1993 CHEVROLET DYNASTY lock

to the rear will be lower than the front brakes. This will
prevent premature rear wheel lock-up and skid. If
hydraulic pressure is lost in one half of the diagonally
split system, the operation of the proportioning valve
in the remaining half is not effected.
ABS BRAKE PROPORTIONING VALVE OPERATION
On vehicles using the ABS braking system, screw in
proportioning valves are used in place of the conven-
tional differential pressure/proportioning valve. Each rear brake circuit has its own screw-in propor-
tioning valve which is attached to the rear brake outlet
ports of the hydraulic assembly. These valves limit
brake pressure to the rear brakes after a certain
pressure is reached. This improves front to rear brake
balance during normal braking.
Screw in proportioning valves can be identified by
the numbers stamped on the body of the valve. The
first digit represents the slope, the second digit repre-
sents the split (cut-in) point, and the arrow represents
the flow direction of the valve. Be sure that the
numbers listed on the replacement valve are the
same as on the valve that is being removed. See
(Fig. 3) for detail of the valve identification.
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 sys-
tems fail.
CAUTION:Make sure air does not enter the hydrau-
lic system during this test procedure. See bleeding
without a pressure bleeder at the beginning of this
section for master cylinder fluid level checking pro-
cedures.
To test the service brake warning system lamp.
Raise the vehicle on a hoist and open a wheel cylin-
der bleeder while a helper depresses the brake pedal
and observes the warning light. If the light fails to light, inspect for a burned out
bulb, disconnected socket, or a broken or discon-
nected wire at the switch. If the bulb is not burned
out and the wire continuity is uninterrupted. 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 correction has been made, if
necessary.
PROPORTIONING VALVES
TESTING PROPORTIONING VALVE UNIT
If premature rear wheel skid occurs on hard brake
application, it could be an indication that a malfunc-
tion has occurred with the proportioning valve unit. The proportioning valve is designed with two sep-
arate systems. One half controls the right rear
brake, and the other half controls the left rear brake.
Therefore, a road test to determine which rear brake
slides first is essential.
RIGHT REAR WHEEL SLIDES FIRST To test the proportioning valve when the right rear
wheel slides first, leave the front brakes connected to
the valve, proceed as follows: (1) Install one gauge and (TEE) of set C-4007-A
between the brake line from the master cylinder sec-
ondary port and the brake valve assembly. (2) Install the second gauge of set C-4007-A to the
right rear brake outlet port (Fig. 4). Using an
adapter tube, made from a short piece of brake tube
and (2) 3/8 x 24 tube nuts. Connect the hose to the
valve. Bleed the hose and gauge. (3) Have a helper exert pressure on the brake
pedal (holding pressure) to get a reading on the valve
inlet gauge and check the reading on the outlet
Fig. 3 ABS PROPORTIONING VALVE IDENTIFICA- TION
Ä BRAKES 5 - 27

WARNING: THE SELF ADJUSTING FEATURE OF THIS
PARKING BRAKE LEVER ASSEMBLY CONTAINS A
CLOCK SPRING LOADED TO APPROXIMATELY 30
POUNDS. CARE MUST BE TAKEN TO PREVENT EX-
CESSIVE JARRING OF THE ASSEMBLY. DO NOT
RELEASE THE SELF ADJUSTER LOCKOUT DEVICE
BEFORE INSTALLING CABLES INTO THE EQUAL-
IZER. KEEP HANDS OUT OF SELF ADJUSTER SEC-
TOR AND PAWL AREA. FAILURE TO OBSERVE CAU-
TION IN HANDLING THIS MECHANISM COULD LEAD
TO SERIOUS INJURY.
When repairs to the hand lever assembly or cable
system are required the self adjuster must be reloaded
and locked out.
