ABS DODGE TOWN AND COUNTRY 2001 Owner's Guide

BRAKE FLUID LEVEL SWITCH
DESCRIPTION
The brake fluid level switch is located in the brake
fluid reservoir of the master cylinder (Fig. 4).
OPERATION
The purpose of the brake fluid level switch is to
provide the driver with an early warning that the
brake fluid level in the master cylinder fluid reser-
voir has dropped below a normal level. This may
indicate:
²Abnormal loss of brake fluid in the master cyl-
inder fluid reservoir resulting from a leak in the
hydraulic system.
²Brake shoe linings which have worn to a point
requiring replacement.
As the brake fluid drops below the minimum level,
the brake fluid level switch closes to complete the red
BRAKE warning indicator (lamp) circuit. This will
turn on the red BRAKE warning indicator. The mas-
ter cylinder fluid reservoir should be checked and
refilled to the Full mark with DOT 3 brake fluid.If
the brake fluid level has dropped below the add
line in the master cylinder fluid reservoir, the
entire brake hydraulic system should be
checked for evidence of a leak.
REMOVAL
(1) Remove wiring harness connector from brake
fluid reservoir level switch (Fig. 4).
(2) Using fingers, compress the retaining tabs on
the opposite end of brake fluid level switch.
(3) With retaining tabs compressed, grasp the con-
nector end of brake fluid level switch and pull it out
of master cylinder brake fluid reservoir.
INSTALLATION
(1) Insert brake fluid level switch into left side of
brake fluid reservoir. Be sure switch is pushed in
until retaining tabs lock it to brake fluid reservoir.
(2) Connect vehicle wiring harness connector to
brake fluid level switch (Fig. 4).
Tubes, Master Cylinder Bleed 8358
Adapter, Master Cylinder Pressure Bleed Cap 6921
Dial Indicator, C-3339
Gauge, Brake Safe-Set
Handle, Universal C±4171
Installer, Dust Boot C-4689 or C-4842
RSBRAKES - BASE5-9
BRAKES - BASE (Continued)
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observed if the automatic adjuster is working prop-
erly. If one or more adjusters do not function prop-
erly, the respective drum must be removed for
adjuster servicing.
BRAKE LINES
DESCRIPTION - BRAKE TUBES AND HOSES
The brake tubes are steel with a corrosion-resis-
tant nylon coating applied to the external surfaces.
The flex hoses are made of reinforced rubber with fit-
tings at each end.
The primary and secondary brake tubes leading
from the master cylinder to the ABS ICU Hydraulic
Control Unit (HCU) or the non-ABS junction block
have a special flexible section. This flexible section is
required due to cradle movement while the vehicle is
in motion (The ICU and non-ABS junction block are
mounted to the cradle).If replacement of these
lines is necessary, only the original factory
brake line containing the flexible section must
be used.
OPERATION - BRAKE TUBES AND HOSES
The purpose of the chassis brake tubes and flex
hoses is to transfer the pressurized brake fluid devel-
oped by the master cylinder to the wheel brakes of
the vehicle. The flex hoses are made of rubber to
allow for the movement of the vehicle's suspension.
INSPECTION - BRAKE TUBES AND HOSES
Flexible rubber hose is used at both front brakes
and at the rear axle. Inspection of brake hoses
should be performed whenever the brake system is
serviced and every 7,500 miles or 12 months, which-
ever comes first (every engine oil change). Inspect
hydraulic brake hoses for surface cracking, scuffing,
or worn spots. If the fabric casing of the rubber hose
becomes exposed due to cracks or abrasions in the
rubber hose cover, the hose should be replaced imme-
diately. Eventual deterioration of the hose can take
place with possible burst failure. Faulty installation
can cause twisting, resulting in wheel, tire, or chassis
interference.
The brake tubing should be inspected periodically
for evidence of physical damage or contact with mov-
ing or hot components.
