FIXED PROPORTIONING VALVE OPERATION
The fixed proportioning valve is made out of alumi-
num and has an integral mounting bracket. The
fixed proportioning valve is non-serviceable compo-
nent and must be replaced as an assembly if found to
be functioning improperly.
The fixed proportioning valve is mounted to the
bottom of the left rear frame rail, just forward of the
rear shock absorber to frame rail mounting location
(Fig. 6). The proportioning valve has 2 inlet ports for
brake fluid coming from the ABS modulator, and 2
outlet ports for brake fluid going to the rear wheel
brakes.
The fixed proportioning valve operates by allowing
full hydraulic pressure to the rear brakes up to a set
point, called the valve's split point. Beyond this split
point the proportioning valve reduces the amount of
hydraulic pressure to the rear brakes according to a
certain ratio.
Thus, on light brake pedal applications the propor-
tioning valve allows approximately equal brake
hydraulic pressure to be supplied to both the front
and rear brakes. On heavier brake pedal applications
though, the proportioning valve will control hydraulic
pressure to the rear brakes, so that hydraulic pres-
sure at the rear brakes will be lower than that at the
front brakes. This controlled hydraulic pressure to
the rear brakes prevents excessive rear wheel ABS
cycling during moderate stops.
HEIGHT SENSING PROPORTIONING VALVE
CAUTION: The use of after-market load leveling or
load capacity increasing devices on this vehicle are
prohibited. Using air shock absorbers or helper
springs on this vehicle will cause the height sens-
ing proportioning valve to inappropriately reduce
the hydraulic pressure to the rear brakes. This inap-
propriate reduction in hydraulic pressure potentiallycould result in increased stopping distance of the
vehicle.
On vehicles not equipped with ABS brakes, the
brake systems hydraulic control unit (HCU) is
replaced by a junction block (Fig. 7). The junction
block is made of aluminum and is mounted to the
front suspension crossmember on the drivers side of
the vehicle in the same location as the (HCU) on an
ABS equipped vehicle. The junction block is perma-
nently attached to its mounting bracket and must be
replaced as an assembly with its mounting bracket.
The junction block is used for diagonally splitting the
brake's hydraulic system.
Vehicles not equipped with ABS brakes use a
height sensing proportioning valve. The height sens-
ing proportioning valve is mounted on the left frame
rail at the rear of the vehicle (Fig. 8). The height
sensing proportioning valve uses an actuator assem-
bly (Fig. 8) to attach the proportioning valve to the
left rear spring for sensing changes in vehicle height.
HEIGHT SENSING PROPORTIONING VALVE OPERATION
The height sensing proportioning valve regulates
the hydraulic pressure to the rear brakes. The pro-
portioning valve regulates the pressure by sensing
the load condition of the vehicle through the move-
ment of the proportioning valve actuator assembly
Fig. 6 Fixed Proportioning Valve Location
Fig. 7 Junction Block Location
Fig. 8 Height Sensing Proportioning Valve
5 - 6 BRAKESNS
DESCRIPTION AND OPERATION (Continued)
micrometer at a radius approximately 25.4 mm (1
inch) from outer edge of rotor (Fig. 18). If thickness
measurements vary by more than 0.013 mm (0.0005
inch), rotor should be removed and resurfaced, or a
new rotor installed. If cracks or burned spots are evi-
dent, rotor must be replaced.
Light scoring and/or wear is acceptable. If heavy
scoring or warping is evident, the rotor must be
refinished or replaced (See Refinishing/RefacingRotor). If cracks are evident in the rotor, replace the
rotor.
PROPORTIONING VALVES
FIXED PROPORTIONING VALVE TEST
PROCEDURE
On a vehicle equipped with ABS, premature or
excessive rear wheel ABS cycling may be an indica-
tion that the brake fluid pressure to the rear brakes
is above the desired output.
Prior to testing a proportioning valve for function,
check that all tire pressures are correct. Also, ensure
the front and rear brake linings are in satisfactory
condition.It is also necessary to verify that the
brakes shoe assemblies on a vehicle being
tested, are either original equipment manufac-
turers (OEM), or original replacement brake
shoe assemblies meeting the OEM lining mate-
rial specification. The vehicles brake system is
not balanced for after market brake shoe
assembly lining material.
