ESP DODGE TRUCK 1993 Service Repair Manual

10 INTRODUCTION
•
INTERNATIONAL CONTROL AND DISPLAY SYMBOLS

ID

HIGH
BEAM P
FOG UGHTS -&
HEADLIGHTS,
PARKING UGHTS, PANEL UGHTS TURN SIGNAL A
HAZARD WARNING WINDSHIELD
WASHER
WINDSHIELD WIPER WINDSHIELD WIPER
AND WASHER WINDSCREEN DEMISTING
AND DEFROSTING *

VENTILATING
FAN 8
M f

REAR
WINDOW DEFOGGER
sp

REARWINLX)W WIPER
CD
l
m

REAR
WINDOW WASHER FUEL ENGINE COOLANT
TEMPERATURE BATTERY CHARGING
CONDITION ENGINE OIL

SEAT
BELT

(©) (®) ky

11 J

LIGHTER

BRAKE
FAILURE
PARKING
BRAKE
FRONT HOOD
REAR
HOOD

(TRUNK)
HORN
11 J

LIGHTER
93IN-9

INTERNATIONAL VEHICLE CONTROL AND DISPLAY

SYMBOLS
The graphic symbols illustrated in the chart below
are used to identify various instrument controls. The
symbols correspond to the controls and displays that are located on the instrument panel.

•

INTRODUCTION
11
MEASUREMENT
AND
TORQUE SPECIFICATIONS
INDEX
page

Metric
and
English/SAE
Conversion
11

Specification
Notations
11

SPECIFICATION NOTATIONS

WARNING:
THE USE OF
INCORRECT
ATTACHING
HARDWARE
CAN
RESULT
IN
COMPONENT
DAM­

AGE
AND/OR
PERSONAL
INJURY.

It is important to retain the original attaching
hardware for assembly of the components. If the at­
taching hardware is not reusable, hardware with
equivalent specifications must be used.

METRIC
AND
ENGLISH/SAE
CONVERSION
The following chart will assist in converting metric
units to equivalent English and SAE units, or vise versa.

TORQUE SPECIFICATIONS
TORQUE
CHARTS
A torque chart for fasteners is provided at the end
of each group (of service information). Refer to the Standard Torque Specifications chart to determine
torque values not listed in the group (Figs. 1 and 2).
It is important to be aware that the torque values
listed in the chart are based on clean and dry bolt
page
Torque Specifications
11
threads. Reduce the torque value by 10 percent when the bolt threads are lubricated and by 20 percent if new.

BOLT
THREAD
AND
GRADE/CLASS
IDENTIFICATION

THREAD
IDENTIFICATION
SAE and metric bolt/nut threads are not the same.
The difference is described in the Thread Notation chart.

GRADE/CLASS
IDENTIFICATION
The SAE bolt strength grades range from grade 2
to grade 8. The higher the grade number, the greater
the bolt strength. Identification is determined by the line marks on the top of each bolt head (Fig. 1). The
actual bolt strength grade corresponds to the number
of line marks plus 2.
• A grade 2 bolt has no line marks on top of the bolt
head
• A grade 5 bolt has 3 line marks on top of the bolt
head • A grade 7 bolt has 5 line marks on top of the bolt
head

CONVERSION FORMULAS
AND
EQUIVALENT
VALUES
Multiply

in-lbs
ft-lbs
By

x
0.11298

x
1.3558
To
Get

=
Newton-Meters (N*m)

=
Newton-Meters (N*m) Multiply
N*m
iy

x
8.851

x
0.7376
BGef

-
in-fbs

-
ft-lbs

Inches
Hg
(60°F)

psi
x
3.377

x
6.895
=
Kilopascals
(kPa)

=
Kilopascals
(kPa)
kPa
kPa
x
0.2961

x
0.145
«
Inches
Hg

- psi

Inches
Feet

Yards
Miles
x 25.4
x
0.3048

x
0.9144

x
1.6093
« Millimeters (mm)

=
Meters (M)

-
Meters (M)

=
Kilometers (Km) mm
M
M
Km
x
0.03937

x
3.281

x
1.0936

x
0.6214
« Inches

-
Feet

=
Yards « Miles

mph

Feet/Sec.
Kilometers/Hr.

mph
x
1.6093

x
0.3048

x
0.27778

x
0.4470
=
Kilometers/Hr. (Km/h)
«
Meters/Sec.
(M/S)
«
Meters/Sec.
(M/S)

=
Meters/Sec.
(M/S)
Km/h

M/S
M/S

M/S
x
0.6214

x
3.281

x
3.600

x
2.237 - mph

=
Feet/Sec.

