service DODGE TRUCK 1993 Service Workshop Manual

3
- 52
REAR SUSPENSION
AND
AXLE

DISASSEMBLY

Service to the Trac-Lok differential requires the
use of Tool Set C-4487 (J-23781). Refer to differential
overhaul in the Model 60 section for differential case
removal and installation. (1) Clamp one axle shaft in a vise (with protective
jaws) with the splined end upward (Fig. 2).
USE

AXLE

SHAFT

AS
HOLDING
FIXTURE
(EXTEND
NO
MORE
THAN
2
3/4 IN.)
J8903-42

~
Fig. 2 Axle Shaft As
Holding
Fixture

(2)
Place shop towels under the differential gear to
avoid gear damage during removal of the ring gear (Fig. 3).
RING GEAR
BOLTS UPWARD

DIFFERENTIAL ON AXLE
SHAFT
(3) Position the differential case on the axle shaft
(Fig. 3). (4) Remove and discard the ring gear bolts. They
are not reusable.
(5) Remove the case from the fixture. Remove the
ring gear from the case by tapping it with brass drift and a hammer.

(6)
Position the case on the fixture.
(7) Remove the pinion gear mate shaft retaining
roll pin (Fig. 4).

DIFFERENTIAL
CASE
PINION

GEAR
MATE SHAFT

PUNCH

LOCKPIN

J9003-95
Fig. 4
Pinion
Gear Mate Shaft
Lock
Pin
Removal
(8) Remove the pinion gear mate shaft. Use a ham­
mer and a brass drift and tap the shaft out.
(9)
Install and lubricate Step Plate C-4487-1 (Fig.

5).

SPECIAL
TOOL

C-4487-1
DIFFERENTIAL

CASE
LOWER

SIDE

GEAR
J9203-4

J8903-43
Fig.
5
Step
Plate
Tool
Installation

Fig.
3
Differential
Case
On Shaft

•

REAR
SUSPENSION
AND
AXLE
3 - 55
(12) Tighten forcing screw
to
compress
the
conned

plates.
Lubricate
and
install pinion gear thrust washers with
a
small screw driver.
(13) Insert and tap
the
pinion shaft into the differ­
ential case (Fig.
13).

(14) Secure pinion shaft with
new
roll pin. Stake
roll
pin
to
differential case.
Fig.
13
Pinion
Gear
Mate
Shaft
installation

POWER-LOK
DIFFERENTIAL

SERVICE
INFORMATION Model
70
rear axles equipped with
a
Power-Lok
differential
are
optionally available
for
Ram
Truck
vehicles (Fig.
1).

FLANGE
BUTTON
BOLTS

PINION

AAATE
SHAFT
J9203-71

Fig.
1
Power-Lok
Differential

DIFFERENTIAL
NOISE
Noise complaints involving
a
Power-Lok should
be

evaluated
to
determine
the
source
of
the noise.
If a

noise occurs while
the
vehicle
is
turning,
the
proba­
ble cause
is
incorrect gear lubricant. Replace axle gear lubricant
and add
MOPAR Hypoid Gear Lubri­
cant Additive. This will correct the condition
in
most
instances. However,
if the
chatter persists, clutch
disc damage could have occurred.

WARNING:
WHEN SERVICING VEHICLES
WITH
A
POWER-LOK
DIFFERENTIAL, DO NOT USE THE EN­

GINE
TO
ROTATE THE AXLE AND
WHEELS.
BOTH
REAR
WHEELS MUST BE
RAISED
FROM THE
SUR­

FACE
AND
THE
VEHICLE SUPPORTED. POWER-

LOK
CAN
EXERT ENOUGH DRIVING FORCE
(IF

ONE
WHEEL IS
IN
CONTACT
WITH
THE SURFACE)
TO
CAUSE
THE VEHICLE TO MOVE.

