CHEVROLET PLYMOUTH ACCLAIM 1993 Service Manual

BASIC DIAGNOSIS GUIDE
Ä BRAKES 5 - 5

BRAKE SYSTEM DIAGNOSTICS
5 - 6 BRAKES Ä

BRAKE SYSTEM DIAGNOSTICS
Ä BRAKES 5 - 7

BRAKE SYSTEM DIAGNOSTICS
5 - 8 BRAKES Ä

BRAKE SYSTEM DIAGNOSTICS
BRAKE SYSTEM DIAGNOSTICS
Ä BRAKES 5 - 9

HYDRAULIC SYSTEM CONTROL VALVES INDEX
page page
General Information ....................... 10
Hydraulic System Service Procedures ......... 11 Pressure Differential Warning Light Switch
...... 10
GENERAL INFORMATION
All models equipped with a Bendix Antilock 4 Brake
System have 2 screw-in type proportioning valves.
There is 1 valve for each individual rear wheel hydrau-
lic brake line. The proportioning valves are mounted
directly into the rear brake outlet ports of the modula-
tor assembly (Fig. 1).
The proportioning valves limit brake pressure to the
rear brakes after a certain pressure (split point) is
reached. This improves front to rear brake balance
during normal braking. Screw-in proportioning valves can be identified by
numbers stamped on the body of the valve. The first
digit represents the slope, the second digit represents
the split (cut-in) point, and the arrow represents the
flow direction of the valve. Be sure numbers listed
on a replacement valve are the same as on the
valve that is being removed. See (Fig. 2) for detail of
the valve identification.
PRESSURE DIFFERENTIAL WARNING LIGHT
SWITCH
The hydraulic brake system, on vehicles equipped
with the Bendix Antilock 4 Brake System is split
diagonally. The left front and right rear brakes are on
one hydraulic system, and the right front and left
rear are on another. Both systems are routed
through, and hydraulically separated by the Pressure
Differential Switch (Fig. 3) mounted in the hydraulic brake tube junction block. The function of the Pressure
Differential Switch is to alert the driver of a malfunc-
tion in the brake hydraulic system.
If hydraulic pressure is lost in one system, the
warning light switch will activate the RED brake
warning light on the instrument panel, when the brake
pedal is depressed. At this point the brakes hydraulic
system requires immediate service. However, since the
brake systems are split diagonally the vehicle will
retain 50% of its stopping capability in the event of a
failure in either half. The warning light switch is the latching type. It
will automatically center itself after the repair is
made and the brake pedal is depressed.
Fig. 1 Rear Brake Proportioning Valve Location On Modulator Assembly
Fig. 2 ABS PROPORTIONING VALVE IDENTIFICA- TION
Fig. 3 Pressure Differential Warning Light Switch InJunction Block.
5 - 10 BRAKES Ä

The instrument panel bulb can be checked each
time the ignition switch is turned to the start posi-
tion or the parking brake is set.
HYDRAULIC SYSTEM SERVICE PROCEDURES
BRAKE WARNING SYSTEM
CHECKING BRAKE WARNING SWITCH UNIT
The Red Brake Warning light will come on when the
parking brake is applied with the ignition key turned
ON. The same light will also illuminate should one of
the two service brake hydraulic systems fail.
CAUTION:Make sure air does not enter the hydraulic
system during this test procedure. See bleeding with-
out a pressure bleeder at the beginning of this section
for master cylinder fluid level checking procedures.
To test the service brake warning system lamp.
Raise vehicle on a hoist and open a wheel cylinder
bleeder while a helper depresses the brake pedal and
observes the warning light.
If light fails to come on, inspect for a burned out bulb,
disconnected socket, or a broken or disconnected wire at
the switch. If the bulb is not burned out and the wire
continuity is not interrupted. Check the service brake
warning switch operation with a test lamp between the
switch terminal and a known good ground. Be sure to
fill master cylinder and bleed brake system after correc-
tion has been made, if necessary.
TESTING ANTILOCK PROPORTIONING VALVES
(1) Install one gauge and (TEE) between modula-
tor assembly and male end (Inlet) of proportioning
valve (Fig. 4). (2) Install second gauge at female end (Outlet) of
proportioning valve (Fig. 4).
(3) Have a helper exert pressure on brake pedal to
obtain and hold required pressure reading on the
valve inlet gauge. (4) Check reading on outlet gauge. If inlet and out-
let pressures do not agree with the following chart,
replace the valve. See (Fig. 3) for proportioning valve
identification.
BENDIX ANTILOCK 4 PROPORTIONING VALVE APPLICATIONS
BENDIX ANTILOCK 4 PROPORTIONING VALVE PRESSURES
Fig. 4 Tube Connections for ABS
Ä BRAKES 5 - 11