The flexible brake tube sections used on this vehi-
cle in the primary and secondary tubes from the
master cylinder to the ABS hydraulic control unit
connections must also be inspected. This flexible tub-
ing must be inspected for kinks, fraying and contact
with other components or with the body of the vehi-
cle.
BRAKE PADS/SHOES - FRONT
REMOVAL - FRONT DISC BRAKE SHOES
(DISC/DISC BRAKES)
(1) Raise the vehicle. (Refer to LUBRICATION &
MAINTENANCE/HOISTING - STANDARD PROCE-
DURE).
(2) Remove both front wheel and tire assemblies.
(3) Begin on one side of the vehicle.
(4) Remove the anti-rattle clip from the outboard
side of the caliper and adapter.
(5) Remove the two caliper guide pin bolts.
(6) Remove caliper from caliper adapter and brake
rotor.
CAUTION: Supporting weight of caliper by the flex-
ible brake fluid hose can damage the hose.
(7) Using wire or cord, hang the caliper from the
front strut assembly (Fig. 12). Support the caliper
firmly to prevent weight of caliper from being sup-
ported by the brake fluid hose.
(8) Remove the outboard brake shoe from the cali-
per adapter.
(9) Pull the inboard brake shoe away from the cal-
iper piston until the retaining clip on shoe is free
from the cavity in the caliper piston (Fig. 13).
(10) Repeat the above procedure on other side of
the vehicle.
Fig. 12 Stored Front Disc Brake Caliper
1 - STEERING KNUCKLE
2 - BRAKE FLEX HOSE
3 - CALIPER ASSEMBLY
4 - WIRE HANGER
5 - STRUT ASSEMBLY
RSBRAKES - BASE5-13
HYDRAULIC/MECHANICAL (Continued)
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STANDARD PROCEDURE - BRAKE FLUID
LEVEL CHECKING
Check master cylinder reservoir fluid level a mini-
mum of twice annually.
Fluid reservoirs are marked with the words FULL
and ADD to indicate proper brake fluid fill level of
the master cylinder.
If necessary, add brake fluid to bring the level to
the bottom of the FULL mark on the side of the mas-
ter cylinder fluid reservoir.
Use only Mopartbrake fluid or equivalent from a
sealed container. Brake fluid must conform to DOT 3
specifications (DOT 4 or DOT 4+ are acceptable).
DO NOTuse brake fluid with a lower boiling
point, as brake failure could result during prolonged
hard braking.
Use only brake fluid that was stored in a tightly-
sealed container.
DO NOTuse petroleum-based fluid because seal
damage will result. Petroleum based fluids would be
items such as engine oil, transmission fluid, power
steering fluid etc.
SPECIFICATIONS
BRAKE FLUID
The brake fluid used in this vehicle must conform
to DOT 3 specifications (DOT 4 and DOT 4+ are
acceptable) and SAE J1703 standards. No other type
of brake fluid is recommended or approved for usage
in the vehicle brake system. Use only MopartBrake
Fluid or equivalent from a tightly sealed container.
CAUTION: Never use reclaimed brake fluid or fluid
from an container which has been left open. An
open container of brake fluid will absorb moisture
from the air and contaminate the fluid.
CAUTION: Never use any type of a petroleum-based
fluid in the brake hydraulic system. Use of such
type fluids will result in seal damage of the vehicle
brake hydraulic system causing a failure of the
vehicle brake system. Petroleum based fluids would
be items such as engine oil, transmission fluid,
power steering fluid, etc.
JUNCTION BLOCK
DESCRIPTION - NON-ABS JUNCTION BLOCK
A junction block is used on vehicles that are not
equipped with antilock brakes (ABS). The junction
block mounts in the same location as the integrated
control unit (ICU) does on vehicles equipped withABS. This allows for use of the same brake tube con-
figuration on all vehicles. The junction block is
located on the driver's side of the front suspension
cradle/crossmember below the master cylinder (Fig.
46).
It has six threaded ports to which the brake tubes
connect. Two are for the primary and secondary
brake tubes coming from the master cylinder. The
remaining four are for the chassis brake tubes going
to each brake assembly.
