Spicer Drive Axles Application Guidelines - Manual (Page 96)

AXAG-0200 June 2009 96
Glossary
Drain Valve
- Used to drain oil and water from air
reservoirs. Valve may be manual or automatic in
operation. Automatic versions, which may be heated
electrically to prevent the valve from freezing open, often
are referred to as spitter valves.
Draw Key -
Fastener in the steer axle that works like a
wedge and provides a mechanism to lock the beam to the
kingpin while allowing rotation of the knuckle on the
kingpin.
Driver-controlled Differential Lock
- Driver-controlled
traction device that can be operated from the vehicle cab
by a switch. During periods of good traction, the
differential lock should not be engaged. When locked,
power transfer will be through the locked differential
casing, gearing, and axle halfshafts together. This provides
maximum traction to both sides, prevents "spinout", and
protects against gearing damage.
Driving Axles, Steerable
- Heavy-duty on- and off-road
vehicles of 4x4 or 6x6 wheel configuration often require
traction and maneuverability that can only be obtained
with a steerable front drive axle.
Drop-in Unit
- Generally refers to rear axle gear assembly
located in axle housing by drop-in.
Drop Socket
- Socket with the ball center not coincident
with the threaded end.
Drum Brake
- A brake system in which two brake shoes
with friction material expand into a rotating drum.
Dry Park Maneuver
- Turning steering wheel / tires
without any forward or reverse movement.
Dual Drive Axle
- See " Tandem Drive Axle ".
Dual Brake System
- A redundant air system (primary
and secondary) designed to retain braking ability in the
event one system fails.
Dual Draw Key
- Arrangement of two draw keys used to
balance load on kingpin to maintain alignment of kingpin
to knuckle/beam bore. (See “ Draw Key ”)
Dual Range
- 2-speed, shiftable drive axles that provide
two gearing ratios, a low range for slow speed hauling off
highway and a high range for cruising speeds on highway.
Dump Body
- A large truck's metal body that is generally
hinged at rear and dumped by hydraulic means. The size is
generally given in cubic yard water level capacity.
Duplex Gauge
- Essentially, a diagnostic device
incorporating two separate air gauges with a common
housing and utilizing indicator needles of different colors.
Device is used to diagnose brake system imbalance within
a combination vehicle via simultaneous connection to two
points (such as the tractor glad-hand and a trailer brake
chamber). It's also used as a dash gauge for dual
reservoirs.
Dust Shield
- Plate made of metal or polyethylene that's
mounted behind a brake drum to minimize entry of dirt
and road splash.
Duty Cycle
- Measurement of the amount of time a
component is fully utilized, expressed as a percentage of
the complete usage of the component
Duty Cycle "Class Definitions"
AA
Turnpike or Interstate - Operation on limited access,
well maintained, multilane highways of excellent
concrete or asphalt with maximum adverse grades
not in excess of 3 percent.
A
On Highway - Exclusive of operation on well-
maintained major highways of excellent concrete or
asphalt construction. Terrain may b level to rolling
with occasional maximum adverse grades to 8
percent. Operations are subject to legal weight and
dimensional limitations.
B
On/Off Highway or Mountainous Highway -
Secondary roads of good concrete or asphalt where
intermittent grades of up to 12 percent adverse may
be encountered or where up to 20 percent of the total
operating time is spent on well maintained off
highway roadways of crushed rock or similar
material. Grades in this class are more frequent and
severe than in Class A operation. Operation is
subject to legal weight and dimensional limitations.
C
Off Highway - Operation exceeding 20 percent of
the time on roads of gravel or maintained crushed
rock surface where the maximum grade is 12 percent
and frequent grades of 8 percent can be encountered.
This operation is not generally subject to legal
weight or dimensional limitations.
D
Off Road - Exclusively off highway on private
roadways with partial operation off road in areas
with no maintained hard surface. Grades and surface
conditions may be variable. Operation is not subject
to legal weight or dimensional limitations.