If brake shoe assembly lining material is of satis-
factory condition, and of the correct material specifi-
cation, check for proper proportioning valve function
using the following procedure.
(1) Road test vehicle to be sure the vehicle is truly
exhibiting a condition of excessive rear wheel ABS
cycling. Since ABS cycles both rear brakes together
both proportioning valves of the assembly(Fig.
19) must be tested. Use the following procedure to
test the proportioning valve.
(2) Remove one of the chassis brake lines (Fig. 19)
coming from the ABS modulator, at
(3) the proportioning valve assembly. Remove the
hydraulic brake line going to one of the rear wheels
of the vehicle from the proportioning valve (Fig. 19)
Fig. 17 Minimum Rotor Thickness Markings
Fig. 18 Checking Rotor For Thickness Variation
Fig. 19 Rear Brake Proportioning Valve And Brake
Tube Locations
5 - 16 BRAKESNS
DIAGNOSIS AND TESTING (Continued)
(4) Remove the 2 bolts (Fig. 19) attaching the pro-
portioning valve to the frame rail.
CAUTION: When lowering the proportioning valve,
care must be taken not to kink any of the chassis
brake lines.
(5) Carefully lower the proportioning valve for
clearance to install the proportioning valve test fit-
tings.
(6) Install the required fitting from Pressure Test
Fittings, Special Tool 6833 (Fig. 20) into the inlet
port of the proportioning valve assembly, from which
the chassis brake line was removed. Install the
removed chassis brake line into the Pressure Test
Fitting (Fig. 20). Install the required fitting from
Pressure Test Fittings, Special Tool 6833 into the
required outlet port of the proportioning valve.
Install the required fitting from Pressure Test Fit-
tings, Special Tool 6833 into the required outlet port
of the proportioning valve (Fig. 20). Then install the
removed chassis brake line into the Pressure Test
Fitting (Fig. 20).
(7) Install a pressure gauge from Gauge Set, Spe-
cial Tool C-4007-A into each pressure test fitting (Fig.
21). Bleed air out of hose from pressure test fittings
to pressure gauges, at the pressure gauges (Fig. 21).
Then bleed air out of the brake line being tested, at
that rear wheel cylinder.
(8) With the aid of a helper, apply pressure to the
brake pedal until a pressure of 6895 kPa (1000 psi) is
obtained on the proportioning valve inlet gauge.
Then based on the type of brake system the vehicle is
equipped with and the pressure specification shown
on the following table, compare the pressure reading
on the outlet gauge to the specification. If outlet
pressure at the proportioning valve is not within
specification when required inlet pressure is
obtained, replace the proportioning valve.(9) Repeat steps 2 through 7 for the other propor-
tioning valve of the assembly.
CAUTION: When mounting the original or a
replacement proportion valve on the frame rail of
the vehicle install the mounting bolts in only the
two forward holes of the mounting bracket (Fig. 19).
HEIGHT SENSING PROPORTIONING VALVE
CAUTION: The use of after-market load leveling or
load capacity increasing devices on this vehicle are
prohibited. Using air shock absorbers or helper
springs on this vehicle will cause the height sens-
ing proportioning valve to inappropriately reduce
the hydraulic pressure to the rear brakes. This inap-
propriate reduction in hydraulic pressure potentially
could result in increased stopping distance of the
vehicle.
When a premature rear wheel skid is obtained on a
brake application, it may be an indication that the
hydraulic pressure to the rear brakes is above the
specified output from the proportioning valve. This
condition indicates a possible malfunction of the
height sensing proportioning valve, which will
require testing to verify that it is properly controlling
the hydraulic pressure allowed to the rear brakes.
Premature rear wheel skid may also be caused by an
incorrectly adjusted proportioning valve actuator
assembly, or contaminated front or rear brake lin-
ings.
