With terms like Axle Shafts, Ball Joints, ull Floater Gaskets, and Limited Slips, drivetrain lingo can get confusing quickly. Fortunately our experts have put together a thorough glossary of terms to help you learn. A glossary of terms for various drivetrain-related items, including Axle Shafts, Ball Joints, Bearings, C Clips, Calipers, Carriers, Carrier Bearings, Cross Shafts, Crown Gears and more.
Axle Shaft - An Axle Shaft is the part of an axle assembly that is turned by the side gear of the differential and transfers the power either directly to the wheel or to the wheel hub that the wheel is bolted to, depending on the style of axle.
C Clip - “C” clips are commonly used on semi-floating axles to retain the axle shaft. On the spline of the axle shaft there is a receiver groove cut into the end for the C clip to grab the axle. There is a pocket machined into the side gear of the carrier that the OD of the C clip fits into. With the cross shaft removed, the axle is inserted into the side gear. At this point the C clip is placed onto the shaft and the shaft is pulled out until the clip is seated in the pocket. Now the cross shaft is reinserted and the axle can no longer move in or out except for its appropriate end play.
Caliper - Referred to as a brake caliper, it applies pressure on a spinning disc (rotor) to slow a vehicle.
Coast Side - The Coast side of the gear tooth is the concave side. The coast side is loaded when the vehicle is decelerating or in reverse. The exception to this rule is in standard rotation front axles where it is the driven side.
Concave - An Inward curving surface, like a bowl.
Convex - An Outward curving surface, like a crown.
CV - A slang term short for Constant Velocity. A type of axle shaft mainly used in independent suspensions requiring a smooth, long travel axle. The Term CV, when used to describe a driveshaft or propeller shaft, is referring to a Double Cardin Joint. The Double Cardin Joint looks like two U-Joints in close proximity to each other and is used in shafts that have harsh angles on them.
Drag - Drag is a load or resistance keeping something from turning freely.
Drive Side - The Drive side of the gear refers to the convex or crowned side of the ring gear. This side of the gear is the side of the tooth that the pinion gear pushes off to turn the ring gear when accelerating forward. This holds true in all but standard rotation front differentials where it is reversed.
Drop Out - The drop out refers to a particular type of axle that has a separate gear case assembly that can be removed from the housing (picture A). This is opposed to an axle that has the gears installed into the physical axle housing (picture B).
Flange - The word Flange is used to describe many different items in a vehicle, but generally it refers to a flat mounting surface to couple two pieces together.
Full Floater - Full Floater is a term used to describe a type of axle retention system. The full floater axle is a non-load carrying axle that does not have a wheel mounted to it. This axle usually bolts to a wheel hub that rides on a set of bearings on a spindle that is part of the axle housing. It is called a full floater because the axle requires no support, and thus it is “floating” between the wheel hub and the side gear.
Hub - The word “hub” describes a number of things, but in our automotive world it describes a wheel mounting device that transfers power to the wheel. This is not to be confused with a locking hub, which is called a hub as well. This unit usually is supported by two bearings and is driven by the axle shaft.
King Pin - King pin is a type of steering knuckle pivot. This system shares the same job as a typical ball joint but is believed to be stronger than the ball joint. This system has basically been phased out by ball joints.
Knuckle - The steering knuckle is the main component that allows a solid axle to perform its steering function. The knuckle is usually retained to the housing by the ball joints or king pins.
Limited Slip - The Limited Slip is basically a preloaded open differential. Also known as a Posi, these units usually use a set of clutch springs to preload the spider gear set between 150-450 ft. lbs. This preload provides a breakaway setting. This breakaway is the force required to allow the axles to differentiate.
Locker - Most lockers use a type of ratcheting devise to lock the axles together when power is applied to the unit and allow one wheel to disengage while turning. These units are suited for the more aggressive wheeler as these units do have some drivability concerns. Although minor, these units usually clunk and bang but are better suited for the street than a spool. These units will turn both tires even if one is off the ground.
Locking Hub - The locking Hub is a device that allows the wheel bearing hub to be disengaged from the axle shaft. This function is used in part time 4 wheel drive vehicles to reduce the additional drag of the drivetrain when the 4 wheel drive is not needed.
Mini Spool - A mini spool is a device that goes inside a factory differential carrier, replacing the spider gear assembly and converting it into a spool. A full spool is a one-piece unit that replaces the carrier as well. Neither provides a differential action between the shafts.
