clean
off
all
bleeder connections at all four wheel cylinders.
Attach
bleeder
hose
and fixture to right
rear
wheel
cylinder
bleeder screw and place end of tube in a
glass jar, and submerged in brake fluid. Open the bleeder valve one-half to three-quarters of a
turn.
See
Fig.
P-5.
Depress the
foot
pedal, allowing it to return very
slowly. Continue this pumping action to force the
fluid
through the line and out of the bleeder
hose
which
carries with it any air in the system. When bubbles cease to appear at the end of the bleeder
hose, close the bleeder valve and remove the hose.
After
the bleeding operation at each wheel cylinder
has been completed,
fill
the master cylinder reser
voir
and replace the filler plug.
Do not re-use the liquid which has been removed
from
the lines through the bleeding process because
of air bubbles and
dirt.
P-8.
Brake Hoses
a.
Hydraulic
lines (tubing and hose) are the means
of transmitting fluid under pressure between the master cylinder and the wheel cylinders.
Note:
On
some
vehicles a proportioning valve is
located in the
rear
brake line along the inside left
frame
side
rail.
The valve is not serviceable and
must be replaced as an assembly.
Should
replacement be necessary make certain the valve is properly positioned with the centerline of
the hex plug (in the bottom of the valve) in the
vertical
position. Refer to Fig. P-l.
The
hoses
are the flexible links between the wheels
or
axles and the frame or body. The
hoses
must
withstand
the fluid pressures without expansion
and
must be free to flex during spring deflection
and
wheel turns without causing damage to the
hose.
b.
Hydraulic
lines are subject to damage and
deterioration. Hoses should be inspected for cuts,
chafing,
cracks,
twists and
loose
frame supports.
Hydraulic
tubing should be inspected for signs of
leakage (due to faulty flares or
loose
connections);
restrictions
(due to dents or corrosion); and wear (due to friction against other metal parts). Always
use correct type and size of wrench on fittings.
Avoid
damage to female fittings by supporting fit
ting with tube nut during removal of assembly.
c.
On fittings where gaskets are used, always use
a
new gasket. Copper gaskets take a set and may
not form a
good
seal if reused.
d.
When replacing hydraulic brake hose, attach
hose
to wheel cylinder and securely tighten hose,
then attach
opposite
end to frame fitting or tubing.
Avoid
twists in
hose
when assembling to frame fitting
or
tubing. Hold
hose
end securely with
wrench
while attaching tubing to hose. If
hose
end
clip
is used, make certain clip is assembled properly.
Check
for interference during spring deflection or
rebound and during front wheel turns.
e.
Check
for any possible contact between front
brake
hose
and inner sidewall of tire when the front
wheels are in maximum
turn
position.
Check
for sufficient but not excessive length of
hose
between
the clamp and the wheels by turning the wheels
from
one extreme
turn
position to the otherl
f.
Check
that there is no possibility of any contact between the
tail
pipe and
rear
brake
hose
under
all
operating conditions.
P-9.
Brake Pedal Adjustment
There
should always be at least W [12,7 mm.]
free pedal travel before the push rod
engages
the master cylinder piston.
This
adjustment is accomplished by shortening or 326