SELF ADJUSTING PROCEDURES (AG & AJ BODY)
TO RELOAD SELF ADJUSTER
(1) Remove ash receiver or courtesy light from rear
of center console to gain access to self adjuster. Also,
remove carpet from sides of console. (2) Pull on equalizer/output cable to wind up sprin-
g(requires greater than 30 pounds effort). Continue
until self adjuster lockout pawl is positioned about
midway on the self adjuster sector (Fig. 6). Rotate
lockout pawl into self adjuster sector by turning allen
screw clockwise. Rotating lockout device requires
very little effort. Do not force or failure of lock-
out device will occur. (3) When repairs are complete, adjust rear brakes
before adjusting parking brake. On drum-in-hat type of
rear disc brake adjust shoe diameter to 171.5 mm (6.75
inch).
ADJUST PARKING BRAKE (AG & AJ BODY)
Be sure that the cables are properly assembled to the
equalizer bracket prior to cable adjustment. (1) Insert a 7/32 inch allen wrench into hex socket
and turn counter-clockwise through approximately 15É
of rotation (Fig. 4). In turning lockout device, self
adjuster release is a loud snapping noise followed by
reaching a more felt than heard detent. Very light
effort is required to seat lockout arm into detent.
Follow through to the detent is important in prevent-
ing the lockout rod from rattling. Note: The parking brake handle can be in any
position when releasing self adjuster. (2) Cycle lever to position cables. Rear wheels should
rotate freely without dragging.
REAR PARKING BRAKE CABLE REMOVAL (AA, AC,
AP, AY BODY)
The rear brake cables are attached to rear connec-
tors. Should it become necessary to remove either parking
brake cable for installation of a new cable, proceed as
follows: With vehicle jacked up on a suitable hoist, remove
wheel and tire assembly (Fig. 6). Back off cable adjusting nut to provide slack and
disconnect rear brake cable from connector.
DRUM BRAKES
(1) Disconnect park brake cable from park brake
lever in rear wheel brakes. (2) Using an aircraft type hose clamp compress re-
tainers on end of cable housing and start cable out of
retaining hole in the support plate. Remove clamp
when retainers are free of the mounting hole in the
support plate, (Fig. 6).
(3) Remove clip from brake cable at support
bracket and pull cable away from trailing arm as-
sembly (Figs. 3 and 4).
DISC BRAKES
(1) Remove disc brake caliper from adapter, and
brake disc (rotor) from rear hub.
Fig. 5 Self Adjusting Parking Brake Lever Assembly
Fig. 6 Removing Brake Cable from Support Plate
Ä BRAKES 5 - 61

PARKING BRAKE HAND LEVER ASSEMBLY
REMOVAL AND INSTALLATION
REMOVAL (AG AND AJ BODY)
Remove ash receiver or courtesy light from rear of
console. Remove carpet from sides of console. Remove
parking brake trim cover from passenger side of con-
sole (pulls off). Load and lockout parking brake self adjuster (Fig.
6). Disconnect rear cables from equalizer bracket. Remove the 3 hold down nuts and remove hand le-
ver assembly through opening created by removing
console trim cover. Passenger seat might have to be
removed. Also, if metal tab at bottom of console pre-
vents removal of hand brake assembly, bend tab out
of the way. (Bend the tab back to original position af-
terR&Rof hand brake).
INSTALLATION (AG AND AJ BODY)
Install hand lever assembly through side opening
in console and bolt into place. Connect rear parking brake cables to equalizer.
Adjust parking brakes.
Install console trim cover, carpet, passenger seat
and rear ash receiver or courtesy light.
REMOVAL AND INSTALLATION PARKING BRAKE
SHOES
ALL WITH REAR DISK BRAKES
(1) Remove rear disc brake caliper assembly from
adapter and braking disc (See Disc Brake Shoe Re-
moval). (2) Remove rear braking disc from rear hub (See
Removing Braking Disk). (3) Remove grease cap.
(4) Remove cotter pin, lock nut, hub bearing re-
taining nut, and washer. (5) Remove hub and bearings.(See Wheel Bearing
Section) (6) Remove forward brake shoe assembly hold
down clip (Fig. 1). (7) Turn parking brake, brake shoe adjuster wheel
until adjuster is at shortest length. (8) Remove the parking brake, shoe adjuster as-
sembly (Fig. 2). (9) Remove upper parking brake, shoe to shoe
spring (Fig. 3). (10) Pull front parking brake shoe, away from an-
chor. Then remove front parking brake shoe and
lower spring (Fig. 4). (11) Remove rear parking brake shoe hold-down
clip. Then remove rear parking brake shoe assembly
(Fig. 5).
