1993 CHEVROLET DYNASTY abs

WARNING: FAILURE TO DE-PRESSURIZE HYDRAU-
LIC ASSEMBLY/ACCUMULATOR PRIOR PERFORM-
ING THIS OPERATION. MAY RESULT IN PERSONAL
INJURY AND/OR DAMAGE TO PAINTED SURFACES
OF THE VEHICLE.
(2) Using Oil Filter Band Wrench, Special Tool
C-4065 or equivalent loosen bladder accumulator.
Then remove the bladder accumulator and brake
fluid shield from the hydraulic assembly (Fig. 17).
INSTALL
(1) Install the brake fluid spray shield onto the hy-
draulic accumulator (Fig. 1). (2) Install the bladder accumulator onto the hy-
draulic assembly by hand. Be sure that the O-Ring
on the bladder accumulator is fully seated into the
hydraulic assembly. (3) Using Oil Filter Band Wrench, Special Tool
C-4065 or equivalent, (Fig. 17) torque the bladder ac-
cumulator to 48 N Im (35 ft. lbs.)
(4) Turn ignition switch to the run position to en-
ergize the pump/motor assembly and pressurize hy-
draulic system. Check for leakage at the hydraulic
assembly to hydraulic bladder accumulator fitting. (5) Again de-pressurize accumulator by pumping
brake pedal a minimum of 40 times. Use procedure
described in De-Pressurizing Hydraulic Accumulator
in this section of the service manual. (6) Then check the brake fluid level in the hydrau-
lic assembly reservoir. If brake fluid level is low, fill
reservoir to proper level (Fig. 15) with Mopar tbrake
fluid or equivalent conforming to DOT 3 require-
ments.PROPORTIONING VALVES (FIG. 18)
CAUTION: Proportioning valves should never be dis-
assembled or repaired in any way, repair is by re-
placement only.
REMOVE (1) Fully de-pressurize the hydraulic accumulator by
pumping brake pedal a minimum of 40 times. Use
procedure described in De-Pressurizing Hydraulic Ac-
cumulator listed earlier in this section.
WARNING: FAILURE TO FULLY DE-PRESSURIZE THE
HYDRAULIC ASSEMBLY/ACCUMULATOR PRIOR TO
REMOVING THE PROPORTIONING VALVE. MAY RE-
SULT IN PERSONAL INJURY AND/OR DAMAGE TO
PAINTED SURFACES OF THE VEHICLE.
(2) Remove fresh air intake ducts and air cleaner.
(3) Remove pressure and return hose (Fig. 5) from
hydraulic unit. (See Pressure and Return Hose Section
For Proper Removal Procedure). (4) Remove brake tube from the proportioning valve
that requires servicing. (5) Remove proportioning valve requiring service
from the hydraulic assembly (Fig. 19).
INSTALL (1) Install proportioning valve on hydraulic assem-
bly and tighten to 40 N Im (30 ft. lbs.) torque.
(2) Install brake tube on proportioning valve.
Tighten tube nut to 16 N Im (145 in. lbs.) torque.
(3) Install hydraulic pressure and return hoses.
Torque pressure hose to hydraulic assembly fitting to
16 N Im (145 in. lbs). Torque return hose to metal tube
hose clamp to 1 N Im (10 in. lbs.).
(4) Install fresh air intake duct and air cleaner.
(5) Bleed the affected brake line, see Bleeding Brake
System in this section.
Fig. 17 Remove And Install Bladder Accumulator
Fig. 18 ABS Proportioning Valve
5 - 102 ANTI-LOCK 10 BRAKE SYSTEM Ä

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

CAUTION: Do not insert dual function pressure
switch into hydraulic assembly using the socket
and ratchet. Cross threading of the switch may oc-
cur. (1) Install the dual function pressure switch into
the hydraulic assembly by hand until the O-ring
seals are seated. (2) Using Socket, Special Tool 6607, (Fig. 10)
torque the dual function pressure switch into the hy-
draulic assembly to 12 N Im (9 ft. lbs.).
(3) Connect the wiring harness connectors (Fig. 9)
onto the dual function pressure switch and the boost
pressure transducer. Be sure the locking tabs on the
connectors are fully engaged on the switches. (4) Lower the vehicle.
