check engine DODGE TRUCK 1993 Service User Guide

0
- 32
LUBRICATION
AND
MAINTENANCE

•

Fig.
5 Parking Brake Ratio Lever Lubrication (2) Note any indication of brake overheating,
wheel dragging or the vehicle pulling to one side.
(3) Evaluate any performance complaints received
from the owner/operator. (4) Repair the brake system as necessary (refer to
Group 5—Brakes for additional information and ser­
vice procedures).

BODY
COMPONENT
MECHANISMS
LUBRICATION REQUIREMENTS
All operating mechanisms and linkages should be
lubricated when necessary. This will maintain ease of operation and provide protection against rust and
excessive wear. The door weatherstrip seals should
be lubricated to prolong their life as well as to im­ prove door sealing.

LUBRICANT SPECIFICATIONS
All applicable exterior and interior vehicle operat­
ing mechanisms should be:
• Inspected • Cleaned
• All the pivoting/sliding contact areas on the mech­ anisms should then be lubricated.
MOPAR®Multi-Mileage Lubricant or an equiva­
lent, should be used to lubricate the mechanisms.
The door weatherstrip seals should be lubricated
with silicone lubricant spray. Refer to the Body Lu­
bricant Specifications chart below for additional lu­
bricant applications.

LUBRICATION
(1) When necessary, lubricate the cab and cargo
box operating mechanisms with the specified lubri­
cants.

(2) Apply silicone lubricant to a cloth and wipe it
on door seals to avoid over-spray that can soil pas­
senger clothing. (3) Before applying lubricant, the component
should be wiped clean. After lubrication, any excess
lubricant should be removed.
(4) The hood latch, latch release mechanism, latch
striker and safety latch should be lubricated periodi­
cally.
(5) The door lock cylinders should be lubricated 2
times each year (preferably autumn and spring): • Spray a small amount of lock cylinder lubricant di­
rectly into the lock cylinder
• Apply a small amount to the key and insert it into
the lock cylinder • Rotate it to the locked position and then back to
the unlocked position several times
• Remove the key. Wipe the lubricant from it with a
clean cloth to avoid soiling of clothing.

TIRES
RECOMMENDED MAINTENANCE
The condition of the tires should be inspected. The
inflation pressures tested/corrected at the same time as the engine oil is changed and the oil filter is re­
placed.
The tires/wheels should be rotated periodically to
ensure even tread wear. The tires/wheels should be
rotated at the first 12 000 km (7,500-miles) interval.
Thereafter, at each 24 000 km (15,000-miles) inter­
val.
INSPECTION
Inspect the tires for excessive wear, damage. Test
the tires for the recommended inflation pressure and adjust the pressure accordingly. Refer to the tire in­
flation pressure decal located on the left door face. Also to Group 22—Tires And Wheels for tire pres­sure charts, tire replacement, and treadwear indica­

tors.

ROTATION
Tires/wheels should be rotated according to the rec­
ommended interval. The first tire/wheel rotation is
the most important for establishing the prevention of uneven tread wear. After rotation, adjust the tire in­
flation pressure to the air pressure recommended on
the decal located on the left door face.
Refer to Group 22—Tires And Wheels for the rec­
ommended method of tire/wheel rotation.

HEADLAMPS

MAINTENANCE SCHEDULE
Every six months check the headlamp beams to en­
sure that the headlamp beams are correctly posi­
tioned.

AIM
ADJUSTMENT
Refer to Group 8L—Lamps for headlamp aim ad­
justment procedures.

•

FRONT
SUSPENSION
AND
AXLE
2 - 5 (4) Front wheels for excessive radial, lateral
runout and unbalance. Refer to Group 22, Wheels and Tires for diagnosis information.
(5) Suspension components for wear and noise. Check
components for correct torque. Refer to Groups 2 and 3, Suspension and Axle for additional information.

