Lesson 2/Learning Event 1
A trailer axle may support almost all or just part of the total vehicle weight. On small
single-axle trailers, most of the weight is supported by the axle assembly. Large
semitrailers are designed so that the towing vehicle (truck tractor) supports as much of
the load as the trailer axles. On trailers with brakes controlled by the operator of the
towing vehicle, the axle must withstand the twisting force of the wheels as the brakes are
applied. While in motion, the axle will move up and down under the load of the trailer as
the wheels follow the surface of the road.
With only a few moving parts, the dead axle assembly does not require a large amount of
lubrication. The wheel bearings are removed from the assembly and packed with
automotive and artillery grease (GAA) at the intervals required by the lubrication order
(LO). Steering knuckles and linkages on front axles are lubricated with automotive and
artillery greases by means of lubricating fittings.