1993 CHEVROLET DYNASTY wheel

ABS HYDRAULIC CIRCUITS AND VALVE
OPERATION
Through the following operation descriptions and
diagrams. The function of the various hydraulic con-
trol valves in the ABS system will be described. The
fluid control valves mentioned below, control the flow
of pressurized brake fluid to the wheel brakes during
the different modes of Anti-Lock Braking.
NORMAL BRAKING
ISOLATION VALVES
Open to primary and secondary master cylinder
brake fluid supply (Fig. 11)
DECAY AND BUILD VALVES
Closed, not allowing for the build-up or release of
brake fluid supply (Fig. 11). The brake pedal is applied. The travel of the brake
pedal closes primary, secondary and booster servo
circuits from fluid supply at the fluid reservoir.
Brake fluid from the primary and secondary circuits
flows through the open isolation valves and applies
the wheel brakes. Fluid from the booster servo cir- cuit does not flow to the wheel brakes. The fluid flow
is blocked by the closed build valves and check
valves.
POWER ASSIST
The boost control valve shuttles between its three
positions to provide power assisted braking (Fig. 11).
ABS BRAKING-BUILD PRESSURE
ISOLATION VALVES
Closed, isolating wheel brakes from master cylin-
der primary and secondary fluid supplies and open to
booster servo circuit pressure through open build
valves (Fig. 12)
DECAY VALVES
Closed, not allowing the escape of pressurized fluid
supply from the hydraulic system (Fig. 12).
BUILD VALVES
Open, allowing booster servo circuit pressure to
flow to the wheel brakes through the isolation valves
(Fig. 12).
Fig. 11 Normal Braking - Hydraulic Control
Ä ANTI-LOCK 10 BRAKE SYSTEM 5 - 85

POWER ASSIST The boost control valve shuttles between its three
positions to provide power assisted braking (Fig. 12).
ABS BRAKING-HOLD PRESSURE
For explanation purposes we will assume all speed
sensors are sending the same wheel speed informa-
tion, requiring the same modulation at the same
rate.
ISOLATION VALVES Closed, isolating the wheel brakes from the master
cylinder primary and secondary fluid supplies. Build
and decay valves are closed preventing any fluid
from reaching the open isolation valves (Fig. 13).
DECAY AND BUILD VALVES Closed, not allowing fluid supply to reach the open
isolation valves (Fig. 13).
ABS BRAKING-DECAY PRESSURE
ISOLATION VALVES
Closed, isolating the wheel brakes from the master
cylinder primary and secondary fluid supplies (Fig.
14)
DECAY VALVES Open, allowing release of fluid pressure through
decay valve to the fluid reservoir (Fig. 14)
BUILD VALVE Closed, blocking booster servo circuit fluid to wheel
brakes (Fig. 14).
Fig. 12 Build Pressure - Hydraulic Control
5 - 86 ANTI-LOCK 10 BRAKE SYSTEM Ä

In order to effectively diagnose an Anti-Lock Brake
System (ABS) condition. It is important to read Sec-
tion 1 of this manual, Anti-Lock Brake System De-
scription. This section will give you information on
the function of the ABS components. Then follow the
diagnostic procedures outlined in this section. Many conditions that generate customer com-
plaints of the ABS system may be normal operating
conditions. These conditions though are judged to be
a problem due to unfamiliarity with the ABS system.
These conditions can be recognized without perform-
ing extensive diagnostic work, given adequate under-
standing of operating principles and performance
characteristics of the ABS system. See Section 1 of
this manual to familiarize yourself with the operat-
ing principles of the ABS system.
DEFINITIONS
Several abbreviations are used in this manual.
They are presented here for reference.
² CABÐController Anti-Lock Brake
² ABSÐAnti-Lock Brake System
² PSIÐPounds per Square Inch (pressure)
² WSSÐWheel Speed Sensor
ABS CONTROLLER ANTI-LOCK BRAKE (CAB) SER-
VICE PRECAUTIONS
The ABS system uses an electronic control module,
the (CAB). This module is designed to withstand nor-
mal current draws associated with vehicle operation.
However care must be taken to avoid overloading the
(CAB) circuits. In testing for open or short circuits, do
not ground or apply voltage to any of the circuits unless
instructed to do so by the appropriate diagnostic pro-
cedure. These circuits should only be tested using a
high impedance multi-meter, special tools or the DRB
II tester as described in this section. Power should
never be removed or applied to any control module with
the ignition in the ON position. Before removing or
connecting battery cables, fuses, or connectors, always
turn the ignition to the OFF position.
