Peterbilt 579 Operator's Manual page 213

Starting-Up
1. Unlock the inter-axle differential
before starting.
2. Put the Range Selector in the
LOW range. Shift the transmission
to start the vehicle moving.
3. When you are driving on rough
terrain and secondary roads, or
under a very heavy load, keep the
axle in the LOW range. Shift the
transmission to maintain proper
road speed.
WARNING!
Never shift the axle when moving
downhill. Engine driveline disengage-
ment may occur, eliminating engine
retardation and allowing the wheels to
spin faster than the current speed of
the engine. This may require severe
braking to slow the vehicle down and
can result in an accident. Failure to
comply may result in death, personal
injury, equipment or property damage.
(04/13)
Proper shifting of the axle depends on
the synchronization of engine/driveline
and wheel speed. When you shift
the axle, the connection between the
engine and wheels is momentarily
disengaged while the gearing is
synchronized. Normally when the axle
is shifted the speed of the engine, axle,
and wheels adjust, allowing for proper
gear engagement.
When going downhill the wheels will
not slow down, but will tend to speed
up, which makes gear synchronization
almost impossible. As a result, the
axle is neither in HIGH nor LOW range
and all engine/driveline retardation is
lost. Without engine retardation it is
more difficult to slow the vehicle down
and greater stress is put on the brake
system.
Y53-6047–2C
CAUTION
To avoid damaging your vehicle shift
the axle at slower travel speeds until
you are used to driving with a dual
range axle.
AXLE
4
4-41