=
Kilometers/Hr.
» mph
COMMON
MITRIC
EQUIVALENTS

1
Inch
=
25 Millimeters
1
Cubic
Inch
»
16
Cubic
Centimeters

1
Foot
-
0.3 Meter
1
Cubic
Foot
«
0.03
Cubic
Meter
1
Yard
=
0.9 Meter
1
Cubic
Yard
=
0.8
Cubic
Meter

1
Mile =1.6 Kilometers
J91IN-1

12

INTRODUCTION

STANDARD
TORQUE
SPECIFICATIONS
BOLT TORQUE
BOLT ORAM
5

GRADES

SIZE
M*fn

ft-lbs
Nfft

ft-abs

(in-lbs)
(In-lbs)

1/4-20
11
(95) 14
(125)

1/4-28
11 (95) 17 (150)

5/16-18
23 (200) 31 (270)

5/16-24
27 20 34 25

3/8-16
41
30 54
40

3/8-24
48 35 61 45

7/16-14
68
50 88 65

7/16-20
75 55 95 70

1/2-13
102
75 136 100

1/2-20
115 85 149 110

9/16-12
142
105 183 135

9/16-18
156 115 203 150

5/8-11
203 150 264 195

5/8-18
217 160 285 210

3/4-16
237 175
305 225

J89IN-9

THREAD
NOT A
TION—SAE
AND
METRIC

INCH

5/16-18
METRIC
M8
X 1.25

THREAD MAJOR
DIAMETER
IN INCHES NUMBER
OF
THREADS

PER
INCH
THREAD DISTANCE
MAJOR BETWEEN
DIAMETER IN THREADS
IN

MILLIMETERS MILLIMETERS

PR606B

•
A grade 8 bolt has 6 line marks on top of the bolt
head
The most commonly used metric bolt strength
classes are 9.8 and 12.9. The metric strength class identification number is imprinted on the head of the
bolt (Fig. 2). The higher the class number, the
SAE
CLASSIFICATION
GRADE
5

GRADE
8
MARKINGS
FOUND

ON TOP OF BOLT HEAD INDICATE
GRADE
120°
60°

GRADE
2
GRADE
5
GRADE
8

(SAE) BOLTS—IDENTIFICATION
MARKS
CORRESPOND
TO BOLT STRENGTH—INCREASING NUMBERS

REPRESENT
INCREASING STRENGTH.
J89IN-11
Fig.
1 SAE
Bolt
Grade
Identification

greater the bolt strength. Some metric nuts are im­
printed with a single-digit strength class on the nut

face.
METRIC BOLTS—IDENTIFICATION
CLASS
NUMBERS

CORRESPOND
TO BOLT STRENGTH— INCREASING NUMBERS
REPRESENT
INCREASING STRENGTH.
J89IN-10

Fig.
2
Metric
Bolt
Class
Identification

METRIC
CONVERSION
Refer to the Metric Conversion chart to convert
torque values listed in metric Newton-meters (N»m).

Also,
use the chart to convert between millimeters (mm) and inches (in.)