Fig. 1 Removing Brake Shoe Hold-Down Clip
Fig. 2 Removing Adjuster Assembly
Ä BRAKES 5 - 63

INSTALLING PARKING BRAKE SHOES
(1) Install rear parking brake shoe and holddown
clip (Fig. 6). (2) Install lower parking brake, shoe to shoe re-
turn spring (Fig. 7). (3) Pull forward parking brake shoe over anchor
block until properly located on adapter. (4) Install upper parking brake, shoe to shoe re-
turn spring (Fig. 8). (5) Install parking brake shoe adjuster assembly
with star wheel forward (Fig. 9). (6) Install front, parking brake shoe holddown clip
(Fig. 10). (7) Adjust parking brake shoes to a diameter to
171 mm (6.75 inch). (8) Install hub assembly on spindle.
(9) Install outer bearing, thrust washer and nut.
(10) Tighten wheel bearing adjusting nut to 27 to
34 N Im (240 to 300 in. lbs.) torque while rotating
hub. This seats the bearings. (11) Back off adjusting nut 1/4 turn (90É) then
tighten adjusting nut finger tight. (12) Position lock on nut with one pair of slots in
line with cotter pin hole. Install cotter pin. (13) Install grease cap.
(14) Install rear braking disc.
(15) Install rear, disc brake caliper on the adapter
(See Brake Shoe Removal).
Fig. 3 Removing Upper Spring
Fig. 4 Removing Shoe and Lower Spring
Fig. 5 Removing Rear Holddown Clip and Shoe
Fig. 6 Installing Rear Shoe and Hold-Down Clip
5 - 64 BRAKES Ä

MASTER CYLINDER INDEX
page page
Brake Fluid Level Sensor .................. 66
General Information ....................... 66 Master Cylinder Service Procedures
.......... 67
Testing the Master Cylinder ................. 66
GENERAL INFORMATION
The tandem master cylinder (Fig. 1) has a glass re-
inforced nylon reservoir and an anodized aluminum
body. Do not hone the bore of the cylinder, as this will
remove the anodized surface. The reservoir is indexed to prevent installation in
the wrong direction (Fig. 2). The cap diaphragms are
slit to allow atmospheric pressure to equalize on both
sides of the diaphragm. The primary and secondary outlet tubes from the
master cylinder are connected to the valve mounted
under the master cylinder. The front part of this
block connects to the secondary outlet tube and sup-
plies the right rear and left front brakes. The rear
portion of the block connects to the primary outlet
tube and supplies the right front and left rear
brakes.
BRAKE FLUID LEVEL SENSOR
The Brake Fluid Level sensor is found only in the
AJ body vehicles with the visual electronic message
center. The purpose of the sensor is to provide the
driver with an early warning message that brake
fluid in master cylinder reservoir has dropped to a
below normal. As the fluid drops below the design level the sensor
closes the warning message circuit. Approximately
15 seconds later the message BRAKE FLUID LOW
appears on the instrument panel. At this time the master cylinder reservoir should be checked and filled
to the bottom of the rings with DOT 3 brake fluid. To check the operation of the Brake Fluid Level
sensor, with ignition on and wiring still attache-
d,remove sensor from master cylinder and hold in
upright position. Within 30 seconds the instrument
panel message BRAKE FLUID LOW should appear.
Next invert the sensor. The instrument panel message
should turn off immediately. If the above sequence
occurs the sensor is operating properly. If the message
does not appear remove the wiring from the sensor and
using a jumper wire connect both sides of the plug. The
instrumental panel message BRAKE FLUID LOW
should appear within 30 seconds. If the message does
not appear a problem exists in the wiring or instru-
mentation. If the message does appear the sensor is
faulty and must be replaced. The Brake Fluid Level
sensor is not a repairable item (Fig. 2).
TESTING THE MASTER CYLINDER
Be sure master cylinder vents at both ports.
