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

Operating Instructions
going down steep grades or traveling faster than 25 mph,
or while wheels are spinning or traction is minimal; lock it
before you encounter these conditions.
Understeer Condition
02871
2. Put the inter-axle differential lock switch, labeled MAIN
DIFFERENTIAL LOCK, in the LOCK position. A light
(DIFF LOCK) in the warning module on the dash will turn
on, indicating that the differential is locked (engaged).
Operating the Rear/Drive Axle
3. If you LOCK or UNLOCK the inter-axle differential while
moving, let up momentarily on the accelerator pedal to
relieve torque on the gearing and allow full engagement
of the clutch (the mechanism that locks the wheels).
NOTE: If your vehicle has an automatic transmission,
it may be necessary to shift the transmission
to the Neutral position momentarily to
allow the main inter-axle differential lock splines
to fully engage or disengage.
4. Drive the vehicle through the poor traction area, keeping
your speed under 25 mph (40 km/h).
To UNLOCK the inter-axle differential:
1. When you reach dry pavement or better road conditions
where the differential lock is not needed, switch the differential
lock to UNLOCK.
2. Let up momentarily on the accelerator pedal to relieve
torque and allow the clutch to disengage.
3. When you unlock the differential, normal vehicle handling
will resume and the light on the warning module will
turn off.
Medium Duty (R10/06) Y53-6008 – 97 –