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)
(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)
THERMOSTAT OPERATION
2.5 VM DIESEL
The engine cooling thermostats are wax pellet
driven, reverse poppet choke type. They are designed
to provide the fastest warm up possible by prevent-
ing leakage through them and to guarantee a mini-
mum engine operating temperature (Fig. 10). The
thermostat has a hole to bleed off air in the cooling
system during engine warm up. The thermostat
begins to open at 80É C62É (176É F64É).
PRESSURE/VENT CAP
WARNING: Engine coolant can reach temperatures
of 200É fahrenheit or greater. If the cooling system
is opened with coolant at a high temperature, hot
coolant can be forced out of the system under high
pressures, causing personal injury. Allow system to
cool down prior to removing the pressure cap.
The pressure/vent cap is secured to the coolant
tank neck by a means of a cam lock system. This cap
releases excess pressure at some point within a
range of 90-117 kPa (13- 17 psi) for gasoline engines,
and 110±124 kPa (16±18 psi) for diesel engines. The
actual pressure relief point (in pounds) is labeled on
top of the cap (Fig. 11).
The cooling system will operate at pressures
slightly above atmospheric pressure. This results in a
higher coolant boiling point allowing increased radi-
ator cooling capacity. The cap (Fig. 11) contains a
spring-loaded pressure relief valve. This valve opens
when system pressure reaches approximately 103
kPa (15 psi).
When the engine is cooling down, vacuum is
formed within the cooling system. To prevent collapse
of the radiator and coolant hoses from this vacuum, a
vacuum valve is used within the cap. This valve pre-
vents excessive pressure differences from occurring
between the closed cooling system and the atmo-
sphere. If the vacuum valve is stuck shut, the radia-
tor and/or cooling system hoses will collapse on cool-
down.
Fig. 7 Water PumpÐ2.0L Gasoline Engine
Fig. 8 Water PumpÐ2.0L Gasoline Engine
Fig. 9 Water PumpÐ2.5L VM Diesel
Fig. 10 Thermostat and Housing Ð 2.5L VM Diesel
7 - 4 COOLING SYSTEMNS/GS
DESCRIPTION AND OPERATION (Continued)
located in the Power Distribution Center (PDC).
Refer to the PDC cover for proper fuse.
CHARGING TIME REQUIRED
WARNING: NEVER EXCEED 20 AMPS WHEN
CHARGING A COLD -1ÉC (30ÉF) BATTERY. PER-
SONAL INJURY MAY RESULT.
The time required to charge a battery will vary
depending upon the following factors.
SIZE OF BATTERY
A completely discharged large heavy-duty battery
may require more recharging time than a completely
discharged small capacity battery, refer to the Bat-
tery Charging Timetable for charging times.
TEMPERATURE
A longer time will be needed to charge a battery at
-18ÉC (0ÉF) than at 27ÉC (80ÉF). When a fast charger
is connected to a cold battery, current accepted by
battery will be very low at first. In time, the battery
will accept a higher rate as battery temperature
warms.
CHARGER CAPACITY
A charger which can supply only five amperes will
require a much longer period of charging than a
charger that can supply 20 amperes or more.
STATE OF CHARGE
A completely discharged battery requires more
charging time than a partially charged battery. Elec-
trolyte is nearly pure water in a completely dis-
charged battery. At first, the charging current
amperage will be low. As water is converted back to
sulfuric acid inside the battery, the current amp rate
will rise. Also, the specific gravity of the electrolyte
will rise, bringing the green ball (Fig. 1) into view at
approximately 75 percent state-of-charge.
