Glossary


 

Accelerate: To increase speed.

Additives: Chemicals added to lubricants to improve or modify the operating characteristics.

Aerodynamic drag: The wind resistance of air moving over a vehicle.

Aftermarket: Nonfactory parts, accessories, and upgrades to a motor vehicle.

All-wheel drive (AWD): A drive system that can drive both the front and rear wheels through all phases of operation and road surfaces. (Also called full-time 4WD.)

Alternating current (AC): An electric current that reverses its direction at regular intervals.

Ammeter: A meter used to measure electrical current.

Amperes (A, amp): The unit of measurement for electrical flow.

Anaerobic sealant: A chemical that cures in the absence of air; used in tight, smooth areas to form a gasket to prevent fluid leaks.

Annulus gear: An internal, or ring, gear used in a planetary gear set.

Antilock braking system (ABS): A system that senses wheel lockup during braking and momentarily reduces braking forces to maintain wheel rotation.

Asbestosis: A health condition where asbestos causes scar tissue to form in the lungs, causing shortness of breath.

Auburn assembly: A type of pressure plate assembly that can be identified by the pressure springs being mounted to the release levers.

Automated manual transmission (AMT): A manual transmission design that automatically shifts gears and applies and releases the clutch.

Automatic hub: 4WD locking hubs that automatically lock when needed.

Automatic transmission: A transmission that automatically changes forward gear speeds.

Automatic transmission fluid (ATF): The fluid designed for use in an automatic transmission.

Auxiliary transmission: An additional transmission with reduction and/or overdrive ratios.

Axial: A direction parallel to the shaft or bearing bore.

Axial runout: The wobble of a spinning object.

Axis: The centerline of a rotating part.

Axle gears: The two bevel gears in a differential that attach to the axles.

[return to top]

B-: Symbol used to identify ground or the negative side of a circuit.

B+: Symbol used to identify the positive side of a circuit.

Backlash: The amount of clearance or movement between two meshed gears; also called lash.

Backlash variation: The variation in backlash caused by ring gear runout.

Balancing: A process of correcting the imbalance of a part that could cause vibration.

Ball and trunnion joint: A type of U-joint that utilizes a shaft with bearings at each end that rides in a grooved housing.

Ball bearing: A nonfriction bearing that uses steel balls as the rolling element.

Bearing cage: A spacer that keeps the balls or rollers in a bearing separated and in the proper position.

Bearing cap: A device that is bolted in place to secure a bearing.

Bearing cone: The inner race of a tapered roller bearing.

Bearing cup: The outer race for the needles of a U-joint bearing and of a tapered roller bearing.

Bearing race: The hardened surface on which the balls, needles, or rollers of a bearing run.

Bearing retained axle: An axle that is retained at the outer end of the axle.

Bearing spacer: Shim used to position bearings and maintain bearing preload.

Bench bleed: The process of removing all air from a hydraulic component before installation.

Belleville spring: A conical steel spring that gives a spring action because of its resistance to flattening.

Bellows-type boot: An accordion-pleated rubber cover used to protect a mechanical device inside of it.

Bevel gear: Gears that are cut at an angle and used to transfer power between nonparallel shafts.

Blanchard grinding: A resurfacing procedure in which metal is removed by grinding as the surface is rotated.

Bleed: A procedure to remove the air from a hydraulic system.

Blocker ring clearance: A check to determine the amount of blocker ring wear.

Blocker rings: See Synchronizer ring.

Bolt: A type of threaded fastener used with a nut to secure parts together.

Bore runout: The amount the clutch housing bore is off-center.

Borg and Beck assembly: A type of pressure plate assembly that can be identified by wide, stamped-steel release levers.

Break (open): A disconnected or incomplete circuit that will not allow the flow of electricity.

Brinelling: A wear pattern that presses or wears a series of grooves or dents in a bearing surface.

Bump cap: A hard plastic hat to protect a technician’s head from bumps.

Burnish: To smooth or polish through rubbing action.

Burr: Deformed metal that leaves a protruding sharp edge.

Bushing: A simple bearing, usually made from a soft metal, that requires oil or grease to reduce friction.

[return to top]

Cam: A part of the shift mechanism that transfers motion from the shift shaft to the shift fork.

Cancelling angles: Equal and opposite angles of two U-joints, used to cancel vibrations generated by the U-joints.

Cap screw: A bolt that is threaded into a casting.

Cardan joint: The common U-joint used in most RWD driveshafts.

Carrier: The casting section of a drive axle that contains the differential and ring and pinion gears.

Carrier bearing preload: The load placed on carrier bearings during assembly.

Carrier bearings: The bearings that support the differential carrier.

Case: The rigid housing for a drive axle, transaxle, transmission, or transfer case.

