Wheels DODGE RAM 1500 1998 2.G Service Manual

(4) Bottom the caliper pistons into the caliper by
prying the caliper over.
(5) Remove the caliper slide bolts.
(6) Remove the disc brake caliper from the mount.
CAUTION: Never allow the disc brake caliper to
hang from the brake hose. Damage to the brake
hose will result. Provide a suitable support to hang
the caliper securely.
(7) Remove the inboard and outboard brake pads
(Fig. 39).
(8) Remove the anti-rattle clips (Fig. 39).
(9) Remove the caliper adapter mounting bolts
(Fig. 39).
(10) Remove the caliper adapter.
INSTALLATION
INSTALLATION - FRONT
(1) Install the caliper adapter to the steering
knuckle (Fig. 38).
(2) Install the caliper adapter mounting bolts and
tighten to 176 N´m (130 ft.lbs.) (Fig. 38).
(3) Install the disc brake caliper (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPERS - INSTALLATION).
(4) Install the tire and wheel assembly (Refer to 22
- TIRES/WHEELS/WHEELS - STANDARD PROCE-
DURE).
(5) Remove the support and lower the vehicle.
INSTALLATION - REAR
(1) Install the caliper adapter mounting bolts.
Tighten the mounting bolts to 135 N´m (100 ft.lbs)
(Fig. 39).(2) Install the anti-rattle clips (Fig. 39).
(3) Install the inboard and outboard pads (Fig. 39).
(4) Install the caliper mounting bolts.
(5) Install the tire and wheel assembly
DISC BRAKE CALIPER
ADAPTER MOUNT
REMOVAL - REAR
(1) Remove wheel and tire assembly.
(2) Remove the disc brake caliper (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPERS - REMOVAL).
(3) Remove the caliper adapter (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPER ADAPTER - REMOVAL).
(4) Remove the rotor (Refer to 5 - BRAKES/HY-
DRAULIC/MECHANICAL/ROTORS - REMOVAL).
(5) Remove the axle shaft (Refer to 3 - DIFFER-
ENTIAL & DRIVELINE/REAR AXLE - 9 1/4/AXLE
SHAFTS - REMOVAL).
(6) Remove the park brake shoes (Refer to 5 -
BRAKES/PARKING BRAKE/SHOES - REMOVAL).
(7) Remove the parking brake cable from the
brake lever.
(8) Remove the bolts attaching the support plate to
the axle and remove the support plate (Fig. 65).
(9) Remove the caliper adapter mount from the
axle housing (Fig. 40).
INSTALLATION
(1) Install the caliper adapter mount on the axle
housing (Fig. 40).
(2) Install support plate on axle flange (Fig. 66).
Tighten attaching bolts to 115 N´m (85 ft. lbs.).
Fig. 39 CALIPER MOUNT
1 - DISC BRAKE PADS
2 - ANTI-RATTLE CLIPS
3 - CALIPER ADAPTER
4 - MOUNTING BOLTS
Fig. 40 CALIPER ADAPTER MOUNT - REAR
1 - CALIPER ADAPTER MOUNT
2 - AXLE TUBE
3 - MOUNTING STUDS
5 - 22 BRAKES - BASEDR
DISC BRAKE CALIPER ADAPTER (Continued)

REMOVAL - REAR
(1) Raise and support the vehicle
(2) Remove the tire and wheel assembly.
(3) Remove the disc brake caliper, (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPERS - REMOVAL).
(4) Remove the caliper adapter bolts (Fig.
61).(Refer to 5 - BRAKES/HYDRAULIC/MECHANI-
CAL/DISC BRAKE CALIPER ADAPTER -
REMOVAL)
(5) Remove the retaining clips and rotor assembly
(Fig. 61).
REMOVAL - REAR DUAL WHEELS
(1) Raise and support the vehicle
(2) Remove the tire and wheel assembly.
(3) Remove the disc brake caliper, (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPERS - REMOVAL).
(4) Remove the caliper adapter bolts.
(5) Remove the rear axle shaft from the housing
on dual rear wheels, (Refer to 3 - DIFFERENTIAL &
DRIVELINE/REAR AXLE - 286RBI/AXLE SHAFTS -
REMOVAL).
(6) Remove the hub and rotor assembly (C3500
only) (Fig. 62).
INSTALLATION
INSTALLATION - FRONT
(1) On models with all-wheel antilock system
(ABS), check condition of tone wheel on hub/bearing.