OPERATION - NON-ABS JUNCTION BLOCK
The junction block distributes the brake fluid com-
ing from the master cylinder primary and secondary
ports to the four chassis brake tubes leading to the
brakes at each wheel. Since the junction block
mounts in the same location as the ABS integrated
control unit (ICU), it allows for the common use of
brake tubes going to the brakes whether the vehicle
is equipped with or without ABS.
NOTE: Although the brake tubes coming from the
master cylinder to the junction block or ABS ICU
may appear to be the same, they are not. They are
unique to each brake system application.
REMOVAL - NON-ABS JUNCTION BLOCK
(1) Using a brake pedal depressor, move and lock
the brake pedal to a position past its first 1 inch of
travel. This will prevent brake fluid from draining
out of the master cylinder when the brake tubes are
removed from the junction block.
(2) Disconnect the battery negative cable.
(3) If the vehicle is equipped with speed control,
perform the following:
(a) Disconnect the battery positive cable.
(b) Remove the battery (Refer to 8 - ELECTRI-
CAL/BATTERY SYSTEM/BATTERY - REMOVAL).
(c) Disconnect the vacuum hose connector at the
tank built into the battery tray.
(d) Remove the screw securing the coolant filler
neck to the battery tray.
(e) Remove the battery tray (Refer to 8 - ELEC-
TRICAL/BATTERY SYSTEM/TRAY - REMOVAL).
(f) Remove the fasteners and move the speed
control servo off to the side, out of the way.
CAUTION: Before removing the brake tubes from
the junction block, the junction block and the brake
tubes must be thoroughly cleaned. This is required
to prevent contamination from entering the brake
hydraulic system.
5 - 32 BRAKES - BASERS
FLUID (Continued)
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(4) Remove the four chassis brake tubes from the
top of the junction block (Fig. 46).
(5) Remove the primary and secondary brake
tubes from the top of the junction block.
(6) Remove the bolts attaching the junction block
mounting bracket to the front suspension crossmem-
ber (Fig. 46), then remove the junction block.
INSTALLATION - NON-ABS JUNCTION BLOCK
(1) Install the junction block and mounting bracket
on the front suspension crossmember (Fig. 46).
Install the mounting bolts and tighten to a torque of
28 N´m (250 in. lbs.).
(2) Install the primary and secondary brake tubes
from the master cylinder in their ports. Tighten tube
nuts to a torque of 17 N´m (145 in. lbs.).Take care
not to twist tubes when tightening tube nuts.
They must be properly positioned to allow free
movement with rubber isolated suspension
crossmember.
(3) Install the four chassis brake tubes into the
outlet ports of the junction block. Tighten all 6 tube
nuts to a torque of 17 N´m (145 in. lbs.).
(4) If the vehicle is equipped with speed control,
perform the following:
(a) Install the speed control servo with its
mounting nuts.
(b) Connect the wiring harness to the speed con-
trol servo.
(c) Install the battery tray (Refer to 8 - ELEC-
TRICAL/BATTERY SYSTEM/TRAY - INSTALLA-
TION).(d) Install the screw securing the coolant filler
neck to the battery tray.
(e) Reconnect the vacuum hose connector at the
tank built into the battery tray.
(f) Install the battery (Refer to 8 - ELECTRI-
CAL/BATTERY SYSTEM/BATTERY - INSTALLA-
TION).
(g) Install the battery shield.
(5) Remove the brake pedal holder.
(6) Connect negative cable back on negative post of
the battery.
(7) Bleed the brake system thoroughly to ensure
that all air has been expelled from the hydraulic sys-
tem. (Refer to 5 - BRAKES - STANDARD PROCE-
DURE).
(8) Road test the vehicle to verify proper operation
of the brake system.
MASTER CYLINDER
DESCRIPTION
The master cylinder is located on the power brake
booster in the engine compartment on the driver's
side (Fig. 47). This vehicle uses 3 different master
cylinders. Master cylinder usage depends on what
type of brake system the vehicle is equipped with.