DIAGNOSIS AND TESTING
BATTERY BUILT-IN TEST INDICATOR
USING TEST INDICATOR
The Test Indicator (Fig. 1), (Fig. 2) and (Fig. 3)
measures the specific gravity of the electrolyte. Spe-
cific Gravity (SG) of the electrolyte will show state-
of-charge (voltage). The test indicator WILL NOT
show cranking capacity of the battery. Refer to Bat-
tery Load Test for more information. Look into the
sight glass (Fig. 1), (Fig. 3) and note the color of the
indicator. Refer to the following description of colors:
NOTE: GREEN = 75 to 100% state-of-charge
The battery is adequately charged for further test-
ing and may be returned to use. If the vehicle will
not crank for a maximum 15 seconds, refer to BAT-
TERY LOAD TEST in this Group for more informa-
tion.
NOTE: BLACK OR DARK=0to75%state-of-charge
The battery is INADEQUATELY charged and must
be charged until green dot is visible, (12.4 volts or
greater) before the battery is tested or returned to
BATTERY CHARGING TIMETABLE
Charging
Amperage5
Amperes10
Amperes20
Amperes
Open Circuit
VoltageHours Charging at 21ÉC (70ÉF)
12.25 to 12.39 6 hours 3 hours 1.5 hours
12.00 to 12.24 8 hours 4 hours 2 hours
11.95 to 11.99 12 hours 6 hours 3 hours
10.00 to 11.94 14 hours 7 hours 3.5 hours
less than 10.00 See Charging Completely
Discharged Battery
Fig. 1 Reading Test Indicator
Fig. 2 Battery Construction and Test Indicator
8A - 2 BATTERYNS
DESCRIPTION AND OPERATION (Continued)
BATTERY OPEN CIRCUIT VOLTAGE TEST
An open circuit voltage no load test shows the
state of charge of a battery and whether it is ready
for a load test at 50 percent of the battery's cold
crank rating. Refer to Battery Load Test. If a battery
has open circuit voltage reading of 12.4 volts or
greater, and will not pass the load test, replace the
battery because it is defective. To test open circuit
voltage, perform the following operation.
(1) Remove both battery cables, negative cable
first. Battery top, cables and posts should be clean. If
green dot is not visible in indicator, charge the bat-
tery. Refer to Battery Charging Procedures.
(2) Connect a Volt/Ammeter/Load tester to the bat-
tery posts (Fig. 6). Rotate the load control knob of the
Carbon pile rheostat to apply a 300 amp load. Apply
this load for 15 seconds to remove the surface charge
from the battery, and return the control knob to off
(Fig. 7).
(3) Allow the battery to stabilize for 2 minutes,
and then verify the open circuit voltage (Fig. 9).
(4) This voltage reading will approximate the state
of charge of the battery. It will not reveal battery
cranking capacity. Refer to Battery Open Circuit
Voltage table.
SERVICE PROCEDURES
BATTERY CHARGING
WARNING: DO NOT CHARGE A BATTERY THAT
HAS EXCESSIVELY LOW ELECTROLYTE LEVEL.
BATTERY MAY SPARK INTERNALLY AND
EXPLODE. EXPLOSIVE GASES FORM OVER THE
BATTERY. DO NOT SMOKE, USE FLAME, OR CRE-
ATE SPARKS NEAR BATTERY. DO NOT ASSIST
BOOST OR CHARGE A FROZEN BATTERY. BAT-
TERY CASING MAY FRACTURE. BATTERY ACID IS
POISON, AND MAY CAUSE SEVERE BURNS. BAT-
TERIES CONTAIN SULFURIC ACID. AVOID CON-
TACT WITH SKIN, EYES, OR CLOTHING. IN THE
EVENT OF CONTACT, FLUSH WITH WATER AND
CALL PHYSICIAN IMMEDIATELY. KEEP OUT OF
REACH OF CHILDREN.
CAUTION: Disconnect the battery NEGATIVE cable
first. (Fig. 4) before charging battery to avoid dam-
age to electrical systems. Do not exceed 16.0 volts
while charging battery. Refer to the instructions
supplied with charging equipment
NOTE: The battery cannot be refilled with water, it
must be replaced.
A battery is considered fully charged when it will
meet all the following requirements.