Center differential: A differential used with AWD to allow a speed difference between the front and rear axles.

Centrifugal force: The force on a revolving object that pulls it away from the center of rotation.

Chamfer: A beveled edge on a shaft or bore.

Chatter: A clutch problem in which there is a rapid apply and release of the clutch that causes the drivetrain to shake.

Chip: A small fragment of metal broken out of a part.

Circlip: A snap-ring type of ring with a round cross section used to position a shaft in a bore.

Circuit breaker: A circuit protection device that can be manually or automatically set.

Clash: The grinding sound that is heard when trying to mesh two gears that are operating at different speeds.

C-lock: A C-shaped locking device used to retain an axle shaft. Sometimes called a C-clip.

C-lock-retained axle: An axle that is retained by C-lock on the inner end of the axle.

Closed case: A transmission design that mounts the shift levers through the case, thus eliminating any large openings.

Closed knuckle: A large, rounded housing that encloses a CV joint on a front drive axle.

Cluster gear: A group of gears that are machined from one piece of metal, or individual gears combined into one group so they operate together; also called a counter gear or layshaft .

Clutch: A device that controls the power transfer between two components by either allowing or not allowing a power transfer.

Clutch cable: A cable that transmits the motion of the clutch pedal to the release bearing.

Clutch disc: The clutch member that transmits torque to the transmission input shaft.

Clutch fork: The clutch member that transmits motion from the linkage to the release bearing.

Clutch housing: The casting that surrounds the flywheel and clutch; often called a bell housing .

Clutch pedal free travel: The distance a clutch pedal moves before the release bearing contacts the release levers.

Clutch plate: See Clutch disc.

Clutch shaft: The shaft splined to the clutch disc that is the input to the transmission.

Clutch slippage: A clutch problem in which the clutch does not transmit the torque load and the engine overrevs.

Clutch spin down: A diagnostic test to determine clutch drag.

Coast: A load condition in which the vehicle is driving the engine, as during deceleration.

Coast side: The concave side of a gear tooth.

Coefficient of friction: A reference to the relative friction between two surfaces.

Collapsible spacer: See Crush sleeve.

Complete circuit: A complete path from battery B+ to ground required for electrical current to flow.

Composite rings: Synchronizer rings that are lined with carbon, metal, or paper-based composite material.

Cone clutch: A type of clutch that uses conical driving and driven members.

Constant mesh: Gears that are constantly in contact (meshed) and are not moved when the transmission is shifted.

Constant-velocity joint (CV joint): A type of U-joint that transmits power without changing the velocity.

Contact pattern: See Gear contact pattern.

Contamination: Scratches, pitting, or scoring in a scattered pattern.

Continuity: A circuit or component that has a complete path for current to flow.

Continuously variable transmission (CVT): A transmission that varies the gear ratio in a continuous, rather than stepwise, manner.

Control module: Electronic device that controls electrical circuits.

Countershaft: The shaft used in some transmissions to support the cluster gear.

Countertrack: A CV plunge joint that uses eight drive balls.

Coupler: A clutchlike device that can connect or disconnect the power flow between two components.

Cover: The outer part of a pressure plate assembly that contains the other parts.

Crack: A surface break that appears as a line.

Cross and yoke joint: Most common type of RWD U-joint; also known as a Cardan joint.

Cross groove joint: A plunge joint similar to a Rzeppa joint.

Crosstrack: A fixed-type CV joint that uses eight drive balls.

Crush sleeve: A collapsible spacer used to maintain pinion bearing preload.

Cushioned disc: A clutch disc with a damper assembly.

[return to top]

Damper: A device that reduces the torsional vibrations between the engine and transmission.

Dead axle: An axle that supports a wheel but does not transmit power.

Decelerate: To reduce speed.

Deflection: The bending or movement caused by a load.

Department of Transportation (DOT): A governmental agency that is concerned with transportation.

Detent: A spring-loaded device used to correctly position a shift fork.

Diagnostic trouble code (DTC): Codes generated by a control module that are used when diagnosing a problem.

Dial caliper: A measuring device similar to a vernier caliper that uses a dial readout.

Dial indicator: An instrument used to measure travel/clearance.

Diaphragm: A type of pressure plate assembly that uses a diaphragm spring.

Diaphragm spring: A round, conical-shaped spring; a Belleville spring.

Differential: A gear arrangement that allows the drive wheels to be driven at different speeds.

Differential clearance: A check to determine the amount of differential wear.

Digital multimeter (DMM): A meter that has multiple functions for measuring electrical activity and uses a digital readout.

Diode: An electrical one-way check valve.

Direct current (DC): Electrical current that only flows in one direction.

Direct drive: A 1:1 gear ratio.