•
• —
LUiRICATlON
AND
MAINTENANCE
0 - 1
CONTENTS

page
page

CHASSIS
AND
BODY
28
ENGINE MAINTENANCE
14
DRIVETRAIN
.,,, 22
GENERAL INFORMATION
1

GENERAL
INFORMATION INDEl

page

Classification
of
Lubricants
. 3

Components
Requiring
No
Lubrication
4

Fuel Requirements
. 2
Introduction
1

Lubrication
and
Replacement Parts Recommendation
3
page

Routine Maintenance
2

Starting
Assistance (Jump Starting)
9

Vehicle
Lifting
Recommendations
............ 10

Vehicle Noise
Control
2

Vehicle Towing Recommendations
11

INTRODUCTION
Lubrication and maintenance is divided into re­
quired and recommended service tasks. The required service tasks must be completed to verify the emis­
sion controls function correctly. The recommended
service tasks should be completed to maintain safety
and durability. This information will assist the service personnel
in providing maximum protection for each owner's
vehicle. Conditions can vary with individual driving habits.
It is necessary to schedule maintenance as a time in­
terval as well as a distance interval. It is the owner's responsibility to determine the ap­
plicable driving condition. Also to have the vehicle serviced according to the maintenance schedule, and
to pay for the necessary parts and labor. Vehicles with a Gross Vehicle Weight Rating
(GVWR) of 3 855 kg (8,500 lbs.) or less must conform
to light duty emission standards. Vehicles with a Gross Vehicle Weight Rating (GVWR) of 3 856 kg
(8,501 lbs.) or more must conform to heavy duty
emission standards. The GVWR for each vehicle is listed on the Safety
Certification Label. This label is affixed to the driver
side door pillar (Fig. 1).
Additional maintenance and lubrication informa­
tion is listed in the Owner's Manual.
Mm
rv
CHRYSLER
DATE
OF MFR
MFD BY CORPORATION
GVWR
GAWR FRONT
GAWR REAR
WITH
TIRES

WITH
TIRES
RIMS
AT

RIMS
AT

PSI
COLD

PSI
COLD THIS VEHICLE CONFORMS
TO
ALL APPLICABLE FEDERAL MOTOR VEHICLE SAFETY

STANDARDS
IN
EFFECT ON
THE
DATE
OF
MANUFACTURE SHOWN ABOVE.

SINGLE
DUAL

BAR
CODE

VEHICLE MADE
IN

4648503
J9UN-25

Fig. 1 Vehicle Safety
Certification
Label

SEVERE DRIVING
CONDITIONS
Vehicles subjected to severe driving conditions
should decrease the interval between component
maintenance. Severe driving conditions are defined
as:

• Frequent short trip driving less than 24 km (15
miles)
• Frequent driving in dusty conditions
• Trailer towing
• Extensive engine idling
• Sustained high speed operation
• Desert operation
• Frequent starting and stopping
• Cold climate operation

LUBRICATION
AND
MAINTENANCE

2
- 6
FRONT
SUSPENSION
AND
AXLE

•
(5) Position the adjustment sleeve clamps so the
ends are not located at the sleeve slot. Tighten the
clamp bolt nuts to 26 N*m (225 in. lbs.) torque.
Tighten Model D350 and all 4WD vehicle (heavy
duty tie rods) nuts to 34 N*m (25 ft. lbs.) torque. En­
sure clamp bolts are located at the underside of the
sleeve.
CLAMP
RN1036

Fig.
3 Toe Position Adjustment
(Typical)

ALIGNMENT
SPECIFICATIONS

ALIGNMENT
(4WD)
ASGSPTABLE RANGE
PREFERRED

Camber
-rto+r
0°

"Caster
+
1/2°
to
37*°
+2°

King
Pin
Inclination
8.5° 8.5°

Toe-In
(at
Hub
Height)
-0.05°
to
+0.45° 0.20°

ALIGNMENT
(2WD)
ACCEPTABLE RANGE PREFERRED

Camber
0°to 1°
+1/2°

'Caster
-1°
to
+2°
+1/2°

Toe-in
(at
Hub
Height)
0°
to
0.50° 0.25°

Turning
Angle
(Base
Tire)
Left
and
Right
33°

33°
J9102-64

*lf vehicle
wanders,
caster
should
be increased. If steering
effort
is very
high
(especially when cornering), caster
should
be decreased.
TIE
RODS