²It has an open circuit voltage charge of at least
12.4 volts.
²It passes the 15 second load test, refer to the
Load Test Temperature chart.
²The built in test indicator dot is GREEN (Fig.
1).
Battery electrolyte will bubble inside of battery
case while being charged properly. If the electrolyte
boils violently, or is discharged from the vent holes
while charging, immediately reduce charging rate or
turn off charger. Evaluate battery condition. Battery
damage may occur if charging is excessive.
Some battery chargers are equipped with polarity
sensing devices to protect the charger or battery from
being damaged if improperly connected. If the bat-
tery state of charge is too low for the polarity sensor
to detect, the sensor must be bypassed for charger to
operate. Refer to operating instructions provided
with battery charger being used.
CAUTION: Charge battery until test indicator
appears green. Do not overcharge.
It may be necessary to jiggle the battery or vehicle
to bring the green dot in the test indicator into view.
Fig. 9 Testing Open Circuit Voltage
BATTERY OPEN CIRCUIT VOLTAGE
Open Circuit VoltsCharge Per-
centage
11.7 volts or less 0%
12.0 volts 25%
12.2 volts 50%
12.4 volts 75%
12.6 volts or more 100%
8A - 6 BATTERYNS
DIAGNOSIS AND TESTING (Continued)
After the battery has been charged to 12.4 volts or
greater, perform a load test to determine cranking
capacity. Refer to Battery Load Test in this Group. If
the battery passes the load test, return the battery to
use. If battery will not endure a load test, it must be
replaced. Properly clean and inspect battery hold
downs, tray, terminals, cables, posts, and top before
completing service.
CHARGING COMPLETELY DISCHARGED BATTERY
The following procedure should be used to recharge
a completely discharged battery. Unless procedure is
properly followed, a good battery may be needlessly
replaced. Refer to Battery Charging Rate table.
(1) Measure the voltage at battery posts with a
voltmeter accurate to 1/10 volt (Fig. 10). If below 10
volts, charge current will be low, and it could take
some time before it accepts a current in excess of a
few milliamperes. Such low current may not be
detectable on amp meters built into many chargers.
(2) Connect charger leads. Some chargers feature
polarity protection circuitry that prevents operation
unless charger is connected to battery posts correctly.
A completely discharged battery may not have
enough voltage to activate this circuitry. This may
happen even though the leads are connected properly.
(3) Battery chargers vary in the amount of voltage
and current they provide. For the time required for
the battery to accept measurable charger current at
various voltages, refer to Battery Charging Rate
table. If charge current is still not measurable after
charging times, the battery should be replaced. Ifcharge current is measurable during charging time,
the battery may be good, and charging should be
completed in the normal manner.
VISUAL INSPECTION
CAUTION: Do not allow baking soda solution to
enter vent holes, as damage to battery can result.
(1) Clean top of battery with a solution of warm
water and baking soda.
(2) Apply soda solution with a bristle brush and
allow to soak until acid deposits loosen (Fig. 11).
(3) Rinse soda solution from battery with clear
water and blot battery dry with paper toweling. Dis-
pose of toweling in a safe manner. Refer to the
WARNINGS on top of battery.
(4) Inspect battery case and cover for cracks, leak-
age or damaged hold down ledge. If battery is dam-
aged replace it.
(5) Inspect battery tray for damage caused by acid
from battery. If acid is present, clean area with bak-
ing soda solution.
(6) Clean battery posts with a battery post clean-
ing tool (Fig. 12).
(7) Clean battery cable clamps with a battery ter-
minal cleaning tool (Fig. 13). Replace cables that are
frayed or have broken clamps.