Disc alignment: The procedure of aligning a clutch disc before replacing the pressure plate.

Disc runout: The checking procedure to make sure that a clutch disc runs true.

Dog clutch: A type of clutch that uses gearlike driving and driven members. It is engaged when one member is slid against the other.

Dog clutch teeth: The set of teeth on a speed gear that engage with the synchronizer sleeve.

Dogs: See Keys.

Double-Cardan joint: Two Cardan joints separated by a ball and spring to maintain equal operating angles.

Double cone: A synchronizer design that uses two or more clutch cones.

Double-lip seal: Used to seal two lubricant-containing units so that the lubricant will not pass between them.

Double-offset joint: A plunging CV joint typically used as the inboard CV joint on FWD shafts.

Dowel: A round metal pin used to ensure proper alignment.

Drag: The resistance or friction created by one object moving over or through another.

Drive: A load condition in which the engine is applying power to the drive wheels.

Drive axle: An axle that supports the vehicle and provides a method of driving the wheels.

Driveline: Another name for a driveshaft.

Drive pinion gear: The smaller drive gear in a ring and pinion gear set.

Driveshaft: A device that transmits power from one unit to another.

Drive side: The convex side of a gear tooth.

Drivetrain: The combination of components that power a vehicle, which includes the engine, transmission, driveline, and final drive.

Dual mass flywheel: A two-part flywheel that drives the secondary flywheel through a set of long damper springs.

Dynamic friction: The relative friction between two surfaces that have different speeds.

Dynamic shift test: A shift test that is made with the engine running.

[return to top]

Eccentric: Two circles that do not have the same center.

Electric arcing: A series of small burn marks around a bearing or shaft caused by electrical sparks.

Electronic control module (ECM): An electronic device that uses various inputs to determine the needed output reaction to efficiently control a vehicle operating system.

Electronic traction control (ETC): A system to increase overall vehicle traction by preventing the wheels from spinning.

Electrostatic discharge (ESD): A momentary flow of electricity that occurs when an excess of electric charge finds a path to ground.

End float: See Endplay.

Endplay: Free movement of a part in a sideways direction.

Energy: The ability to do work.

Engagement modulation: The ability to engage the clutch in order to produce a smooth, slip-free engagement.

Engine support: A device that supports the engine so that the transaxle can be removed.

Environmental Protection Agency (EPA): A governmental agency that is charged with protecting human health and with safeguarding the natural environment: air, water, and land.

Excessive wear: Wear that causes a part to become unusable.

Extension rod: See Stabilizer bar.

Extreme-pressure (EP) lubricant: A lubricant designed to stay in place and keep parts from touching when under extremely high pressure.

[return to top]

Face: The area of a gear tooth above the pitch line.

Face runout: The checking procedure to ensure that the face of the clutch housing is true to the flywheel.

Facing: The friction material on a clutch disc.

Feeler gauge: Thin metal strips of precise thickness, used to measure the clearance between two parts.

Fiber composites: A mixture of fiber threads (glass, graphite, or other materials) and a resin.

Final drive: The last set of reduction gears before the power flows to the differential gears and drive axles.

Final drive ring gear: The larger driven gear in a ring and pinion gear set.

Fixed joint: A CV joint that does not change length.

Flank: The area of a gear tooth below the pitch line.

Float: A load condition in which two parts are turning at the same speed with no driving force between them; also a condition in which a shaft is supported by a gear that, in turn, is supported by a bearing.

Fluid clutch: A type of clutch that drives through fluid; similar to a torque converter.

Flywheel: The rotating metal mass attached to the crankshaft that helps even out power surges, has the starter ring gear around its circumference, and provides a mounting point and friction surface for the clutch.

Force: A push or pull measured in pounds or kilograms.

Formed-in-place gasket (FIPG): A gasket material that comes from a tube, which is applied to metal surfaces to form a gasket during assembly.

Four-wheel drive (4WD): A drive system that can drive both the front and rear wheels.

Fretting: Small particles that decay and break off bearing races.

Friction: The resistance in motion between two bodies in contact with each other.

Friction disc: A flat disc that is faced with friction materials; it is driven when it is clamped between two flat metal surfaces.

Friction modifier: An additive that increases the slipperiness of a lubricant.

Front drive axle: The driving axle at the front of a 4WD vehicle.

Front-wheel drive (FWD): A drive system that drives only the front wheels.

Fulcrum: The pivot or supporting point for a lever.

Full-floating axle: An axle supported by two bearings at the wheel end that transfers vehicle weight from the axle housing to the wheel.

Full-time 4WD: See All-wheel drive (AWD).

Fuse: A circuit protection device that will break (open) a circuit if the current flow exceeds the rating of the fuse.