Prior to testing a proportioning valve for function,
check that all tire pressures are correct. Also, ensure
the front and rear brake linings are in satisfactory
condition.It is also necessary to verify that the
brakes shoe assemblies on a vehicle being
tested, are either original equipment manufac-
turers (OEM), or original replacement brake
Fig. 20 Proportioning Valve Test Fitting Installation
Fig. 21 Pressure Gauges Installed On Pressure Test
Fittings
NSBRAKES 5 - 17
DIAGNOSIS AND TESTING (Continued)
MASTER CYLINDER BLEEDING PROCEDURE
CAUTION: When clamping master cylinder in vise,
only clamp master cylinder by its mounting flange,
do not clamp on primary piston, seal\boot or body
of master cylinder.
(1) Clamp the master cylinder in a vise using only
the mounting flange (Fig. 30).
NOTE: Two different size bleeding tubes are used
depending on which type of master cylinder the
vehicle is equipped with. Vehicles equipped with
traction control use a center port master cylinder
with a larger diameter brake tube. Vehicles not
equipped with traction control use a compensating
port master cylinder using a standard 3/16 inch
diameter brake tube. Be sure the correct size bleed-
ing tubes are used when bleeding the master cylin-
der.
(2) Install the Bleeding Tubes, Special Tool 6920
for a non traction control master cylinder or Special
Tool 8129 for a traction control master cylinder on
the master cylinder (Fig. 102). Position bleeding
tubes so the outlets of bleeding tubes will be below
surface of brake fluid when reservoir is filled to its
proper level.
(3) Fill brake fluid reservoir with brake fluid con-
forming to DOT 3 specifications such as Mopar or an
Equivalent.
(4) Using a wooden dowel, depress push rod slowly,
and then allow pistons to return to released position.
Repeat several times until all air bubbles are
expelled from master cylinder.
(5) Remove bleeding tubes from master cylinder
outlet ports, and then plug outlet ports and install
fill cap on reservoir.
(6) Remove master cylinder from vise.(7) Install the filler cap from the master cylinder
filler neck, on the master cylinder fluid reservoir.
(8) Install the master cylinder assembly on the
power brake vacuum booster.
NOTE: Note: It is not necessary to bleed the ABS
hydraulic control unit (HCU) after replacing the
master cylinder. But, the base brake hydraulic sys-
tem must be bled to ensure no air is entered the
hydraulic system when the master cylinder was
removed.
ROTOR MACHINING (FRONT/REAR)
BRAKE ROTOR MACHINING PROCEDURES
Any servicing of the rotor requires extreme care to
maintain the rotor to within service tolerances to
ensure proper brake action.
If the rotor surface is deeply scored or warped, or
there is a complaint of brake roughness or brake
pedal pulsation, the rotor should be resurfaced,
refaced (Fig. 32) or (Fig. 33) or replaced.
NOTE: All rotors have markings for minimum
allowable thickness cast on an un-machined sur-
face of the rotor (Fig. 34) or (Fig. 35).
This marking includes 0.76 mm (0.030 inch) allow-
able rotor wear beyond the recommended 0.76 mm
(0.030 inch) of rotor refacing.
The collets, shafts and adapters used on the brake
lathe and the bearing cups in the rotor MUST be
clean and free from any chips or contamination.
When mounting the rotor on the brake lathe, strict
attention to the brake lathe manufacturer's operating
instructions is required.
If the rotor is not mounted properly, the lateral
runout will be worse after refacing or resurfacing
than before.
Fig. 30 Master Cylinder Mounted In Vise
Fig. 31 Bleed Tubes Installed On Master Cylinder
5 - 22 BRAKESNS
SERVICE PROCEDURES (Continued)
BRAKE DRUM MACHINING
Measure the runout and diameter of the rear brake
using only accurate measuring equipment. There
should be no variation in the drum diameter greater
than 0.090 mm (0.004 inch). Drum runout should not
exceed 0.15 mm (0.006 inch) out of round. If the
drum runout or diameter variation exceed these val-
ues the drum should be refaced. For best results in
eliminating the irregularities that cause brake rough-
ness and surge, the amount of material removed dur-
ing a single cut should be limited to 0.13 mm (0.005
inch). When the entire braking surface has been
cleaned. A final cut of 0.0254 mm (0.001 inch) will
assure a good drum surface providing the equipment
used is capable of the precision required for resurfac-
ing brake drums. Deeper cuts are permissible for the
sole purpose of removing deep score marks.Do not
reface more than 1.52 mm (0.060 inch) over the
standard drum diameter.
