Other Features 67
NOTE
For vehicles equipped with the Antilock
Braking System (ABS), as the wheels start to
lock up on slippery roads, the output retarder
automatically deactivates until the wheels roll
freely.
JACOBS ENGINE BRAKE
The JACOBS engine brake is an optional diesel
engine retarder which uses engine compression
to aid in slowing and controlling the vehicle.
When activated, (refer to "Controls &
Instruments" chapter) the JACOBS brake alters
the operation of the engine's exhaust valves so
that the engine works as a power-absorbing air
compressor. This provides a retarding action to
the wheels.
The engine brake is a vehicle-slowing device,
not a vehicle-stopping device. It is not a
substitute for the service braking system. The
service brake must be used to bring the vehicle
to a complete stop.
Effectiveness of the engine brake system will
vary according to the transmission range in use.
The engine brake system is more effective in
lower ranges and at higher engine speeds.
WARNING
When descending significant grades, use the
service brake as little as possible. If the
engine does not slow the vehicle to a safe
speed, apply service brake and shift to a lower
range. Let the engine (and engine brake) slow
the vehicle. Keep brakes cool and ready for
emergency stopping.
NOTE
Each time the engine brake system is in
operation, the stoplights automatically
illuminate.
ANTILOCK BRAKING SYSTEM (ABS)
The purpose of the Antilock Braking System
(ABS) is to maintain vehicle stability and control
during braking and to minimize the stopping
distance in any road condition.
On slippery roads and more generally in
emergency situations, over-braking frequently
induces wheel locking. Wheel locking greatly
increases breaking distance on any road
surface. Locked wheels also impede directional
control and cause severe tire abrasion. An
antilock braking system provides maximum
braking performance while maintaining
adequate control on slippery roads.
The basis of ABS is constant monitoring of
wheel parameters during braking. Sensors on
each wheel of the front and drive axles
constantly measure wheel speed during braking.
This information is transmitted to a four-channel
electronic processor which senses when any
wheel is about to lock. Modulating valves
quickly adjust brake pressure (up to 5 times
every second) to prevent wheel lock. Each
wheel is therefore controlled according to the
available grip.
In this way, the vehicle is brought to a stop in the
shortest possible time while remaining stable
and under the driver's control.
WARNING
Vehicles following ABS-equipped vehicles
may not be able to brake as fast on slippery
roads.
DRIVER CONTROLLED
DIFFERENTIAL LOCK (DCDL)
By actuating the electric switch, the driver can
lock or unlock differential action.
The purpose of the DCDL is to provide
maximum vehicle traction and control on
unfavorable road or highway surfaces. When the
DCDL is actuated, a clutch collar completely
locks the differential case, gearing, and axle
shafts together. This feature maximizes traction
to both wheels. The lock position will also
protect against spinout damage to the
differential. The DCDL should not be actuated
when favorable road conditions exist.
OPERATION TIPS
1. The DCDL can be locked or unlocked if the
vehicle is standing still or moving at a
constant low speed when the wheels are not
spinning, slipping, or losing traction.
2. When the DCDL is locked, operate the
vehicle at low speeds. DCDL will not engage
and will disengage in speed higher than 5
MPH (8 km/h).
3. When the DCDL is locked, the vehicle’s
turning radius will increase. This condition is
called “understeer.” The driver must use
caution, good judgment and drive at low
speeds when operating the vehicle with the
DCDL locked.
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