If teeth on wheel are damaged, hub/bearing assembly
will have to be replaced (tone wheel is not serviced
separately).
(2) Install the rotor onto the hub/bearing wheel
studs.
(3) Install the caliper adapter assembly,(Refer to 5
- BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPERS - INSTALLATION) and tighten
adapter bolts to:
(4) Install the wheel and tire assembly, (Refer to
22 - TIRES/WHEELS/WHEELS - STANDARD PRO-
CEDURE) and lower the vehicle.
(5) Apply the brakes several times to seat brake
pads. Be sure to obtain firm pedal before moving
vehicle.
INSTALLATION - REAR
(1) Install the rotor to the axleshaft (Fig. 61).
Fig. 60 8 LUG ROTOR ASSEMBLY
1 - SPRING
2 - SHOCK
3 - UPPER AND LOWER SUSPENSION ARMS
4 - DISC BRAKE CALIPER
5 - DISC BRAKE CALIPER ADAPTER
6 - ROTOR
Fig. 61 REAR ROTOR
1 - ROTOR
2 - CALIPER ADAPTER
3 - CALIPER
Fig. 62 ROTOR / HUB REMOVAL
5 - 34 BRAKES - BASEDR
ROTORS (Continued)

(2) Install the caliper adapter (Fig. 61) (Refer to 5
- BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPER ADAPTER - INSTALLATION).
(3) Install the caliper adapter bolts (Fig. 61) and
tighten the mounting bolts to 135 N´m (100 ft.lbs).
(4) Install the disc brake caliper, (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPERS - INSTALLATION).
(5) Install the tire and wheel assembly (Refer to 22
- TIRES/WHEELS/WHEELS - STANDARD PROCE-
DURE).
(6) Lower the vehicle.
INSTALLATION - REAR DUAL WHEELS
(1) Install the hub to the rotor. Tighten the bolts to
128 N´m (95 ft. lbs.) (Fig. 63).
(2) Install the hub and rotor assembly.
(3) Install the rear axle shaft to the housing with
dual wheels, (Refer to 3 - DIFFERENTIAL & DRIV-
ELINE/REAR AXLE - 286RBI/AXLE SHAFTS -
INSTALLATION).
(4) Install the caliper adapter bolts.
(5) Install the disc brake caliper, (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPERS - INSTALLATION). (Fig. 64).
(6) Install the tire and wheel assembly, (Refer to
22 - TIRES/WHEELS/WHEELS - STANDARD PRO-
CEDURE).
(7) Lower the vehicle.
SUPPORT PLATE
REMOVAL
(1) Remove wheel and tire assembly.(2) Remove the disc brake caliper (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPERS - REMOVAL).
(3) Remove the caliper adapter (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPER ADAPTER - REMOVAL).
(4) Remove the rotor (Refer to 5 - BRAKES/HY-
DRAULIC/MECHANICAL/ROTORS - REMOVAL).
(5) Remove the axle shaft (Refer to 3 - DIFFER-
ENTIAL & DRIVELINE/REAR AXLE - 9 1/4/AXLE
SHAFTS - REMOVAL).
(6) Remove the park brake shoes (Refer to 5 -
BRAKES/PARKING BRAKE/SHOES - REMOVAL).
(7) Remove the parking brake cable from the
brake lever.
(8) Remove the bolts attaching the support plate to
the axle and remove the support plate (Fig. 65).
Fig. 63 ROTOR TO HUB
1 - Hub Bolts
2 - Socket
Fig. 64 ROTOR INSTALLED
Fig. 65 SUPPORT PLATE
1 - SUPPORT PLATE
2 - MOUNTING STUDS
DRBRAKES - BASE 5 - 35
ROTORS (Continued)

INSTALLATION
(1) Install support plate on axle flange (Fig. 66).
Tighten attaching bolts to 115 N´m (85 ft. lbs.).
(2) Install parking brake cable in the brake lever.
(3) Install the park brake shoes (Refer to 5 -
BRAKES/PARKING BRAKE/SHOES - INSTALLA-
TION). (Fig. 66).
(4) Install axle shaft, (Refer to 3 - DIFFEREN-
TIAL & DRIVELINE/REAR AXLE - 9 1/4/AXLE
SHAFTS - INSTALLATION).
(5) Adjust brake shoes to drum with brake gauge
(Refer to 5 - BRAKES/PARKING BRAKE/SHOES -
ADJUSTMENTS).