Fusible link: A circuit protection device that is made of wire four gauge sizes smaller than the circuit wire. The wire will melt (open) if the current flow exceeds the ability of the wire to pass the current.

[return to top]

Galling: Wear that transfers metal and is caused by metal-to-metal contact without proper lubrication.

Gasket: A compressible material used as a seal between two mating surfaces.

Gauge (wire): The cross-section size of a wire. AWG uses low numbers for large wires and higher numbers for smaller wires.

Gear: A metal wheel with teeth that transmit power or motion to another gear.

Gear clash: The noise created when gears rotating at different speeds are shifted.

Gear contact pattern: The pattern made as a result of two gears contacting each other.

Gear marking compound: A paint compound that is placed on the gear teeth to make the gear contact pattern more visible.

Gear ratio: The ratio between the number of teeth on the driving gear and the driven gear; it is calculated by dividing the number of teeth on the driven gear by the number of teeth on the driving gear.

Gear rattle: A noise created when one of the gears in mesh tries to change speed.

Gear reduction: A condition in which the driving gear is smaller than the driven gear; the result will be an increase in torque and a reduction in speed.

Grab: A clutch problem in which the clutch applies suddenly, more rapidly than desired.

Grade: The strength rating of a bolt.

Grade resistance: One-hundredth of the vehicle weight times the angle of the grade in percent.

Graphite: A very fine carbon dust that is used as a dry lubricant or a fiber that is combined with resin to form very strong and lightweight objects, such as driveshaft tubing.

Gravity bleeding: A method of removing air from the hydraulic system using gravity.

Grease: A thick lubricant typically made of oil and lithium soap.

Grease spray: A spray of grease that came from a faulty seal of a rotating part—typically a CV joint.

Ground: The return path of a circuit. The chassis of a vehicle usually provides the ground.

Grounded circuit: A circuit that has an unwanted connection to ground, causing a short circuit.

[return to top]

Halfshaft: The driveshaft used to connect the differential to the drive wheels on drive axles with independent suspension.

Hard shift: A shift that takes more effort than normal.

Hat: Another name for a clutch pressure plate cover.

Hazardous waste materials: Chemicals or components that are no longer needed and pose a danger to the environment or people.

Heel: The outer end of a bevel or hypoid ring gear tooth.

Helical gear: A gear with teeth cut at an angle.

High Efficiency Particulate Air (HEPA) filter: A type of air filter that can theoretically remove at least 99.97% of airborne particles.

High-resistance circuit: High resistance prevents current flow. The higher the resistance the lower the current flow.

Hooke joint: See Cross and yoke joint.

Hotchkiss driveshaft: A type of rear suspension that uses leaf springs to absorb drive axle housing torque reactions.

Hub: The center part of a wheel; the surface where a wheel mounts.

Hub and damper assembly: The center of a clutch disc that connects to the transmission shaft with the damper springs.

Hunting gear set: A gear set design in which the driving gear will mesh with every tooth on the driven gear as they rotate.

Hydra-Lok: A differential that uses hydraulically applied clutches to prevent wheel spin.

Hydraulic clutch: A clutch operating system that uses hydraulic pressure to transfer motion and pressure.

Hydraulics: A branch of science dealing with the transfer of power through fluids under pressure.

Hypoid gear: A special form of bevel gear that positions the gear axis on nonintersecting planes and is commonly used in drive axles.

Hypoid gear set: A matched set of hypoid gears.

[return to top]

Idler gear: A gear positioned between two other gears causing a change in the direction of rotation of the output shaft.

Inboard joint: The inner CV joint that can change angle and length (plunge).

Inclinometer: A device used to measure mounting positions relative to true level.

Indentation: A dent showing the displacement of metal caused by heavy contact.

Independent rear suspension (IRS): A type of rear suspension in which the two rear wheels can move vertically without changing the other’s position.

Index: To align two parts in the proper position before assembly.

Index mark: A mark placed on parts during disassembly to aid in proper assembly.

Inertia: The physical property maintaining that a body at rest tends to remain at rest and a body in motion tends to remain in motion and travel in a straight line.

Input shaft: The shaft that carries the driving torque into a gear box.

Insert plates: See Keys.

Integral: Manufactured into; part of.

Integral carrier: A rear axle carrier that is integrated with the axle housing; it cannot be removed for service.

Integrated microchips: Very small electrical circuits contained in a small package.

Integrated wheel end disconnect: A system that is used to connect and disconnect the outboard CV joint with the wheel hub.

Interaxle differential: See Center differential.

Interlock: A transmission mechanism that prevents two shift rails or forks from moving at the same time.

Intermediate shaft: The output shaft of the transmission portion of a transaxle that drives the differential.

Internal gear: A gear with the teeth pointing inward toward the center of the gear.

