Chrysler 300M, Dodge Interpid. Manual — part 37
The power brake booster can be identified by the
tag attached to the body of the booster assembly (Fig.
73). This tag contains the following information:
• the production part number
• the date it was built
• who manufactured it
NOTE: The power brake booster assembly is not a
repairable part and must be replaced as a complete
unit if it is found to be faulty in any way. The power
booster vacuum check valve is not repairable but
can be replaced as an assembly.
OPERATION
The purpose of the power brake booster is to
reduce the amount of force required by the driver
(foot-pedal pressure) to obtain the required hydraulic
pressure in the brake system to stop the vehicle. This
vehicle utilizes a Bosch power brake booster to
accomplish this task in all brake applications.
The power brake booster is vacuum operated. The
vacuum is supplied from the intake manifold on the
engine through the vacuum hose and power brake
booster check valve (Fig. 72).
As the brake pedal is pressed, the power brake boost-
er’s input rod moves forward. This opens and closes
valves in the power brake booster, creating a vacuum on
one side of a diaphragm and allowing atmospheric pres-
sure to enter on the other. This difference in pressure
forces the output rod of the power booster out against
the primary piston of the master cylinder. As the pis-
tons in the master cylinder move forward this creates
the hydraulic pressure in the brake system.
DIAGNOSIS AND TESTING - POWER BRAKE
BOOSTER
BASIC TEST
(1) With engine off, depress and release the brake
pedal several times to purge all vacuum from the
power brake booster.
(2) Depress and hold the pedal with light effort (15
to 25 lbs. pressure), then start the engine.
The pedal should fall slightly, then hold. Less effort
should be needed to apply the pedal at this time. If the
pedal fell as indicated, perform the VACUUM LEAK
TEST listed after the BASIC TEST. If the pedal did not
fall, continue on with this BASIC TEST.
(3) Disconnect the vacuum hose on the side of the
vacuum check valve that leads to the speed control,
then connect a vacuum gauge to the open vacuum
port on the valve.
(4) Start the engine.
(5) When the engine is at warm operating temper-
ature, allow it to idle and check the vacuum at the
gauge.
If the vacuum supply is 12 inches Hg (40.5 kPa) or
more, the power brake booster is defective and must
be replaced. If the vacuum supply is below 12 inches,
continue on with this BASIC TEST.
(6) Shut off the engine.
(7) Connect the vacuum gauge to the vacuum ref-
erence port on the engine intake manifold.
(8) Start the engine and observe the vacuum gauge.
If the vacuum is still low, check the engine tune
and repair as necessary. If the vacuum is above 12
inches, the hose or check to the booster has a restric-
tion or leak.
Once an adequate vacuum supply is obtained,
repeat the BASIC TEST.
VACUUM LEAK TEST
(1) Disconnect the vacuum hose on the side of the
power brake booster vacuum check valve that leads
to the speed control, then connect a vacuum gauge to
the open vacuum port on the valve.
(2) Remove the remaining hose on the vacuum
check valve that is not the vacuum supply hose com-
ing from the intake manifold. Cap off the open port
on the check valve.
(3) Start the engine.
(4) Allow the engine to warm up to normal operat-
ing temperature and engine idle.
(5) Using vacuum line pliers, close off the vacuum
supply hose near the booster and observe the vacuum
gauge.
Fig. 73 Power Brake Booster Identification
1 - VACUUM CHECK VALVE
2 - MASTER CYLINDER PUSH ROD
3 - POWER BRAKE BOOSTER ASSEMBLY
4 - MASTER CYLINDER MOUNTING STUDS
5 - PART IDENTIFICATION TAG
LH
BRAKES - BASE BRAKE SYSTEM
5 - 43
POWER BRAKE BOOSTER (Continued)
If the vacuum drop exceeds 1.0 inch Hg (3.3 kPa)
in one minute, repeat the above steps to confirm the
reading. The vacuum loss should be less than 1.0
inch Hg in one minute time span. If the loss is more
than 1.0 inch Hg, replace the power brake booster. If
it is not, continue on with this test.
(6) Remove the pliers from the hose temporarily.
(7) Apply light effort (approximately 15 lbs. of
force) to the brake pedal and hold the pedal steady.
Do not move the pedal once the pressure is applied
or the test results may vary.
(8) Have an assistant reattach the pliers to the
vacuum supply hose.
(9) Allow 5 seconds for stabilization, then observe
the vacuum gauge.