All drums will show markings of maximum allow-
able diameter (Fig. 36). For example, a drum will
have a marking of MAX. DIA. 251.55 mm (9.90 inch).
This marking includes 0.76 mm (0.030 inch) for
allowable drum wear beyond the recommended 1.52
mm (0.060 inch) of drum refacing
BRAKE TUBE REPAIR PROCEDURE
CAUTION: When repairing brake chassis lines or
flex hoses, the correct fasteners must be used to
attach the routing clips or hoses to the front sus-
pension cradle. The fasteners used to attach com-
ponents to the front suspension cradle have an
anti-corrosion coating due to the suspension cradle
being made of aluminum. Only Mopar replacement
fasteners with the required anti-corrosion coating
are to be used if a replacement fastener is required
when installing a brake chassis line or flex hose.
Only double wall 4.75mm (3/16 in.) steel tubing
with Al-rich/ZW-AC alloy coating and the correct tube
nuts are to be used for replacement of a hydraulic
brake tube.
NOTE: On vehicles equipped with traction control,
the primary and secondary hydraulic tubes between
the master cylinder and the hydraulic control unit
are 6 mm (15/64 in.). These tubes are also coated
with the Al-rich/ZW-AC alloy and must be replaced
with tubes having the same anti-corrosion coating.
Be sure the correct tube nuts are used for the
replacement of these hydraulic brake tubes.
Care should be taken when repairing brake tubing,
to be sure the proper bending and flaring tools and
procedures are used, to avoid kinking. Do not route
the tubes against sharp edges, moving components or
into hot areas. All tubes should be properly attached
with recommended retaining clips.
If the primary or secondary brake line from the
master cylinder to the ABS Hydraulic Control Unit,
or the flexible brake lines between the hydraulic con-
trol unit and the proportioning valve require replace-
mentonlythe original factory brake lines containing
a flexible section can be used. This is required due to
the movement of the front suspension cradle while
the vehicle is in motion.
Using Tubing Cutter, Special Tool C-3478-A or
equivalent, cut off damaged seat or tubing (Fig. 37).
Ream out any burrs or rough edges showing on
inside of tubing (Fig. 38). This will make the ends of
tubing square (Fig. 38) and ensure better seating of
ROTOR REFINISHING LIMITS
Braking RotorRotor Thick-
nessMinimum Rotor
ThicknessRotor Thick-
ness VariationRotor Run
Out*Rotor Micro
Finish
Front Rotor 23.87-24.13 mm
.939 -.949 in.22.4 mm
.881 in..013 mm
.0005 in..08 mm
.003 in.15-80 RMS
Rear Rotor 12.75-12.25 mm
.502 -.482 in.11.25 mm
.443 in..013 mm
.0005 in..08 mm
.003 in.15-80 RMS
* TIR Total Indicator Reading (Measured On Vehicle)
Fig. 36 Rear Brake Drum Maximum Diameter
Identification
5 - 24 BRAKESNS
SERVICE PROCEDURES (Continued)
CAUTION: When installing the tension clip on the
automatic adjuster, it must be located on only the
threaded area of the adjuster assembly (Fig. 66). If
it is located on a non-threaded area of the adjuster,
the function of the automatic adjuster will be
affected.
(7) Install the tension clip (Fig. 66) attaching the
upper return spring to the automatic adjuster assem-
bly.
(8) Install the brake shoe to brake shoe lower
return springs on the brake shoes (Fig. 64) and (Fig.
65).
(9) Install automatic adjustment lever on the lead-
ing brake shoe of the rear brake assembly (Fig. 63).
(10) Install the actuating spring on the automatic
adjustment lever and leading brake shoe assembly
(Fig. 62).