WHEEL
ALIGNMENT
MEASUREMENTS/ADJUSTMENTS
The front wheel alignment positions must be set to
the specified limits. This will prevent abnormal tire
tread wear. The equipment manufacturer's recommenda­
tions for use of their
equipment
should always
be followed. All
damaged
front suspension sys­
tem components
should
be replaced. Do not at­ tempt to straighten any
bent
component.

CAMBER AND CASTER-2WD VEHICLES Camber and caster angle adjustments involve repo­
sitioning the upper suspension arm cam adjustment
bolts (Fig. 2). Alignment adjustments are accom­
plished by loosening the nuts and changing the posi­
tion of the cam bolt.
(1) Remove all foreign material from the adjust­
ment bolt threads.
(2) Record the camber and caster measurements
before loosening the adjustment bolt nuts.
(3) The camber angle should be adjusted as near as
possible to the preferred angle. The caster should be
the same at both sides of the vehicle. Refer to the Specifications chart.
CAMBER AND CASTER—4WD VEHICLES For 4WD vehicles, the correct wheel camber (verti­
cal tilt) angle is factory preset at zero degree (0°).
Camber cannot be altered by adjustment.
CAUTION: Do not attempt to
adjust
the
camber
an­
gle by
heating
or bending the axle or any
suspen­

sion
component. If camber angle is
incorrect,
the
component(s)
causing
an
incorrect
angle must be replaced.
(1) It is important that the camber (vertical tilt)
angle be the same for both front wheels.
(2) The camber angle should be measured with ac­
curate wheel alignment equipment. The acceptable
range is -1° to +1°. Refer to the Specifications chart.
Road test the vehicle and observe the steering
wheel return-to-center position. Before road testing,
check
and
correct
the tire
inflation pressures. Inflate
both
of the front tires
with exactly the
same
pressure.
During the road test, make vehicle turns to both
the left and right. If the steering wheel returns to­
ward the center position unassisted, the caster angle is correct. However, if the steering wheel does not re­ turn toward the center position unassisted, an incor­
rect caster angle is probable.
(1) The caster angle is factory preset at positive
two degrees
(
+
2°).
The acceptable range is +1/2° to +
3
1/2°.
(2) The caster angle should be measured with ac­
curate wheel alignment equipment.
(3) Caster angle can be adjusted by installing ta­
pered shims between the front axle pads and the spring brackets. The caster angle should be adjusted
as near as possible to the preferred angle.
(4) Record the caster measurement before remov­
ing the original shims from the spring pads.
(5) The caster should be the same at both sides of
the vehicle. Refer to the Specifications chart.
RN1030

Fig.
2 Caster &
Camber
Adjustment Location—2WD
Vehicles

WHEEL TOE POSITION The wheel toe position adjustment should be the fi­
nal front wheel alignment adjustment. In all in­ stances, follow the equipment manufacturer's
recommended procedure.
(1) Secure the steering wheel with the front wheels
in the straight-ahead position. For vehicles equipped
with power steering, start the engine before straight­ ening the wheels.
With power steering, the engine should be op­
erating during the wheel toe position adjust­
ment.
(2) Loosen the tie rod adjustment sleeve clamp
bolts (Fig. 3).
(3) Adjust the wheel toe position by rotating the
tie rod adjustment sleeve (Fig. 3). Rotate each tie-rod end in the direction of
sleeve rotation during the adjustment (Fig. 3).
This will ensure that both tie-rod ends are at the center of their travel.
(4) If applicable, turn the ignition switch off.

2 - 28
FRONT
SUSPENSION
AND
AXLE

DISCONNECT
AXLE/SHIFT
MOTOR
DIAGNOSIS
TWO-WHEEL DRIVE
OPERATION
DIAGNOSIS
FOUR-WHEEL DRIVE
INDICATOR
LIGHT
WILL NOT GO OUT WHEN
TRANSFER CASE SELECTOR
IS
MOVED FROM 4H TO 2H POSITION.

RAISE
VEHICLE SO ALL FOUR WHEELS ARE
FREE
TO ROTATE. INSPECT INDICATOR
SWITCH AND WIRING ON SHIFT MOTOR HOUSING FOR DAMAGE AND SHORT-CIRCUIT.

