BRAKES
18.
TWIN
BORE
MASTER CYLINDER
19.
Description
This unit consists of a body which has two
identical bores, one connected to the brakes
and the second to the clutch. Each of the
bores accommodates a piston having a rubber
cup loaded into its head by a return spring
;
in order that the cup shall not tend to be
drawn into the holes of the piston head, a
piston washer is interposed between these
parts. At the inner end
of
the bore connected
to the brakes, the return spring also loads a
valve body, containing a rubber cup, against
a valve seat; the purpose of this check
valve is to prevent the return to the master
cylinder of fluid pumped back into the line
whilst bleeding the
br& system, thereby
ensuring a charge of fresh fluid being de-
livered at each stroke of the brake pedal
and a complete purge of air from the
system.
During normal operation, fluid returning
under pressure and assisted by the brake
shoe pull-off springs, lifts the valve off
its seat, thereby permitting fluid to return
to the master cylinder and the brake shoes
to the
"
off" position.
There is
no check valve fitted
in
the
bore connected to the clutch,
this
precludes the risk of residual line pressure
which would tend to engage the clutch, or
keep the ball release bearing in contact with
the release levers.
The by-pass ports, which break into each
bore, ensure that the systems are maintained
full of fluid at all times
and allow full
20,
compensation for expansion and contraction
of fluid due to change of temperature.
They also serve to release additional fluid
drawn into the cylinder through the small
holes in the piston after a brake or clutch
application.
If
this additional
fluid
is not
released to the reservoir, due to the by-pass
port being covered by the main cup, as a
result of incorrect pedal adjustment, or
to the hole being choked by foreign matter,
pressure will build up in the systems and
the brakes will drag, or the clutch tend to
disengage.
TO REMOVE
MASTER CYLINDER
(a)
Drain hydraulic system of operating
fluid.
(h)
Remove the square panel under the
dash, which forms the rear wall of the
master cylinder pocket from inside the
car. Remove also the rubber grommet,
from the inside wall of the pocket, to
facilitate the withdrawal of the rear
master cylinder attachment bolt.
(c)
Disconnect the Bundy tubing from the
connections at the rear of the master
cylinder. Care must be exercised
when removing the clutch Bundy
tubing
;
this is connected first to
an adapter and then to the cylinder
body.
It
will be necessary to hold
the adapter with one spanner, whilst
loosening the Bundy tubing nut
with a second. The connection for
the brake operation is made direct to
the master cylinder.
(d)
Withdraw the clevis pins from the lever
push rod fulcrums by removing the
split pins, plain washers and double
coil spring washers.
(e)
Remove the nuts, lock and plain
washers, from the master cylinder
attachment bolts and withdraw the
bolts, the rearmost one being passed
through the aperture in the wall of the
pocket into the car.
(f)
The master cylinder is now free to be
lifted from its support bracket. Empty
any fluid that may still be in the
reservoir.
TO
FIT
MASTER CYLINDER
(a)
Ensure that the connection adapter
is secure in the left-hand (clutch)
outlet of the master cylinder.
(b)
Place theassembly in themaster cylinder
support bracket, connections to the
rear, and secure at the front end, with
the attachment bolt and washers, but
leave the nut finger tight at this
juncture.
(c)
The rear attachment bolt is fed in from
inside the car, through the aperture
in the pocket
wall.
This bolt passes
through two adjustment brackets, one
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