(11) Verify that the automatic adjuster lever has
positive contact with the star wheel on the automatic
adjuster assembly.
(12) When all components of both rear brake
assemblies are correctly and fully installed, remove
the locking pliers from the front park brake cable.
(13) Adjust brake shoes assemblies so as not to
interfere with brake drum installation.
(14) Install the rear brake drums on the hubs.
(15) Adjust rear brake shoes per Adjusting Rear
Brakes procedure in the service adjustments section
of the service manual.
(16) Install the wheel and tire assembly.
(17) Push the park brake pedal to the floor once
and release pedal. This will automatically remove the
slack from and correctly adjust the park brake
cables.
(18) Tighten the wheel mounting stud nuts in
proper sequence until all nuts are torqued to half
specification. Then repeat the tightening sequence to
the full specified torque of 130 N´m (95 ft. lbs.).
(19) Road test vehicle. The automatic adjuster will
continue the brake adjustment during the road test
of the vehicle.
BRAKE SUPPORT PLATE (REAR DRUM BRAKES)
REMOVE
(1) Raise vehicle on jackstands or centered on a
frame contact type hoist. See Hoisting in the Lubri-
cation and Maintenance section of this service man-
ual for required lifting procedure.
(2) Remove wheel and tire.
(3) Remove brake drum from hub/bearing.
(4) Remove brake shoes from brake support plate.
Refer to Rear Brake Shoe Removal in the removal
and installation section in this group of the service
manual for the required procedure.(5) Disconnect the park brake cable from the park
brake actuation lever.
(6) Remove the rear wheel speed sensor from the
rear hub/bearing flange (Fig. 74). This will prevent
damage to the speed sensor during removal and
installation of the hub/bearing.The rear wheel
speed sensor bolts to the hub/bearing. It can
not be removed unless the speed sensor is
removed first.
CAUTION: When working in the area of the rear
hub/bearing and when removing it from the rear
axle, care must be used so the teeth on the tone
wheel are not damaged. Damage to the teeth on the
tone wheel will result in false ABS cycling and cor-
rosion of the tone wheel.
(7) Remove the 4 bolts (Fig. 75) attaching the hub/
bearing to the flange of the rear axle .
Fig. 74 Rear Wheel Speed Sensor
Fig. 75 Rear Hub/Bearing Mounting Bolts
NSBRAKES 5 - 37
REMOVAL AND INSTALLATION (Continued)
(3) Remove the rear wheel cylinder attaching bolts
(Fig. 81). Then pull wheel cylinder assembly off the
brake support plate.
INSTALL
(1) Apply MopartGasket In-A-Tube or equivalent
sealant around wheel cylinder mounting surface in
brake support plate.
(2) Install wheel cylinder onto brake support, and
tighten the wheel cylinder to brake support plate
attaching bolts (Fig. 81) to 8 N´m (75 in. lbs.).
(3) Attach hydraulic brake tube to wheel cylinder,
(Fig. 81) and tighten tube to wheel cylinder fitting to
16 N´m (142 in. lbs.).
(4) Install brake shoes on support plate.
(5) Install rear brake drum onto rear hub. Install
rear wheel and tire assembly, tighten wheel stud
nuts to 129 N´m (95 ft. lbs.).
(6) Adjust the rear brakes, (See Adjusting Service
Brakes) in Service Adjustments section in this group
of the service manual.
(7) Bleed the entire brake system. See (Bleeding
Brake System) in Service Adjustments section in this
group of the service manual.
HUB/BEARING
FRONT WHEEL DRIVE
REMOVE
(1) Raise vehicle on jackstands or centered on a
frame contact type hoist. See Hoisting in the Lubri-
cation and Maintenance section of this service man-
ual for required lifting procedure.
(2) Remove wheel and tire.
(3) Remove brake drum from hub/bearing.
(4) Remove rear wheel speed sensor from rear hub/
bearing (Fig. 82). This will prevent damage to the
speed sensor during removal and installation of the
hub/bearing.The rear wheel speed sensor bolts
to the hub/bearing. It can not be removed
unless the speed sensor is removed first.