International Automotive Technicians Network (iATN): A web-based group that shares vehicle repair information.

[return to top]

Journal: A bearing surface for a shaft, gear, or bearing to rotate on.

Jumps out of gear: A transmission problem that occurs when the transmission shifts to neutral on its own.

[return to top]

Keys: A synchronizer part that pushes the synchronizer rings into contact with the gear cone.

[return to top]

Lash: (1) The play or clearance between two parts (for example, meshed gears); see backlash. (2) Excessive clearance in a drivetrain that can cause a “clunk” when torque load is changed.

Leak: Fluid escaping from a housing.

Level protractor: A tool used to check U-joint or driveshaft angles.

Limited slip differential: A differential that uses internal clutches to limit the speed difference between the axles.

Lining: See Facing.

Linkage: The series of rods, levers, cables, etc., used to transmit motion of force from one point to another.

Linkage adjustment: The procedure to ensure that the transmission gears shift completely in or out of mesh as the shift lever is moved.

Live axle: An axle that transmits power.

Locked differential: A condition that will not allow differential action to occur.

Locked into gear: A condition in which a transmission cannot be shifted out of a gear.

Locking hub: A 4WD front hub that will unlock for highway use and lock for off-road use.

Loctite: A brand of adhesive used to prevent screws and bolts from coming loose after installation.

Long assembly: A type of pressure plate assembly that can be identified by weights on the outer end of the release levers.

Lubricant check: A check to determine the fluid level and condition.

Lung cancer: A serious illness that can result from exposure to asbestos or other hazardous materials.

[return to top]

μ: The Greek letter (mu) that is used as the symbol for micron.

Magnetic clutch: A clutch that is applied and released by magnetic force.

Main drive gear: The transmission’s input gear.

Mainshaft: The transmission’s output shaft.

Make (close) : Allowing current to flow; when a switch is closed it will make the circuit.

Malfunction indicator light (MIL): An indicator light on the dash that alerts the driver to a problem.

Manual transmission: A transmission in which the gear ratios are changed by manually shifting.

Manual transmission fluid (MTF): The lubricant required for a transmission that uses composite synchronizer rings.

Marcel: A series of wave springs between the two lining sections of a clutch disc.

Match mark: See Index mark.

Material Safety Data Sheets (MSDSs): Forms containing data regarding the properties of a particular substance.

Mechanical hub: A 4WD locking front hub that must be manually switched.

Mesh: Engagement of the teeth of two gears.

Mesothelioma: A fatal type of cancer of the lining of the chest or abdominal cavity, which can be caused by asbestos inhalation.

Micrometer: A precision measuring instrument used to measure parts. Micrometers are designed to measure outside diameter, inside diameter, or depth.

Mineral oil: A refined oil product that comes from a crude oil base.

Misalignment: A wear pattern that leaves a diagonal polish on bearing races.

Modular clutch: An assembly that combines the flywheel, clutch disc, and pressure plate.

Multiple-disc clutch: A clutch that uses more than one friction disc.

[return to top]

Needle bearing: A very thin roller bearing.

Neutral: A condition in a transmission where the input shaft rotates and the output shaft is not driven.

Neutral rattle/rollover: Gear rattle that occurs while the transmission is in neutral.

Newton-meter (N-m): The metric measurement for torque.

Nick: A break or notch caused by impact.

Nodular iron: A type of cast iron that incorporates graphite to increase strength.

Noisy transmission: Unusual noises that indicate a potential problem.

Nominal shim: A shim of designated thickness used when beginning a gauging process.

Nonhunting: A gear ratio in which the same drive and driven teeth make contact every revolution.

Nut: A threaded fastener that is used with a bolt.

[return to top]

Occupational Safety and Health Administration (OSHA): A governmental agency that regulates workplace safety.

Ohmmeter: A meter used to measure the resistance of a circuit or component.

Ohms (O, Ω): Unit of measurement for resistance.

Oiling funnel: A transmission part that feeds oil into a shaft.

One-way clutch: An overrunning clutch that locks in one direction and freewheels or overruns in the other direction.

Open case: A transmission design that mounts the shift levers through an opening in the case.

Open circuit: A break or interruption in a circuit that will not allow current to flow.

Open design: A 4WD front drive axle design that uses ball joints and Cardan joints.

Open differential: A differential that will split torque equally between axles and does not limit the speed difference between the axles.

Original equipment manufacturer (OEM): The manufacturer of a particular vehicle.

“O”-ring: A sealing ring with a round cross section.

Outboard joint: The outer CV joint that only changes angle.

Output shaft: The shaft that carries the torque out of a gearbox.

Overdrive: A gear arrangement that causes the output shaft to turn faster than the input shaft.