2
- 10
FRONT SUSPENSION
AND
AXLE

• INSTALLATION
(1) Position the spring and isolation pad on the
suspension arm. Install the spring compressor tool.
Compress the spring until the lower suspension arm
can be properly positioned in the steering knuckle.
(2) Install the nuts on the ball studs. Tighten the
upper nut to 142 Nnn (105 ft. lbs.) torque. Tighten
the lower nut.
* 11/16-16 bolt, to 183 Nnn (135 ft. lbs.) torque
• 3/4-16 bolt, to 237 Nnn (175 ft. lbs.) torque Install replacement cotter pins.
(3) Install the strut.
(4) Connect the stabilizer bar.
(5) Install the shock absorber.
(6) Install the brake splash shield on the steering
knuckle. Tighten the screws to 23 Nnn (200 in. lbs.)
torque.
(7) Carefully install the hub/rotor and bearings.
(8) Install the brake caliper, refer to Group 5, Brakes.
(9) Install the wheel and tire, refer to Wheel and Tire
Installation within this section. Lower the vehicle. (10) Test the vehicle brakes and the suspension for
proper operation.

LOWER SUSPENSION
ARM
REMOVAL
(1) Follow procedure under Coil Spring Removal.
(2) Remove hex-head mounting bolt from the cross-
member. (3) Remove the lower suspension arm from vehicle.
INSTALLATION (1) Position lower suspension arm on vehicle.
(2) Install mounting bolt, tighten finger-tight.
(3) Follow procedure under Coil Spring Installa­
tion.
(4) Lower the vehicle to the surface with the
wheels/tires supporting the vehicle weight. Tighten
the lower suspension arm mounting bolt to 305 Nnn (225 ft. lbs.) torque.

LOWER
BALL
STUD

INSPECTION
(1) Raise the front of the vehicle. Install safety
floor stands under both lower suspension arms as far outboard as possible. The upper suspension arms
must not contact the rebound bumpers. (2) Install a dial indicator and clamp assembly to
the lower suspension arm. (3) Position indicator plunger against knuckle arm
and zero indicator. (4) Raise and lower the wheel with a pry bar under
the center of the tire. Measure the axial movement of
the knuckle with respect to the suspension arm.
(5) If the travel of the suspension arm is 0.020
inch (0.51 mm) or more, replace the ball joint. REMOVAL
(1) Follow procedure under Coil Spring Removal.
(2) Remove ball joint seal. Use assembled Remov­
er/Installer C-4212 to force the ball stud out of the
lower suspension arm bore (Fig. 6).

Fig.
6
Lower
Bail
Stud
Removal

INSTALLATION (1) Force the replacement ball stud into the lower
suspension arm bore with assembled Remover/In­
staller C-4212 (Fig. 7).
Fig.
7
Lower
Ball
Stud
Installation

REAR SUSPENSION
ANi
AXLE
3 - 17
(3) Eliminate any side play in the differential case.
Attach Dial Indicator to Pilot stud C-3288-B. Place
the indicator plunger at a right angle (90°) to the ring gear (Fig. 11). The plunger should exert a slight
force against the gear face.

DIAL

INDICATOR

Fig.
11
Ring
Gear
Runout
Measurement
(4) Measure the runout by turning the ring gear
several complete revolutions. Observe the dial indica­
tor pointer. Mark the ring gear and the differential
case at the areas of maximum runout. The ring gear
runout should not exceed 0.005 inch (0.13 mm). If the
runout exceeds 0.005 inch (0.13 mm), a damaged
dif­

ferential case could be the cause.
The marking on the differential case will be
very useful later during the differential case
runout. Remove the rear wheel anti-lock (RWAL) sensor.
(5) Mark the differential housing and the differen­
tial bearing caps for installation reference (Fig. 12).
(6) Remove the bearing threaded adjuster lock
from each bearing cap. Loosen the bolts, but do not
remove the bearing caps.
(7) Loosen the threaded adjusters with Wrench
C-4164 (Fig. 13).
(8) Hold the differential case in place. Remove the
bearing caps (Fig. 14), adjusters and the differential
case.

Each differential bearing cup and threaded
adjuster must be kept with their respective bear­
ing.