REPAIR
AS NECESSARY.
YES
i
START ENGINE DEPRESS BRAKE
PEDAL.
PLACE TRANSFER

CASE
SELECTOR IN 2H POSITION AND TRANSMISSION IN
DRIVE
(AUTOMATIC)
OR FIRST

GEAR
(MANUAL). EASE OFF FROM
BRAKE
AND LET WHEELS ROTATE SLOWLY. TEST COMPLETE
FRONT DRIVE SHAFT DOES
NOT ROTATE. FRONT DRIVE
SHAFT ROTATES.
FOUR-WHEEL DRIVE INDICATOR
LIGHT
REMAINS
ON. INSPECT TRANSFER

CASE
LINKAGE.

PLACE
TRANSMISSION IN NEUTRAL. TEST FOR VACUUM
IN VACUUM HOSE

THAT
CONNECTS TO INBOARD SHIFT MOTOR PORT.
(VACUUM SHOULD BE
BETWEEN 10-20 IN. HG.)
CHECK
TRANSFER

CASE.
REPAIR

AS
NECESSARY.
NO VACUUM
OR LOW VACUUM. VACUUM OK
INSPECT INTAKE MANIFOLD
VACUUM SUPPLY HOSE CONNECTION,
TRANSFER CASE VACUUM SWITCH
CONNECTION, VACUUM RESERVOIR, AND SHIFT SYSTEM VACUUM HOSES
FOR PROPER CONNECTION, RESTRICTION,
AIR LEAKS, AND DAMAGE. REPAIR OR REPLACE
AS
NECESSARY. STOP ENGINE
—r~
FRONT AXLE

DISCONNECTS.

INSPECT VACUUM

HOSES
FOR AIR LEAKS, KINKS, ETC.
REPAIR
AS NECESSARY. FRONT AXLE

DOES
NOT
DISCONNECT.
REMOVE SHIFT MOTOR
HOUSING COVER. CONNECT VACUUM PUMP TO
SHIFT MOTOR PORT.

REPLACE
SHIFT MOTOR
IF ARMATURE DOES
NOT MOVE IN AND OUT FREELY. FRONT AXLE
WILL NOT DISCONNECT.

J9002-95
REMOVE SHIFT MOTOR HOUSING
COVER. INSPECT SHIFT FORK, COLLAR, AND AXLE SHAFTS.
REPAIR
OR REPLACE AS
NECESSARY

FRONT
SUSPENSION AND
AXLE
2 - 29
DISCONNECT AXLE/SHIFT MOTOR DIAGNOSIS
(CONT'D)

FOUR-WHEEL
DRIVE
OPERATION
DIAGNOSIS
FOUR-WHEEL DRIVE INDICATOR
LIGHT
DOES NOT
LIGHT
WHEN TRANSFER CASE SELECTOR IN 4H OR 4L POSITION.

RAISE
VEHICLE SO ALL FOUR
WHEELS ARE FREE TO ROTATE.
START ENGINE, DEPRESS BRAKE PEDAL.

PLACE
TRANSFER CASE SELECTOR IN 4H
POSITION AND TRANSMISSION LEVER IN DRIVE
(AUTOMATIC)
OR IN FIRST GEAR
(MANUAL) TO CONFIRM TRANSFER CASE ENGAGEMENT IN 4H. LET WHEELS ROTATE SLOWLY.
FRONT DRIVE SHAFT DOES
NOT ROTATE. FRONT DRIVE
SHAFT TURNS.
INSPECT TRANSFER
CASE
LINKAGE.

CHECK
TRANSFER
CASE.
REPAIR AS
NECESSARY.
FRONT AXLE
CONNECTS.
FOUR-WHEEL DRIVE INDICATOR
LIGHT
DOES
NOT LIGHT.
INSPECT FWD INDICATOR SWITCH, WIRING, AND
LAMP FOR DAMAGE.