(6) Install the rotor (Refer to 5 - BRAKES/HY-
DRAULIC/MECHANICAL/ROTORS - INSTALLA-
TION).
(7) Install the caliper adapter (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/DISC
BRAKE CALIPER ADAPTER - INSTALLATION).
(8) Install the caliper (Refer to 5 - BRAKES/HY-
DRAULIC/MECHANICAL/DISC BRAKE CALIPERS
- INSTALLATION).
(9) Install the wheel and tire assembly (Refer to 22
- TIRES/WHEELS/WHEELS - STANDARD PROCE-
DURE).
PARKING BRAKE
DESCRIPTION
The parking brakes are operated by a system of
cables and levers attached to a primary and second-
ary shoe positioned within the drum section of the
rotor.
The drum-in-hat design utilizes an independent set
of shoes to park the vehicle (Fig. 67).
OPERATION
To apply the parking brake the pedal is depressed.
This creates tension in the cable which pulls forward
on the park brake lever. The lever pushes the park
brake shoes outward and into contact with the drum
section of the rotor. The contact of shoe to rotor parks
the vehicle.
A torsion locking mechanism is used to hold the
pedal in an applied position. Parking brake release is
accomplished by the hand release.
A parking brake switch is mounted on the parking
brake lever and is actuated by movement of the
lever. The switch, which is in circuit with the red
warning light in the dash, will illuminate the warn-
ing light whenever the parking brake is applied.
Parking brake adjustment is controlled by a cable
tensioner mechanism. The cable tensioner, once
adjusted at the factory, should not need further
adjustment under normal circumstances. Adjustment
may be required if a new tensioner, or cables are
installed, or disconnected.
CABLES
REMOVAL
REMOVAL - FRONT PARKING BRAKE CABLE
(1) Raise and support vehicle.
(2) Lockout the parking brake cable (Fig. 69).
(3) Loosen adjusting nut to create slack in front
cable.
(4) Remove the front cable from the cable connec-
tor.
Fig. 66 SUPPORT PLATE WITH BRAKES MOUNTED
1 - SUPPORT PLATE
2 - MOUNTING NUTS
Fig. 67 SUPPORT PLATE WITH BRAKES MOUNTED
1 - SUPPORT PLATE
2 - MOUNTING NUTS
5 - 36 BRAKES - BASEDR
SUPPORT PLATE (Continued)

(8) Install the tire and wheel assembly (Refer to 22
- TIRES/WHEELS/WHEELS - STANDARD PROCE-
DURE).
(9) Lower the vehicle.
ADJUSTMENTS
ADJUSTMENT - PARKING BRAKE SHOES
CAUTION: Before adjusting the park brake shoes be
sure that the park brake pedal is in the fully
released position. If park brake pedal is not in the
fully released position, the park brake shoes can
not be accurately adjusted.
(1) Raise vehicle.
(2) Remove tire and wheel.
(3) Remove disc brake caliper from caliper adapter
(Refer to 5 - BRAKES/HYDRAULIC/MECHANICAL/
DISC BRAKE CALIPERS - REMOVAL).
(4) Remove rotor from the axleshaft (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/ROTORS -
REMOVAL).
NOTE: When measuring the brake drum diameter,
the diameter should be measured in the center of
the area in which the park brake shoes contact the
surface of the brake drum.
(5) Using Brake Shoe Gauge, Special Tool C-3919,
or equivalent,accuratelymeasure the inside diam-
eter of the park brake drum portion of the rotor (Fig.
79).
(6) Using a ruler that reads in 64th of an inch,
accurately read the measurement of the inside diam-
eter of the park brake drum from the special tool
(Fig. 80).
(7) Reduce the inside diameter measurement of
the brake drum that was taken using Special ToolC-3919 by 1/64 of an inch. Reset Gauge, Brake Shoe,
Special Tool C-3919 or the equivalent used, so that
the outside measurement jaws are set to the reduced
measurement (Fig. 81).
(8) Place Gauge, Brake Shoe, Special Tool C-3919,
or equivalent over the park brake shoes. The special
tool must be located diagonally across at the top of
one shoe and bottom of opposite shoe (widest point)
of the park brake shoes.
(9) Using the star wheel adjuster, adjust the park
brake shoes until the lining on the park brake shoes
just touches the jaws on the special tool.
(10) Repeat step 8 above and measure shoes in
both directions.