(5) Turn the ignition switch to the on position and
let the system pressurize. Check for any leaks at the
dual function pressure switch. (6) Fully de-pressurize the hydraulic assembly a
second time. This will purge any air out that may
have entered hydraulic assembly when the switch
was removed. Turn the ignition switch to the on po-
sition and let the system pressurize again. (7) Road test vehicle to insure that the brake sys-
tem is performing correctly.
PRIMARY PRESSURE TRANSDUCER
REMOVE
WARNING: FAILURE TO FULLY DE-PRESSURIZE
THE HYDRAULIC BLADDER ACCUMULATOR PRIOR
TO REMOVING PRIMARY PRESSURE TRANS-
DUCER. WILL RESULT IN PERSONAL INJURY
AND/OR DAMAGE TO PAINTED SURFACES OF THE
VEHICLE.
To remove primary pressure transducer (Fig. 11),
from hydraulic assembly, removal of hydraulic as-
sembly from vehicle is notrequired.
(1) Fully de-pressurize the hydraulic accumulator
by pumping brake pedal a minimum of 40 times. Use
procedure described in De-Pressurizing Hydraulic Ac-
cumulator listed earlier in this section. (2) Remove as much brake fluid as possible from
the brake fluid reservoir, using a syringe or equiva-
lent method. (3) Using oil filter band wrench, Special Tool
C-4065 or equivalent, (Fig. 12) loosen bladder accu-
mulator. Then remove bladder accumulator and
brake fluid spray shield from hydraulic assembly. (4) Remove high pressure banjo fitting (Fig. 13)
from hydraulic assembly. (5) Using needle nose pliers, remove the 3 fluid
reservoir retaining pins from the hydraulic assembly
(Fig. 14). Compress barb on opposite side of retaining
pin, to prevent pin from breaking. CAUTION: Be extremely careful during the following
procedure to avoid damaging or puncturing brake
fluid reservoir during its removal.
(6) Remove brake fluid reservoir from hydraulic
assembly by carefullyprying between reservoir and
hydraulic assembly using a blunt pry bar (Fig. 15).
Use a rocking motion to help disengage reservoir
from grommets while prying. (7) Remove brake fluid level sensor from reservoir
and remove fluid reservoir from vehicle. (8) Remove hydraulic assembly wiring harness
connector from the primary pressure transducer (Fig.
16).
Fig. 11 Primary Pressure Transducer Location On Hydraulic Assembly
Fig. 12 Removing Bladder Accumulator
5 - 108 ANTI-LOCK 10 BRAKE SYSTEM Ä

ANTI-LOCK BRAKE SYSTEMÐBENDIX ANTI-LOCK 6 AA,AG,AJ,AP BODY INDEX
page page
ABS Brake System Diagnosis .............. 123
ABS Brake System Diagnostic Features ...... 125
ABS Computer System Service Precautions . . . 124
ABS General Service Precautions ........... 124
Anti-Lock Brake System Components ........ 116
Anti-Lock Brake System Definitions .......... 113
Anti-Lock Brakes Operation and Performance . . 115
Anti-Lock System Relays and Warning Lamps . . 120
Controller Anti-Lock Brake (CAB) ............ 119
Diagnostic Connector ..................... 120
Electronic Components ................... 130 General Information
...................... 113
Hydraulic Circuits and Valve Operation ....... 121
Major Components ...................... 114
Mechanical Diagnostics and Service Procedures . 125
Normal Braking System Function ............ 114
On-Car ABS Brake System Service .......... 126
Specifications .......................... 135
System Self-Diagnostics .................. 115
Vehicle Performance ..................... 115
Warning Systems Operation ............... 116
GENERAL INFORMATION
The purpose of the Anti-Lock Brake System (ABS)
is to prevent wheel lock-up under heavy braking con-
ditions on virtually any type of road surface. Anti-
Lock Braking is desirable because a vehicle which is
stopped without locking the wheels will retain direc-
tional stability and some steering capability. This al-
lows the driver to retain greater control of the
vehicle during heavy braking. This section of the service manual covers the de-
scription, diagnostics, and on car service for the Ben-
dix Anti-Lock 6 Brake System. If other service is required on the non ABS related components of the
brake system. Refer to the appropriate section in this
group of the manual for the specific service procedure
required.
ANTI-LOCK BRAKE SYSTEM DEFINITIONS
In this section of the manual several abbreviations
are used for the components that are in the Anti-
Lock Braking System They are listed below for your
reference.