DIFFERENTIAL
TEST
(1) Drive
the
vehicle
to
thoroughly warm
up the

lubricant
in
the
rear axle.
(2) Place
a
large piece
of
Kraft paper over
a

smooth Formica board. Ensure Formica board
is on a

flat and level surface.
(3) Drive
the
vehicle over
the
Formica board until
one rear wheel
is in the
center
of
the board
and
pa­

per. (4) Place
a
block
of
wood that
is 2
inches high
and

a minimum
of 3
inches wide
in
front
of
one
of
the

front tires.
(5) With
a
gradual throttle opening, attempt
to

slowly drive
the
vehicle over
the
block
of
wood.
(6)
If
the Kraft paper slips out from under the rear
wheel before
the
front tire moves over
the
block
of
wood; reposition
the
vehicle
so
paper
and
board
are
under
the
opposite rear wheel. Attempt
to
drive over
the block
of
wood
the
second time.

3
- 56
REAR SUSPENSION
AND
AXLE
CLUTCH

PLATES

J9203-72
BUTTON

HALF

FLANGE
HALF
Fig.
2
Case
Marked
(7)
If the front wheel moves over the block of wood,
the axle can be considered to be functioning normally.

LUBRICANTS
The lubricant recommended for Power-Lok differ­
ential is API grade GL 5. A container of Trac-Lok
Lubricant (friction modifier) should be added after
service. Refer to Group 0, Lubrication and Maintenance for
additional information.
FLANGE
HALF
CLUTCH

RING
J9203-73

Fig.
3
Cover
Half
Removal

DISASSEMBLY

(1) Mark the ring gear half and cover half for in­
stallation reference (Fig. 2). (2) Remove the case attaching bolts and remove
the button cover half (Fig. 3). (3) Remove the pinion mate gear, side gear (clutch)
ring and clutch pack shaft (Fig. 4). Keep these parts with the button cover half for correct installation in
their original positions.
PINION MATE

GEAR

SCREW

PLATE
DISHED

DISC
PLATE

DISHED

DISC PINION AAATE
CROSS
SHAFT
BUTTON HALF

J9203-74

Fig.
4
Power-Lok
Components

•

BRAKES
BRAKES
5 - 1

CONTENTS

page

BENDIX
DISC
BRAKE
37

BRAKE
ADJUSTMENTS-BRAKE BLEEDING .. 7

BRAKE
DIAGNOSIS
3

CHRYSLER
DISC
BRAKE
27
DRUM
BRAKES-ELEVEN
INCH 46
DRUM
BRAKES-TWELVE
INCH 50

GENERAL
INFORMATION 1
MASTER
CYLINDER-COMBINATION
page

VALVE-BRAKE
LINES 10

PARKING
BRAKES
56

POWER
BRAKE
BOOSTER-BRAKE
PEDAL .. 20

POWER
BRAKE
VACUUM PUMP-DIESEL
ENGINE
...22

REAR
WHEEL ANTILOCK (RWAL)
BRAKES
.. 59

SPECIFICATIONS
65

GENERAL INFORMATION
INDEX

page

Antilock
Rear
Wheel
Brakes
1
Brake
Components 1

BRAKE
COMPONENTS
AD models are equipped with front disc and rear
drum brakes. Power assist brakes and rear wheel an­
tilock brakes are standard equipment on all models. A dual reservoir master cylinder and single or dual
diaphragm, vacuum operated power brake booster is
used for all applications. Models with the Cummins
diesel engine option are also equipped with a vacuum
pump assembly to operate the power brake booster. Front disc brake units consist of single piston, slid-
ing-type calipers with semi metallic brakeshoe lin­ ing. Vented disc brake rotors are used on all models. Bendix calipers are used on 4-wheel drive models
and on diesel engine models. Chrysler disc brake cal­
ipers are used for all other applications. Rear drum brakes are dual shoe units with an au­
tomatic adjustment mechanism. Bendix and Chrysler drum brake assemblies are used. A combination valve is used on all models. The
valve consists of a front brake metering (hold-off)
valve and a front/rear pressure differential switch. A red, brake indicator and warning light is used to
alert the driver if a pressure differential exists be­
tween the front and rear hydraulic systems. The light also alerts the driver when the parking brakes
are applied. The light is located at the left side of the
instrument cluster. An additional indicator light is used for the anti-
lock system. This light is amber and is located in the
page

Brake
Fluid/Lubricants/Cleaning
Solvents
1

Brake
Safety Precautions 2
same side of the instrument cluster as the red indi­
cator light. The antilock light alerts the driver if a system fault occurs.

