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A warning valve is located between the master cylin-
der and the brake lines for both the circuits. The
valve is
connected to
the same warning lamp which
indicates when the
handbrake is
applied. The
lamp
will
light
during
brake
application
if there is too
larg
e
a
pressure difference (about 10 kg/cm
2
=
142
Ib/sq.in.)
between the two brake
circuits.
When the
press ure in the master cylinder rises as a result of
brake
appl ication,
the
pistons are displaced and
press
the
lin
ing pads against the rotating friction
surface of the brake disc,
see
Fig. 5-12.
The
pressure
applied, and thus the brake effect, varies in propor-
tion to the foot effort applied to the pedal. When
the pistons are displaced, the
sea
ling
rings
are ten-
sioned
lateral/y.
They remain
in this
state as
long
as the
footbrake
is
applied.
When the brake pedal
is
released,
the pistons are
relieved of
hydraulic
pressure.
Since
there is no residual hydraulic pressure
in
the
system
lin
e
,
the tension in the
sealing
rings is
sufficient to move t·he pistons
back
to
a certain ex-
tent, see
Fig.
5-11.
The return movement forms the
c1earance between -j-he brake
lining
s
and the brake
_
Secondary circuit,
pressure above
34 kg /cm
2
(484 Ib/sq .in.
)
Secondary circuit,
reduced
pressure
f
-
Primary circuil,
pressure above
34
kg /cm
2
(484
Ib/s
q.in
.)
Primary circu it,
reduced pressure
Fig. 5-12. Brake application
disc. This means that, in the rest position, the brake
linings
are always at a certain distance from the
brake
disc
regardless
of
wear,
so
that
the
wheel
brakes
are se lf-ad
justing.
Shou
ld
leakage o
cc
ur in
one
of the
circuits,
full
braking
effecl'
is
still
obtained on both the front
wheels
and
one rear wheel if pedal pressure
is
in-
creased. Fig. 5-13 shows
how this operates when
leakage
occurs in the secondary
circuit.
When there
is
a pressure difference in the brake
circuits
of about
10 kg/cm
2
(1
42
Ib/sq.in.), the warning valve piston is
pressed over
to
the
side
with less pressure and the
warning
lamp
lights. The warning
lamp
wil/ remain
lighted until
the
leakage in the
circuit concerned
is
repaired.
A.S.B. DEVICE (REAR BRAKE
CALIPERS)
When the
brake
is released,
see Fig. 5-14,
there is
a
c1earance
A between
the brake pad and the disc
and a
lso
a c1earance B between the washer
and
the
spring. With brake application,
see
the figure, the
Secondary
circuit,
pressureless
_
Pri.mary cir-
cuil,
pressure
abo
ve
34 kg/
cm
2
(484
Ib/
sq.in.)
Primary cir-
cuit, reduced
pressure
Fig.
5-13.
Brake app
li
cat io
n,
leakage
in
secondary
circu it
5:9
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