ABS SYSTEM GENERAL SERVICE PRECAUTIONS
TEST DRIVING ABS COMPLAINT VEHICLES
Most ABS complaints will require a test drive as a
part of the diagnostic procedure. The purpose of the
test drive is to duplicate the condition. Before test driving a brake complaint vehicle,
especially if the Red Brake Warning Lamp is on.
Test the brake function at low speed to be sure
that the car will stop normally. Remember that
conditions that result in illumination of the Red
Fig. 14 Decay Pressure - Hydraulic Control
5 - 88 ANTI-LOCK 10 BRAKE SYSTEM Ä

Brake Warning Lamp may indicate reduced
braking ability. The following procedure should
be used to test drive an ABS complaint:(1) Ignition on. Turn the ignition to the ON position
without starting the car and wait until the Red Brake
Warning Lamp and Amber Anti-Lock Warning Lamp
turn off. This will allow the pump to charge the
accumulator to operating pressure. If the warning
lamp(s) do not turn off, go to step 3. (2) Ignition off for 15 seconds.
(3) Start car. Wait for displays to return to normal
operating mode before proceeding. (4) With Shift lever in PARK, slowly depress brake
pedal and release. (5) Drive vehicle a short distance. During this test
drive, be sure that the vehicle achieves at least 20 mph.
Then brake to at least one complete stop and accelerate
slowly back up to at least 20 mph. (6) If a functional problem with the A.B.S. system is
determined while test driving a vehicle. Refer to the
Bendix Anti-Lock 10 Diagnostics Manual for required
test procedures and proper use of the DRB II tester.
CAUTION: The following are general precautions that
should be observed when servicing and diagnosing
the ABS system and/or other vehicle systems. Failure
to observe these precautions may result in ABS
system damage.
(1) If welding work is to be performed on the vehicle
using an arc welder, the (CAB) should be disconnected
before the welding operation begins. (2) The (CAB) and hydraulic assembly 10 way con-
nectors should never be connected or disconnected with
the ignition on. (3) Some components of the ABS system are not
serviced separately and must be serviced as complete
assemblies. Do not disassemble any component which
is designated as non-serviceable. (4) Always de-pressurize the Hydraulic Accu-
mulator when performing any work that re-
quires disconnecting any hydraulic tube, flex
hose or fitting. The ABS system uses brake fluid
at high pressure. Failure to de-pressurize the
accumulator may result in personal injury
and/or damage to painted surfaces. Brake fluid will damage painted surfaces. If brake
fluid is spilled on any painted surfaces, wash off with
water immediately.
DE-PRESSURIZING HYDRAULIC ACCUMULA- TOR
The ABS pump/motor assembly keeps the hydraulic
accumulator charged between approximately 11,032
and 13,790 kPa (1600 and 2000 psi) anytime key is in the ON position. The pump/motor assembly
cannot run if the ignition is off or either battery ca-
ble is disconnected. Unless otherwise specified, the hydraulic accumu-
lator should be de-pressurized before disassembling
any portion of the hydraulic system. The following
procedure should be used to de-pressurize the hy-
draulic accumulator: (1) With ignition off, or either battery cable discon-
nected, pump the brake pedal a minimum of 40 times
using approximately 50 pounds of pedal force. A no-
ticeable change in pedal feel will occur when the ac-
cumulator becomes discharged. (2) When a definite increase in pedal effort is felt,
pump the pedal a few additional times. This will in-
sure removal of all hydraulic pressure from the
brake system.
WHEEL SPEED SENSOR CABLES
Proper installation of wheel speed sensor cables is
critical to continued ABS system operation. Be sure
that cables are installed and routed properly. Failure
to install cables in their retainers, as shown in Sec-
tion 3 of this manual. May result in contact with
moving parts or over extension of cables, resulting in
an open circuit.
MECHANICAL DIAGNOSTICS AND SERVICE
PROCEDURES
SPECIAL SERVICE TOOLS
Some diagnostic procedures in this section require
the use of special service tools. Each of these tools is
described below.