Overhung pinion: A pinion that hangs over, past the support bearing.

[return to top]

Parallel circuit: An electrical circuit that has more than one load, with each load sharing a common battery ground connection.

Partial nonhunting: A gear ratio that allows contact of the same drive and driven gear teeth in a regular pattern.

Part-time 4WD: A 4WD vehicle that allows the front drive axle to be disconnected for highway use and applied for off-road use; commonly called 4WD.

Passing gear: A forced downshift from a higher gear to the next lower gear.

Pawl: A locking device that holds a gear stationary.

Peeling: A slight scraping away of material from a bearing race.

Peen: A process of striking a metal surface with a hammer or steel shot to upset or harden the surface.

Phasing: The placement of U-joints in a driveshaft relative to each other.

Pilot bearing: A bearing in the end of the crankshaft used to support the front end of the transmission input shaft.

Pinion bearing preload: The load placed on the pinion bearings during assembly.

Pinion depth: The pinion gear’s position relative to the ring gear.

Pinion gear: A small gear that meshes with a larger gear.

Pitch: The distance between threads of a bolt and nut; the relative number of teeth or spacing of the teeth on a gear.

Pitch diameter: The effective diameter of a gear; midpoint of gear tooth. Also called pitch line.

Pitch line: The line of contact between driving and driven gears.

Pivot shaft: A shaft that runs through the clutch housing that transfers force from the clutch linkage to the release bearing. Also called a cross shaft.

Planetary gear set: A gear system composed of a sun gear, a planet carrier with planet pinions, and a ring gear that can produce one or more gear ratios.

Plug-in connection: A method of holding the inboard CV joint into the differential side gear using a circlip.

Plunge joint: A CV joint that allows a driveshaft to change length.

Positraction: The brand name of limited slip differentials used in Chevrolets.

Power: The rate at which work is done.

Power source: The source of electrical power. The battery, generator, and capacitors are typical automotive power sources.

Powertrain: The mechanism that transfers and modifies the driving torque from the engine crankshaft to the drive wheels; also called drivetrain.

Powertrain control module (PCM): An electronic control module for the engine and transmission.

Power transfer unit (PTU): A gearbox added to a FWD transaxle to control the power flow to a rear drive axle.

Preload: An adjustment that removes all clearance and places a load on the parts.

Preshift: The action in a dual clutch transmission where a synchronizer is shifted to engage the next gear ratio before that clutch is applied.

Pressure: A force per unit area measured in pounds per square inch (psi) or units of atmospheric pressure (bars or kilopascals).

Pressure plate: The metal disc that applies pressure on the friction disc to transmit torque.

Pressure plate assembly: The clutch part that combines the pressure ring, cover, release levers, and spring(s).

Pressure ring: Part of the pressure plate assembly that squeezes the clutch disc against the flywheel.

Pressure springs: Part of the pressure plate assembly that pushes the pressure ring against the clutch disc.

Propeller shaft: See Driveshaft.

Protection devices: Devices that protect an electrical circuit from excessive current flow.

[return to top]

Quill: The extension from the transmission input bearing retainer that supports the clutch release bearing.

[return to top]

Race: A hardened surface for the bearing rollers or balls to roll on.

Rack and pinion gear set: A gear set combining a straight gear (the rack) with a pinion gear so that the rack moves sideways when the pinion is rotated.

Radial: A direction perpendicular to the rotating axis.

Radial runout: The amount that a round component like a flywheel is out of round or off-center. Excessive radial runout can cause a vibration.

Rail: A metal rod/shaft on which the shift forks are mounted.

Rear-wheel drive (RWD): A drive system that drives only the rear wheels.

Reduction: A gear ratio that increases torque and reduces speed.

Relay: A device that uses a small electrical current to control a larger electrical current.

Release bearing: The bearing that is forced against the pressure plate assembly to release a clutch. Also called throwout bearing .

Release bearing support: A transmission part, usually the front bearing retainer, that provides a place for the release bearing to slide on.

Release levers: The levers that move the pressure plate into and out of contact with the clutch disc.

Reluctor: A toothed ring used with a speed sensor to monitor the speed or position of a rotating part.

Removable carrier: A rear axle carrier that can be removed from the housing for service.

Resistance: The opposition to current flow.

Reverse idler gear: See Idler gear.

Reverse idler shaft: The shaft that supports the reverse idler gear.

Right-to-Know laws: Laws that state that employees have a right to know when the materials they use at work are hazardous.

Ring gear: See Annulus gear.

Ring gear runout: The side-to-side wobble of the ring gear as it is rotated.

Roller clutch: A one-way clutch that uses a set of rollers and a special cam as the locking mechanism.

Rolling friction: The drag of the tires on the road plus bearing friction.

