Volvo VNL 780 Operator's Manual page 411

MAINTENANCE AND LUBRICATION 401
Remove the driveshaft from the rear axle before moving the vehicle, unless it only needs to
be moved a small distance for safety reasons. When the transmission is driven from the rear
wheels without the engine running, there is no lubrication in the transmission.
Axle shafts must be removed if the vehicle is to be towed at speeds over 40 km/h (25 mph)
or for a long distance. Openings should be covered to prevent loss of oil and entry of dirt
and grit. Where oil-lubricated bearings are used, openings should be thoroughly sealed with
metal discs and new gaskets before towing.
If the vehicle is towed with the drive wheels still in contact with the road surface, the vehicle
axle shafts or driveline must be removed or disconnected.
T0006670
The vehicle may now be towed. It is recommended that a wrecker with a lift bar is used
since the service brakes will not function. The system must be filled with air to release the
parking brake or follow the mechanical spring brake caging procedures on "Caging Spring
Brake Chambers" page 408.
Note: The power steering does not function when towing a vehicle with a disabled engine.