DRB II DIAGNOSTIC TESTER
Some of the diagnostic procedures that are ex-
plained in this section require the use of the DRB II
DIAGNOSTICS TESTER to insure that proper diag-
nostics are performed. Refer to those sections for
proper testing procedures and the DRB II manual for
its proper operational information.
MST-6163 PRESSURE TESTER
Some diagnostic procedures in this manual require
the use of the MST-6163 pressure gauge and adaptor
(Fig. 2). Pressure Gauge, Special Tool MST-6163 is
required to measure accumulator pressure during
certain phases of ABS operation. The pressure gauge
and adaptor should be installed as follows: (1) De-pressurize the accumulator by pumping the
brake pedal a minimum of 40 times with the ignition
off. The procedure is fully explained under De-Pres-
surizing Hydraulic Accumulator which is described
earlier in this System Diagnosis Section.
Ä ANTI-LOCK 10 BRAKE SYSTEM 5 - 89

pressurized. When a definite increase in pedal effort
is felt, pump pedal a few additional times. This will
insure removal of all hydraulic pressure from the
brake system.(2) Thoroughly clean both reservoir caps and sur-
rounding area of reservoir before cap removal. This
will avoid getting dirt into the reservoir and brake
fluid. (3) Inspect the fluid level, see instructions on top
of reservoir (Fill To Top Of The White Screen In
Front Filter/Strainer). (4) Fill reservoir to top of white screen on filter/
strainer (Fig. 1) as required. Use only brake fluid
conforming to DOT 3 specifications such as Mopar t
or an Equivalent.
(5) Replace reservoir cap.
BLEEDING ABS BRAKE SYSTEM
The Anti-Lock brake system must be bled anytime
air is permitted to enter the brake hydraulic system,
due to disconnection of brake lines or hoses for ser-
vice. It is important to note that excessive air in the
brake system may set a primary pressure/delta P
fault in the (CAB). Refer to Diagnosis, for further in-
formation. Pressure bleeding or manual bleeding procedures
can be used when bleeding the (ABS) hydraulic sys-
tem, after brake lines or hoses have been discon-
nected. Bleeding the (ABS) hydraulic system is also
necessary after the replacement of the hydraulic as-
sembly or wheel brakes. During bleeding operations, be sure that the brake
fluid level remains close to the FULL level in the
reservoir. Check the fluid level periodically during the bleeding procedure and add only DOT 3 brake
fluid to the reservoir as required.
PRESSURE BLEEDING (FIG. 2)
The brake lines may be pressure bled, using a
standard diaphragm type pressure bleeder. Only dia-
phragm type pressure bleeding equipment should be
used to prevent air, moisture, and other contami-
nants from entering the system. The following proce-
dure should be used for pressure bleeding of the
master cylinder and wheel circuits (Fig. 2) (1) Ignition should be turned off and remain off
throughout this procedure. (2) Fully de-pressurize hydraulic accumulator by
pumping brake pedal a minimum of 40 times. The
procedure is fully described in this section of the ser-
vice manual under De-Pressurizing Hydraulic Accu-
mulator.
WARNING: FAILURE TO DE-PRESSURIZE HYDRAU-
LIC ACCUMULATOR, BEFORE PERFORMING THIS
OPERATION, MAY RESULT IN PERSONAL INJURY
AND/OR DAMAGE TO PAINTED SURFACES.
(3) Remove both reservoir caps (Fig. 2).
(4) Install pressure bleeder adapter, on front reser-
voir port and a dummy cap on the rear port of the
reservoir (Fig. 2) (5) Attach bleeding equipment to bleeder adapter
(Fig. 2). Charge pressure bleeder to approximately
138 kPa (20 psi).
(6) Connect a transparent hose to the caliper bleed
screw (Fig. 3). Submerge the free end of the hose in a
clear glass container, which is partially filled with
clean, fresh brake fluid.
Fig. 1 ABS Fill Level On Filter/Strainer
Fig. 2 Pressure Bleeding Brake System
5 - 94 ANTI-LOCK 10 BRAKE SYSTEM Ä

(7) With the pressure bleeder turned on, open the
caliper bleed screw 3/4 to one full turn allowing brake
fluid to flow into the container. Leave bleed screw open
until a clear, bubble-free flow of brake fluid is coming
from the hose in the container. If the reservoir has been
drained or the hydraulic assembly removed from the
car before the bleeding operation. Slowly pump the
brake pedal one or two times while the bleed screw is
open and fluid is flowing. This will help purge any
trapped air from the hydraulic assembly. Tighten
bleeder screw to 10 N Im (7.5 ft. lbs.) torque.