CAUTION: Master cylinders are not interchangeable
between systems. Performance and stopping dis-
tance issues will result if the incorrect master cyl-
inder is installed on the vehicle.
Fig. 46 NON-ABS JUNCTION BLOCK
1 - MASTER CYLINDER
2 - JUNCTION BLOCK
3 - SUSPENSION CROSSMEMBER
4 - MOUNTING BOLTS
Fig. 47 MASTER CYLINDER AND BOOSTER
LOCATION
1 - MASTER CYLINDER
2 - POWER BRAKE BOOSTER
RSBRAKES - BASE5-33
JUNCTION BLOCK (Continued)
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For information on master cylinder application,
bore and type, view the following table:
BRAKE SYSTEMMASTER CYLINDER
BORE/TYPE
Disc/Drum - ABS23.8 mm Conventional
Compensating Port
Disc/Drum - Non-ABS23.8 mm Conventional
Compensating Port
Disc/Disc - ABS25.4 mm (1-1/16 in.)
Conventional
Compensating Port
Disc/Disc ABS With
Traction Control25.4 mm (1-1/16 in.) Dual
Center Port
CAUTION: When replacing a master cylinder, be
sure to use the correct master cylinder for the type
of brake system the vehicle is equipped with.
The body of the master cylinder is an anodized alu-
minum casting. It has a machined bore to accept the
master cylinder pistons and threaded ports with
seats for the hydraulic brake line connections.
The brake fluid reservoir is mounted on the top of
the master cylinder. It is made of a see-through
polypropylene type plastic for easy fluid level view-
ing. A brake fluid level switch is attached to the
brake fluid reservoir.
The master cylinder is not a repairable component
and must be replaced if diagnosed to be functioning
improperly. The brake fluid reservoir and brake fluid
level switch can be replaced separately.
CAUTION: Do not hone the bore of the cylinder as
this will remove the anodized surface from the bore.
OPERATION
When the brake pedal is depressed, the master cyl-
inder primary and secondary pistons apply brake
pressure through the chassis tubes to the brakes at
each tire and wheel assembly.
The master cylinder primary outlet port supplies
hydraulic pressure to the right front and left rear
brakes. The secondary outlet port supplies hydraulic
pressure to the left front and right rear brakes.
STANDARD PROCEDURE - MASTER CYLINDER
BLEEDING
CAUTION: When clamping master cylinder in vise,
only clamp master cylinder by its mounting flange,
do not clamp on primary piston, seal or body of
master cylinder.(1) Clamp the master cylinder in a vise using only
the mounting flange.
NOTE: Two different size bleeding tubes need to be
used depending on which type of master cylinder
the vehicle is equipped with. Vehicles equipped
with traction control have different size brake tubes
and nuts at the master cylinder than the non-trac-
tion control equipped vehicles. Be sure the correct
size bleeding tubes are used when bleeding the
master cylinder.
(2) Thread Bleeding Tubes, Special Tool 8358, for a
non-traction control master cylinder or Special Tool
8129 for a traction control master cylinder into mas-
ter cylinder primary and secondary ports. Position
outlet ends of bleeding tubes in reservoir with the
outlets below surface of brake fluid when reservoir is
filled to its proper level.
(3) Fill brake fluid reservoir with Mopartbrake
fluid or equivalent conforming to DOT 3 (DOT 4 and
DOT 4+ are acceptable) specifications.
(4) Using a wooden dowel, depress push rod slowly,
and then allow pistons to return to released position.
Repeat several times until all air bubbles are
expelled from master cylinder.
(5) Remove bleeding tubes from master cylinder
outlet ports, and then plug outlet ports and install
fill cap on reservoir.
(6) Remove master cylinder from vise.
(7) Install the filler cap on master cylinder fluid
reservoir.
