Spicer Drive Axles Application Guidelines - Manual (Page 101)

AXAG-0200 June 2009 101
Glossary
Pneumatic Timing Balance
- Achieved when individual
air chambers sequentially receive air within a timeframe
that ensures each brake in the system will do its fair share
of the work. In a combination vehicle, lack of proper
timing is likely to occur because tractor brakes receive air
faster than trailer brakes. See " Trailer Push ".
Pole Trailer
- Trailer used to transport utility poles.
Polished Drums
- A brake drum with a friction surface
polished to a mirror-like finish by unsuitable brake linings.
Remove gloss from drum with 80-grit emery cloth.
Pop-off Valve
- Jargon for a pressure-relief valve, installed
in the service reservoir or wet tanks as insurance against
over-pressurization.
Power Divider
- See " Interaxle Differential '.
Power Line Carrier
- See " PLC ".
Pressure Differential
- Difference between the inlet and
outlet air pressure of an open brake valve. Also, difference
in air pressure between any two points within a brake
system.
Pressure Level Balance
- Is obtained when all of the
vehicles brake chambers are receiving the required level of
air pressure (once pressures have stabilized). This does not
necessarily mean the same pressure. Different design
brakes on the same vehicle may require different levels of
air pressure. Pressures may be varied on different axles to
compensate for different size brakes or different amount of
underbody cooling received by the brakes.
Propeller Shaft
- Driveshaft used to transmit torque from
engine or transmission to rear axle.
Pumping the Brakes
- Phrase denoting a rapid series of
brake application (a.k.a. fanning) used to avoid locking
brakes on axles during sudden stops. Phrase also may apply
to a slower series of heavy brake application (a.k.a.
snubbing) used in an attempt to prevent brake overheating
and resultant fade on long downgrades.
Pup
- See " Dolly ".
Pusher Axle
- A "dead axle" (no driving capability) used
to give vehicle more weight carrying capacity. A pusher
axle is ahead of the drive axle. A tag axle is behind the
drive axle. This type of axle may have the capability of
being raised or lowered and some are made to be steerable.
Push Rod
- A rod, protruding from a brake chamber,
which is connected to the arm of a slack adjuster via a
clevis pin.
Quick-release Valve
- Designed to reduce the chance of
brake drag, a valve that speeds the process of exhausting
air from brake chambers when driver releases the brake
treadle.
Radio Frequency Interference
- See " RFI ".
Ratio Limiting Valve
- Prevents locking of front brakes by
automatically limiting application pressure to steer axle
during normal braking. Progressively harder braking,
however, will progressively increase steer axle braking
until maximum air pressure is applied.
Regional Haul
- On-highway usage within a region,
typically a one day round trip.
Relay Valve
- Valve located near a reservoir that is
activated by a control signal from another valve that
usually is farther away. It's used to speed the application of
brakes on drive and trailer axles.
Release Time
- Time between release of brake treadle and
total disengagement of brake linings and brake drums. Or,
per FMVSS-121, that time required to reduce pressure to 5
psi from 95 psi within all service chambers.
Relief Pressure
- Maximum pressure where the steering
gear is protected from providing too much load into the
steering system.
Retarder
- Auxiliary speed-reducing device.
Return Springs
- Springs which retract brake shoes upon
release of the brake treadle.
Reverse Cam Rotation
- When the axle is installed into
the vehicle in such a way that the brake cam rotates
opposite to the forward normal turning direction of the tire.
RFI (Radio Frequency Interference)
- External
interference or false signals from such sources as radar,
citizens-band radio, other types of radio transmissions and
television signals. While the effects of this interference on
ABS were a concern during the 1970s, today's technology
has virtually eliminated the problem.
Ring Gear
- The large bevel, circular gear that is attached
to the flange or carrier of the differential case. It meshes
with the drive pinion on the end of the propeller shaft.
Rolled Over
- Axle used when engine is located behind
axle, typically the pinion will be above the centerline.
Rolling Resistance
- Sum of the forces at area of contact
between a vehicle's tires and road surface acting against the
direction of movement.