REPAIR
AS NECESSARY. RECOMMENDATION:

CHECK
VACUUM SHIFT SYSTEM FOR PROPER
OPERATION.
PLACE
TRANSMISSION
LEVER IN NEUTRAL POSITION. FRONT AXLE

DOES
NOT
CONNECT.
REMOVE VACUUM HOSES FROM AXLE SHIFT MOTOR PORTS.
START ENGINE. TEST FOR VACUUM AT HOSE REMOVED FROM
OUT­

BOARD
PORT ON SHIFT MOTOR,
SHOULD BE BETWEEN 10-20 IN HG.
NO VACUUM
OR LOW VACUUM. STOP ENGINE
H VACUUM OK
INSPECT INTAKE MANIFOLD
VACUUM SUPPLY HOSE CONNECTION, TRANSFER CASE VACUUM SWITCH
CONNECTION, VACUUM RESERVOIR, AND SHIFT
SYSTEM VACUUM HOSES FOR PROPER CONNECTION, RESTRICTION, LEAKS, AND DAMAGE.
REPAIR
OR REPLACE AS NECESSARY. CONNECT A VACUUM PUMP
TO THE OUTBOARD
SHIFT MOTOR PORT.
APPLY 15 INCHES HG. VACUUM AND ROTATE LEFT WHEEL.
NO VACUUM FRONT AXLE
CONNECTED.

CHECK
TRANSFER CASE
VACUUM SWITCH. REPLACE OR REPAIR IF SWITCH
PLUNGER IS DIFFICULT TO MOVE OR BINDS. FRONT AXLE

DOES
NOT
CONNECT.
INSPECT VACUUM HOSES FOR LEAKS, KINKS, ETC.
REPAIR
AS NECESSARY. REMOVE SHIFT MOTOR
HOUSING COVER. CONNECT VACUUM PUMP TO
SHIFT MOTOR PORT.

REPLACE
SHIFT MOTOR
IF ARMATURE DOES
NOT MOVE IN AND OUT FREELY. REMOVE SHIFT MOTOR HOUSING
COVER. INSPECT SHIFT FORK, COLLAR, AND AXLE SHAFTS.
REPAIR
OR REPLACE AS
NECESSARY.
*
REMOVE SHIFT MOTOR HOUSING
COVER. INSPECT SHIFT FORK, COLLAR, AND AXLE SHAFTS.
REPAIR
OR REPLACE AS
NECESSARY.
FRONT AXLE
WILL NOT CONNECT.
REMOVE SHIFT MOTOR HOUSING
COVER. INSPECT SHIFT FORK, COLLAR, AND AXLE SHAFTS.
REPAIR
OR REPLACE AS
NECESSARY.
FRONT AXLE
WILL NOT CONNECT.
REMOVE SHIFT MOTOR HOUSING
COVER. INSPECT SHIFT FORK, COLLAR, AND AXLE SHAFTS.
REPAIR
OR REPLACE AS
NECESSARY.

J9002-96

3
- 6
REAR SUSPENSION
AND
AXLE

•

NUT PIPE
SOCKET
WRENCH
(DRIVER)

FLAT
THREADED
WASHER
ROD
J8917-20

Fig.
6
Spring
Eye
Bushing
Removal
(3) Align
the
bushing with
the
spring
eye and

tighten
the nut
located
at the
socket wrench
end of

the threaded
rod.
Tighten until
the
bushing
is
forced into
the
spring
eye.

The bushing must
be
centered
in the
spring

eye.
The
ends
of the
bushing must
be
flush
or
slightly recessed within
the end
surfaces
of the

spring
eye.
8ERW1GE DIAGNOSIS
INDEX
page

Driveline
Snap
8

Gear
and
Bearing Noise
7

General
Information
6
Limited
Slip
Differential
8
page
Low Speed Knock
.........................
8
Rear
Axle
Alignment
.......................
7

Tire
Noise
7
Vibration
8

GENERAL INFORMATION
Axle bearing problem conditions
are
usually caused
by: • Insufficient
or
incorrect lubricant
• Foreign matter/water contamination
• Incorrect bearing preload torque adjustment When serviced,
the
bearings must
be
cleaned thor­
oughly. They should
be
dried with lint-free shop tow­

els.
Never
dry
bearings with compressed
air.