Room-temperature vulcanizing (RTV): A formed-in-place gasket material; a rubberlike material that vulcanizes at room temperature.

Runout: Deviation in an item’s rotation or a mounting plane.

Rzeppa joint: The most commonly used outboard CV joint.

[return to top]

Schematic: See Wiring diagram.

Scoring: A tear or break in a metal surface caused by heavy contact.

Seizing: Parts that are partially or completely welded together from friction-generated heat.

Selective fit: Parts that are available in different thicknesses so that a technician can select the correct size.

Self-induction: The generation of current in a coil circuit when the coil is first completed (made) or opened (broken).

Semi-floating axle: A rear drive axle that is supported by a bearing at one end and the differential side gear at the other end.

Sensor: A device that measures (motion, pressure, position, and so on) and sends (electrically) information to a control unit.

Sequential transmission: A transmission that shifts through its gears in linear sequence with no gear skipping (1 to 2, 2 to 3, 3 to 4 or 4 to 3, 3 to 2, 2 to 1) one gear at a time, either up or down. The shift lever is moved one direction for upshifts and the opposite direction for downshifts. Motorcycles use sequential transmissions.

Series circuit: An electrical circuit that has the loads connected one after the other.

Service spacer: Shims used to space the carrier bearings and maintain carrier bearing preload.

Shift blockout: A circumstance occurring when a transmission cannot be shifted into one or more gears.

Shift effort test: A check to determine the amount of effort required to complete a shift.

Shift fork: The part that transfers motion from the shift shaft to the synchronizer sleeve.

Shim: A thin metal spacer used to adjust clearance or preload.

Shorted circuit: An electrical circuit that has a path that bypasses part of the circuit.

Side bearings: See Carrier bearings.

Side gears: See Axle gears.

Sleeve: The synchronizer part that slides to engage the speed gear’s dog teeth.

Slider clutch: A clutch designed to slip until a certain rpm, preventing the transfer of too much torque to the drive wheels.

Slip fit: A free-running or sliding fit.

Slip joint: A splined joint in a driveshaft to allow it to change length.

Slipping: A loss in torque transfer accompanying an increase in engine rpm.

Slip yoke: The part that allows for length change in a RWD driveshaft.

Solenoid: An electromechanical device that has a movable core.

Solvents: Usually colorless liquids that are used to remove grease and oil.

Spalling: A condition where surface metal breaks away from a bearing race.

Special Service Tools (SSTs): Tools developed by OEM to aid in service or repair procedures.

Speed gears: The gears that are meshed with the cluster gear that transfer motion to the synchronizer assembly.

Speed sensitive: A condition associated with a vibration that is noticeable with a change in engine or vehicle speed.

Spiral bevel gear: A type of bevel gear that uses curved teeth that are spiral cut to provide quieter operation.

Spline: A slot or groove cut in a shaft or bore that is used to connect to a matching spline.

Split case: A transmission design that splits the case vertically into two halves.

Spontaneous combustion: Self-ignition of oily rags without the use of an ignition source.

Sprag: The locking element in a one-way sprag clutch.

Sprag clutch: A type of one-way clutch.

Spur bevel gear: A type of bevel gear with straight-cut teeth, commonly used in differentials.

Spur gear: A gear with teeth cut parallel to the axis of the gear.

S spring: A steel spring shaped like the letter S.

Stabilizer bar: A brace connecting the shift linkage to the transaxle case.

Stall: A condition where the engine is running but the transmission input shaft is not rotating.

Stall speed: A condition where the engine is running at maximum speed but the automatic transmission input shaft is not turning.

Standard transmission: At one time the standard equipment transmission in a new vehicle. See Manual transmission.

Static friction: The relative amount of friction between two stationary surfaces or two surfaces that are moving at the same speed.

Static shift test: A shift test that is made with the engine off.

Stepped flywheel: A flywheel that is thicker at the rim than at the clutch friction surface.

Step wear: Heavy wear that produces a step that can be seen or felt.

Straddle mounting: Mounting a gear between two bearings.

Struts: See Keys.

Stud: A short rod with threads on both ends.

Swage: Deforming metal to hold/lock a part in place.

Switch: An electrical device used to control a circuit by opening (breaking) and closing (making) a circuit.

Symbols (circuit components): Used to represent components in an electrical circuit.

Synchronize: To bring two objects to the same rotating speed.

Synchronizer assembly: A group made up of a hub, sleeve, synchronizer rings, keys, and energizer springs.

Synchronizer ring: Part of a synchronizer assembly that blocks a shift until the speeds are synchronized.

Synthetic oil: A lubricating oil with significant man-made modifications.

[return to top]

Tapered roller bearing: A nonfriction bearing that uses tapered steel rollers as the rolling element.