(11) Install brake rotor on the axleshaft (Refer to 5
- BRAKES/HYDRAULIC/MECHANICAL/ROTORS -
INSTALLATION).
Fig. 79 Measuring Park Brake Drum Diameter
Fig. 80 Reading Park Brake Drum Diameter
1 - SPECIAL TOOL C-3919
2 - RULER
Fig. 81 Setting Gauge To Park Brake Shoe
Measurement
1 - RULER
2 - SPECIAL TOOL C-3919
DRBRAKES - BASE 5 - 41
SHOES (Continued)

(12) Rotate rotor to verify that the park brake
shoes are not dragging on the brake drum. If park
brake shoes are dragging, remove rotor and back off
star wheel adjuster one notch and recheck for brake
shoe drag against drum. Continue with the previous
step until brake shoes are not dragging on brake
drum.
(13) Install disc brake caliper on caliper adapter
(Refer to 5 - BRAKES/HYDRAULIC/MECHANICAL/
DISC BRAKE CALIPERS - INSTALLATION).
(14) Install wheel and tire.
(15) Tighten the wheel mounting nuts in the
proper sequence until all nuts are torqued to half the
specified torque. Then repeat the tightening sequence
to the full specified torque of 180 N´m (135 ft. lbs.)
1500 & 2500 Series or 195 N´m (145 ft. lbs.) 3500
Series.
(16) Lower vehicle.
(17) Apply and release the park brake pedal one
time. This will seat and correctly adjust the park
brake cables.
CAUTION: Before moving vehicle, pump brake
pedal several times to ensure the vehicle has a firm
enough pedal to stop the vehicle.
NOTE: On a new vehicle or after parking brake lin-
ing replacement, it is recommended that the park-
ing brake system be conditioned prior to use. This
is done by making one stop from 25 mph on dry
pavement or concrete using light to moderate force
on the parking brake foot pedal.
(18) Road test the vehicle to ensure proper func-
tion of the vehicle's brake system.
ADJUSTMENT - WITH ADJUSTING TOOL
Adjustment can be made with a standard brake
gauge or with adjusting tool. Adjustment is per-
formed with the complete brake assembly installed
on the backing plate.
(1) Be sure parking brake lever is fully released.
(2) Raise vehicle so rear wheels can be rotated
freely.
(3) Remove plug from each access hole in brake
support plates.
(4) Loosen parking brake cable adjustment nut
until there is slack in front cable.
(5) Insert adjusting tool through support plate
access hole and engage tool in teeth of adjusting
screw star wheel (Fig. 82).
(6) Rotate adjuster screw star wheel (move tool
handle upward) until slight drag can be felt when
wheel is rotated.
(7) Back off adjuster screw star wheel until brake
drag is eliminated.(8) Repeat adjustment at opposite wheel. Be sure
adjustment is equal at both wheels.
(9) Install support plate access hole plugs.
(10) Adjust parking brake cable and lower vehicle.
(11) Depress park brake pedal and make sure park
brakes hold the vehicle staionary.
(12) Release park brake pedal.
PEDAL
REMOVAL
(1) Release the parking brake.
(2) Raise the vehicle.
(3) Loosen the cable tensioner nut at the equalizer
to create slack in the front cable.
(4) Lower the vehicle.
(5) Remove the knee bolster, (Refer to 23 - BODY/
INSTRUMENT PANEL/STEERING COLUMN
OPENING COVER - REMOVAL).
(6) Disconnect the brake lamp wire from the
switch on the pedal assembly.
(7) Roll the carpet back, loosen the front cable
grommet from the floorpan and the cable retainer.
(8) Disengage the release rod (Fig. 83) from the
arm on the pedal assembly.
(9) Remove the bolts/nuts from the pedal assembly
and remove the assembly.
INSTALLATION
(1) Position the replacement pedal assembly on the
dash and cowl.
Fig. 82 Brake Adjustment
1 - STAR WHEEL
2 - LEVER
3 - BRAKE SHOE WEB
4 - SCREWDRIVER
5 - ADJUSTING TOOL
6 - ADJUSTER SPRING
5 - 42 BRAKES - BASEDR
SHOES (Continued)

(2) Install the bolts/nuts and tighten to 28 N´m (21
ft. lbs.) (Fig. 84).
(3) Install the park brake release rod.
(4) Connect the front cable to the arm on the pedal
assembly.
