directed via the command valve (5) onto clutch K1
(6).
Simultaneously the clutch B1 (7) is subjected to
overlap pressure by the overlap regulating valve (2).
The pressure in the clutch B1 (7) as it disengages is
controlled during the shift phase depending on
engine load by the modulating pressure and the
applying clutch pressure (the shift pressure in clutch
K1). The controlled pressure in clutch B1 (7) is
inversely proportional to the capacity of the clutch
being engaged. The rising shift pressure (p-S) at
clutch K1 (6) acts on the annular face of the overlap
regulating valve (2) and reduces the overlap pressure
regulated by the overlap regulating valve (2). When a
corresponding pressure level is reached at the hold-
ing pressure shift valve (4), this valve switches over.
VAAUTOMATIC TRANSMISSION NAG1 - SERVICE INFORMATION 21 - 27
Overlap Regulating Valve
During the shift phase the pressure (Fig. 114) in
the deactivating shift actuator is regulated in rela-
tion to the engine load (modulating pressure, p-Mod)
and the pressure in the activating actuator. The reg-
ulated pressure is inversely proportional to the trans-
fer capacity of the activating shift actuator (regulated
overlap).
Fig. 114 Overlap Regulating Valve
1 - OVERLAP REGULATING VALVE
2 - ANNULAR SURFACE ON OVERLAP REGULATING VALVE
VAAUTOMATIC TRANSMISSION NAG1 - SERVICE INFORMATION 21 - 115
Radial-ply tires must always be used in sets of
four. Under no circumstances should they be used on
the front only. They may be mixed with temporary
spare tires when necessary. A maximum speed of 50
MPH is recommended while a temporary spare is in
use.
Radial-ply tires have the same load-carrying capac-
ity as other types of tires of the same size. They also
use the same recommended inflation pressures.
The use of oversized tires, either in the front or
rear of the vehicle, can cause vehicle drive train fail-
ure. This could also cause inaccurate wheel speed
signals when the vehicle is equipped with Anti-Lock
Brakes.
The use of tires from different manufactures on the
same vehicle is NOT recommended. The proper tire
pressure should be maintained on all four tires.
DESCRIPTION - TIRE PRESSURE FOR HIGH
SPEEDS
Where speed limits allow the vehicle to be driven
at high speeds, correct tire inflation pressure is very
important. For speeds up to and including 120 km/h
(75 mph), tires must be inflated to the pressures
shown on the tire placard. For continuous speeds in
excess of 120 km/h (75 mph), tires must be inflated
to the maximum pressure specified on the tire side-
wall.
Vehicles loaded to the maximum capacity should
not be driven at continuous speeds above 75 mph
(120 km/h).
For emergency vehicles that are driven at speeds
over 90 mph (144 km/h), special high speed tires
must be used. Consult tire manufacturer for correct
inflation pressure recommendations.
DESCRIPTION - REPLACEMENT TIRES
The original equipment tires provide a proper bal-
ance of many characteristics such as:
²Ride
²Noise
²Handling
²Durability
²Tread life
²Traction
²Rolling resistance
²Speed capability
It is recommended that tires equivalent to the orig-
inal equipment tires be used when replacement is
needed.
Failure to use equivalent replacement tires may
adversely affect the safety and handling of the vehi-
cle.The use of oversize tires may cause interference
with vehicle components. Under extremes of suspen-
sion and steering travel, interference with vehicle
components may cause tire damage.
WARNING: FAILURE TO EQUIP THE VEHICLE WITH
TIRES HAVING ADEQUATE SPEED CAPABILITY
CAN RESULT IN SUDDEN TIRE FAILURE.
DESCRIPTION - TIRE INFLATION PRESSURES
Under inflation will cause rapid shoulder wear, tire
flexing, and possible tire failure (Fig. 12).
Over inflation will cause rapid center wear and
loss of the tire's ability to cushion shocks (Fig. 13).
Improper inflation can cause:
²Uneven wear patterns
²Reduced tread life
²Reduced fuel economy
²Unsatisfactory ride
Fig. 12 Under Inflation Wear
1 - THIN TIRE THREAD AREAS
Fig. 13 Over Inflation Wear
1 - THIN TIRE THREAD AREA
22 - 8 TIRES/WHEELSVA
WHEELS
DESCRIPTION
Original equipment wheels are designed for the
specified Maximum Vehicle Capacity.
All models use steel or aluminum wheels.
Aluminum wheels require special balance weights
and alignment equipment.
(1) On vehicles equipped with dual rear wheels,
The slots in the wheel must be aligned to provide
access to the valve stem.
OPERATION
The wheel (Fig. 19) has raised sections between
the rim flanges and the rim well. Initial inflation of
the tire forces the bead over these raised sections. In
case of tire failure, the raised sections hold the tire
in position on the wheel until the vehicle can be
brought to a safe stop.
DIAGNOSIS AND TESTING
WHEEL INSPECTION
Inspect wheels for:
²Excessive run out
²Dents or cracks
²Damaged wheel lug nut holes
²Air Leaks from any area or surface of the rim
NOTE: Do not attempt to repair a wheel by hammer-
ing, heating or welding.
If a wheel is damaged an original equipment
replacement wheel should be used. When obtaining
replacement wheels, they should be equivalent in
load carrying capacity. The diameter, width, offset,pilot hole and bolt circle of the wheel should be the
same as the original wheel.
WARNING: FAILURE TO USE EQUIVALENT
REPLACEMENT WHEELS MAY ADVERSELY
AFFECT THE SAFETY AND HANDLING OF THE
VEHICLE. USED WHEELS ARE NOT RECOM-
MENDED. THE SERVICE HISTORY OF THE WHEEL
MAY HAVE INCLUDED SEVERE TREATMENT OR
VERY HIGH MILEAGE. THE RIM COULD FAIL WITH-
OUT WARNING.