ANTILOCK
REAR
WHEEL
BRAKES
All AD models are equipped with antilock rear
brakes. The system is designed to retard wheel lockup during periods of high wheel slip when brak­
ing. Retarding wheel lockup is accomplished by modu­
lating fluid pressure to the wheel brake units. Refer
to the Rear Wheel Anti-Lock Brake section for oper­ ation and service information.

BRAKE
FLUID/LUBRICANTS/CLEANING SOLVENTS Recommended fluid for all AD models is Mopar
brake fluid or equivalent meeting SAE J1703 and DOT 3 standards. Use Mopar multi mileage grease to lubricate cali­
per slide surfaces, drum brake pivot pins and shoe contact points on the backing plates. Use GE 661 or
Dow 111 silicone grease (or equivalent) on caliper
bushings and slide pins. Use fresh brake fluid or Mopar brake cleaner to
clean or flush brake system components. These are
the only cleaning materials recommended.

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.

i - 8
BRAKES

•
BRAKE
SHOE'S

Fig. 2 Adjusting Brakeshoes To Gauge standstill at each stop. Incomplete, rolling stops will
not activate the automatic adjusters.

ADJUSTMENT
WITH
TOOL
C-3784
(1) Release parking brakes fully. Be sure there is
slack in cables. (2) Raise vehicle so all wheels are free to turn.
(3) Remove rubber plugs from access holes in sup­
port plates. (4) Insert adjusting Tool
0-3784
into star wheel of
adjuster screw. Turn star wheel counterclockwise
(move tool upward) until slight drag is felt when
road wheel is rotated.

(5)
Insert thin screwdriver or length of welding rod
into support plate access hole and push adjuster lever
out of engagement with star wheel (Fig. 3). Do not
bend lever or distort lever spring.
(6) Hold adjuster lever away from star wheel. Then
back off star wheel until shoe drag on drum is elim­ inated.
(7) Repeat above adjustment at opposite wheel. Be
sure adjustment is equal. (8) Install access hole plugs in support plate.
(9) Adjust the parking brake after wheel brake ad­
justment.
(10) Make final adjustment. Drive vehicle and
make one forward stop followed by one reverse stop.
Repeat procedure 8-10 times to actuate adjuster
mechanism and equalize adjustment. Bring vehicle to
complete standstill at each stop. Incomplete, rolling stops will not activate adjuster mechanism.

CHECKING DRUM
BRAKE ADJUSTER
OPERATION

(1) Place vehicle on hoist, with helper in driver
seat to apply brakes.
(2) Remove access plugs from support plates.
(3) Back off adjuster screw star wheel approxi­
mately 20-30 notches. (4) Observe adjuster screw star wheel and spin
drum and road wheel rapidly in a reverse direction. Fig. 3 Rear Brake Adjustment With Tool
C-3784

(5) Have helper apply brakes firmly. Firm applica­
tion will cause secondary shoe to move and engage rotating drum.
(6) Normal shoe "wrap-up" effect should move sec­
ondary shoe enough to cause adjuster cable to pull adjuster lever up and turn star wheel.

BRAKE
SYSTEM BLEEDING
The brake system can be bled manually or with
pressure equipment. Manual bleeding requires the aid of a helper. Pressure equipment allows the sys­
tem to be bled by one person. All models are equipped with a front brake meter­
ing (hold off) valve. The metering valve is located
within the combination valve. The metering valve balances brake action between the front disc and
rear drum brakes during initial brake application. The metering valve is designed to hold off fluid
flow to the front disc brakes at pressures between 3 and 135 psi (20.68 and 930.8 kPa). Pressures generated by gravity or manual type
bleeding techniques will not affect the valve. How­ ever, pressure bleeding equipment will generate
enough fluid pressure (20 to 30 psi) to close the valve and prevent fluid flow to the front brakes. As a re­
sult, the valve must be held open with special tool
C-4121 when using pressure bleeding equipment.
BLEEDING PROCEDURE (1) If new or overhauled master cylinder will be used,
be sure to bleed cylinder before installation. Refer to
bleeding procedure in Master Cylinder section. (2) If master cylinder has not been serviced, clean
master cylinder and cover to prevent dirt entering
reservoirs. Then remove cover.
(3) If pressure bleeding tank C-3496-B will be
used, install adapter C-4578 on master cylinder.
Then prepare tank for bleeding according to instruc­
tions provided by supplier. Be sure to purge air from
tank lines before use.

