Automotive Glossary of Terms - S -
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Definitions for automotive terms and illustrations from sealed beam headlight steering to synthetic motor oil.
SEALED BEAM HEADLIGHT: An automotive headlight. The lens, reflector and filament form a single unit.
SEATBELT INTERLOCK: A system whereby the car cannot be started unless the seatbelt is buckled.
SECONDARY CIRCUIT: The high voltage side of the ignition system, usually above 20,000 volts. The secondary includes the ignition coil, coil wire, distributor cap and rotor, spark plug wires and spark plugs.
SEMI-FLOATING AXLE: In this design, a wheel is attached to the axle shaft, which takes both drive and cornering loads. Almost all solid axle passenger cars and light trucks use this design.
SENDING UNIT: A mechanical, electrical, hydraulic or electromagnetic device which transmits information to a gauge.
SENSOR: Any device designed to measure engine operating conditions or ambient pressures and temperatures. Usually electronic in nature and designed to send a voltage signal to an on-board computer, some sensors may operate as a simple on/off switch or they may provide a variable voltage signal (like a potentiometer) as conditions or measured parameters change.
SERPENTINE BELT: An accessory drive belt, with small multiple v-ribs, routed around most or all of the engine-powered accessories such as the alternator and power steering pump. Usually both the front and the back side of the belt come into contact with various pulleys.
SHEATH: The outer casing for clutch or brake cables.
SHIM: Spacers of precise, predetermined thickness used between parts to establish a proper working relationship.
SHIMMY: Vibration (sometimes violent) in the front end caused by misaligned front end, out of balance tires or worn suspension components.
SHORT CIRCUIT: An electrical malfunction where current takes the path of least resistance to ground (usually through damaged insulation). Current flow is excessive from low resistance resulting in a blown fuse.
SINGLE OVERHEAD CAMSHAFT: See overhead camshaft.
SKIDPLATE: A metal plate attached to the underside of the body to protect the fuel tank, transfer case or other vulnerable parts from damage.
SLAVE CYLINDER: In automotive use, a device in the hydraulic clutch system which is activated by hydraulic force, disengaging the clutch.
SLUDGE: Thick, black deposits in engine formed from dirt, oil, water, etc. It is usually formed in engines when oil changes are neglected.
SNAP RING: A circular retaining clip used inside or outside a shaft or part to secure a shaft, such as a floating wrist pin.
SOHC: Single overhead camshaft.
SOLENOID: An electrically operated, magnetic switching device.
SPARK PLUG: A device screwed into the combustion chamber of a spark ignition engine. The basic construction is a conductive core inside of a ceramic insulator, mounted in an outer conductive base. An electrical charge from the spark plug wire travels along the conductive core and jumps a preset air gap to a grounding point or points at the end of the conductive base. The resultant spark ignites the fuel/air mixture in the combustion chamber.
SPECIFIC GRAVITY (BATTERY): The relative weight of liquid (battery electrolyte) as compared to the weight of an equal volume of water.
SPLINES: Ridges machined or cast onto the outer diameter of a shaft or inner diameter of a bore to enable parts to mate without rotation.
SPONGY PEDAL: A soft or spongy feeling when the brake pedal is depressed. It is usually due to air in the brake lines.
SPRUNG WEIGHT: The weight of a car supported by the springs.
SRS: Supplemental restraint system
STABILIZER (SWAY) BAR: A bar linking both sides of the suspension. It resists sway on turns by taking some of the added load from one wheel and putting it on the other.
STARTER ENGINE: A high-torque electric motor used for the purpose of starting the engine, typically through a high ratio geared drive connected to the flywheel ring gear.
STEERING GEOMETRY: Combination of various angles of suspension components (caster, camber, toe-in); roughly equivalent to front end alignment.
STRAIGHT WEIGHT: Term designating motor oil as suitable for use within a narrow range of temperatures. Outside the narrow temperature range, its flow characteristics will not adequately lubricate.
STROKE: The distance the piston travels from bottom dead center to top dead center.
SUPERCHARGER: An air pump driven mechanically by the engine through belts, chains, shafts or gears from the crankshaft. Two general types of supercharger are the positive displacement and centrifugal types, which pump air in direct relationship to the speed of the engine.
SUPPLEMENTAL RESTRAINT SYSTEM: See air bag.
SYNCHROMESH: A manual transmission that is equipped with devices (synchronizers) that match the gear speeds so that the transmission can be downshifted without clashing gears.
SYNTHETIC MOTOR OIL: Non-petroleum based motor oil.