PINION
GEAR
SHAFT
REMOVAL
(1) Remove the pinion gear nut and washer. Use
Puller C-452 and Wrench C-3281 to remove the pin­
ion gear yoke.
Fig.
12
Housing
&
Caps
Marked For
Installation

Reference
Fig.
13 Threaded Adjuster Tool

Fig.
14
Differential
Bearing Cap
Removed

(2) Use Puller C-748 to remove the pinion seal.
Discard the seal. (3) Force the pinion gear out the front bearing to

3
- 24
REAR SUSPENSION
AND
AXLE
Fig.
30 Threaded Adjuster Tool
(2) Install Dial Indicator (Fig. 31). Position the
plunger against the drive side of a ring gear tooth. Measure the backlash at 4 positions (90 degrees apart) around the ring gear. Locate and mark the
area of minimum backlash.
(3) Rotate the ring gear to the position of the least
backlash. Mark the gear so that all future backlash
measurements will be taken with the same gear
teeth meshed.
(4) Loosen the right-side, tighten the left-side
threaded adjuster. Obtain backlash of 0.003 to 0.004
inch (0.076 to 0.102 mm) with each adjuster tight­
ened to 14 N-m (10 ft. lbs.) torque. Seat the bearing
cups with the procedure described above.
(5) Tighten the differential bearing cap bolts;
• 8 3/8 axles to 95 N-m (70 ft. lbs.) torque
• 9 1/4 axles to 136 N-m (100 ft. lbs.) torque
(6) Use Wrench C-4164 to tighten the right-side
threaded adjuster to 102 N-m (75 ft. lbs.) torque. Seat the bearing cups with the procedure described above. •

Fig.
31
Ring
Gear
Backlash
Measurement Continue to tighten the right-side adjuster and seat
bearing cups until the torque remains constant at 102 N-m (75 ft. lbs.)
(7) Measure the ring gear backlash. The range of
backlash is 0.006 to 0.008 inch (0.15 to 0.203 mm).
Continue increasing the torque at the right-side
threaded adjuster until the specified backlash is ob­ tained.
The left-side threaded adjuster torque should
have approximately 102 N-m (75 ft. lbs.) torque. If the torque is considerably less, the complete adjustment procedure must be repeated. (8) Tighten the left-side threaded adjuster until
102 N-m (75 ft. lbs.) torque is indicated. Seat the
bearing rollers with the procedure described above. Do this until the torque remains constant. (9) Install the threaded adjuster locks . Ensure the
lock finger is engaged with the adjuster hole.
Tighten the lock screws to 10 N-m (90 in. lbs.) torque.
SIDE
GEAR CLEARANCE
MEASUREMENT
AND

ADJUSTMENT

When measuring side gear clearance, check each
gear independently. If it necessary to replace a side
gear, replace both gears as a matched set.
(1) Install the axle shafts and C-clip locks and pin­
ion mate shaft. If necessary, refer to the installation
located within this group. (2) Measure each side gear clearance. Insert a
matched pair of feeler gauge blades between the gear
and differential housing on opposite sides of the hub (Fig. 32).
(3) If side gear clearances is no more than 0,005
inch. Determine if the shaft is contacting the pinion
gear mate shaft. Do not remove the feeler gauges,
inspect the axle shaft with the feeler gauge in­ serted behind the side gear. If the end of the axle
shaft is not contacting the pinion gear mate shaft,
the side gear clearance is acceptable.
• Insufficient adjuster torque will not support the
ring gear correctly and can cause excessive differen­
tial case free-play and ring gear noise
The differential bearing cups will not always
immediately follow the threaded adjusters as they are moved during adjustment. Ensure accu­
rate bearing cup responses to the adjustments. Maintain the gear teeth engaged (meshed) as
marked. The bearings must be seated by rapidly
rotating the pinion gear a half turn back and forth. Do this five to ten times each time the
threaded adjusters are adjusted.
(1) Use Wrench C-4164 to adjust each threaded ad­
juster inward (Fig. 30). Adjust until the differential bearing free-play is eliminated. Allow some ring gear
backlash (approximately 0.01 inch/0.25 mm) between
the ring and pinion gear. Seat the bearing cups with
the procedure described above.

