Axle Related Glossary of
Axle - An axle is a
central shaft for a rotating wheel or gear. The axle transfers power from the
differential to the wheels. The axle shafts have splines at one end fitted
into the carrier and a flange at the
other end that holds the wheel studs.
Axle Bearings - Axle
bearings are press onto the axles
and are retained by the end of the housing. They are held in place by the
retainer plate and 4 bolts. Axle bearings allow the axles to spin in place when power is
applied to them via the differential.
Axle Seals - Axle seals
are seals that rides on a
machined surface on the flanged end of the axle that seals the axle to the
end of the housing so that gear oil cannot escape. When a rear axle
seal goes bad, it's typically noticeable by gear oil leaking all over a
rear wheel, and it may get into the brake drum and reduce rear brake
Bolt Pattern - A series of holes
drilled in axle flange face that correspond with a series of holes drilled
in the brake drum or rotor that wheel studs press into to allow wheels to
bolt to the unit.
Carrier Unit - The inner
differential component that the ring gear bolts to. This unit transfers
power from the driveshaft/pinion gear to the axles. Carriers are available
in various types that are used in different vehicle applications. Common
types are open carrier, traction lock, detroit locker, ARB air locker,
Drum Brakes - Consists of brake
shoes that are mounted to a backing plate that bolts to the rear end
housing, or in the case of older model cars may be present on the front
axles also. The shoes are housed in a round drum that rotate along with
Disc Brakes - Disc brakes consist of
a brake rotor and a caliper. The caliper has friction pads inside it that
when brake pressure it applied the brake pads squeeze against the rotor to
slow the wheel. In stock applications these are used more commonly on
front wheels, but are a desirable upgrade for the rear end.
Gear Case - Cast iron (or optional
aluminum) unit that houses all of the internal differential components
such as the carrier and ring & pinion gears. When all of the internal
differential components are installed into the case, the unit is referred
to as a "third member".
Housing - A steel "tube" assembly
that has the third member "receptacle" in the center and the axle bearing
housings on the ends. This unit spans side to side in the vehicle and
requires brackets to be welded to it to attach it to the vehicle.
Housing Center - Stamped steel
center piece of housing that the third member bolt into, and the housing
tubes press into.
Housing Covers - A plate that covers
the back of a housing unit.
Housing Tubes - Tube that goes
between the housing center and the housing ends that covers the axle
Housing Brackets - Necessary
brackets that weld to the housing and allow for the housing to be bolted
into the vehicle.
Housing Ends - Machined end caps
that weld to the end of the tubes on the housing that are the receptacle
that the axle bearing fits into.
Pinion Seal - A seal that fits into
the front of the pinion support and seals the outside of the yoke to the
Pinion Support - A flange on the
front of the third member that is retained by five 3/8" bolts. The pinion
support houses the 2 front pinion bearings, their races, and the pinion
Retainer Plates - Install on the
axle between the axle flange face and the axle bearing before the bearing
is pressed onto the axle. This plate must have the same 4 hole bolt
pattern on it as the housing ends being used.
Ring & Pinion Gear - Also known as
the rear end gears. The ring and pinion take the rotating of the
driveshaft and transfer it to cause the rotating of the axles. The count
of the teeth on the ring gear and the pinion gear vary, and the difference
in these tooth counts is what creates the gear ratio. The gear ratio is
how many times the pinion gear turns in one rotation of the ring gear.
With a 2.75 ratio ring and pinion, the pinion gear would turn 2 3/4 turns
in one rotation of the ring gear.
Ring Gear Bolts - Special bolts that
attach the ring gear to the carrier.
Spring Pads - Stamped and folded 3
sided steel saddles that are designed to weld to the axle housing tube so
that it may be mounted to a leaf spring.
Shock Mounts - Stamped and folded 3
sided universal weld on steel brackets for mounting shocks to the axle
Spline - Grooves machined in the end
of axle shafts that engage into a female set of grooves in the carrier.
This is what engages the carrier to the axles to cause them to turn when
the carrier turns.
Third Member - When all the internal
differential parts are assembled into the gear case the finished unit is
known as a third member.
U-bolts - U-shaped bolts with
threads on each end designed to fit around the axle tube and go through
the bottom spring plate to hold the axle housing to the leaf springs.
Wheel Studs - Bolts used to attach
the wheel to an axle. Generally these studs have round heads with a knurl
or fine spline immediately below the head that is the same width as the
thickness of the axle face. These studs are installed in holes in the axle
flange face via a press, and the knurl bites into the hole in the axle
flange face to hold them in place.
Yoke - Cast iron component on the
front of the third member that fits onto splines on the pinion gear and is
retained by a nut. The rearmost portion of the yoke has the seal surface
machined on it that seals the yoke to the pinion support using the pinion
seal. The frontmost portion of the yoke is where the U-joint of the
driveshaft attaches to the third member. The U-joint is retained into the
yoke by small U-bolts.