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BRAKES
5 - 1 3
Fig. 7 Master Cylinder Bleeding—Two-Section
Cylinder Shown
(5) Connect front and rear b r a k e l i n e s t o cylinder.
S t a r t brakeline fittings b y h a n d .
(6) T i g h t e n brakeline f i t t i n g s t o 19 N - m (170 i n -
lbs).
(7) Bleed brakes.
COMBINATION VALVE OPERATION
METERING
(HOLD-OFF)
VALVE
The m e t e r i n g valve is used t o balance brake action
between t h e front disc a n d r e a r d r u m brakes. T h e
valve meters (holds-off) f u l l apply pressure t o t h e
front disc brakes u n t i l the rear brakeshoes are i n f u l l
contact w i t h t h e drums. T h e valve is designed t o
m a i n t a i n f r o n t brake f l u i d pressure a t 3-30 psi u n t i l
t h e hold-off l i m i t of 117 psi is reached. A t t h i s p o i n t ,
t h e m e t e r i n g valve opens completly p e r m i t t i n g f u l l
f l u i d apply pressure t o the f r o n t disc brakes.
PRESSURE
DIFFERENTIAL
SWITCH AND
VALVE
The pressure differential s w i t c h is connected t o t h e
brake w a r n i n g l i g h t . The s w i t c h i s triggered b y
movement o f t h e switch valve. T h e purpose o f t h e
switch is t o monitor fluid pressure i n t h e separate
front/rear brake h y d r a u l i c circuits.
A decrease or loss o f f l u i d pressure i n either h y -
draulic circuit w i l l cause the s w i t c h valve to s h u t t l e
forward or r e a r w a r d i n response t o a pressure differ-
e n t i a l . Movement of the s w i t c h valve w i l l push t h e
switch plunger upward. This closes t h e switch i n t e r -
n a l contacts completing the electrical circuit t o t h e
w a r n i n g l i g h t . The switch valve w i l l r e m a i n i n a n
actuated position u n t i l repair restores system pres-
sures t o n o r m a l levels.
COMBINATION VALVE TESTING
TESTING
METERING
VALVE
M e t e r i n g valve operation can be checked v i s u a l l y
and w i t h t h e a i d of a helper. Observe t h e m e t e r i n g
valve stem w h i l e a helper applys a n d releases t h e
brakes. I f t h e valve i s operating correctly, t h e stem
w i l l extend s l i g h t l y w h e n the brakes are applied and
retract w h e n the brakes are released. I f the valve is
faulty, replace the e n t i r e combination valve as a n as-
sembly.
TESTING
PRESSURE
DIFFERENTIAL
SWITCH
(1) Have a helper s i t i n the drivers seat to observe
the brake w a r n i n g l i g h t a n d apply the brake pedal.
(2) Raise the vehicle o n a hoist.
(3) Connect a bleed hose t o one o f the rear wheel
cylinders a n d immerse t h e hose end i n a container
p a r t i a l l y f i l l e d w i t h b r a k e f l u i d .
(4) Have the helper press and hold the brake pedal
a l l the w a y down a n d observe the w a r n i n g l i g h t .
(a) I f the w a r n i n g l i g h t i l l u m i n a t e s , the switch
is operating correctly.
(b) I f the l i g h t fails to i l l u m i n a t e , check the cir-
cuit fuse, b u l b and w i r i n g . Repair as necessary and
repeat test steps (3) a n d (4).
(5) I f t h e w a r n i n g l i g h t s t i l l fails to i l l u m i n a t e ,
check the b r a k e l i g h t a n d p a r k i n g brake switches and
w i r i n g w i t h a test l a m p . Repair or replace parts as
necessary and test d i f f e r e n t i a l pressure switch oper-
ation again.
(6) I f t h e w a r n i n g l i g h t s t i l l does not i l l u m i n a t e ,
the switch i s f a u l t y . Replace t h e combination valve
assembly, bleed t h e b r a k e system and verify proper
switch and valve operation.
COMBINATION VALVE REMOVAL/INSTALLATION
VALVE
REMOVAL
(1) Raise t h e vehicle o n a hoist.
(2) M a r k or t a g t h e brake lines connected t o t h e
valve for assembly reference.
(3) Disconnect the lines a t the valve (Fig. 8).
(4) Disconnect the wires f r o m the differential pres-
sure switch.
(5) Remove t h e bolts a t t a c h i n g the valve to frame
bracket and remove t h e valve.
(6) M o u n t t h e n e w valve
on t h e bracket a n d
t i g h t e n the valve a n d bracket screws/nuts securely.
(7) Connect the brakelines t o t h e valve. T i g h t e n
the f i t t i n g s t o 16 N*m (145 in-lbs)
(8) Connect t h e wires t o t h e pressure differential
switch t e r m i n a l .
(9) Bleed the brakes.
(10) Lower the vehicle and verify proper brake op-
eration.
BRAKE LINES AND HOSES
BRAKE LINE AND HOSE
INSPECTION
Flexible rubber hose is used at both front brakes
and a t the rear axle j u n c t i o n block. Inspect the hoses
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