S
- 10
BRAKES

•
MASTER CYLINDER—COMBINATION
VALVE—BRAKE
LINES

INDEX

page

Bleeding
New
or
Overhauled Master Cylinder
. . . 12

Brake
Lines
and
Hoses
13

Combination Valve Operation
13

Combination Valve Removal/Installation
........
13
Combination Valve Testing
.................
13
page

General
Information
. 10
Master
Cylinder
Installation
12

Master
Cylinder Removal
10

Master
Cylinder Service—Integral Cylinder
11

Master
Cylinder Service—Two-Section Cylinder
. . 11

GENERAL
INFORMATION
Two types
of
master cylinder
are
used
on AD
mod­

els.
A
two-section master cylinder with
a
removable
reservoir
is
used
on D and
W150/250 models
(Fig.
1).

An integral (one-piece) master cylinder with built-in
fluid reservoirs
is
used
on D and W
250/350 heavy duty models
(Fig.
2).

Two-Section
Master
Cylinder
The two-section master cylinder consists
of
the
cyl­
inder body
and a
removable fluid reservoir.
The
pri­
mary
and
secondary pistons
are
located
in the

aluminum body section.
The
removable reservoir
is

made
of
nylon reinforced with glass fiber
and is the

only serviceable component.
The fluid compartments
of the
nylon reservoir
are

interconnected
to
permit fluid level equalization.
However,
the
equalization feature does
not
affect cir­
cuit separation
in the
event
of a
front/rear hydraulic
system malfunction.
The
reservoir compartments
are

designed
to
retain
the
necessary quantity
of
fluid
needed
to
operate
the
functioning circuit.
Care must
be
exercised when removing/installing
the master cylinder connecting lines.
The
threads
in

the fluid ports
can be
damaged
if
care
is not
prac­
ticed. Start
all
brake line fittings
by
hand
to
avoid cross threading.
The aluminum body section
of the
master cyl­
inder
is not a
repairable component.
If
diagnosis
indicates that
an
internal malfunction
has oc­
curred,
the
aluminum body section must
be re­

placed
as an
assembly.

Integral
Master Cylinder
The one-piece master cylinder
is a
venting type
with integral fluid reservoirs.
The
primary
and
sec­
ondary piston assemblies
are
located
in the
cylinder

bore.
The
cylinder
is a
fully serviceable component and
can be
overhauled when necessary.

Combination
Valve
A two-way combination valve
is
used
on all AD

models
(Fig.
3). The
two-way valve contains
a
front
brake metering valve
and a
pressure differential valve
and
switch.
OUTLETS MASTER CYLINDER BODY
RF494

Fig.
2
Integral Master Cylinder
MASTER
CYLINDER REMOVAL

(1) Disconnect primary
and
secondary brake tubes
at master cylinder. (2) Install plugs
in
cylinder outlet ports
and
brake
tubes
to
prevent dirt entry. (3) Remove nuts attaching master cylinder
to

power brake booster. (4) Remove master cylinder from power brake
booster mounting studs.

•

BRAKES
5 - 11

FROM
MASTER CYLINDER
^SWITCH
ASSEMBLY
Fig.
3 Two-Way Combination
Valve
MASTER
CYLINDER SERVICE-TWO-SECTION

CYLINDER
The only serviceable component on the two-
section cylinder is the nylon reservoir. If the cyl­
inder body or internal components are worn or damaged, the cylinder body must be replaced as
an assembly.
RESERVOIR REPLACEMENT- TWO-SECTION CYLINDER (1) Clean reservoir exterior and master cylinder
body. (2) Remove reservoir caps and drain fluid from cyl­
inder. (3) Mount master cylinder in vise. Clamp vise jaws
on aluminum body.
(4) Note position of reservoir before removal. This
is important as reservoir can be installed backwards
if care is not exercised.
(5) Remove reservoir by firmly rocking it from side
to side (Fig. 4). Continue rocking until reservoir is
free of grommets.
Fig.
4 Removing/Installing Cylinder Reservoir
(6) Remove and discard grommets securing reser­
voir in cylinder body. (7) Install new reservoir grommets in cylinder
body. (8) Lubricate new reservoir grommets with clean
brake fluid.