BENDIX ANTILOCK 4 BRAKE SYSTEM INDEX
page page
ABS Brake System Diagnostic Features ....... 24
ABS Computer System Service Precautions .... 23
ABS General Service Precautions ............ 23
Antilock Brake System Components .......... 16
Antilock Brake System Definitions ............ 14
Antilock Brakes Operation and Performance .... 15
Antilock System Relays and Warning Lamps .... 19
Bendix Antilock 4 Brake System Diagnostics .... 22
Bleeding Bendix Antilock 4 Brake System ...... 25
Controller Antilock Brake Cab ............... 18
Diagnostic Connector ..................... 19 Electronic Components
.................... 41
General Information ....................... 12
Hydraulic Circuits and Valve Operation ........ 20
Major Components ....................... 14
Mechanical Diagnostics and Service Procedures . 24
Normal Brake System Function .............. 14
On-Car ABS Brake System Service ........... 25
Specifications ........................... 46
System Self-Diagnostics ................... 15
Vehicle Performance ...................... 15
Warning Systems Operation ................ 16
GENERAL INFORMATION
The purpose of an Anti-Lock Brake System is to
prevent wheel lock-up under heavy braking condi-
tions on virtually any type of road surface. Antilock
Braking is desirable because a vehicle which is
stopped without locking its wheels will retain direc-
tional stability and some steering capability. This al-
lows a driver to retain greater control of the vehicle
during heavy braking. This service manual supplement covers the descrip-
tion, diagnostics, and on car service procedures cov-
ering the Bendix Antilock 4 Brake System. If service
is required on the non Antilock related components
of the brake system, refer to the appropriate section
in Group 5 of the Front Wheel Drive Car Engine,
Chassis And Body service manual.
Fig. 1 Bendix Antilock 4 Brake System Components
5 - 12 ANTILOCK 4 BRAKE SYSTEM Ä

HYDRAULIC BRAKE LINE ROUTING WITH BENDIX ANTILOCK 4 BRAKE SYSTEM
Ä ANTILOCK 4 BRAKE SYSTEM 5 - 13

ANTILOCK BRAKE SYSTEM DEFINITIONS
In this section of the manual several abbreviations
are used for the components that are in the Bendix An-
tilock 4 Brake System, they are listed below for your
reference.
² CABÐController Antilock Brake
² ABSÐAntilock Brake System
² PSIÐPounds per Square Inch (pressure)
² WSSÐWheel Speed Sensor
² ACÐAlternating Current
NORMAL BRAKE SYSTEM FUNCTION
Under normal braking conditions, the Bendix An-
tilock 4 Brake System functions the same as a stan-
dard non-Antilock brake system.
When a wheel locking tendency is detected during a
brake application, the vehicle brake system will enter
the Antilock mode. During Antilock Braking, hydraulic
pressure in the four wheel circuits is modulated to pre-
vent wheels from locking. Each wheel circuit is de-
signed with a set of electrical valves and hydraulic line
to provide modulation, although for vehicle stability,
both rear wheel valves receive the same electrical sig-
nal. The system can modulate pressure at each wheel,
depending on signals generated by the wheel speed sen-
sors (WSS) and received at the 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 Antilock 4 Brake System uses a vehi-
cles standard Master Cylinder/Reservoir and Vacuum
Booster (Fig. 2). The master cylinder primary and
secondary outputs (Fig. 2) go to the frame rail
mounted junction block and then directly to the mod-
ulator assembly inlet ports.
MODULATOR AND PUMP MOTOR/ASSEMBLY
The Modulator Assembly (Fig. 3) contains the elec-
tronic valves used for brake pressure modulation,
and the Pump/Motor assembly.
The Pump/Motor function, as part of the modulator
assembly, is to pump low pressure brake fluid from the
modulator sump into the ABS accumulator, as required.
WHEEL SPEED SENSORS
A Wheel Speed Sensor (Fig. 4) is located at each
wheel to transmit wheel speed information to the CAB.
CONTROLLER ANTILOCK BRAKE CAB
The CAB (Fig. 5) is a small computer which re-
ceives wheel speed information, controls Antilock op-
eration and monitors system operation.
Fig. 2 Master Cylinder And Brake Booster Assembly
Fig. 3 Modulator And Pump/Motor Assembly
Fig. 4 Wheel Speed Sensor
5 - 14 ANTILOCK 4 BRAKE SYSTEM Ä