If the vacuum drop exceeds 3.0 inches Hg (10 kPa)
in 15 seconds, repeat the above steps to confirm the
reading. The vacuum loss should be less than 3.0
inches Hg in 15 seconds time span. If the loss is
more than 3.0 inches Hg, replace the power brake
booster. If it is not, the booster is not defective.
REMOVAL - POWER BRAKE BOOSTER
(1) Remove the battery ground cable from the
ground stud on the right strut tower. Then, correctly
isolate the ground cable by installing the cable isola-
tor on the ground stud (Fig. 74).
(2) Remove caps from both wiper arms at the
attachment to the pivots to expose the wiper arm
attaching nut. Remove the nut attaching each wiper
arm to its pivot (Fig. 75).
(3) Remove the wiper arms from the pivots. Wiper
arms are removed from the pivots by rocking them
back and force on the pivots until they can be pulled
off the pivots.
(4) Remove the wiper module cover and cowl cover
(Fig. 76) from the vehicle.
(5) Remove the 8 bolts, attaching the reinforce-
ment (Fig. 77) to the strut towers and the 1 bolt (Fig.
77) attaching the wiper module to the reinforcement.
Remove the reinforcement from the vehicle.
Fig. 74 Correctly Isolated Remote Ground Cable
1 - CABLE ISOLATOR
2 - GROUND STUD
3 - GROUND CABLE
Fig. 75 Wiper Arm Attachment To Pivot
1 - WIPER ARMS
2 - ATTACHING NUT
3 - ATTACHING NUT
Fig. 76 Wiper Module And Cowl Cover
1 - COWL COVER
2 - WIPER MODULE COVER
Fig. 77 Reinforcement Attachment To Vehicle
1 - RIGHT STRUT TOWER
2 - WIPER MODULE
3 - LEFT STRUT TOWER
4 - ATTACHING BOLTS
5 - ATTACHING BOLT
6 - REINFORCEMENT
7 - ATTACHING BOLTS
5 - 44
BRAKES - BASE BRAKE SYSTEM
LH
POWER BRAKE BOOSTER (Continued)
(6) Disconnect the wire connector from the brake
fluid level sensor on the right side of the master cyl-
inder reservoir.
(7) Remove the 2 nuts (Fig. 78) attaching the mas-
ter cylinder to the vacuum booster.
(8) Carefully slide master cylinder off vacuum booster
with brake lines attached, and position it backwards, on
top of left engine cylinder head cover (Fig. 79).
(9) Disconnect vacuum hose from power brake
booster check valve. DO NOT REMOVE CHECK
VALVE FROM POWER BRAKE BOOSTER.
(10) From under instrument panel, position a
small screwdriver between the center tang on the
power brake booster input rod to brake pedal pin
retaining clip.
(11) Rotate screwdriver enough to allow retainer clip
center tang to pass over end of brake pedal pin and pull
retainer clip off pin. Discard retainer clip it is not to
be reused, replace only with a new retainer clip.
(12) Remove the four nuts that attach the power
brake booster to the vehicle dash panel. Nuts are
accessible from under the dash panel in the area of
the steering column and pedal bracket.
(13) Rotate the windshield wiper motor crank
lever until the crank lever points in the 12 o’clock
position (Fig. 80).
(14) Slide the power brake booster out of the dash
panel and remove from vehicle.
CAUTION: Do not attempt to disassemble the power
brake vacuum booster. It is serviced ONLY as a
complete assembly.
INSTALLATION - POWER BRAKE BOOSTER
(1) Position power brake vacuum booster on dash
panel.
(2) Install and tighten the 4 power brake booster to
dash panel mounting nuts to 28 N·m (250 in. lbs.) torque.
(3) Using lubriplate or equivalent, coat the bearing
surface of brake pedal pin.
(4) Connect booster input rod to brake pedal pin
and install a NEW retainer clip. Use only a new
retainer clip DO NOT USE the old clip.
NOTE: Before installing master cylinder, reposition
under hood wiring harness above master cylinder
mounting studs, in front of booster (Fig. 79).
(5) Carefully position master cylinder on booster.
Position wire harness routing bracket onto right mas-
ter cylinder mounting stud.