STANDARD PROCEDURE
STANDARD PROCEDURE - WHEEL REPLACE-
MENT
The wheel stud/lugs are designed for specific appli-
cations. They must be replaced with equivalent parts.
Do not use replacement parts of lesser quality or a
substitute design.
Before installing the wheel, be sure to remove any
build up of corrosion on the wheel mounting surfaces.
Ensure wheels are installed with good metal-to-metal
contact. Improper installation could cause loosening
of wheel nuts. This could affect the safety and han-
dling of your vehicle.
To install the wheel, first position it properly on
the mounting surface. All wheel nuts should then be
tightened just snug. Gradually tighten them in
sequence to the proper torque specification.Never
use oil or grease on studs.
Wheels must be replaced if they have:
²Excessive runout
²Bent or dented
²Leak air through welds
²Have damaged bolt holes
Wheel repairs employing hammering, heating, or
welding are not allowed.
Original equipment wheels are available through
your dealer. Replacement wheels from any other
source should be equivalent in:
²Load carrying capacity
²Diameter
²Width
²Offset
²Mounting configuration
Failure to use equivalent replacement wheels may
affect the safety and handling of your vehicle.
Replacement withusedwheels is not recommended.
Their service history may have included severe treat-
ment.
STANDARD PROCEDURE - DUAL REAR WHEEL
INSTALLATION
The tires on both wheels must be completely raised
off the ground when tightening the lug nuts. This
Fig. 19 Safety Rim
1 - FLANGE
2 - RIDGE
3 - WELL
VATIRES/WHEELS 22 - 13
information available at the time of publication.
The right is reserved to make changes at any time
without notice.
4.2 SAFETY
4.2.1 TECHNICIAN SAFETY INFORMATION
WARNING: ENGINES PRODUCE CARBON
MONOXIDE THAT IS ODORLESS, CAUSES
SLOWER REACTION TIME, AND CAN LEAD
TO SERIOUS INJURY. WHEN THE ENGINE IS
OPERATING KEEP SERVICE AREAS WELL
VENTILATED OR ATTACH THE VEHICLE
EXHAUST SYSTEM TO THE SHOP EXHAUST
REMOVAL SYSTEM.
Set the parking brake and block the wheels before
testing or repairing the vehicle. If is especially
important to block the wheels on front-wheel drive
vehicles: the parking brake does not hold the drive
wheels.
Some operations in this manual require that
hydraulic tubes, hoses, and fittings, disconnected
for inspection or testing purposes. These systems,
when fully charged, contain fluid at high pressure.
Before disconnecting any hydraulic tubes, hoses,
and fittings, be sure that the system is fully depres-
surized.
When servicing a vehicle, always wear eye pro-
tection, and remove any metal jewelry such as
watchbands or bracelets that might make an inad-
vertent electrical contact.
When diagnosing a Transmission system prob-
lem, it is important to follow approved procedures
where applicable. These procedures can be found in
the service information. Following these procedures
is very important to the safety of individuals per-
forming diagnostic tests.
4.2.2 VEHICLE PREPARATION FOR
TESTING
Make sure the vehicle being tested has a fully
charged battery. If it does not, false diagnostic
DTC's or error messages may occur. It is extremely
important that accurate shift lever position data is
available to the TCM. The accuracy of any DTC
found in memory is doubtful unless the Shift Lever
Test, performed on the DRBIIItScan Tool, passes
without failure.
4.2.3 SERVICING SUB-ASSEMBLIES
Some components of the Transmission system are
intended to be serviced in assembly only. Attempt-
ing to remove or repair certain system sub-
components may result in personal injury and/orimproper system operation. Only those components
with approved repair and installation procedures in
the service information should be serviced.
4.2.4 DRBIIITSAFETY INFORMATION
WARNING: EXCEEDING THE LIMITS OF THE
DRBIIITMULTIMETER IS DANGEROUS. IT
CAN EXPOSE YOU TO SERIOUS OR
POSSIBLY FATAL INJURY. CAREFULLY
READ AND UNDERSTAND THE CAUTIONS
AND THE SPECIFICATION LIMITS.
²Follow the vehicle manufacturer's service speci-
fications at all times.
²Do not use the DRBIIItif it has been damaged.
²Do not use the test leads if the insulation is
damaged or if metal is exposed.
²To avoid electrical shock, do not touch the test
leads, tips or the circuit being tested.
²Choose the proper range and function for the
measurement. Do not try voltage or current mea-
surements that may exceed the rated capacity.
²Do not exceed the limits shown in the table.
FUNCTION INPUT LIMIT
Volts 0-500 volts peak AC
0-500 volts DC
Ohms (resistance)* 0-1.12 megohms
Frequency measured
Frequency generated0-10 khz
Temperature -58-1100ÉF
-50-600C
*Ohms cannot be measured if voltage is present.
Ohms can be measured only in a non-powered
circuit.
²Voltage between any terminal and ground must
not exceed 500v DC or 500v peak AC.
²Use caution when measured voltage above 25v
DC or 25v AC.
²The circuit being tested must be protected by a
10A fuse or circuit breaker.
²Use the low current shunt to measure circuits up
to 10A. Use the high current clamp to measure
circuits exceeding 10A.
²When testing for the presence of voltage or cur-
rent, make sure the meter is functioning cor-
rectly. Take a reading of a known voltage or
current before accepting a zero reading.
²When measuring current, connect the meter in
series with the load.
6
GENERAL INFORMATION