Sunbeam ALPINE I SERIES: APLINE II SERIES, Workshop Manual

Page: 287 / 413

5th re-Issue
,.,..
WSM.124
Sutlort K ( ....... )
RAPIER
MASTER CYLINDER
Description (See fig. 18)
The master cylinder Is situated under the bonnet
on the bulkhead, Immediately In front of the brake
pedal. It consists of a fluid reservoir soldered to a
cylinder body, containing a piston, seals and other
parts as illu.strated in Fig. 18.
On depressing the foot pedal, the push rod (11)
moves the piston (9) down Its bore. The displaced
fluid In front of the piston is forced through holes
In the check valve (4), lifting the rubber seal clear
of the holes to provide an unblocked passage to the
wheel cylinders. On releasing the brake pedal the
return spring (S) thrusts the piston (9) back against
Its stop faster than fluid Is able to return from the
wheel cylinders. This creates a partial vacuum In
the cylinder, which causes fluid to be drawn past
the lip of the main cup (7) from the reservoir via the
main port (A) and the small holes In the head of the
piston (9). Meanwhile fluid returning from the
wheel cylinders lifts the check valve (4) away from
its seat and re-enters the master cylinder.
When the piston has fully returned, a small by-pass
port (B) Is uncovered which allows release of excess
fluid to the reservoir, and also compensates for
contraction and expansion of the fluid due to
changes In temperature.
The purpose of the check valve (4) Is to prevent the
re-entry Into the master cylinder of fluid pumped
Into the line during the "bleeding" operation; this
ensures a fresh charge of fluid at each stroke of the
pedal.
To remove
Disconnect the metal fluid pipe from Its connection
at the front of the cylinder by unscrewing the union
nut, collecting any escaping fluid In a suitable
container.
Disconnect the push rod from the brake pedal by
removing the clevis pin.
Remove the two bolts securing the master cylinder
to the bulkhead.
The master cylinder can now be removed by easing
It forwards.
To refit
Refitting Is a reversal of the above instructions.
Care should be taken not to over-tighten the feed
pipe union nut. (See under "Maintenance" for
torque figure).
After refitting, the brakes should be bled as des­
cribed under "Bleeding the system".
To dismantle (See fig. 18)
Remove the master cylinder from the car as
previously described.
Remove the filler cap (1) and drain the brake fluid
Into a clean container.
Depress and withdraw return spring cap to release
return spring.
Detach the rubber boot (13) from the end of the
barrel.
Depress the push rod to relieve the load of the
spring (5) and remove the clrclip (12).
Remove the piston (9), piston washer (8), main cup
(7), retainer (6), return spring (5), and check valve
(4). The removal of the main cup may be simplified
by applying gentle air pressure to the pipe con­
nection at the end of the barrel.
Remove the secondary cup (10) by stretching It
over the end flange of the piston (9).
To reassemble (See Fig. 18)
It Is Important that all parts are meticulously
cleaned with brake fluid before reassembly. Do not
use petrol, trlchlorethylene or any other similar
cleaning agents to wash the parts.
flt the secondary cup (10) onto the piston (9) so
that the lip of the cup faces towards the head
(drilled end) of the piston. Gently work the cup
round the groove with the fingers to ensure that It
Is properly seated.
Flt the spring retainer (6) onto the small end of the
spring (5) and the check valve (4) Into the large end.
Insert the spring assembly Into the cylinder bore,
large end first.