Axle Related Glossary of Terms

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 feel.

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, spool, etc.

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 the wheel.

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 shaft.

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.

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 seal.

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 tubes.

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.