(5) Install the front cable grommet into the floor-
pan and the cable retainer, roll the carpet back.
(6) Connect the wires to the brake lamp switch.
(7) Install the knee bolster, (Refer to 23 - BODY/
INSTRUMENT PANEL/STEERING COLUMN
OPENING COVER - INSTALLATION).
(8) Raise the vehicle.
(9) Adjust the parking brake cable tensioner (Refer
to 5 - BRAKES/PARKING BRAKE/CABLE TEN-
SIONER - ADJUSTMENTS).
CABLE TENSIONER
ADJUSTMENTS
ADJUSTMENT
NOTE: Tensioner adjustment is only necessary
when the tensioner, or a cable has been replaced or
disconnected for service. When adjustment is nec-
essary, perform adjustment only as described in the
following procedure. This is necessary to avoid
faulty park brake operation.
(1) Raise the vehicle.
(2) Back off the cable tensioner adjusting nut to
create slack in the cables.
(3) Remove the rear wheel/tire assemblies. Then
remove the brake rotors (Refer to 5 - BRAKES/HY-
DRAULIC/MECHANICAL/ROTORS - REMOVAL).
(4) Verify the brakes are in good condition and
operating properly.
(5) Verify the park brake cables operate freely and
are not binding, or seized.
(6) Check the rear brake shoe adjustment with
standard brake gauge (Refer to 5 - BRAKES/PARK-
ING BRAKE/SHOES - ADJUSTMENTS).
(7) Install the rotors (Refer to 5 - BRAKES/HY-
DRAULIC/MECHANICAL/ROTORS - INSTALLA-
TION) and verify that the rotors rotate freely
without drag.
(8) Install the wheel/tire assemblies, (Refer to 22 -
TIRES/WHEELS/WHEELS - STANDARD PROCE-
DURE).
(9) Lower the vehicle enough for access to the park
brake foot pedal. Then fully apply the park brakes.
NOTE: Leave park brakes applied until adjustment
is complete.
(10) Raise the vehicle again.
(11) Mark the tensioner rod 6.35 mm (1/4 in.) from
edge of the tensioner (Fig. 85).
(12) Tighten the adjusting nut on the tensioner rod
until the mark is no longer visible.
CAUTION: Do not loosen, or tighten the tensioner
adjusting nut for any reason after completing
adjustment.
(13) Lower the vehicle until the rear wheels are
15-20 cm (6-8 in.) off the shop floor.
(14) Release the park brake foot pedal and verify
that rear wheels rotate freely without drag. Then
lower the vehicle.
Fig. 83 PARKING BRAKE PEDAL
1 - RELEASE ROD
2 - PEDAL ASSEMBLY
Fig. 84 PARKING BRAKE ASSEMBLY
1 - PEDAL ASSEMBLY
2 - MOUNTING NUT
DRBRAKES - BASE 5 - 43
PEDAL (Continued)

Brake fluid apply pressure is modulated according
to wheel speed, degree of slip and rate of decelera-
tion. Sensors at each front wheel convert wheel speed
into electrical signals. These signals are transmitted
to the CAB for processing and determination of
wheel slip and deceleration rate.
The ABS system has three fluid pressure control
channels. The front brakes are controlled separately
and the rear brakes in tandem. A speed sensor input
signal indicating a wheel slip condition activates the
CAB antilock program.
There are Two solenoid valves (Isolation and Dump
valve) which are used in each antilock control chan-
nel. The valves are all located within the HCU valve
body and work in pairs to either increase, hold, or
decrease apply pressure as needed in the individual
control channels.
During an ABS stop the ISO valve is energized
which acts to prevent further pressure build-up to
the calipers. Then the Dump valve dumps off pres-
sure until the wheel unlocks. This will continue until
the wheels quit slipping altogether.STANDARD PROCEDURE - ABS BRAKE
BLEEDING
ABS system bleeding requires conventional bleed-
ing methods plus use of the DRB scan tool. The pro-
cedure involves performing a base brake bleeding,
followed by use of the scan tool to cycle and bleed the
HCU pump and solenoids. A second base brake bleed-
ing procedure is then required to remove any air
remaining in the system.
(1) Perform base brake bleeding,(Refer to 5 -
BRAKES - STANDARD PROCEDURE) OR (Refer to
5 - BRAKES - STANDARD PROCEDURE).
(2) Connect scan tool to the Data Link Connector.