This will overheat them
and
brinell
the
bearing surfaces. This will result
in
noisy operation after
repair. Axle gear problem conditions
are
usually
the
result

of:

• Insufficient lubrication
• Incorrect
or
contaminated lubricant
• Overloading (excessive engine torque)
• Incorrect clearance
or
backlash adjustment Insufficient lubrication
is
usually
the
result
of a

housing cover leak.
It can
also
be
from worn axle shaft
or
pinion gear seals. Check
for
cracks
or
porous
areas
in the
housing
or
tubes.
Using
the
wrong lubricant will cause overheating
and gear failure. Gear tooth cracking
and
bearing
spalling
are
indicators
of
this.
Axle component breakage
is
most often
the
result

of:

• Severe overloading
• Insufficient lubricant
• Incorrect lubricant • Improperly tightened components
Common causes
of
overloading
is
from full-throttle
acceleration. Overloading occurs when towing
heavier than normal loads. Component breakage
can
occur when
the
wheels
are
spun excessively. Insuffi­
cient
or
incorrect lubricants contribute
to
breakage
through overheating. Loose differential components can also cause breakage. Incorrect bearing preload
or
gear backlash will
not

result
in
component breakage. Mis-adjustment will
produce enough noise
to
cause service repair before
a

3
- 8
REAR SUSPENSION
AND
AXLE

• level. Where axle bearing damage is slight, the noise
is usually not noticeable at speeds above 30 mph.

LOW SPEED KNOCK
Low speed knock is generally caused by a worn
U-joint or by worn side-gear thrust washers. A worn
pinion gear shaft bore will also cause low speed knock.

VIBRATION
Vibration at the rear of the vehicle is usually
caused by a:
• Damaged drive shaft
• Missing drive shaft balance weight
• Worn, out-of-balance wheel and tires
• Loose wheel lug nuts
• Worn U-joint • Loose spring U-bolts
• Loose/broken rear springs or shackles
• Damaged axle shaft bearings
• Loose pinion gear nut
• Excessive pinion yoke run out
• Bent axle shaft Check for loose or damaged front-end components
or engine/transmission mounts. These components
can contribute to what appears to be a rear-end vi­
bration. Do not overlook engine accessories, brackets and drive belts. All driveline components should be examined be­
fore starting any repair. Refer to Group 22, Wheels and Tires for additional
information.

DRIVELINE SNAP
A snap or clunk noise when the vehicle is shifted
into gear (or the clutch engaged), can be caused by: • High engine idle speed
• Loose engine/transmission/transfer case mounts

9
Worn U-joints
• Loose spring shackles or U-bolts
• Loose pinion gear nut and yoke
• Excessive ring gear backlash
• Excessive differential side gear-to-case clearance A worn bushing in the transmission extension
housing can also cause noise. The source of a snap or a clunk noise can be deter­
mined with the assistance of a helper. Raise the ve­
hicle on a hoist with the wheels free to rotate. Instruct the helper to shift the transmission into gear. Listen for the noise, a mechanics stethoscope is
helpful in isolating the source of a noise.

LIMITED
SLIP DIFFERENTIAL
Under normal traction conditions, engine torque is
divided evenly. With low-traction surfaces, engine
torque is transferred to the wheel with the most tire
traction. When diagnosing a limited-slip differential
problem condition, the wheel with the least traction can continue spinning. The most common problem is a chatter noise when
turning corners. Check for incorrect or contaminated lubricant. Replace the gear lubricant if necessary.
• With Sure-Grip differentials add a container of
MOPAR® Hypoid Gear Additive This will correct the condition in most instances. If
the chatter persists, clutch damage could have oc­ curred. After changing the lubricant, drive the vehicle and
make 10 to 12 slow, figure-eight turns. This maneu­
ver will pump lubricant through the clutches.

•

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.