Apply pedal lightly with engine running and look for
fluid squirting or swirling into reservoirs. In this master cylinder, a special baffle reduces the
amount of fluid entering the secondary reservoir only a
small disturbance may be seen.
Fig. 1 Aluminum Master Cylinder (Cutaway View)
Fig. 2 Brake Fluid Level Sensor
5 - 66 BRAKES Ä

(7) Unfasten brackets on steel heater water line at
dash panel and left frame rail. On Manual Transmis-
sion vehicles, unfasten clutch cable bracket at shock
tower and move aside. (8) Slide the power brake unit up and to the left
(mounting holes are slotted) on the dash panel, then
tilt inboard and up to remove.
CAUTION: Do not attempt to disassemble power
brake unit as this booster is serviced ONLY as a
complete assembly.
INSTALL (1) Position power brake booster onto dash panel.
(2) Install and tighten the 4 power brake booster to
dash panel mounting nuts (Fig. 5) to 29 N Im (250 in.
lbs.) torque. (3) Install steel heater water line and clutch cable
bracket, if so equipped. (4) Carefully position master cylinder on power
brake unit. (5) Install and tighten the 2 master cylinder to
power booster mounting nuts (Fig. 4) to 29 N Im (250
in. lbs.) torque. (6) Connect vacuum hose onto the check valve, lo-
cated on the power brake unit. (7) Using lubriplate, or equivalent, coat the bearing
surface of pedal pin (Fig. 5). (8) Connect power brake 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. (9) Check stop light operation.
WHEEL BEARINGS
FRONT WHEEL BEARINGS
Front wheel drive vehicles are equipped with per-
manently sealed front wheel bearings. There is no
periodic lubrication or maintenance recommended for
these units. However if during servicing of the brake
system, service to the front wheel bearing is required
refer to Group 2, Suspension in this service manual.
REAR WHEEL BEARINGS
NORMAL SERVICE
The lubricant in the rear wheel bearings should be
inspected whenever the hubs are removed to inspect
or service the brake system. Or at least every 30,000
miles (48,000 km). The bearings should be cleaned
and repacked with a High Temperature Multipurpose
E.P. Grease whenever the disc brake rotors are re-
surfaced.
INSPECTION
Check lubricant to see that it is adequate in quan-
tity and quality. If the grease is low in quantity, con-
tains dirt, appears dry or has been contaminated
with water, it will appear milky. The bearings then must be cleaned and repacked.
Do not add grease to
a wheel bearing that already has grease packed
in it. Relubricate completely. Mixing of different
types of greases in wheel bearings should be
avoided since it may result in excessive thinning
and leakage of the grease.
REMOVAL AND INSTALLATION
For the servicing, removal and installation of the
rear wheel bearings follow the procedure listed below. (1) Remove the rear tire and wheel assembly.
(2) On rear disc brake equipped vehicles remove the
caliper and rotor. Support the caliper out of the way.
Do not allow the caliper to hang by the hydraulic
hose. See disc brake section in this group for caliper
removal procedure. (3) Remove grease cap, cotter pin, nut lock, nut,
thrust washer and outer wheel bearing. (4) Carefully slide hub or drum from spindle. Do not
drag inner bearing or grease seal over stub axle
(thread, bearing, and oil seal may be damaged.) Using
an appropriate tool remove the grease seal and inner
bearing from the drum or hub. Discard grease
Fig. 5 Power Brake Booster Mounting
5 - 70 BRAKES Ä

seal, a new seal should be used when reinstalling the
inner bearing. (See Fig. 1) (5) Thoroughly clean all old grease from the outer
and inner bearings, bearing cups and hub cavity (See
Fig. 1). To clean bearings, soak them in an ap-
propriate cleaning solvent. Strike the flat sur-
face of the bearing inner race against a
hardwood block several times. Immerse the
bearings in solvent between the blows to jar
grease loose and wash old particles of hardened
grease from bearings. Repeat this operation un-
til bearings are clean. Bearings can be dried
using compressed air but do not spin the bear-
ings. After cleaning, oil the bearings with engine
oil. Insert the bearing into its appropriate cup,
apply pressure to the bearing while rotating it to
test them for pitting and roughness. Replace all
worn or defective bearings. If bearing shows signs of pitting or roughness they should be
replaced. Bearings must be replaced as a set,
both the cup and the bearing need to be replaced
at the same time. If bearings are suitable for
further use, remove engine oil from bearings
using appropriate solvent and dry bearings. Re-
pack the bearings using a Multi-Purpose NLGI.