(8) Install master cylinder. (Refer to 5 - BRAKES -
BASE/HYDRAULIC/MECHANICAL/MASTER CYL-
INDER - INSTALLATION)
REMOVAL - MASTER CYLINDER
CAUTION: Vacuum in the power brake booster must
be pumped down (removed) before removing mas-
ter cylinder from power brake booster. This is nec-
essary to prevent the power brake booster from
sucking in any contamination as the master cylin-
der is removed. This can be done simply by pump-
ing the brake pedal, with the vehicle's engine not
running, until a firm feeling brake pedal is achieved.
(1) With engine not running, pump brake pedal
until a firm pedal is achieved (4-5 strokes).
(2) Disconnect negative battery terminal.
(3) Disconnect positive battery terminal.
(4) Remove battery shield.
(5) Remove nut and clamp securing battery to tray,
remove battery.
5 - 34 BRAKES - BASERS
MASTER CYLINDER (Continued)
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ASSEMBLY - MASTER CYLINDER (FLUID
RESERVOIR)
(1) Install new master cylinder housing to brake
fluid reservoir sealing grommets in master cylinder
housing (Fig. 51).
(2) Lubricate reservoir mounting area with fresh
clean brake fluid. Place reservoir in position over
sealing grommets. Seat reservoir into sealing grom-
mets using a rocking motion while firmly pressing
down on fluid reservoir.
(3) Be sure fluid reservoir is positioned properly on
master cylinder.Bottom of fluid reservoir is to be
touching the top of both sealing grommets
when properly installed on master cylinder
housing.(4) Install the two fluid reservoir to master cylin-
der retaining pins (Fig. 50).
(5) Install the master cylinder assembly on the
power brake booster. (Refer to 5 - BRAKES/HY-
DRAULIC/MECHANICAL/MASTER CYLINDER -
INSTALLATION)
(6) Fill fluid reservoir to its proper level as indi-
cated on the side of the fluid reservoir.
INSTALLATION - MASTER CYLINDER
CAUTION: Different types of master cylinders are
used on this vehicle depending on brake options. If
a new master cylinder is being installed, be sure it
is the correct master cylinder for the type of brake
system the vehicle is equipped with.
CAUTION: When replacing the master cylinder on a
vehicle, a NEW vacuum seal MUST be installed on
the master cylinder.
(1) Install a NEW vacuum seal on master cylinder
making sure seal fits squarely in groove of master
cylinder casting.
(2) Position master cylinder on studs of power
brake booster, aligning booster push rod with master
cylinder piston.
(3) Install the two master cylinder mounting nuts
(Fig. 49). Tighten both mounting nuts to a torque of
25 N´m (225 in. lbs.).
CAUTION: When tightening the primary and sec-
ondary brake tube nuts at master cylinder, be sure
brake tubes do not contact any other components
within the vehicle and that there is slack in the flex-
ible sections of the tubes. This is required due to
the movement between the ABS ICU and the master
cylinder while the vehicle is in motion.
(4) Connect primary and secondary brake tubes to
master cylinder primary and secondary ports (Fig.
48). Brake tubes must be held securely when tight-
ened to control orientation of flex section. Tighten
tube nuts to a torque of 17 N´m (145 in. lbs.).
(5) Install wiring harness connector to brake fluid
level switch mounted in brake fluid reservoir (Fig.
48).
(6) Install battery, clamp and nut.
(7) Install battery shield.
(8) Connect positive battery terminal.
(9) Connect negative battery terminal.
(10) Fill master cylinder with clean, fresh Mopart
Brake Fluid or equivalent.
(11) Road test vehicle to ensure proper operation of
brakes.
Fig. 50 Fluid Reservoir Retaining Pins (Typical)
1 - FLUID RESERVOIR
2 - RETAINING PINS
3 - MASTER CYLINDER
Fig. 51 Master Cylinder To Fluid Reservoir Seal
Grommets
1 - SEAL GROMMETS
2 - MASTER CYLINDER
5 - 36 BRAKES - BASERS
MASTER CYLINDER (Continued)
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CAUTION: Before removing the master cylinder
from the power brake vacuum booster, the master
cylinder and vacuum booster must be thoroughly
cleaned. This must be done to prevent dirt particles
from falling into the power brake vacuum booster.