² CABÐController Anti-Lock Brake
² ABSÐAnti-Lock Brake System
Fig. 1 Four-Wheel Anti-Lock Brake System Components AA/AG/AJ Body
Ä ANTI-LOCK 6 BRAKE SYSTEM 5 - 113

² PSIÐPounds per Square Inch (pressure)
² WSSÐWheel Speed Sensor
NORMAL BRAKING SYSTEM FUNCTION
Under normal braking conditions, the ABS System
functions the same as a standard brake system with
a diagonally split master cylinder and conventional
vacuum assist. If a wheel locking tendency is detected during a
brake application, the system will enter Anti-Lock
mode. During Anti-Lock Braking, hydraulic pressure
in the four wheel circuits is modulated to prevent
any wheel from locking. Each wheel circuit is de-
signed with a set of electrical valves and hydraulic
line to provide modulation, although for vehicle sta-
bility, both rear wheel valves receive the same elec-
trical signal. The system can build or reduce
pressure at each wheel, depending on signals gener-
ated by the wheel speed sensors (WSS) at each wheel
and received at the Controller Anti-Lock Brake
(CAB).
MAJOR COMPONENTS
The following is a list of major system components.
Details of all components can be found later in this
section. See (Fig. 1) for the general location of the
components in the vehicle.
MASTER CYLINDER AND VACUUM BOOSTER
The Bendix Anti-Lock 6 Brake System uses the ve-
hicles standard Master Cylinder/Reservoir and Vac-
uum Booster (Fig. 2). The master cylinder primary
and secondary outputs go directly to the Modulator
Assembly.
MODULATOR AND PUMP MOTOR/ASSEMBLY
The Modulator Assembly (Fig. 3) contains the
wheel circuit valves used for brake pressure modula-
tion and the Pump/Motor. The Pump/Motor function, as part of the Modulator
Assembly. Is to pump low pressure brake fluid from
the brake fluid sump into the ABS Accumulator.
During a stop which requires the ABS system to be-
come operational.
WHEEL SPEED SENSORS
A Wheel Speed Sensor (Fig. 4) is located at each
wheel to transmit wheel speed information to the
Controller Anti-Lock Brake (CAB).
Fig. 2 Master Cylinder Brake Booster Assemble
Fig. 3 Modulator And Pump/Motor Assembly
Fig. 4 Wheel Speed Sensor
5 - 114 ANTI-LOCK 6 BRAKE SYSTEM Ä

CONTROLLER ANTI-LOCK BRAKE (CAB)
The (CAB) (Fig. 5) is a small control computer
which receives wheel speed information, controls An-
ti-Lock operation and monitors system operation.
ANTI-LOCK BRAKES OPERATION AND
PERFORMANCE
This Anti-Lock Braking System represents the cur-
rent state-of-the-art in vehicle braking systems and
offers the driver increased safety and control during
braking. This is accomplished by a sophisticated sys-
tem of electrical and hydraulic components. As a re-
sult, there are a few performance characteristics that
may at first seem different but should be considered
normal. These characteristics are discussed below.
More technical details are discussed further in this
section.
PEDAL FEEL
Since the Bendix Anti-Lock 6 Braking System uses
the conventional Booster/Master Cylinder. The brake
pedal feel during normal braking is the same as con-
ventional Non ABS equipped cars. When Anti-Lock is activated during hard braking
due to a wheel lockup tendency. Brake pedal effort
will increase do to the master cylinder pressure be-
ing isolated from the brake system. Some brake
pedal movement and associated noises may be felt
and herd by the driver. This is normal of a Anti-Lock
Braking System due to pressurized fluid being trans-
ferred to and from the wheel brakes.
ANTI-LOCK BRAKE SYSTEM OPERATION
During Anti-Lock Braking, brake pressures are
modulated by cycling electric solenoid valves. The cy-
cling of these valves can be faintly heard as a series
of popping or ticking noises. In addition, the cycling
may be felt as a pulsation in the brake pedal, al-
though no pedal movement will be noticed. If Anti-
Lock 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 pres-
sures are modulated.
Although ABS operation is available at virtually
all vehicle speeds. It will automatically turn off at
speeds below 3 to 5 mph. Wheel lockup may be per-
ceived at the very end of an anti lock stop and is con-
sidered normal.
