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A arm

A suspension link shaped like the letter “A” or “V” used to locate the wheel relative to the vehicle body while allowing vertical movement. A-arms are mounted to the chassis with bushings and connect to the wheel hub at the opposite end. Many vehicles use upper and lower A-arms in independent front suspension layouts.

ABS (Anti-lock Brake System)

A braking system that prevents wheel lock-up during heavy braking by modulating brake pressure based on wheel speed. Sensors detect when a wheel is about to lock, and a control unit rapidly varies hydraulic pressure to maintain maximum braking force while retaining steerability.

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ABS Warning Light

An instrument cluster indicator that illuminates when an issue is detected within the anti-lock braking system. It also illuminates briefly at ignition to confirm lamp operation.

Accelerator Interlock

A linkage or mechanism that interacts between the accelerator pedal and the automatic transmission to manage throttle input and gear selection behaviour.

Accumulator

A pressure storage device used in various automotive hydraulic or air systems. In hydraulic contexts, it uses gas (often nitrogen) to store pressurised fluid and smooth out pressure fluctuations. It may also provide short bursts of high pressure when needed.

Acid (Battery)

A corrosive electrolyte used in lead-acid batteries, consisting mainly of sulphuric acid diluted with water. It participates in the electrochemical reactions that provide electrical power.

Ackermann Angle / Steering Geometry

A steering design principle that ensures each front wheel follows its correct turning radius during a corner. Inner wheels turn through a greater angle than outer wheels so that all wheels share a common turning centre, reducing tyre scrub.

Actuator

A device that converts an electrical, hydraulic, or pneumatic signal into controlled mechanical motion. Actuators are used in systems such as throttle control, brake boosters, solenoid valves, and electronically controlled engine components.

AdBlue (AUS32)

A urea-based aqueous solution used in selective catalytic reduction (SCR) exhaust after-treatment systems on diesel vehicles. It chemically reduces oxides of nitrogen (NOx) to nitrogen and water to help meet emissions standards.

Adjustable shock absorber

A suspension damper whose compression and rebound characteristics can be varied to suit different load or road conditions. Adjustment may be manual or electronically controlled.

Adjusting shim

A thin plate inserted between components to alter their relative spacing or clearances as part of calibration or assembly.

Aeration

The mixing of air into a liquid, often leading to a foaming effect that can reduce the effective performance of the fluid, such as brake fluid in a hydraulic system.

Air-Assisted Hydraulic Brake System

A hybrid brake system in which compressed air assists a hydraulic power unit to augment brake pedal force, often used on larger vehicles.

Airbag (Supplementary Restraint)

A passive safety device that inflates rapidly during certain collisions to cushion and reduce the risk of occupant injury by limiting contact with the dashboard, steering wheel, or windscreen.

Airbag (Suspension)

A suspension springing element that uses pressurised air contained in flexible bellows in place of conventional metal springs to support vehicle load and provide ride comfort.

Air Brakes

A braking system in which compressed air actuates brake mechanisms, typically found on heavy commercial vehicles. Compressed air applies force to actuators that then apply the mechanical brakes.

Air Dryer

A component in an air brake system that removes moisture from compressed air before it enters the brake circuits, helping prevent corrosion and freezing.

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Air Filter / Cleaner

A device that removes dust and other particulates from intake air before it enters the engine’s combustion chamber.

Align

To bring two or more parts into correct relative position;
To adjust wheels or components so they lie in a straight reference line.

Alignment gauge

A tool used to assess wheel alignment parameters such as toe and camber.

Alloy

A material composed of two or more elements, designed to achieve properties such as strength, reduced weight, or corrosion resistance.

Alloy wheel

A road wheel made from an aluminium or magnesium alloy rather than steel, typically lighter and offering improved heat dissipation.

All Wheel Drive (AWD)

A drivetrain configuration that can distribute engine torque to all four wheels automatically without driver intervention. AWD systems enhance traction under variable road conditions and often differ from part-time 4WD systems by operating full-time with torque distribution managed electronically or mechanically.

Related pages: Transmission & Driveline Overview

Alternator

An engine-driven electrical generator that produces alternating current (AC), which is then rectified to DC to power the vehicle’s electrical system and charge the battery.