(3) Select ANTILOCK BRAKES, followed by MIS-
CELLANEOUS, then ABS BRAKES. Follow the
instructions displayed. When scan tool displays TEST
COMPLETE, disconnect scan tool and proceed.
(4) Perform base brake bleeding a second time,(Re-
fer to 5 - BRAKES - STANDARD PROCEDURE) OR
(Refer to 5 - BRAKES - STANDARD PROCEDURE).
(5) Top off master cylinder fluid level and verify
proper brake operation before moving vehicle.
SPECIFICATIONS
TORQUE CHART
TORQUE SPECIFICATIONS
DESCRIPTION N´m Ft. Lbs. In. Lbs.
ABS Assembly
Mounting Bolts15 11 Ð
ABS Assembly
CAB Screws3.5 Ð 31
ABS Assembly
Brake Line Fittings19 Ð 170
Wheel Speed Sensors
Front Sensor Bolt21 Ð 190
Wheel Speed Sensors
Bracket To Knuckle6.7 Ð 60
Wheel Speed Sensors
Rear Sensor Stud22.5 Ð 200
Controller
Mounting Screws6Ð53
RWAL Module
Mounting Bolts15 11 Ð
RWAL Valve
Brake Line Fittings19 Ð 170
Rear Wheel Speed
Sensor
Mounting Bolt24 Ð 200
5 - 46 BRAKES - ABSDR
BRAKES - ABS (Continued)

TONE WHEEL
DIAGNOSIS AND TESTING - REAR WHEEL
SPEED SENSOR
Diagnosis of base brake conditions which are
mechanical in nature should be performed first. This
includes brake noise, lack of power assist, parking
brake, or vehicle vibration during normal braking.
The Antilock brake system performs several self-
tests every time the ignition switch is turned on and
the vehicle is driven. The CAB monitors the system
inputs and outputs circuits to verify the system is
operating properly. If the CAB senses a malfunction
in the system it will set a DTC into memory and trig-
ger the warning lamp.
NOTE: The MDS or DRB III scan tool is used to
diagnose the Antilock Brake system. For test proce-
dures refer to the Chassis Diagnostic Manual.
HYDRAULIC/MECHANICAL
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).
OPERATION - ELECTRONIC VARIABLE BRAKE
PROPORTIONING
EVBP is able to decrease, hold and increase rear
brake pressure without activating full ABS control.
Upon entry into EVBP the inlet valve for the rear
brake circuit is switched on so that the fluid supply
from the master cylinder is shut off. In order to
decrease the rear brake pressure, the outlet valve for
the rear brake circuit is pulsed. This allows fluid to
enter the low pressure accumulator (LPA) in the
hydraulic control unit (HCU) resulting in a drop in
fluid pressure to the rear brakes. In order to increase
the rear brake pressure, the outlet valve is switched
off and the inlet valve is pulsed. This increases the
pressure to the rear brakes.
The EVBP will remain functional during many
ABS fault modes. If both the red BRAKE and amber
ABS warning indicators are illuminated, the EVBP
may not be functioning.
HCU (HYDRAULIC CONTROL
UNIT)
DESCRIPTION
The HCU consists of a valve body, pump motor, low
pressure accumulators, inlet valves, outlet valves and
noise attenuators.
OPERATION
Accumulators in the valve body store extra fluid
released to the system for ABS mode operation. The
pump provides the fluid volume needed and is oper-
ated by a DC type motor. The motor is controlled by
the CAB.
The valves modulate brake pressure during
antilock braking and are controlled by the CAB.
The HCU provides three channel pressure control
to the front and rear brakes. One channel controls
the rear wheel brakes in tandem. The two remaining
channels control the front wheel brakes individually.
During antilock braking, the solenoid valves are
opened and closed as needed.
During normal braking, the HCU solenoid valves
and pump are not activated. The master cylinder and
power booster operate the same as a vehicle without
an ABS brake system.
NOTE: The three modes mentioned below do occur
but not necessarily in the order listed everytime.
During antilock braking, solenoid valve pressure
modulation occurs in three stages, pressure increase,
pressure hold, and pressure decrease. The valves are
all contained in the valve body portion of the HCU.
PRESSURE DECREASE
The outlet valve is opened and the inlet valve is
closed during the pressure decrease cycle.