5
- 4
BRAKES

• (3) During road test, make normal and firm brake
stops in 25-40 mph (40-64 Km/h) range. Note faulty
brake operation such as pull, grab, drag, noise, low
pedal, etc.
(4) Inspect suspect brake components and refer to
problem diagnosis information for causes of various
brake conditions.

COMPONENT
INSPECTION
Fluid leak points and dragging brake units can usu­
ally be located without removing any components. The
area around a leak point will be wet with fluid. The
components at a dragging brake unit (wheel, tire, rotor)
will be quite warm or hot to the touch.
Other brake problem conditions will require compo­
nent removal for proper inspection. Raise the vehicle and remove the necessary wheels for better visual ac­

cess.

DIAGNOSING BRAKE
PROBLEMS

PEDAL FALLS
AWAY
A
brake pedal that falls away under steady foot
pressure is the result of a system leak. The leak
point could be at a brakeline, fitting, hose, or caliper. Internal leakage in the master cylinder caused by
worn or damaged piston cups, may also be the prob­ lem cause.
If leakage is severe, fluid will be evident at or around
the leaking component. However, internal leakage in
the master cylinder may not be physically evident. Re­ fer to the cylinder test procedure in this section.

LOW PEDAL
If a low pedal is experienced, pump the pedal sev­
eral times. If the pedal comes back up, worn lining
and worn rotors or drums are the likely causes.
A decrease in fluid level in the master cylinder res­
ervoirs may only be the result of normal lining wear.
Fluid level can be expected to decrease in proportion to wear. It is a result of the outward movement of
caliper and wheel cylinder pistons to compensate for
normal wear. Top off the reservoir fluid level and
check brake operation to verify proper brake action.
SPONGY PEDAL. A spongy pedal is most often caused by air in the sys­
tem. Thin brake drums or substandard brake lines and
hoses can also cause a spongy pedal. The proper course
of action is to bleed the system and replace thin drums and suspect quality brake lines and hoses.

HARD PEDAL
OR
HIGH
PEDAL
EFFORT
A hard pedal or high pedal effort may be due to
lining that is water soaked, contaminated, glazed, or
badly worn. The power booster or check valve could also be faulty. On diesel engine models, high pedal effort may be
the result of a low vacuum condition. If the booster and check valve are OK, the problem may be related
to a vacuum pump hose, hose connection, hose fit­
ting, pump diaphragm, or drive gear. Vacuum pump output can be checked with a standard vacuum
gauge. Vacuum output should range from 8.5 to 25 inches vacuum. If vacuum pump output is within

limits,
check the power booster and check valve as
described in this section.

BRAKE DRAG
Brake drag occurs when the lining is in constant
contact with the rotor or drum. Drag can occur at
one wheel, all wheels, fronts only, or rears only. It is a product of incomplete brakeshoe release. Drag can
be minor or severe enough to overheat the linings,
rotors and drums.
Brake drag can also effect fuel economy. If undetec­
ted, minor brake drag can be misdiagnosed as an en­ gine or transmission/torque converter problem.
Minor drag will usually cause slight surface charring
of the lining. It can also generate hard spots in rotors and drums from the overheat-cool down process. In most

cases,
the rotors, drums, wheels and tires are quite
warm to the touch after the vehicle is stopped.
Severe drag can char the brake lining all the way
through. It can also distort and score rotors and drums to the point of replacement. The wheels, tires and brake components will be extremely hot. In se­
vere cases, the lining may generate smoke as it chars
from overheating.
Some common causes of brake drag are:
• seized or improperly adjusted parking brake cables
• loose/worn wheel bearing
• seized caliper or wheel cylinder piston
• caliper binding on corroded bushings or rusted
slide surfaces
• loose caliper mounting bracket
• drum brakeshoes binding on worn or damaged sup­
port plates
• misassembled components. If brake drag occurs at all wheels, the problem may
be related to a blocked master cylinder return port, or faulty power booster that binds and does not release.