CAUTION:
The reservoir can be installed
back­

wards
if care is not
exercised.
Install the reservoir
so
the fluid
fill
information (on the reservoir
side)
is

on
the
same
side
as the fluid outlet
ports
in the
cyl­
inder
body
(Fig. 4).
(9) Start reservoir into grommets. Then rock reser­
voir side to side until fully seated. Reservoir bottom surface should touch grommets after installation.
(10) Bleed master cylinder before installing it in
vehicle. Refer to procedure in this section.

MASTER CYLINDER SERVICE-INTEGRAL
CYLINDER
The integral (one-piece) cylinder is a fully service­
able component. It can be overhauled to restore per­
formance when necessary. Overhaul procedure is as follows.
INTEGRAL CYLINDER DISASSEMBLY AND INSPECTION
(1) Remove cylinder cover (Fig. 5). (2) Drain fluid from cylinder reservoirs.
(3) Mount cylinder in vise.
(4) Press cylinder pistons inward with wood dowel
and remove piston snap ring (Fig. 6).
(5) Remove primary piston assembly from cylinder

bore.
Discard piston assembly.
(6) If cylinder is equipped with piston stop screw
for secondary piston, remove stop screw before pro­ ceeding. (7) Remove secondary piston with compressed air
applied through brakeline port or compensator port
at bottom of reservoir. Discard piston assembly after
removal.
COVER COVER
CLAMP RF495 Fig.
5 Removing/Installing Cylinder
Cover

•

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.

5
- 20
BRAKES

•
POWER BRAKE BOOSTER—BRAKE PEDAL

INDEX

page
Brake Pedal
Installation
21

Brake Pedal Removal
21

General
Information
.......................
20
page
Power Brake Booster
Installation
.............
21

Power Brake Booster Removal
21

GENERAL
INFORMATION
Power brakes
are
standard
on all AD
models.
A

single
or
dual diaphragm, vacuum power brake
booster
is
used. AD
and W150
models
are
equipped with
a
single
diaphragm booster unit
(Fig. 1). D and
W250/350
models
are
equipped with
a
dual diaphragm booster. The booster unit consists
of a
single housing
di­

vided into separate chambers
by one or two
internal
diaphragms.
The
outer edge
of the
diaphragm
is se­

cured
to the
housing. The booster push
rod,
which connects
the
booster
to

the brake pedal
and
master cylinder,
is
attached
to

the center
of the
diaphragm.
A
check valve
is
used
in

the booster outlet connected
to the
engine intake manifold. Power assist
is
produced
by a
combination
of
vac­
uum
and
atmospheric pressure
to
boost brake assist. The power brake booster
is not a
repairable
component.
The
booster must
be
replaced
as an
assembly
if
diagnosis indicates
a
malfunction
has occurred.
AD models with
the
Cummins diesel engine
are

equipped with
a
dual diaphragm power brake
booster.
A
separate vacuum pump assembly supplies the vacuum needed
for
booster operation
(Fig. 2).

The diesel vacuum pump
and the
power steering
pump
are
combined into
a
single assembly. Both
pumps
are
operated
by a
drive gear pressed onto
the

vacuum pump shaft.
The
drive gear
is
operated
by

the camshaft gear. A suspended-type brake pedal
is
used
for all
appli­
cations.
The
pedal
is
attached
to the
pedal support
bracket with
a
pivot shaft.
The
pedal, bolt
and
bush­ ings
are all
serviceable components.
RESERVOIR
PEDAL
SHAFT

RETAINER
SCREW

MASTER
CYLINDER

AND BOOSTER
ASSEMBLY <5>

I
RETAINER
CLIP

TIGHTENING
TORQUE

'A>
200
IN.-LBS.
(23 N-m)

¥>
35
IN.-LBS.
(4 N.m)
LOCKNUT
«
RK721

Fig.
1
Power
Brake
Booster
And
Pedal
Mounting