TIRE NOISE & MARKS
Although the ABS system prevents complete wheel
lock-up, some wheel slip is desired in order to
achieve optimum braking performance. During brake
pressure modulation, as brake pressure is increased,
wheel slip is allowed to reach up to 30%. This means
that the wheel rolling velocity is 30% 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 inter-
preted as total wheel lock-up. Complete wheel lock up normally leaves black tire
marks on dry pavement. The Anti-Lock Braking Sys-
tem will not leave dark black tire marks since the
wheel never reaches a locked condition. Tire marks
may however be noticeable as light patched marks.
VEHICLE PERFORMANCE
Anti-Lock Brakes provide the driver with some
steering control during hard braking, however there
are conditions where the system does not provide any
benefit. In particular, hydroplaning is still possible
when the tires ride on a film of water. This results in
the vehicles tires leaving the road surface rendering
the vehicle virtually uncontrollable. In addition, ex-
treme steering maneuvers at high speed or high
speed cornering beyond the limits of tire adhesion to
the road surface may cause vehicle skidding, inde-
pendent of vehicle braking. For this reason, the ABS
system is termed Anti-Lock instead of Anti-Skid.
SYSTEM SELF-DIAGNOSTICS
The Bendix Anti-Lock 6 Brake System has been
designed with the following self diagnostics capabil-
ity. The self diagnostic ABS startup cycle begins when
the ignition switch is in the on position. An electrical
check is completed on the ABS components such as
Wheel Speed Sensor Continuity and System and
other Relay continuity. During this check the Amber
Anti-Lock Light is on for approximately 1-2 seconds. Further Functional testing is accomplished once
the vehicle is set in motion. (1) The solenoid valves and the pump/motor are ac-
tivated briefly to verify function. (2) The voltage output from the wheel speed sen-
sors is verified to be within the correct operating
range.
Fig. 5 Controller Anti-Lock Brake (CAB)
Ä ANTI-LOCK 6 BRAKE SYSTEM 5 - 115

If the vehicle is not set in motion within 3 minutes
from the time the ignition switch is set in the on po-
sition. The solenoid test is bypassed but the pump/
motor is activated briefly to verify that it is
operating correctly.
WARNING SYSTEMS OPERATION
The ABS system uses an Amber Anti-Lock Warn-
ing Lamp, located in the instrument cluster. The
purpose of the warning lamp is discussed in detail
below. The Amber Anti-Lock Warning Light will turn on
when the (CAB) detects a condition which results in
a shutdown of the Anti-Lock function. The Amber
Anti-Lock Warning Lamp is normally on until the
(CAB) completes its self tests and turns the lamp off
(approximately 1-2 seconds). When the Amber Anti-
Lock Warning Light is on only the Anti-Lock func-
tion of the brake system if affected. The standard
brake system and the ability to stop the car will not
be affected when only the Amber Anti-Lock Warning
Light is on.
NORMAL OPERATION OF WARNING LAMP
With the ignition in the Crank position, the Red
Brake Warning Lamp will turn on as a bulb check.
The Amber Anti-Lock Warning Lamp will stay on for
1-2 seconds then turn off. Once verification of the self
diagnosis is completed.
ANTI-LOCK BRAKE SYSTEM COMPONENTS
The following is a detailed description of the Anti-
Lock Brake System components. For information on
servicing the Four Wheel Disk Brake System, see the
standard Brake section of this Service Manual.
MODULATOR ASSEMBLY
WARNING: THE ONLY PART OF THE MODULATOR
ASSEMBLY THAT IS A SERVICEABLE COMPONENT
IS THE DELTA P SWITCH. THE REMAINING COM-
PONENTS OF THE MODULATOR ASSEMBLY ARE
NOT SERVICEABLE ITEMS. NO ATTEMPT SHOULD
BE MADE TO REMOVE OR SERVICE ANY OTHER
PARTS OF THE MODULATOR ASSEMBLY.
The Modulator Assembly (Fig. 1) is located under
the battery tray and is covered with an acid shield.
The Modulator Assembly contains the following com-
ponents for controlling the Anti-Lock braking sys-
tem. 2 Isolation Valves, 4 Build/Decay Valves, 4
Shuttle Orifices, 2 Fluid Sumps, 2 Accumulators, a
Pump/Motor and a Pressure Differential Valve/
Switch. Also attached to the Modulator Assembly are
4 brake tubes which are connected to an 8 way con-
nector block. The connector block is mounted to the
left frame rail below the master cylinder in the same location as the non ABS equipped combination valve.
The wheel brake lines are attached to the system via
the connector block.