Ammeter

An instrument that measures electrical current flowing in a circuit, expressed in amperes.

Ampere

The SI unit of electrical current, representing the rate of charge flow past a given point in a circuit.

Ampere-hour

A battery capacity rating quantifying the amount of current (in amperes) a battery can deliver over one hour.

Anchor (Brake)

The fixed support against which the brake shoes rest in certain drum brake designs.

Ancillaries

Engine-driven auxiliary components such as the alternator, power steering pump, fuel pump, or air conditioning compressor.

Anemometer

An instrument that measures the speed or motion of air.

Anneal

A heat-treatment process in which a metal is heated and then cooled slowly to soften it and relieve internal stresses.

Annular / Annular Gear

A ring-shaped gear with internal teeth, commonly used in epicyclic gearsets such as automatic transmissions.

Related Page: Epicyclic gears

Anodized

A surface treatment for aluminium that increases corrosion resistance by forming a controlled oxide layer.

Antechamber

A small auxiliary combustion chamber in some diesel engines that improves combustion efficiency.

Antifreeze

A coolant additive (commonly ethylene glycol) that lowers the freezing point of engine coolant and inhibits corrosion in cooling passages.

Antifriction bearing

A bearing design that uses rolling elements to provide low-friction support for rotating or sliding interfaces.

Anti-knock agent

A fuel additive that increases octane rating and reduces the tendency for detonation (pre-ignition) in spark-ignition engines.

Anti-rattle spring

A small spring used in disc brake assemblies to minimise noise by stabilising friction elements.

Anti-roll bar

A torsional link between left and right suspension that limits body roll during cornering without significantly affecting ride comfort.

Related pages: Suspension Systems Explained

Anti-vibration mounting

A torsional link between left and right suspension that limits body roll during cornering without significantly affecting ride comfort.

Related pages: Suspension Systems Explained

A-pillar

The structural support on either side of a vehicle’s windscreen that supports the roof and defines driver visibility.

Aquaplaning (Hydroplaning)

A condition in which tyres lose effective contact with the road surface due to a film of water, reducing traction and increasing the risk of loss of control.

Aspect ratio

The relationship in a tyre or wheel between the distance from the rim to the tread and the tire's width (i.e., ratio of section height to section width). For example, in a 205/80R17 tire, 80 is the aspect ratio, showing the height is 80% of the width. A lower aspect ratio describes a shorter, wider tire.

ASR

Anti-spin regulation. A Bosch term for traction control

Asymmetrical tread

The tread pattern on an asymmetric car tyre changes across the tread with different parts adapted for particular functions. The outside edge consists of large stiffer tread blocks which help with cornering. The inner tread blocks are smaller and designed to shift water and improve wet grip.

Automatic choke

A device attached to the carburetor that automatically reduces the amount of air (therefore enriching the fuel/air mixture) entering the carburetor by sensing changes in engine temperature.

Automatic transaxle

An automatic transaxle combines the vehicle's automatic transmission and differential in one unit.

Automatic transmission

A drive-train mechanism which takes the power from the engine and transfers it to the driveshaft or wheels with a range of automatically selected gears, selected according to the varying road and load conditions as well as desired speed.

The automatic transmission does not use a traditional. Instead it uses a torque converter, which is a type of fluid coupling to transfer drive from the engine to the transmission. The gear ratios inside the transmission are achieved by a series of epicyclic gear set, with bands and clutches to achieve selections.

Automatic Transmission Fluid

ATF is a low viscosity fluid designed for automatic transmissions where it is required to transmit drive in the torque converted, hydraulically select gears and lubricate the moving parts. Poor transmission performance and gear selection can often be attributed to a low level or poor condition of the automatic transmission fluid.

Axle

An axle is a shaft on which the wheels rotate.

A full-floating axle is used to drive the rear wheels. It does not hold them on nor support them.

A semi-floating or one-quarter floating axle is used to drive the wheels, hold them on, and support them.

A three-quarter floating axle is used to drive the rear wheels as well as hold them on, but it does not support them.

A live axle holds the wheels and transmits power to the wheels. A dead axle or beam axle merely holds the wheels, but does not transmit power to the wheels.

Axle differential

In an axle, the differential allows the wheels to turn at different speeds with equal torque.