•

BRAKES
i - 3 BRAKE DIAGNOSIS

INDEX

page

Brake
Warning Lights
3

Diagnosing
Brake Problems .................
4

Diagnosis
Procedures
3

Low
Vacuum
Switch—Diesel
Models
3
page

Master
Cylinder/Power Booster Test
5

Power
Booster
Check
Valve Test .............
6

Power
Booster
Vacuum
Test .................
6

Testing Diesel
Engine
Vacuum
Pump
Output
.... 6

DIAGNOSIS
PROCEDURES
Brake diagnosis involves determining
if the
prob­
lem
is
related
to a
mechanical, hydraulic
or
vacuum
operated component.
A
preliminary check, road test­
ing
and
component inspection
can all be
used
to de­

termine
a
problem cause. Road testing will either verify proper brake opera­
tion
or
confirm
the
existence
of a
problem. Compo­ nent inspection will,
in
most cases, identify
the
actual part causing
a
problem. The first diagnosis step
is the
preliminary check. This
involves inspecting fluid level, parking brake action,
wheel
and
tire condition, checking
for
obvious leaks
or

component damage
and
testing brake pedal response. A road test will confirm
the
existence
of a
problem.
Final diagnosis procedure involves road test analysis and
a
visual inspection
of
brake components.

BRAKE
WARNING LIGHTS
The
red
brake warning light
is
connected
to the

parking brake switch
and to the
pressure differential switch
in the
combination valve. The
red
light will illuminate when
the
parking
brakes
are
applied
or
when
a
fluid pressure drop
oc­
curs
in the
front
or
rear brake circuit.
The
light will
also illuminate
for
approximately
2-4
seconds
at en­

gine start
up.
This
is a
self test feature designed
to

check bulb
and
circuit operation each time
the en­

gine
is
started. The amber antilock light
is
connected
to the
anti-
lock rear brake hydraulic valve.
The
light will illu­
minate
if a
fault occurs within
the
antilock system.

LOW VACUUM SWITCH-DIESEL MODELS
On diesel models,
the red
brake warning light
is
also
used
to
alert
the
driver
of a low
brake booster vacuum
condition.
The
warning light
is in
circuit with
a
vacuum
warning switch mounted
on the
driver side fender
panel.
The
vacuum side
of the
switch
is
connected
to the

power brake booster.
The
electrical side
of the
switch
is
connected
to the
brake warning light. The
low
vacuum switch monitors booster vacuum
level whenever
the
engine
is
running.
If
booster vac­
uum falls below
8.5
inches vacuum
for a
minimum
of
10 seconds,
the
switch completes
the
circuit
to the

warning light causing
it to
illuminate.
The
warning light
is
designed
to
differentiate between
a low
vac­
uum condition
and a
hydraulic circuit fault.

PRELIMINARY
BRAKE CHECK
(1) Check condition
of
tires
and
wheels. Damaged
wheels
and
worn, damaged,
or
underinflated tires
can
cause pull, shudder, tramp,
and a
condition similar
to
grab.

(2)
If
complaint
was
based
on
noise when braking,
check suspension components. Jounce front
and
rear
of

vehicle
and
listen
for
noise that might
be
caused
by

loose, worn
or
damaged suspension
or
steering compo­

nents.

(3) Inspect brake fluid level
and
condition. Note
that
the
front disc brake reservoir fluid level will drop
in
proportion
to
normal lining wear. Also note
that brake fluid tends
to
darken over time. This
is normal
and
should
not be
mistaken
for
con­
tamination.
If the
fluid
is
still clear
and
free
of

foreign material,
it is OK.

(a)
If
fluid level
is
abnormally
low,
look
for
evi­
dence
of
leaks
at
calipers, wheel cylinders, brake-
lines
and
master cylinder.
(b)
If
fluid appears contaminated, drain
out a

sample.
If
fluid
is
separated into layers,
or
obvi­
ously contains
oil or a
substance other than brake
fluid,
the
system seals
and
cups will have
to be re­

placed
and the
hydraulic system flushed.
(4) Check parking brake operation. Verify free
movement
and
full release
of
cables
and
pedal. Also
note
if
vehicle
was
being operated with parking
brake partially applied.
(5) Check brake pedal operation. Verify that pedal
does
not
bind
and has
adequate free play.
If
pedal
lacks free play, check pedal
and
power booster
for be­

ing loose
or for
bind condition.
Do not
road test until
condition
is
corrected.
(6)
If
components checked appear
OK,
road test
the

vehicle.

ROAD
TESTING (1)
If
complaint involved
low
brake pedal, pump
the pedal
and
note
if the
pedal comes back
up to
nor­ mal height.
(2) Check brake pedal response with transmission
in Neutral
and
engine running. Pedal should remain
firm under steady foot pressure.