Grade 2 EP Grease such as Mopar or equivalent,
and place them in a clean covered container
until ready for installation. If a bearing packer is
not available, hand pack grease into all cavities
between bearing cage and rollers. (6) If bearings and cups are to be replaced, remove
cups from the drum or hub using a brass drift or
suitable remover. (7) Replace bearing cups with appropriate installing
tool. (8) Install inner bearing in grease coated hub and
bearing cup, and install new grease seals using the
appropriate seal installer. (9) Coat hub cavity and cup with grease.
(10) Before installing hub or drum assembly, inspect
stub axle and seal surface for burrs or roughness, and
smooth out all rough surfaces. (11) Coat the stub axle with Multi-Purpose NLGI,
Grade 2 EP grease such as Mopar or equivalent. (12) Carefully slide the hub of drum assembly onto
the stub axle. Do not drag seal or inner bearing
over the threaded area of the stub axle. (13) Install outer bearing, thrust washer and nut.
(14) Tighten the wheel bearing adjusting nut to 27 to
34 N Im (240 to 300 in. lbs.) while rotating hub or drum
assembly. This seats the bearings. (15) Back off adjusting nut 1/4 turn (90É) then
tighten adjusting nut only finger tight. (16) Position the nut lock over the bearing adjusting
nut with one pair of slots in line with the cotter pin hole
in the stub axle, and install cotter pin. (17) Install the grease caps and the wheel and tire
assemblies. Tighten wheel stud nuts to 115 N Im (85 ft.
lbs.) on all models. reinstall wheel covers if so
equipped.
Fig. 1 Rear Wheel Bearings
Ä BRAKES 5 - 71

ANTI-LOCK BRAKE SYSTEMÐBENDIX ANTI-LOCK 10 AC/Y BODY INDEX
page page
ABS Brake System Diagnostic Features ....... 92
ABS Braking System Diagnosis .............. 87
ABS Controller Anti-Lock Brake (CAB) Service Precautions ........................... 88
ABS Equipped Vehicle Performance .......... 75
ABS Hydraulic Circuits and Valve Operation .... 85
ABS System Diagnostic Connector ........... 82
ABS System General Service Precautions ...... 88
ABS System Self-Diagnostics ............... 75
ABS Warning Systems Operation ............ 75
Anti-Lock Brake System Components ......... 76 Anti-Lock Brake System Definitions
........... 72
Anti-Lock Operation and Performance ......... 73
Anti-Lock System Relays and Warning Lamps . . . 82
Controller Anti-Lock Brake (CAB) ............. 80
Electronic Components ................... 103
General Information ....................... 72
General Service Precautions ................ 93
Major ABS Components ................... 73
Mechanical Diagnostics and Service Procedures . 89
Normal Braking System Function ............. 72
On Car Hydraulic ABS Component Service ..... 93
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.
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
² PSIÐPounds per Square Inch (pressure)
² WSSÐWheel Speed Sensor
NORMAL BRAKING SYSTEM FUNCTION
Under normal braking conditions, the ABS System
functions much the same as a standard brake system
with a diagonally split master cylinder. The primary
difference is that power assist is provided by hydrau-
lic power assist instead of the conventional vacuum
assist. If a wheel locking tendency is noticed 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 of the vehicle
has a set of electrical solenoid valves and hydraulic
line to provide hydraulic modulation. For vehicle sta-
bility, though both rear wheel valves receive the
same electrical signal. The system can build, hold or
reduce pressure at each wheel of the vehicle. This is
determined by the signals generated by the wheel
Four-Wheel Anti-Lock Brake System
5 - 72 ANTI-LOCK 10 BRAKE SYSTEM Ä