BRAKE FADE
Brake fade is a product of overheating caused by
brake drag. However, brake overheating and subse­ quent fade can also be caused by riding the brake
pedal, making repeated high deceleration stops in a short time span, or constant braking on steep moun­
tain roads. Refer to the Brake Drag information in
this section for additional causes.

PEDAL
PULSA
TION
Pedal pulsation is caused by components that are
loose, out of round, or worn beyond tolerance limits.

•

BRAKES
5 - 5 Disc brake rotors with excessive lateral runout or
thickness variation, or out of round brake drums are
the primary causes of pulsation. Other causes are loose
wheel bearings or calipers and worn, damaged tires.

PULL A
front pull condition could be the result of con­
taminated lining in one caliper, seized caliper piston,
binding caliper, loose caliper, loose or corroded slide

pins,
improper brakeshoes, or a damaged rotor.
A worn, damaged wheel bearing or suspension compo­
nent are further causes of pull. A damaged front tire (bruised, ply separation) can also cause pull.
A common and frequently misdiagnosed pull condi­
tion is where direction of pull changes after a few
stops.
The cause is a combination of brake drag fol­
lowed by fade at one of the brake units.
As the dragging brake overheats, efficiency is so
reduced that fade occurs. Since the opposite brake
unit is still functioning normally, its braking effect is
magnified. This causes pull to switch direction in fa­
vor of the normally functioning brake unit.
When diagnosing a change in pull condition, re­
member that pull will return to the original direction
if the dragging brake unit is allowed to cool down (and is not seriously damaged).

REAR BRAKE GRAB
OR
PULL
Rear grab or pull is usually caused by an improperly
adjusted or seized parking brake cable, contaminated
lining, bent or binding shoes and support plates, or im­
properly assembled components. This is particularly
true when only one rear wheel is involved. However,
when both rear wheels are affected, the master cylinder or proportioning valve could be at fault.

BRAKES
DO NOT
HOLD
AFTER
DRIVING
THROUGH
DEEP
WATER
PUDDLES

This condition is generally caused by water soaked
lining. If the lining is only wet, it can be dried by driv­
ing with the brakes very lightly applied for a few min­

utes.
However, if the lining is thoroughly wet and dirty,
disassembly and cleaning will be necessary.

BRAKE NOISE

Squeak/Squeal
Brake squeak or squeal may be due to linings that
are wet or contaminated with brake fluid, grease, or oil. Glazed linings and rotors with hard spots can also con­
tribute to squeak. Dirt and foreign material embedded in the brake lining can also cause squeak/squeal.
A very loud squeak or squeal is frequently a sign of
severely worn brake lining. If the lining has worn
through to the brakeshoes in spots, metal-to-metal con­
tact occurs. If the condition is allowed to continue, ro­ tors can become so scored that replacement is necessary.
Thump/Clunk

Thumping or clunk noises during braking are fre­
quently not caused by brake components. In many

cases,
such noises are caused by loose or damaged steering, suspension, or engine components. How­
ever, calipers that bind on the slide pins, or slide sur­

faces,
can generate a thump or clunk noise. Worn
out, improperly adjusted, or improperly assembled
rear brakeshoes can also produce a thump noise.

Chatter
Brake chatter is usually caused by loose or worn
components, or glazed/burnt lining. Rotors with hard
spots can also contribute to chatter. Additional
causes of chatter are out of tolerance rotors, brake
lining not securely attached to the shoes, loose wheel
bearings and contaminated brake lining.
Brakelining Contamination Brakelining contamination is usually a product of
leaking calipers or wheel cylinders, driving through
deep water puddles, or lining that has become cov­
ered with grease and grit during repair.
Wheel and
Tire
Problems Some conditions attributed to brake components
may actually be caused by a wheel or tire problem.
A damaged wheel can cause shudder, vibration and
pull. A worn or damaged tire can also cause pull.
Severely worn tires with very little tread left can
produce a grab-like condition as the tire loses and re­ covers traction. Flat-spotted tires can cause vibration and wheel
tramp and generate shudder during brake operation. A tire with internal damage such as a severe
bruise or ply separation can cause pull and vibration.