(8) Step 7 above should be done at all wheel brakes,
following the order wheel by wheel as listed below. a) Left rear.
b) Right rear.
c) Left front.
d) Right front.
(9) After bleeding is completed at all four wheel
brakes. Remove pressure bleeding equipment and
adapter by closing pressure bleeder valve and slowly
unscrewing bleeder adapter from hydraulic assembly
reservoir. Failure to release pressure in the reser-
voir will cause spillage of brake fluid, and could
result in personal injury or damage to painted
surfaces. (10) Using a syringe or equivalent method, remove
excess fluid from the reservoir to bring the brake fluid
to the required fill level (Fig. 1). If brake fluid is below
the proper level add Mopar tbrake fluid or equivalent
conforming to DOT 3, requirements. (11) Install the reservoir caps and turn on the igni-
tion to allow the (ABS) pump to charge the accumula-
tor.
MANUAL BLEEDING
Brake lines can be bled, using the manual bleeding
method. Manual bleeding is a two person operation,
one to pump the brake pedal and the other to bleed
each wheel brake. The following procedure should be
used: De-pressurizing the hydraulic accumulator is done
by following the steps described below. (1) Verify that the ignition switch is in the off posi-
tion. (2) Fully de-pressurize the hydraulic accumulator by
pumping brake pedal a minimum of 40 times. Use the
procedure as described in De-Pressurizing Hydraulic
Accumulator listed earlier in this section.
WARNING: FAILURE TO DE-PRESSURIZE HYDRAU-
LIC ACCUMULATOR, PRIOR TO PERFORMING THIS
OPERATION, MAY RESULT IN PERSONAL INJURY
AND/OR DAMAGE TO PAINTED SURFACES.
(3) Connect a transparent hose to the bleed screw on
the wheel cylinder or brake caliper that is to be bled (Fig. 3). Submerge the free end of the hose in a
clear glass container, which is partially filled with
clean, fresh brake fluid.
(4) Slowly pump the brake pedal several times,
using full strokes of the pedal and allowing approxi-
mately five seconds between pedal strokes. After two or
three strokes, continue to hold pressure on the pedal,
keeping it at the bottom of its travel. (5) With pressure on the pedal, open the bleed screw
3/4 to 1 full turn. Leave bleed screw open until fluid no
longer flows from the hose. Tighten the bleed screw
and release the pedal. Be sure that the bleed screw
it tightened before brake pedal is released, or air
may be drawn back into hydraulic system. (6) Repeat Steps 3, 4 and 5 on each wheel brake,
until clear, bubble-free fluid flows from the hose. (7) Repeat the above sequence at each wheel brake,
in the following order: a) Left rear.
b) Right rear.
c) Left front.
d) Right front.
(8) Fill the hydraulic assembly to the proper fill level
(Fig. 1) using Mopar tor equivalent brake fluid meet-
ing DOT 3, requirements. (9) Install both reservoir caps on reservoir.
(10) Turn the ignition switch to the RUN position to
allow the Pump/Motor to turn on and recharge the
accumulator.
Fig. 3 Bleeding Brake System
Ä ANTI-LOCK 10 BRAKE SYSTEM 5 - 95

SYSTEM RELAY, ANTI-LOCK WARNING LAMP RELAY AND PUMP/MOTOR RELAYS (FIG. 2)
REMOVE
See (Fig. 2) Power Distribution Center. Find the lo-
cation of the pump/motor relay in the (PDC). Remove
pump/motor relay by pulling upward and install by
pushing firmly into position. Do not twist the relay
when removing or installing it. See (Fig. 10) in the Relay And Warning Lamp Sec-
tion of this group, for the location of the Anti-Lock
system relay and the Yellow Lamp relay. Remove
the relay from the vehicle using the following proce-
dure. (1) Disconnect the wiring harness connectors from
the relays. Connectors are removed from the relays
by disengaging the connector locking tab from relay
and pulling strait off relay, do not twist. (2) Then remove the relay pack to inner fender at-
taching bolt.
