Chrysler Pacifica. Manual — part 458
(6) Install parking brake shoe adjuster spring (Fig.
84).
(7) Install bolt securing parking brake cable to
knuckle (Fig. 80). Tighten bolt to 28 N·m (21 ft. lbs.)
torque.
(8) Using Brake Shoe Gauge, Special Tool C-3919,
or equivalent, measure inside diameter of parking
brake drum portion of rotor (Fig. 85).
(9) Place Gauge over parking brake shoes at wid-
est point (Fig. 86).
(10) Using adjuster star wheel (Fig. 86), adjust
parking brake shoes until linings on both park brake
shoes just touch jaws on gauge. This will give a good
preliminary adjustment of parking brake shoes,
before a final adjustment is made at end of this pro-
cedure.
(11) Install hub and bearing with wheel speed sen-
sor as well as all components necessary to access it.
(Refer to 2 - SUSPENSION/REAR/HUB / BEARING -
INSTALLATION)
(12) Lower vehicle.
(13) Unlock automatic adjuster in parking brake
lever. (Refer to 5 - BRAKES/PARKING BRAKE -
STANDARD PROCEDURE)
(14) Perform final adjustment of parking brake
shoes. (Refer to 5 - BRAKES/PARKING BRAKE/
SHOES - ADJUSTMENTS)
ADJUSTMENTS
ADJUSTMENT - PARKING BRAKE SHOES
(1) Place parking brake lever in “full released”
position.
(2) Raise and support vehicle. (Refer to LUBRICA-
TION & MAINTENANCE/HOISTING - STANDARD
PROCEDURE)
(3) Remove plug in parking brake shoe support to
access adjuster star-wheel (Fig. 87).
NOTE: Through the access hole, rotate the adjuster
star wheel in the following direction to expand the
shoes outward against the drum.
•
Left brake – Rotate star-wheel toward rear of
vehicle.
•
Right brake – Rotate star-wheel toward front of
vehicle.
(4) Using an appropriate tool, turn adjuster star
wheel until wheel will not rotate (dead lock).
(5) Back off adjuster six detents (teeth).
(6) Rotate wheel, checking for light drag. If drag is
too heavy, continue to back off adjuster one detent at
a time until light drag is present. Do not back off
Fig. 85 Measuring Parking Brake Drum Diameter
Fig. 86 Measuring Parking Brake Shoes
1 - BRAKE SHOE GAUGE
2 - ADJUSTER STAR WHEEL
Fig. 87 Access To Shoe Adjuster Star-Wheel
1 - ADJUSTER STAR WHEEL
2 - ACCESS HOLE
CS
BRAKES - BASE
5 - 47
PARKING BRAKE SHOES (Continued)
star-wheel more than 17 detents from wheel
lock.
(7) Install access plug.
(8) Adjust opposite wheel parking brake shoes
using same method.
(9) Lower vehicle.
(10) Apply and release parking brake lever once to
ensure proper operation of parking brakes.
5 - 48
BRAKES - BASE
CS
PARKING BRAKE SHOES (Continued)
BRAKES - ABS
TABLE OF CONTENTS
page
page
BRAKES - ABS
SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
DESCRIPTION - ELECTRONIC VARIABLE
BRAKE PROPORTIONING . . . . . . . . . . . . . . . 49
DESCRIPTION - TRACTION CONTROL
SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
OPERATION - ANTILOCK BRAKE SYSTEM
OPERATION - ELECTRONIC VARIABLE
BRAKE PROPORTIONING . . . . . . . . . . . . . . . 51
SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
STANDARD PROCEDURE - ANTILOCK BRAKE
. . . . . . . . . . . . . . . . . . . 52
. . . . . . . . . . . . . . . 52
TONE WHEEL
. . . . . . . . . . . . . . . . . . . . . . . . . 53
WHEEL SPEED SENSOR - FRONT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
. . . . . . . . . . . . . . . . . . . . . . . . . 53
WHEEL SPEED SENSOR - REAR
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
. . . . . . . . . . . . . . . . . . . . . . . . . 54
HYDRAULIC CONTROL UNIT
. . . . . . . . . . . . . . . . . 54
. . . . . . . . . . . . . . . . 54
OPERATION - HYDRAULIC CIRCUITS AND
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
INTEGRATED CONTROL UNIT - MK25
. . . . . . . . . . . . . . . . . . . . . . . . . 59
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
. . . . . . . . . . . . . . . . . . . . . . . . . 62
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
. . . . . . . . . . . . . . . . . . . . . . . . . 62
INTEGRATED CONTROL UNIT - MK25E
. . . . . . . . . . . . . . . . . . . . . . . . . 63
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
. . . . . . . . . . . . . . . . . . . . . . . . . 65
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
. . . . . . . . . . . . . . . . . . . . . . . . . 67
BRAKES - ABS
DESCRIPTION
DESCRIPTION - ANTILOCK BRAKE SYSTEM
Early production vehicles feature an Antilock
Brake System (ABS) designated MK25. Later produc-
tion vehicles feature an Antilock Brake System (ABS)
designated MK25e. For additional information on the
individual ABS system components, (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/ICU
(INTE-
GRATED CONTROL UNIT) - DESCRIPTION).
The purpose of the antilock brake system (ABS) is
to prevent wheel lockup under braking conditions on
virtually any type of road surface. Antilock braking is
desirable because a vehicle that is stopped without
locking the wheels retains directional stability and
some steering capability. This allows the driver to
retain greater control of the vehicle during braking.