CAUTION: When working in the area of the rear
hub/bearing and when removing it from the rear
axle, care must be used so the teeth on the tone
wheel are not damaged. Damage to the teeth on the
tone wheel will result in false ABS cycling and cor-
rosion of the tone wheel.
(5) Remove the 4 bolts (Fig. 83) attaching the hub/
bearing to the rear axle.
CAUTION: Corrosion may occur between the hub/
bearing and the axle. If this occurs the hub/bearing
will be difficult to remove from the axle. If the hub/
bearing will not come out of the axle by pulling onit by hand, do not pound on the hub/bearing to
remove it from the axle. Pounding on the hub/bear-
ing to remove it from the axle will damage the hub/
bearing. This damage will result in noise or failure
of the bearing.
(6) If hub/bearing cannot be removed from the axle
by hand, use Remover Special Tool 8214 (Fig. 84) and
following procedure to press the hub/bearing out of
the axle.
(a) Place Special Tool 8214-1 over tone wheel
and against cast flange of hub/bearing (Fig. 84)
(b) Put a dab of grease in the bolt pilot hole on
the back of Special Tool 8214-1.
(c) Insert Special Tool 8214-2 into the hole in the
bottom of the end casting on the axle (Fig. 84).
Special Tool 8214-2 should be against and sup-
ported by the axle plate (Fig. 84) when pressing
the wheel bearing out of the axle.If Special Tool
8214-2 will not fit into the hole in the end
casting, file or grind the flashing from the
hole until tool fits properly.
Fig. 82 Rear Wheel Speed Sensor
Fig. 83 Rear Hub/Bearing Mounting Bolts
5 - 40 BRAKESNS
REMOVAL AND INSTALLATION (Continued)
NOTE: Two different size bleeding tubes are used
depending on which type of master cylinder the
vehicle is equipped with. Vehicles equipped with
traction control use a center port master cylinder
with a larger diameter brake tube. Vehicles not
equipped with traction control use a compensating
port master cylinder using a standard 3/16 inch
diameter brake tube. Be sure the correct size bleed-
ing tubes are used when bleeding the master cylin-
der.
(2) Install the Bleeding Tubes, Special Tool 6920
for a non traction control master cylinder or Special
Tool 8129 for a traction control master cylinder on
the master cylinder (Fig. 102). Position bleeding
tubes so the outlets of bleeding tubes will be below
surface of brake fluid when reservoir is filled to its
proper level.(3) Fill brake fluid reservoir with brake fluid con-
forming to DOT 3 specifications such as Mopar or an
Equivalent.
(4) Using a wooden dowel, (Fig. 102) depress push
rod slowly, and then allow pistons to return to
released position. Repeat several times until all air
bubbles are expelled from master cylinder.
(5) Remove bleeding tubes from master cylinder
outlet ports, and then plug outlet ports and install
fill cap on reservoir.
(6) Remove master cylinder from vise.
NOTE: Note: It is not necessary to bleed the ABS
hydraulic control unit (HCU) after replacing the
master cylinder. But, the base brake hydraulic sys-
tem must be bled to ensure no air is entered the
hydraulic system when the master cylinder was
removed.
INSTALL
CAUTION: When replacing the master cylinder on
a vehicle, a NEW vacuum seal MUST be installed on
the master cylinder. Use only procedure detailed
below for installing the vacuum seal onto the mas-
ter cylinder.
(1) Install aNEWvacuum seal on master cylinder
making sure seal sits squarely in groove of master
cylinder casting (Fig. 103).
(2) Position master cylinder on studs of power
brake unit, aligning push rod on power brake vac-
uum booster with master cylinder push rod.
(3) Install the 2 master cylinder to power brake
unit mounting nuts. Then tighten both mounting
nuts to a torque of 25 N´m (225 in. lbs.).
Fig. 101 Master Cylinder Correctly Mounted In Vise
Fig. 102 Bleeding Tubes Installed On Master
Cylinder
Fig. 103 Vacuum Seal Installed On Master Cylinder
5 - 46 BRAKESNS
REMOVAL AND INSTALLATION (Continued)