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(249)
BRAKES
OPERATION
8-5
Figure 8-S-Master Cylinder-Settional View
e. Parking Brake Lever and Cables
The parking brake mechanism consists of a
foot operated lever and cables which operate
the rear wheel brake shoes only. The parking
brake lever, located on left side of body cowl,
will automatically lock when the release knob is
pushed forward and the lever is pushed for-
ward by foot to apply the brakes. The lever is
I
ing parts. See figure 8-5. A breather port (G)
and a compensating port (H) permit passage
of fluid between reservoir and cylinder barrel
under certain operating conditions. The reser-
voir is closed at the top by a gasket (B) and a
vented filler cap nut (C) containing a baffle
(E) to' prevent loss of fluid through the vent
holes (D).
The outlet end of the cylinder barrel is closed
by a head nut
(J)
and gasket
(I).
The opposite
end of cylinder barrel is closed by a stop plate
(L) through which a push rod (K) extends to
actuate the piston (0). The outer end of the
double-headed piston is provided with a rubber
cup (N) to provide a fluid-tight seal, and a
rubber boot (F) closes the end of the cylinder
barrel to exclude foreign matter. A check valve
(T) is held in place against a rubber washer
(U) on the head nut by a coil spring (R) which
also holds a rubber cup
(Q)
against the inner
end of the piston. See figure 8-5.
,
a. When Brakes are Released
When the brake pedal is in fully released po-
sition the master cylinder piston (0) is held
against the stop plate (L) by the coil spring
(R) which also holds the check valve (T)
against the rubber washer (U) on head nut
(J)
with sufficient pressure to maintain 6 to 8
pounds static pressure in. brake pipes and wheel
cylinders. With piston against stop plate the
compensating port (H) is not covered by the
piston primary cup
(Q)
and the breather port
(G) is also open, so that the cylinder barrel
(S) is completely filled with fluid from the
reservoir. See figure 8-5.
The static pressure maintained in the lines
and wheel cylinders is not sufficient to operate
the brake shoes, therefore the shoes are fully
released and held in contact with the anchor
pins by the brake shoe springs. See figure
8-3.
b. Application of Brakes
When the brake pedal is depressed to apply
service brakes, the push rod (K) forces the
master cylinder piston (0) and primary cup
(Q)
toward the head nut
(J).
As soon as the
primary cup covers the compensating port (H),
pressure is built up in the cylinder barrel (S)
and fluid is forced through holes in the check
valve (T) into the pipes leading to all wheel
cylinders. See figure 8-5.
The brake fluid enters each of the wheel cyl-
inders (fig. 8-4) causing the cylinder pistons
and connecting links to move outward and force
the brake shoes into contact with the drums.
This part of the brake action is accomplished
with very light pressure on the pedal. Since the
pressure must be equal in all parts of the hy-
8-3 OPERATION OF HYDRAULIC
SERVICE BRAKES
released by pulling the release knob on the
lever.
A conduit enclosed cable extends from the
parking brake lever to a sheave or equalizer lo-
cated near the rear end of torque tube. Another
cable runs through the sheave to the brake
lever in each rear brake assembly so that when
the parking brakes are applied the rear brake
cable applies equal pressure to the brake shoes
at both rear wheels. An adjustment to take up
slack is provided where the brake lever cable
passes through the brake cable sheave. A spring
attached to the sheave pulls the cables rear-
ward to assure full release when parking brake
lever is in released position. See figure
8-2.
l. STOP PLATE
M
.
LOCK RING
N
.
PISTON SECONDARY CUP
O. PISTON
P.
BLEEDER HOlES IN PISTON
Q
.
PISTON PRIMARY CUP
R. SPRING AND RETAINER
S.
CYLINDER BARREL IN BODY
T. CHECK VALVE
U. HEAD NUT WASHER
A
.
MASTER CYLINDER BODY
B. FILLER CAP GASKET
C.
FILLER CAP NUT
D.
VENT HOlES IN FILLER CAP NUT
E.
BAFflE IN FillER CAP NUT
F.
MASTER CYLINDER BOOT
G
.
BREATHER PORT IN BODY
H.
COMPENSATING PORT IN BODY
I.
HEAD NUT GASKET
J.
HEAD NUT
K.
PUSH ROD AND STOP
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