DESCRIPTION - ELECTRONIC VARIABLE
BRAKE PROPORTIONING
Vehicles equipped with ABS use electronic variable
brake proportioning (EVBP) to balance front-to-rear
braking. The EVBP is used in place of a rear propor-
tioning valve. The EVBP system uses the ABS sys-
tem to control the slip of the rear wheels in partial
braking range. The braking force of the rear wheels
is controlled electronically by using the inlet and out-
let valves located in the integrated control unit
(ICU).
EVBP activation is invisible to the customer since
there is no pump motor noise or brake pedal feed-
back.
DESCRIPTION - TRACTION CONTROL SYSTEM
Traction control reduces wheel slip and maintains
traction at the driving wheels at speeds below 64
km/h (40 mph) when road surfaces are slippery. The
traction control system reduces wheel slip by braking
the wheel that is losing traction.
The traction control system may be turned off (or
back on) by depressing the traction control OFF
CS
BRAKES - ABS
5 - 49
switch button located on the center console next to
the ash tray.
OPERATION
OPERATION - ANTILOCK BRAKE SYSTEM
There are a few performance characteristics of the
Antilock Brake System that may at first seem abnor-
mal, but in fact are normal. These characteristics are
described below.
NORMAL BRAKING
Under normal braking conditions, the ABS func-
tions the same as a standard base brake system with
a diagonally split master cylinder and conventional
vacuum assist.
ABS BRAKING
ABS operation is available at all vehicle speeds
above 3–5 mph. If a wheel locking tendency is
detected during a brake application, the brake sys-
tem enters the ABS mode. During ABS braking,
hydraulic pressure in the four wheel circuits is mod-
ulated to prevent any wheel from locking. Each
wheel circuit is designed with a set of electric sole-
noids to allow modulation, although for vehicle sta-
bility, both rear wheel solenoids receive the same
electrical signal. Wheel lockup may be perceived at
the very end of an ABS stop and is considered nor-
mal.
During an ABS event, the integrated control unit
(ICU) regulates hydraulic pressure at all four of the
vehicle’s wheels.
The hydraulic pressure at each front wheel is con-
trolled independently (relative to the amount of slip
at each wheel) in order to maximize the braking force
generated by the front brakes. The rear wheels are
controlled such that the hydraulic pressure at either
rear wheel does not exceed that of the highest slip
rear wheel in order to maintain vehicle stability.
The system can build and release pressure at each
wheel, depending on signals generated by the wheel
speed sensors (WSS) at each wheel and received at
the Controller Antilock Brake (MK25) or the Antilock
Brake Module (MK25e).
NOISE AND BRAKE PEDAL FEEL
During ABS braking, some brake pedal movement
may be felt. In addition, ABS braking will create
ticking, popping, or groaning noises heard by the
driver. This is normal and is due to pressurized fluid
being transferred between the master cylinder and
the brakes. If ABS operation occurs during hard
braking, some pulsation may be felt in the vehicle
body due to fore and aft movement of the suspension
as brake pressures are modulated.
At the end of an ABS stop, ABS is turned off when
the vehicle is slowed to a speed of 3–4 mph. There
may be a slight brake pedal drop anytime that the
ABS is deactivated, such as at the end of the stop
when the vehicle speed is less than 3 mph or during
an ABS stop where ABS is no longer required. These
conditions exist when a vehicle is being stopped on a
road surface with patches of ice, loose gravel, or sand
on it. Also, stopping a vehicle on a bumpy road sur-
face activates ABS because of the wheel hop caused
by the bumps.
TIRE NOISE AND MARKS
Although the ABS system prevents complete wheel
lockup, some wheel slip is desired in order to achieve
optimum braking performance. Wheel slip is defined
as follows: 0 percent slip means the wheel is rolling
freely and 100 percent slip means the wheel is fully
locked. During brake pressure modulation, wheel slip
is allowed to reach up to 25–30 percent. This means
that the wheel rolling velocity is 25–30 percent less
than that of a free rolling wheel at a given vehicle
speed. This slip may result in some tire chirping,
depending on the road surface. This sound should not
be interpreted as total wheel lockup.
Complete wheel lockup normally leaves black tire
marks on dry pavement. The ABS will not leave dark
black tire marks since the wheel never reaches a
fully locked condition. However, tire marks may be
noticeable as light patched marks.
START-UP CYCLE
When the ignition is turned on, a popping sound
and a slight brake pedal movement may be noticed.
The ABS warning lamp will also be on for up to 5
seconds after the ignition is turned on. When the
vehicle is first driven off, a humming may be heard
or felt by the driver at approximately 20–40 kph
(12–25 mph). All of these conditions are a normal
function of ABS as the system is performing a diag-
nosis check.
PREMATURE ABS CYCLING
Symptoms of premature ABS cycling include: click-
ing sounds from the solenoid valves; pump/motor
running; and pulsations in the brake pedal. Prema-
ture ABS cycling can occur at any braking rate of the
vehicle and on any type of road surface.
Premature ABS cycling is a condition that needs to
be correctly assessed when diagnosing problems with
the antilock brake system. It may be necessary to use
a scan tool to detect and verify premature ABS
cycling.
Check the following common causes when diagnos-
ing premature ABS cycling: damaged wheel bearings
(causing tone wheel issues); damaged wheel bearing
5 - 50
BRAKES - ABS
CS
BRAKES - ABS (Continued)
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