(12) Clean area where master cylinder assembly
attaches to power brake booster. Use only a solvent
such as MopartBrake Parts Cleaner or equivalent.
(13) Disconnect primary and secondary brake
tubes from ABS integrated control unit or non-ABS
junction block (Fig. 55). Install sealing plugs in the
now open brake tube ports and install caps on ends
of tubes.
NOTE: It is not necessary to remove the brake
tubes from the master cylinder when removing the
master cylinder from the vacuum booster.
(14) Remove two nuts attaching master cylinder to
power brake booster (Fig. 55).
(15) Slide master cylinder straight out of power
brake booster. Remove master cylinder with primary
and secondary tubes from vehicle.
CAUTION: A seal on the rear of the master cylinder
is used to create the seal for holding vacuum in the
power brake vacuum booster. The vacuum seal on
the master cylinder MUST be replaced whenever the
master cylinder is removed from the power brake
vacuum booster.(16) Disconnect vacuum hose from check valve
located on vacuum booster.DO NOT REMOVE
CHECK VALVE FROM POWER BRAKE
BOOSTER.
(17) Inside vehicle, remove silencer panel under
instrument panel below steering column.
(18) Locate the booster input rod to brake pedal
connection under the instrument panel. Position a
small screwdriver between the center tang on the
power brake booster input rod to brake pedal pin
retaining clip (Fig. 56).
Fig. 54 MASTER CYLINDER AND BOOSTER
1 - POWER BRAKE BOOSTER
2 - BOOSTER IDENTIFICATION LABEL
3 - FLUID LEVEL SWITCH CONNECTOR
4 - PRIMARY BRAKE TUBE NUT
5 - SECONDARY BRAKE TUBE NUT
6 - MASTER CYLINDER
Fig. 55 MASTER CYLINDER MOUNTING
1 - MASTER CYLINDER MOUNTING NUTS
2 - MASTER CYLINDER
3 - SECONDARY TUBE NUT AT ICU
4 - PRIMARY TUBE NUT AT ICU
Fig. 56 Vacuum Booster Input Rod Retaining Pin
1 - BRAKE PEDAL
2 - INPUT ROD
3 - SCREWDRIVER
4 - RETAINING CLIP
5 - BRAKE PEDAL PIN
RSBRAKES - BASE5-39
POWER BRAKE BOOSTER (Continued)
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CAUTION: The master cylinder (and its rear seal) is
used to create the seal for holding vacuum in the
vacuum booster. The vacuum seal on the master
cylinder MUST be replaced with a NEW seal when-
ever the master cylinder is removed from the vac-
uum booster.
CAUTION: When removing the vacuum seal from
the master cylinder do not use a sharp tool.
(8) Using a soft tool such as a trim stick, remove
the vacuum seal from the master cylinder mounting
flange.
(9) Install a NEW vacuum seal on rear mounting
flange of the master cylinder (Fig. 60).
(10) Position master cylinder on studs of booster,
aligning push rod on booster with master cylinder
piston.
(11) Install the two nuts mounting the master cyl-
inder to the booster (Fig. 55). Tighten both mounting
nuts to a torque of 25 N´m (225 in. lbs.).
(12) Connect wiring harness connector to brake
fluid level switch in the master cylinder fluid reser-
voir (Fig. 54).
(13) Connect primary and secondary brake tubes
to ABS ICU or non-ABS junction block (Fig. 55).
Tighten the tube nuts to 17 N´m (145 in lbs.).
(14) Install wiper module (unit). (Refer to 8 -
ELECTRICAL/WIPERS/WASHERS/WIPER MOD-
ULE - INSTALLATION)
(15) If equipped with speed control, install speed
control servo and connect wiring connector. Tighten
the mounting nuts to a torque of 14 N´m (124 in.
lbs.).(16) Install the battery tray. Install the two nuts
and one bolt attaching the battery tray to the vehicle.
