Triumph TR6 - Vacuum Servo Unit Function

REGULAR
MAINTENANCE
HYDRAULIC
SYSTEM
Description
The
foot
operated hydraulic
braking
system
employs
a tandem
master
cylinder
for
transmitting
pressure to independent
front
and rear braking
systems.
L.H. Steering Cars
only
Both systems
are connected
to opposing
sides
of
a pressure
differential warning
actuator
(P.D.W.A.)
which
operates
an
electrical
switch when
a pressure
drop on
one
side of the valve
causes a shuttle to
move
from
its
mid-position.
The P.D.W.A.
switch operates a rvarning light
on
the
facia
(Fig.
2)
which is
series/parallel connected with
the
oil warning light.
Thus
when
the brakes
are
working
correctly,
the brake
warning light
and
the
oil
warning light
are both
extinguished
as the engine
speed
is increased from idle
(giving
regular
assurance
that the
biake
warning
light
is functioning).
In
the
event
of
a partial brake
failure the brake warning
system is
earthed
directly,
causing the
warning light to
glow brightly.
Bleeding
the
Hydraulic
Braking
System
General
If air has entered
either
of
the hydraulic
braking
systems then
onlyLhe system affected
need
be bled.
(L.H.
steering
cars-During
bleeding, exercise
care,
as
described
in
the following
procedure,
to avoid
moving
the
shuttle from
its
mid-position.
F{owever,
if the shuttle
has moved
during
bleeding
or subsequent
to
a
fault
condition,
centralise the
shuttle
by
performing
operations
5
-
9 below).
Preparation
for Bleeding
Before
commencing
to
bleed the brakes
ensure that
all
the
bleed
nipples
(Figs.
81
and 83)
are clean and, taking
care to
avoid
dirt
entering the fluid
reservoir,
remove its
filler
cap and top-up
with
new hydraulic fluid.
During
the
bleeding
operation
keep
the
level
of
fluid
above the
dividing partition
in
the
reservoii.
Do
not
use
fluid
bled from
the
system for
topping-up.
Use
only
new fluid
from
a sealed
container,
re-sealing
the
container
after
use.
Procedure
Commence with the
brake,
of the
pair
being bled, farthest
from
the master
cylinder. If
both
systems
are to be bled,
bleed
the rear brakes first.
When
bleeding the
rear
brakes, release
the handbrake
and turn the
brake adjusters
to
lock
the
shoes
against
the
drums. When
the bleeding is
completed
adjust
the
brakes
as detailed
on page 58.
1. Attach
a
rubber
tube of approx.
i"
(6
mm.)
bore
to the
brake
bleed nipple
allowing the other
end of the
tube
to hang
submerged in
a
jar
containing
a
quantity
of
clean brake
fluid
2.
IJnscrew the
bleed-screw
enough to
allow the fluid
to
be
pumped out
(half
a
turn is
normally
sufficient).
59