MASTER
CYLINDER/POWER BOOSTER TEST
(1) Start engine and check booster vacuum hose
connections. Hissing noise indicates a vacuum leak. Correct any leaks before proceeding. (2) Stop engine and shift transmission into Neu­
tral (3) Pump brake pedal until all vacuum reserve in
booster is depleted. (4) Press and hold brake pedal under light foot
pressure. (a) If pedal holds firm, proceed to step (5).
(b) If pedal does not hold firm and falls away,
master cylinder is faulty (internal leakage). (5) Start engine and note pedal action. (a) If pedal falls away slightly under light foot
pressure then holds firm, proceed to step (6). (b) If pedal is effort is high, or no pedal action is
discernible, power booster or vacuum check valve is
faulty. Install known good check valve and repeat steps (2) through (5).

5
- 6
BRAKES

• (c) On diesel models, vacuum pump hose or
pump component may have malfunctioned. Check
pump output with vacuum gauge and repair as necessary. Refer to service procedures in Power
Booster/Vacuum Pump section.
(6) Rebuild booster vacuum reserve as follows: Re­
lease brake pedal. Increase engine speed to 1500
rpm, close throttle and immediately turn off ignition. (7) Wait a minimum of 90 seconds and try brake ac­
tion again. Booster should provide two or more vacuum assisted pedal applications. If vacuum assist is not pro­
vided, perform booster and check valve vacuum tests.
Also check vacuum output on diesel models.

POWER
BOOSTER
CHECK
VALVE
TEST
(1) Disconnect vacuum hose from check valve.
(2) Remove check valve and valve seal from
booster (Fig. 1). (3) Hand operated vacuum pump can be used for
test (Fig. 2). (4) Apply 15-20 inches (50-67 kPa) vacuum at
large end of check valve (Fig. 1). (5) Vacuum should hold steady. If gauge on pump
indicates any vacuum loss, valve is faulty and must
be replaced.
BOOSTER

CHECK
VALVE
APPLY
TEST
\
VACUUM
HERE

Fig.
1
Vacuum
Check
Vaive
And
Seal
J9005-80

Fig.
2 Typical
Hand
Operated
Vacuum
Pump

POWER
BOOSTER
VACUUM
TEST
(1) Connect a vacuum gauge to the booster check
valve with a short length of hose and a T-fitting (Fig.

3).
(2) Start and run engine at idle speed for one
minute.
(3) Clamp hose shut between vacuum source and
check valve (Fig. 3).
(4) Stop engine and observe vacuum gauge.
(5) If vacuum drops more than one inch vacuum
(33 millibars) within 15 seconds, either booster dia­
phragm or check valve are faulty.
SHORT

CONNECTING
CHECK

VACUUM
GAUGE

J9005-81
Fig.
3
Booster
Vacuum
Test
Connections

TESTING
DIESEL
ENGINE
VACUUM
PUMP
OUTPUT
On models with a Cummins turbo diesel engine, a
low vacuum condition in the brake booster will cause
the brake warning light to illuminate. The following test checks output and condition of the
vacuum pump and interconnecting hoses. However, a
more comprehensive testing procedure is provided in
the Power Brake Booster-Brake Pedal-Vacuum Pump section. Refer to the procedure for "Diagnosing A Low
Vacuum Condition" in that section. (1) Check pump vacuum and booster hoses and
connections. Make sure hoses are in good condition and securely attached. Run engine and check for vac­
uum leaks. Replace leaking hoses before proceeding. (2) Disconnect vacuum hose at booster and connect
vacuum gauge to hose end. (3) Run engine at curb idle speed and note vacuum
reading. Then run engine at 1/2 to 3/4 throttle and
note vacuum reading again. (4) Vacuum should range from 8.5 to 25 inches
vacuum at various throttle openings. Vacuum should
hold steady and not drop below 8.5 inches. (5) If vacuum output is OK, check booster and
check valve as described in this section. However, if
vacuum is low, or does not hold steady, vacuum
hoses or pump components are faulty.