BATTERY CHARGING RATE
Voltage Hours
16.0 volts maximum up to 4 hours
14.0 to 15.9 volts up to 8 hours
13.9 volts or less up to 16 hours
Fig. 10 Voltmeter Accurate to 1/10 Volt (Connected)
Fig. 11 Cleaning Battery
NSBATTERY 8A - 7
SERVICE PROCEDURES (Continued)
SPECIFICATIONS
BATTERY SPECIFICATIONS
CRANKING RATING
The current battery can deliver for 30 seconds and
maintain a terminal voltage of 7.2 volts or greater at
specified temperature.
RESERVE CAPACITY RATING
The length of time a battery can deliver 25 amps
and maintain a minimum terminal voltage of 10.5
volts at 27ÉC (80ÉF).
TORQUE
DESCRIPTION TORQUE
Battery Hold Down Bolt Clamp
Bolt....................14N´m(125 in. lbs.)
Fig. 19 Speed Control Servo Removal
Load Test
(Amps)Cold Cranking
Rating @ 0ÉFReserve
Capacity
250 Amp 500 Amp 110 Minutes
300 Amp 600 Amp 120 Minutes
340 Amp 685 Amp 125 Minutes
8A - 10 BATTERYNS
REMOVAL AND INSTALLATION (Continued)
(6) If battery passes load test, it is in good condi-
tion and further tests are not necessary. If it fails
load test, it should be replaced.
BATTERY OPEN CIRCUIT VOLTAGE TEST
An open circuit voltage no load test shows the
state of charge of a battery and whether it is ready
for a load test at 50 percent of the battery's cold
crank rating. Refer to Battery Load Test. If a battery
has open circuit voltage reading of 12.4 volts or
greater, and will not pass the load test, replace the
battery because it is defective. To test open circuit
voltage, perform the following operation.
(1) Remove both battery cables, negative cable
first. Battery top, cables and posts should be clean. If
green dot is not visible in indicator, charge the bat-
tery. Refer to Battery Charging Procedures.
(2) Connect a Volt/Ammeter/Load tester to the bat-
tery posts (Fig. 6). Rotate the load control knob of the
Carbon pile rheostat to apply a 300 amp load. Apply
this load for 15 seconds to remove the surface charge
from the battery, and return the control knob to off
(Fig. 7).(3) Allow the battery to stabilize for 2 minutes,
and then verify the open circuit voltage (Fig. 9).
(4) This voltage reading will approximate the state
of charge of the battery. It will not reveal battery
cranking capacity (Fig. 10).
SERVICE PROCEDURES
BATTERY CHARGING
WARNING: DO NOT CHARGE A BATTERY THAT
HAS EXCESSIVELY LOW ELECTROLYTE LEVEL.
BATTERY MAY SPARK INTERNALLY AND
EXPLODE. EXPLOSIVE GASES FORM OVER THE
BATTERY. DO NOT SMOKE, USE FLAME, OR CRE-
ATE SPARKS NEAR BATTERY. DO NOT ASSIST
BOOST OR CHARGE A FROZEN BATTERY. BAT-
TERY CASING MAY FRACTURE. BATTERY ACID IS
POISON, AND MAY CAUSE SEVERE BURNS. BAT-
TERIES CONTAIN SULFURIC ACID. AVOID CON-
TACT WITH SKIN, EYES, OR CLOTHING. IN THE
EVENT OF CONTACT, FLUSH WITH WATER AND
CALL PHYSICIAN IMMEDIATELY. KEEP OUT OF
REACH OF CHILDREN.
Fig. 8 Load 50% Cold Crank Rating
Load Test Temperature
Minimum VoltageTemperature
ÉF ÉC
9.6 volts 70É and
above21É and
above
9.5 volts 60É 16É
9.4 volts 50É 10É
9.3 volts 40É 4É
9.1 volts 30É -1É
8.9 volts 20É -7É
8.7 volts 10É -12É
8.5 volts 0É -18É
Fig. 9 Testing Open Circuit Voltage
Fig. 10 Battery Open Circuit Voltage
8A - 6 BATTERYNS/GS
DIAGNOSIS AND TESTING (Continued)