Peterbilt Medium Duty Trucks Operator's Manual after 1-07

Operating the Rear/Drive Axle
In the LOCK position, an air operated clutch positively locks
both sets of axles together, providing greater traction on slippery
road surfaces; however, steering around corners and on
dry pavement is more difficult. Continuous operation on a
paved, dry surface stresses the tandem axles, possibly causing
internal damage.
Use this feature only when driving on surfaces with poor traction,
such as wet slippery roads, heavy mud or snow, or loose
gravel. And do not use it when going downhill or at speeds
greater than 25 mph (40 km/h).
Lock the inter-axle differential when you encounter road conditions
such as these:
• Ice or snow — with or without tire chains.
• Dirt roads.
• Loose sand, mud, or other rough road conditions.
WARNING! Do not put the differential lock in the
LOCK position while the wheels are spinning
freely (slipping), you could lose control of the
vehicle or cause axle damage—you could be
injured. Switch to LOCK only when the wheels
are not spinning.
Operating Instructions
• Look ahead for wet, muddy, or icy patches on the road,
stop your vehicle and switch to LOCK ahead of time.
WARNING! Do not operate the vehicle on dry
pavement with the differential locked. This could
lead to an injury accident. On dry pavement, you
will not be able to steer well with the differential
locked. Lock the differential only when operating
on surfaces with poor traction, such as wet, slippery
roads or loose gravel.
Inter–Axle Differential Lock Operation
WARNING! Do not use the inter-axle differential
lock when travelling downhill or at speeds above
25 mph (40 km/h). When it is engaged under
these conditions, your vehicle will exhibit
“understeer” handling characteristics. This
“understeer” condition will cause your vehicle
to turn less quickly and more steering effort will
be required, which can cause an injury accident.
To LOCK the inter-axle differential:
1. Anticipate when you might need increased traction, slow
down to a steady speed under 25 mph (40 km/h) or stop
the vehicle. Do not lock the inter-axle differential while
– 96 – Y53-6008 Medium Duty (R10/06)