INSTALL The Anti-Lock system and Yellow Lamp relay are
installed using the following procedure. (1) Mount the relay pack to the inner fender with
the anti-rotation tab on the bracket around lip of in-
ner fender hole (Fig. 10). (2) Install the relay pack to inner fender mounting
bolt and torque to 4 N Im (35 in. lbs.). (3) Connect the wiring harness connectors onto the
relays until the locking tabs on the connectors and
relays are fully engaged. Do not twist connectors when
installing them on the relays.
WHEEL SPEED SENSORS
INSPECTION
Inspect tone wheels (Fig. 3) for any missing or broken
teeth, this can cause erratic speed sensor signals.
Tone wheels should show no evidence of contact with
the wheel speed sensor. If contact was made, determine
cause and correct. Excessive runout of the tone wheels can cause erratic
wheel speed sensor signals. Replace assembly if runout
exceeds approximately 0.25 mm (0.010 inch).
FRONT WHEEL SPEED SENSOR
REMOVAL
(1) Raise vehicle and remove front wheel and tire
assembly. (2) Remove screw from clip (Fig. 4) that holds sensor
assembly grommet into fender shield. (3) Carefully, pull sensor assembly grommet from
fender shield. When removing grommet from
fender shield, do not pull on speed sensor cable. (4) Unplug speed sensor cable connector, from ve-
hicle wiring harness. (5) Remove the 2 screws (Fig. 4) that secure the
speed sensor cable, routing tube to the fender well. (6) Remove the 2 sensor assembly grommets from
the retainer bracket, on the strut damper (Fig. 4). (7) Remove speed sensor assembly to steering
knuckle attaching bolt (Fig. 4). (8) Carefully, remove sensor head from steering
knuckle. If the sensor has seized, due to corrosion, use
a hammer and punch to tap edge of sensor ear
Fig. 2 Pump/Motor and Anti-Lock System Relays
Fig. 3 Tone Wheel (Typical)
5 - 104 ANTI-LOCK 10 BRAKE SYSTEM Ä

(Fig. 5), rocking the sensor side to side until free. DO
NOT USE PLIERS ON SENSOR HEAD.
INSTALLATION (1) Connect the wheel speed sensor cable connec-
tor, to the vehicle wiring harness. (2) Push sensor assembly grommet into hole in
fender shield. Install clip and screw (Fig. 4). Torque
screw to 4 N Im (35 in. lbs.).
(3) Install speed sensor cable grommets in bracket
on strut damper (Fig. 4). (4) Install speed sensor cable routing tube to fender
well (Fig. 4). Torque both screws to 4 N Im (35 in. lbs.).
(5) Coat the speed sensor with High Temperature
Multi-purpose E.P. Grease before installing into the
steering knuckle. Install speed sensor attaching screw
and tighten to 7 N Im (60 in. lbs.)
CAUTION: Proper installation of wheel speed sensor
cables is critical to continued system operation. Be
sure that cables are routed correctly and installed in
all retainers. Failure to properly route and install
cables in retainers, as shown in this section. May
result in contact with moving parts and/or over ex-
tension of cables, resulting in an open circuit.
REAR WHEEL SPEED SENSOR (FIGS. 6 AND 8)
REMOVAL
(1) Raise vehicle and remove wheel and tire assem-
bly. (2) Remove sensor assembly grommet from under-
body and pull harness through hole in underbody. (3) Unplug connector from harness.
(4) Remove sensor grommet bracket screw from
body hose bracket, just forward of trailing arm bush-
ing. (5) Remove sensor assembly clip, located on the
inboard side of trailing arm. (6) Remove sensor wire fastener from rear brake
hose bracket. (7) Remove outboard sensor assembly retainer nut.
(8) Remove sensor head screw.
(9) Carefully, remove sensor head from adapter as-
sembly. If the sensor has seized, due to corrosion, DO
NOT USE PLIERS ON SENSOR HEAD. Use a ham-
mer and a punch (Fig. 7) and tap edge of sensor ear,
rocking the sensor side to side until free.
INSTALLATION
Installation is reverse order of removal. Be sure to
coat sensor with High Temperature Multi-purpose E.P.
Grease before installing into adapter assembly.
Tighten screw to 7 N Im (60 in. lbs.) torque. Avoid
getting grease on the pickup area of the speed sensor
assembly.
Fig. 4 Front Wheel Speed Sensor Routing
Fig. 5 Removing Speed Sensor (Typical)
Ä ANTI-LOCK 10 BRAKE SYSTEM 5 - 105