ISOLATION VALVES
The Isolation Valves are used to isolate the master
cylinder from the rest of the brake hydraulic circuit
during an Anti-Lock stop. Two Isolation Valves are
used, one for the primary circuit and one for the sec-
ondary circuit. The Isolation Valves are spring
loaded in the released position. In the released posi-
tion the Isolation Valves provide a fluid path from
the master cylinder outputs to the wheel brakes via
the Build/Decay valves. When actuated it provides a
fluid path from the accumulator (which was charged
by the Pump/Motor during ABS operation) to the
Build/Decay valves through the Shuttle Orifices.
BUILD/DECAY VALVES
There are 4 Build/Decay valves, one for each
wheel. In the released position they provide a fluid
path from the wheel brakes to the Isolation Valve
through the shuttle orifices. In the actuated (decay)
position, they provide a fluid path from the wheel
brakes to the sump. The Build/Decay valves are
spring loaded in the released (build) position.
SHUTTLE ORIFICE
There are 4 Shuttle Orifice Valves, one for each
wheel. The Shuttle Orifice Valve is a hydraulically
actuated valve which shuttles when the Build/Decay
valve is actuated. Actuating of the Build/Decay valve
causes a pressure differential to be created across the
Shuttle Orifice Valve. This acts like placing an ori-
fice (restriction) in the line between the Isolation
Valve and the Build/Decay Valve. This restriction
provides a controlled build rate to each wheel brake
during an Anti-Lock stop. The Shuttle Orifice Valve
will remain in the orificed position until the ABS cy-
cle is complete. When the ABS cycle has been com-
pleted the Isolation and Build/Decay valves will
return to their released position which will equalize
the pressure across the Shuttle Orifice Valves. When
the pressure equalizes, the spring loaded Shuttle Or-
ifice valves will return to the unrestricted position.
FLUID SUMPS
There are two Fluid Sumps in the Hydraulic As-
sembly, one each for the primary and secondary hy-
draulic circuits. The Fluid Sumps store the brake
fluid that is decayed from the wheel brakes during
ABS cycle. This fluid is then pumped to an accumu-
lator and/or the hydraulic system in order to provide
build pressure. The typical pressure in the sumps is
50 psi, During ABS operation only.
5 - 116 ANTI-LOCK 6 BRAKE SYSTEM Ä

HYDRAULIC SPRING ACCUMULATOR
The Hydraulic Spring Accumulators (Fig. 2) (one
on each circuit) are used to store pressurized hydrau-
lic brake fluid during ABS operation only. This fluid
is used during hard braking when the ABS system is
activated, to supplement brake pressure when re-
quired. During normal Non ABS braking operation
there is NO pressurized brake fluid stored in the ac-
cumulators. The Hydraulic Spring Accumulators are
not a serviceable part of the Modulator Assembly
and should never be removed from the assembly.
PRESSURE DIFFERENTIAL VALVE/SWITCH
(DELTA P SWITCH)
The Pressure Differential Valve/Switch is located
inside the hydraulic assembly. This valve/switch func-
tions the same as the Pressure Differential
Valve/Switch located in the combination valve on stan-
dard brake systems. The delta P switch monitors the
primary and secondary hydraulic circuits for a differ-
ence in pressure. A pressure difference greater than
225 psi. Will move and latch the shuttle to ground the
Red Brake Warning Light circuit. This will in turn,
turn on the Red Brake Warning Light in the instru-
ment panel to warn the driver of a hydraulic system
problem. This Pressure Differential Valve Switch is a
replaceable item of the Modulator Assembly. The Red
Brake Warning Light indicates a problem with
the foundation brake system and not the Anti-
Lock system.
PUMP/MOTOR ASSEMBLY
The Modulator Assembly contains 2 Pump Assem-
blies, one each for the primary and secondary hydrau-
lic circuits. Both pumps are driven by a common
electric motor which is part of the Modulator Assembly.
The pumps pick up fluid from the sumps to supply
pressure to the accumulators or hydraulic system via
the isolation valves during an Anti-Lock stop. The
motor only runs during an ABS stop and is controlled
by the (CAB) via the Pump/Motor Relay. The
Pump/Motor Assembly is not a serviceable item. If it
requires service the Modulator Assembly must be re-
placed.
Fig. 1 Modulator Assembly
Fig. 2 Hydraulic Spring Accumulator
Ä ANTI-LOCK 6 BRAKE SYSTEM 5 - 117