Pattern - Pattern refers to contact pattern between the gears. This contact pattern is used to see how the pinion gear is contacting the ring gear. By reading this print, you can determine if different shims are required to set up the proper gear mesh.
Pinion Gear - The pinion gear is the drive gear that turns the ring gear
Pinion Angle - Pinion angle refers to the angle that the axle yoke is at compared to the drive shaft and the transfer case or transmission.
Pinion Pre Load - Pinion Pre Load is the amount of drag that is required to turn the pinion shaft. Drag is a load or resistance keeping something from turning freely
Pinion Yoke - Pinion Yoke is a part that connects the pinion shaft to the drive shaft.
Posi - Posi is another name for a Limited Slip. The Limited Slip is basically a preloaded open differential. These units usually use a set of clutch springs to preload the spider gear set between 150-450 ft. lbs. This preload provides a breakaway setting. This breakaway is the force required to allow the axles to differentiate.
Preload - Pre load or drag is a load or resistance keeping something from turning freely.
Race - The Race, or cup as it is also called, is a press-in hardened surface for a bearing to ride on.
Ratio - A ratio is a quantity that denotes the proportional amount of one quantity relative to another.
Example: If your drive shaft turns four times for every one turn of the wheel, your gear ratio is 4 to 1 or 4:1.
Reverse Rotation Gear - The reverse rotation gear set was developed for use in front axle applications. The standard gear, when used in a front application, is running in reverse. This means the coast side of the gear is being used as the drive side. The convex (Drive) side of the gear is capable of carrying more load than the concave (coast) side. On a reverse ring and pinion, this problem has been corrected to create a stronger axle assembly. This was also done to help with driveline angles and reduce vibration.
Semi Float - A semi-floating axle is one that is supported at the inner spline end then is supported by a bearing before the outer end, carrying vehicle weight.
Shim - A shim is a thin piece of material used to fill small gaps or spaces between objects. Shims are typically used in order to support, adjust for better fit, or be used as spacers to fill gaps between parts.
Side Gear - The Side Gear is an internally splined gear that receives the axle shaft. The spider pinion gear then drives this gear.
Spanner - The Spanner is also known as a side bearing adjuster. This adjuster is used to move the carrier assembly side-to-side to set back lash.
Spanner Wrench - The Spanner wrench is used to grip and turn the spanner nut.
Spider Gear - Spider gear is also called spider pinion gear. These are the small gears that make up the spider gear assembly. This assembly is usually made up of two side gears and between 2 –4 spider gears. The spider pinion gears are driven by the cross pin of the carrier.
Spline - Splines are the raised portions that look like teeth. Splines provide a strong and effective way of easily joining two parts together that will need to be removed at a later date. Splines are usually seen as an external (male) and internal (female) receiver variety.
External Spline Internal & External Spline
Spool - A spool is used to permanently lock axles together. Spools are usually used in competition vehicles that require no differential action between the axles. Spools are not recommended for street use.
Third Member - Also referred to as Drop Out. The drop out refers to a particular type of axle with a separate gear case assembly that can be removed from the housing (picture A). This is opposed to an axle that has the gears installed into the physical axle housing (picture B).
Toe - The Toe of the gear tooth is the inner half closest to the carrier. This is the part that sees pinion contact last.
Torque - Torque is the rotational force needed to move an object. In our case, it refers to the amount of force needed to turn a bolt or pinion. Torque is measured with a special tool called a Torque Wrench.
Torque Wrench -A Torque Wrench is a special tool that is used to measure the amount of force required to turn a bolt. This torque is measured in either in foot pounds or inch pounds depending on the quantity of force needed. There are a variety of different types of torque wrenches, but the two most common are the bar graph and the click types.
U-Joint - U-Joint is short for Universal joint, also known as a Cardin joint. The U-joint allows a rigid shaft to bend in any direction. It consists of a pair of hinge-like crosses located close together, but oriented at 90° relative to each other.
Wheel Hub - The word “hub” describes a number of things. In our automotive world, it describes a wheel mounting device that transfers power to the wheel. This is not to be confused with a locking hub, which is called a hub as well. This unit usually is supported by two bearings and is driven by the axle shaft.
Wheel Flange - The Wheel Flange is the flat mounting surface that the wheel is mounted to. This flange is either part of the wheel hub or made into the axle shaft depending on which type of axle is in question.