Tighten the bolt and nuts to a torque of 14 N´m (124
in. lbs.).
(17) If vehicle is equipped with speed control, con-
nect the servo vacuum hose to the vacuum tank on
the battery tray.
(18) Install the air inlet resonator and hoses as an
assembly on the throttle body and air cleaner hous-
ing. Securely tighten hose clamp at air cleaner hous-
ing and throttle body.
(19) Secure the engine coolant filler neck to the
battery tray with its mounting screw.
(20) Install the battery, clamp and mounting nut.
(21) Install the positive battery cable on the bat-
tery.
(22) Install the negative battery cable on the bat-
tery.
(23) Install the battery thermal guard shield.
(24) Bleed the base brakes as necessary. (Refer to
5 - BRAKES - STANDARD PROCEDURE)
(25) Road test vehicle to ensure operation of the
brakes.
PROPORTIONING VALVE
DESCRIPTION - PROPORTIONING VALVE
(HEIGHT SENSING)
NOTE: Only vehicles without antilock brakes (ABS)
have a proportioning valve. Vehicles with ABS uti-
lize electronic brake distribution which is controlled
through the ABS integrated control unit.
Vehicles not equipped with ABS use a height sens-
ing proportioning valve. It is mounted to the body of
the vehicle above the rear axle (Fig. 61). It has an
actuator lever that attaches to the rear axle and
moves with the axle to help the valve sense the vehi-
cle height.
CAUTION: The height sensing proportioning valve
is not adjustable. No attempt should be made to
adjust it. It is replaced as a complete assembly.
CAUTION: The use of after-market load leveling or
load capacity increasing devices on this vehicle are
prohibited. Using air shock absorbers or helper
springs on this vehicle will cause the height sens-
ing proportioning valve to inappropriately reduce
the hydraulic pressure to the rear brakes. This inap-
propriate reduction in hydraulic pressure potentially
could result in increased stopping distance of the
vehicle.
Fig. 60 Vacuum Seal (Typical)
1 - MASTER CYLINDER ASSEMBLY
2 - VACUUM SEAL
RSBRAKES - BASE5-41
POWER BRAKE BOOSTER (Continued)
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OPERATION - PROPORTIONING VALVE
(HEIGHT SENSING)
Vehicles not equipped with ABS use a height sens-
ing proportioning valve.
The height sensing proportioning valve operates
similarly to a standard proportioning valve in the fol-
lowing way. As hydraulic pressure is applied to the
valve, full input hydraulic pressure is supplied to the
rear brakes up to a certain pressure point, called the
split point. Beyond the split point, the proportioning
valve reduces the amount of hydraulic pressure to
the rear brakes according to a given ratio. Thus, on
light brake applications, approximately equal
hydraulic pressure will be transmitted to both the
front and rear brakes. Upon heavier brake applica-
tions, the hydraulic pressure transmitted to the rear
brakes will be lower than the front brakes. This will
prevent premature rear wheel lockup and skid.
Here is how the height sensing proportioning valve
differs from a standard proportioning valve. As the
height of the rear suspension changes, the height
sensing portion of the proportioning valve changes
the split point of the proportioning valve. When the
height of the rear suspension is low, the proportion-
ing valve interprets this as extra load and the split
point of the proportioning valve is raised to a higher
pressure to allow for more rear braking. When the
height of the rear suspension is high, the proportion-
ing valve interprets this as a light load and the split
point of the proportioning valve is lowered to a lower
pressure and rear braking is reduced.
The height sensing proportioning valve regulates
the pressure by sensing the load condition of thevehicle through the movement of the proportioning
valve actuator lever (Fig. 61). As the position of the
rear axle changes, depending on the load the vehicle
is carrying, the movement is transferred to the pro-
portioning valve. The proportioning valve adjusts the
hydraulic pressure accordingly.