Technical Service Bulletin (TSB): A form that describes a particular vehicle concern and the recommended corrective action.

Telescopic gauge: A gauge used with a micrometer to measure the inside diameter of a hole or bore.

Throw-out bearing: See Release bearing.

Thrust: A motion of a gear or shaft along its axis.

Thrust washer: A bearing that is used to separate rotating parts from stationary parts or parts that are rotating at different speeds.

Toe: The inner end of a bevel or hypoid ring gear tooth.

Tone ring: See Reluctor.

Torque: A turning or twisting effort that is normally measured in footpounds or Newton-meters.

Torque bias check: Measures the torque required to rotate one wheel while the other wheels are held stationary.

Torque bias ratio (TBR): The relative amount of torque that each drive wheel will receive.

Torque converter: A type of fluid coupling used with automatic transmissions that will multiply engine torque. It self-releases to allow the vehicle to stop with the engine running and the transmission in gear.

Torque sensitive: A condition associated with a vibration that is noticeable with a change in torque.

Torque tube: Steel tube used to position the rear axle.

Torsen®: Torque-sensing worm gear differential.

Traction: The relative amount of grip between a tire and the road surface.

Traction control: A system used to sense wheel spin and reduce drive wheel torque to the traction available.

Tractive effort: The amount of thrust the engine and drivetrain can generate at the road surface.

Tractive resistance: The load that the drivetrain works against.

Transaxle: A transmission that is combined with the final drive and differential and is normally used in FWD and mid-engine vehicles.

Transfer case: An auxiliary transmission used in most 4WD vehicles to divide and control the power flow to the front and rear drive axles.

Transistors: A semiconductor device that can work like a relay or amplifier.

Transmission: A device in the powertrain that provides different forward gear ratios, a neutral, and a reverse.

Transverse: A position that is crossways to the vehicle.

Tripod joint: A type of fixed, outboard CV joint.

Tripod tulip joint: A plunge, inboard joint commonly used on FWD shafts.

Trough: An area inside a transmission case raised to direct oil to a shaft or bearing.

Trunnion: The projecting arms of a U-joint cross that form the bearing journals.

Tunnel case: A transmission design that installs the gear and shaft assembly through the end of the case.

Twin-traction axle: A Ford front drive axle that utilizes a swing axle system.

[return to top]

U-joint angle: See U-joint operating angle.

U-joint operating angle: The angle between a U-joint’s input and output shafts.

UNC: Unified National Coarse.

Uneven wear: Unevenly distributed wear.

UNF: Unified National Fine.

Universal joint (U-joint): A mechanical device used to transfer power and motion at changeable angles.

Upset: The action of displacing metal with hammer blows.

Used brake fluid: Brake fluid that is no longer useful and has been removed from a vehicle.

Used coolant: Coolant that is no longer useful and has been removed from a vehicle.

Used oil: Any petroleum-based or synthetic oil that has been used.

[return to top]

Vacuum motor: A vacuum-operated device that does work.

Vari-lock: Jeep’s name for a Hydra-Lok differential.

Vehicle emission control information (VECI): An underhood label with emission control information.

Vehicle identification number (VIN): An alphanumeric code used to identify a vehicle, the location of manufacture, year of manufacture, engine type, and so on.

Vernier caliper: A precision measuring instrument used to measure outside and inside diameters as well as depth.

VIN: Vehicle identification number.

Viscosity: A fluid’s resistance to flow.

Viscous: The tendency of a fluid to resist flow: thick = high viscosity; thin = low viscosity.

Viscous coupling: A sealed clutch filled with a viscous fluid that will transfer power as the fluid is heated.

Visual check: A visual inspection to determine the overall condition.

Visual inspection: A careful inspection of a part or vehicle using sight and feel.

Volts (V): Unit of measurement for electrical pressure.

[return to top]

Washer: A thin metal disk with a hole used to support the load of a threaded fastener.

Watts (W): The unit of measurement for electrical work (amps x volts = watts).

Wave spring: A spring that resembles a flat, wavy washer.

Wet clutch: A clutch that operates in fluid.

Wheel end: The outer end of the axle housing where the axle bearing is situated.

Wheel speed sensor (WSS): An electronic device to sense the speed of a wheel, typically used with ABS brakes and traction control.

Wiring diagram: A diagram consisting of symbols and lines to represent an electrical circuit.

Work: The result of force that changes the speed or direction of an object.

Workplace Hazardous Materials Information Systems (WHIMS): A Canadian form that contains data regarding the properties of a particular substance.

Worm gear: A type of gear with teeth that resemble screw threads.

[return to top]

Yoke: A U-shaped part of a shaft that connects to a U-joint cross.

[return to top]