•

BRAKES
5 - 13
COMBINATION VALVE OPERATION

METERING (HOLD-OFF) VALVE The metering valve is used to balance brake action
between the front disc and rear drum brakes. The
valve meters (holds-off) full apply pressure to the front disc brakes until the rear brakeshoes are in full
contact with the drums.
The valve is designed to maintain front brake fluid
pressure at 3-30 psi until the hold-off limit of 117 psi is reached. At this point, the metering valve opens completely permitting full fluid apply pressure to the
front disc brakes.
PRESSURE DIFFERENTIAL SWITCH AND VALVE The pressure differential switch is connected to the
brake warning light. The switch is triggered by movement of the switch valve. The purpose of the switch is to monitor fluid pressure in the separate
front/rear brake hydraulic circuits.
A decrease or loss of fluid pressure in either hy­
draulic circuit will cause the switch valve to shuttle
forward or rearward in response to a pressure differ­ ential.
Movement of the switch valve will push the switch
plunger upward. This closes the switch internal con­ tacts completing the electrical circuit to the warning light. The switch valve will remain in an actuated
position until repair restores system pressures to nor­ mal levels.

COMBINATION VALVE TESTING
TESTING METERING VALVE Metering valve operation can be checked visually
and with the aid of a helper.
Observe the metering valve stem while a helper
applies and releases the brakes. If the valve is oper­
ating correctly, the stem will extend slightly when
the brakes are applied and retract when the brakes are released.
If the valve is faulty, replace the entire combina­
tion valve as an assembly.
TESTING PRESSURE DIFFERENTIAL SWITCH (1) Have helper sit in drivers seat to observe brake
warning light and to operate brake pedal.
(2) Raise vehicle on hoist.
(3) Connect bleed hose to left or right rear wheel
cylinder. Then immerse hose end in glass jar par­
tially filled with brake fluid.
(4) Have helper press and hold brake pedal all the
way down and observe warning light.
(a) If warning light illuminates, switch is operat­
ing correctly. (b) If light fails to illuminate, check circuit fuse,
bulb and wiring. Repair as necessary and repeat test steps (3) and (4). (5) If warning light still fails to illuminate, check
brakelight and park brake switches (and wiring) with test lamp. Repair or replace parts as necessary and test differential pressure switch operation again.
(6) If warning light still does not illuminate,
switch is faulty. Replace combination valve, bleed
brakes and verify proper switch and valve operation.

COMBINATION VALVE REMOVAL/INSTALLATION
VALVE REMOVAL (1) Raise vehicle on hoist.
(2) Mark or tag brake lines connected to valve for
assembly reference.
(3) Disconnect lines at valve (Fig. 8).
(4) Disconnect wires from differential pressure
switch.
(5) Remove bolts attaching valve to frame bracket
and remove valve.
VALVE INSTALLATION (1) Mount new valve on bracket and tighten valve
and bracket screws/nuts securely.
(2) Connect brakelines to valve. Tighten fittings to
16 N*m (145 in. lbs.)
(3) Connect wires to pressure differential switch
terminal. (4) Bleed brakes.
(5) Lower vehicle and verify proper brake opera­
tion.

BRAKE
LINES AND
HOSES

BRAKE LINE AND HOSE INSPECTION Flexible rubber hose is used at both front brakes
and at the rear axle junction block. Inspect the hoses
whenever the brake system is serviced, at every en­ gine oil change, or whenever the vehicle is in for ser­

vice.

Inspect the hoses for surface cracking, scuffing, or
worn spots. Replace any brake hose immediately if
the fabric casing of the hose is exposed by cracks or abrasion.
Also check brake hose installation. Faulty installa­
tion can result in kinked, twisted hoses, or contact with the wheels and tires or other chassis compo­
nents.
All of these conditions can lead to scuffing,
cracking and eventual failure.
The steel brake lines should be inspected periodi­
cally for evidence of corrosion, twists, kinks, leaks, or
other damage. Heavily corroded lines will eventually
rust through causing leaks. In any case, corroded or damaged brake lines should be replaced.