Fig. 78 Master Cylinder Mounting
1 - MASTER CYLINDER MOUNTING NUTS
2 - POWER BRAKE BOOSTER
3 - MASTER CYLINDER
Fig. 79 Master Cylinder Positioning
1 - BOOSTER
2 - MASTER CYLINDER
3 - ENGINE CYLINDER HEAD COVER
Fig. 80 Wiper Crank Lever Positioning
1 - WIPER MOTOR CRANK LEVER
2 - BRAKE BOOSTER
LH
BRAKES - BASE BRAKE SYSTEM
5 - 45
POWER BRAKE BOOSTER (Continued)
(6) Install and tighten the 2 master cylinder to
booster mounting nuts (Fig. 78) to 28 N·m (250 in.
lbs.) torque.
(7) Reconnect brake fluid level sensor connector.
(8) Connect all vacuum hoses onto the booster vac-
uum check valve.
(9) Check brake lamp switch operation.
(10) Install the wiper module reinforcement on the
vehicle (Fig. 77). Install the 8 bolts, attaching the
reinforcement to the strut towers. Install the bolt
attaching the wiper module to the reinforcement.
(11) Install the covers over the wiper module and
the cowl (Fig. 76). Install and securely tighten the
attaching screws.
(12) Reconnect the battery ground cable to the
ground stud on the shock tower.
(13) Turn windshield wipers ON, then OFF, in
order to park wipers in the proper position before
installing wiper arms.
(14) Install the wiper arms on the pivots (Fig. 75).
Install and securely tighten the wiper arm to pivot
attaching nuts. Install the caps on the wiper arms
covering the pivot nuts.
(15) Verify proper operation of the power brake
booster and brake system.
PROPORTIONING VALVE
DESCRIPTION
Two proportioning valves are used on each vehicle
without antilock brakes. One valve is used for each
rear
brake
hydraulic
circuit.
The
proportioning
valves that are located in the junction block (Refer to
5 - BRAKES - BASE/HYDRAULIC/MECHANICAL/
JUNCTION BLOCK - DESCRIPTION). The valves
are not serviceable and must be replaced as part of
the junction block.
OPERATION
Proportioning valves balance front to rear braking
by controlling (at a given ratio) brake hydraulic pres-
sure to the rear brakes above a preset level (split
point). On light pedal applications equal brake pres-
sure is transmitted to both the front and rear brakes.
On heavier pedal applications, through the use of
proportioning valves, the pressure transmitted to the
rear will be lower than the front brakes. This pre-
vents premature rear wheel skid.
If hydraulic pressure is lost in one-half of the diag-
onally split brake hydraulic system, the operation of
the proportioning valve in the remaining half is not
affected.
DIAGNOSIS AND TESTING - PROPORTIONING
VALVE
Vehicles without Antilock Brakes have two propor-
tioning valves. One proportioning valve controls the
right rear brake, and the other proportioning valve
controls the left rear brake. The proportioning valves
are located in the junction block. Vehicle’s with ABS
do not have proportioning valves to test, they use
Electronic Variable Brake Proportioning which is
built into the Integrated Control Unit (ICU).
If premature wheel skid occurs on a hard brake
application, it could be an indication that a malfunc-
tion has occurred with one of the two rear brake pro-
portioning valves. Test the valve that controls the
side of the vehicle on which the skid occurs. Both
proportioning valves have the same pressure specifi-
cations and are tested in the same way.
(1) If the left rear proportioning valve is suspect,
disconnect the tube nut fitting at the master cylinder
primary port (port closest to power brake booster).
Install Adapter, Special Tool 8494-2, in its place on
the master cylinder.
(2) If the right rear proportioning valve is suspect,
disconnect the tube nut fitting at the master cylinder
secondary port (port furthest from power brake boost-
er). Install Adapter, Special Tool 8494-2, in its place
on the master cylinder.
(3) Connect primary brake tube to Adapter.
(4) Install
a
Pressure
Gauge,
Special
Tool
C-4007-A, to the Adapter.
(5) Tighten all tube nut fittings to 17 N·m (145 in.
lbs.) torque.
(6) Remove screw fastening the speed control servo
to the upper radiator closure panel (Fig. 81).
(7) Remove screw fastening the washer filler tube
to the upper radiator closure panel (Fig. 81).
Fig. 81 Servo And Filler Tube Fasteners
1 - SPEED CONTROL SERVO
2 - WINDSHIED WASHER FILLER TUBE
3 - SCREW
4 - SCREW
5 - 46
BRAKES - BASE BRAKE SYSTEM
LH
POWER BRAKE BOOSTER (Continued)
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