The height sensing proportioning valve allows the
brake system to maintain the optimal front to rear
brake balance regardless of the vehicle load condi-
tion. Under a light load condition, hydraulic pressure
to the rear brakes is minimized. As the rear load con-
dition increases, so does the hydraulic pressure to
the rear brakes.
DIAGNOSIS AND TESTING - PROPORTIONING
VALVE (HEIGHT SENSING)
CAUTION: The use of aftermarket load leveling or
load capacity increasing devices on this vehicle is
prohibited. Using air shock absorbers or helper
springs on this vehicle will cause the height sens-
ing proportioning valve to inappropriately reduce
the hydraulic pressure to the rear brakes. This inap-
propriate reduction in hydraulic pressure potentially
could result in increased stopping distance of the
vehicle.
When a premature rear wheel skid is obtained on a
brake application, it may be an indication that the
hydraulic pressure to the rear brakes is above the
specified output from the proportioning valve. This
condition indicates a possible malfunction of the
height sensing proportioning valve, which will
require testing to verify that it is properly controlling
the hydraulic pressure allowed to the rear brakes.
Premature rear wheel skid may also be caused by
contaminated front or rear brake linings.
Prior to testing a proportioning valve for function,
check that all tire pressures are correct. Also, ensure
the front and rear brake linings are in satisfactory
condition.It is also necessary to verify that the
brakes shoe assemblies on a vehicle being
tested are either original equipment manufac-
turers (OEM) or original replacement brake
shoe assemblies meeting the OEM lining mate-
rial specification. This vehicles brake system is
not balanced for aftermarket brake shoe assem-
bly lining material.
If both front and rear brakes check OK, proceed
with the following test procedure for the height sens-
ing proportioning valve.
(1) Road test the vehicle to determine which rear
wheel brake is exhibiting premature wheel skid.
Fig. 61 HEIGHT SENSING PROPORTIONING VALVE
1 - PROPORTIONING VALVE
2 - ACTUATOR LEVER
3 - AXLE BRACKET
4 - REAR AXLE
5 - 42 BRAKES - BASERS
PROPORTIONING VALVE (Continued)
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(11) Support caliper to prevent the weight of the
caliper from damaging the flexible brake hose (Fig.
86).
(12) Remove the rotor from the hub/bearing.
(13) Remove the horseshoe clip (Fig. 87) from the
retainer on the end of the park brake cable.
(14) Remove the end of the park brake cable from
the actuator lever on the adapter (Fig. 87).(15) Remove the end of the park brake cable from
the adapter. Park brake cable is removed from
adapter using a 1/2 wrench slipped over the park
brake cable retainer as show in (Fig. 88) to compress
the locking tabs on the park brake cable retainer.
(16) Remove the attaching bolt from the wheel
speed sensor (Fig. 89). Then remove wheel speed sen-
sor from hub/bearing and adapter.
Fig. 85 Removing/Installing Caliper
1 - LIFT THIS END OF CALIPER AWAY FROM ADAPTER FIRST
2 - DISC BRAKE CALIPER
3 - ADAPTER ABUTMENT
4 - OUTBOARD BRAKE SHOE HOLD DOWN CLIP
5 - OUTBOARD BRAKE SHOE
6 - ROTOR
7 - ADAPTER
Fig. 86 Correctly Supported Caliper
1 - WIRE
2 - CALIPER
3 - ADAPTER
4 - ROTOR
5 - INNER FENDER
Fig. 87 Park Brake Cable Attachment To Actuator
1 - ADAPTER
2 - PARK BRAKE CABLE
3 - ACTUATOR
4 - AXLE
5 - DRIVESHAFT
6 - PARK BRAKE CABLE RETAINER
7 - HORSESHOE CLIP
Fig. 88 Park Brake Cable Removal From Adapter
1 - DRIVESHAFT
2 - 1/2º WRENCH
3 - PARK BRAKE CABLE
4 - PARK BRAKE CABLE RETAINER
5 - ADAPTER
RSBRAKES - BASE5-55
SHOES (Continued)
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