A pressure decrease cycle is initiated when speed
sensor signals indicate high wheel slip at one or
more wheels. At this point, the CAB closes the inlet
then opens the outlet valve, which also opens the
return circuit to the accumulators. Fluid pressure is
allowed to bleed off (decrease) as needed to prevent
wheel lock.
Once the period of high wheel slip has ended, the
CAB closes the outlet valve and begins a pressure
increase or hold cycle as needed.
PRESSURE HOLD
Both solenoid valves are closed in the pressure
hold cycle but only the inlet valve is energized. Fluid
apply pressure in the control channel is maintained
at a constant rate. The CAB maintains the hold cycle
until sensor inputs indicate a pressure change is nec-
essary.
DRBRAKES - ABS 5 - 49

PRESSURE INCREASE
The inlet valve is open and the outlet valve is
closed during the pressure increase cycle. The pres-
sure increase cycle is used to reapply thew brakes.
This cycle controls re-application of fluid apply pres-
sure.
REMOVAL
(1) Install a prop rod on the brake pedal to keep
pressure on the brake system.
(2) Disconnect the battery cables from the battery.
(3) Remove the battery.
(4) Disconnect the two electrical harness connec-
tors (Fig. 5).
(5) Remove the five brake lines from the HCU
(Fig. 5).
(6) Remove HCU/CAB mounting bolts and remove
the HCU/CAB (Fig. 5).
INSTALLATION
NOTE: If the CAB is being replaced with a new CAB
is must be reprogrammed with the use of a DRB III.
(1) Install HCU/CAB on the mounts and Tighten
the bolts to 15N´m (11 ft. lbs.) (Fig. 5).
(2) Install the five brake lines to the HCU and
tighten to 19 N´m (170 in. lbs.) (Fig. 5).
(3) Install the two electrical harness connectors to
the HCU/CAB and push down on the release to
secure the connectors.
(4) Install the battery.
(5) Install the battery cables to the battery.
(6) Remove the prop rod on the brake pedal.
(7) Bleed ABS brake system (Refer to 5 - BRAKES
- STANDARD PROCEDURE).
RWAL VALVE
DESCRIPTION
Rear Wheel Antilock (RWAL) brake system is stan-
dard equipment on 1500 series vehicles. The RWAL
brake system is designed to prevent rear wheel
lock-up on virtually all types of road surfaces. RWAL
braking is desirable because a vehicle which is
stopped without locking the rear wheels will retain
directional stability. This allows the driver to retain
greater control of the vehicle during braking.
The valve is located on the drivers side inner
fender under the hood. The valve modulates hydrau-
lic pressure to the rear brakes.
The RWAL components include:
²RWAL Valve
²Controller Antilock brake (CAB)
²Rear Wheel Speed Sensor (WSS)
OPERATION
When the brakes are applied, hydraulic fluid is
routed from the master cylinder's secondary circuit to
the RWAL valve. From there hydraulic fluid is routed
to the rear brakes. The Controller Antilock Brake
(CAB) contains an Electronic Variable Brake Propor-
tioning (EVBP) control algorithm, which proportions
the applied braking force to the rear wheels during
braking. The EVBP function of the RWAL system
takes the place of a conventional hydraulic propor-
tioning valve. The CAB monitors the rear wheel
speed through the rear wheel speed sensor and cal-
culates an estimated vehicle deceleration. When an
established deceleration threshold is exceeded, an
isolation valve is closed to hold the applied brake
pressure to the rear brakes constant. Upon further
increases in the estimated vehicle deceleration, the
isolation valve is selectively opened to increase rear
brake pressure in proportion to the front brake pres-
sure. If impending rear wheel lock-up is sensed, the
CAB signals the RWAL valve to modulate hydraulic
brake pressure to the rear wheels to prevent lock-up.
NORMAL BRAKING Since the RWAL valve also
performs the EVBP or proportioning function, vehicle
deceleration under normal braking may be sufficient
to trigger the EVBP function of the RWAL system
without full RWAL activity as would normally occur
during an impending rear wheel lock-up. As previ-
ously mentioned, the isolation valve is selectively
closed and opened to increase rear brake pressure in
proportion to the front brake pressure under EVBP
control. Slight brake pedal pulsations may be noticed
as the isolation valve is opened.
Fig. 5 HYDRAULIC CONTROL UNIT
1 - HYDRAULIC CONTROL UNIT
2 - MOUNTING BOLTS
5 - 50 BRAKES - ABSDR
HCU (HYDRAULIC CONTROL UNIT) (Continued)