Educational Mechanics
Backlash
The clearance or play between meshing gears, measured as the movement of one gear before it engages with the connecting gear. Backlash affects noise, wear, and gear engagement quality.
Backplate
A rigid metal plate fixed to a brake axle housing on which the brake shoes, wheel cylinders, and associated hardware are mounted in drum brake assemblies.
Back pressure (Exhaust)
A rigid metal plate fixed to a brake axle housing on which the brake shoes, wheel cylinders, and associated hardware are mounted in drum brake assemblies.
Baffle
A partition or plate that redirects or slows fluid or gas flow, commonly used inside engine cooling shrouds, fuel tanks, and exhaust chambers to manage flow behaviour.
Baulk Ring
A component in synchromesh transmissions that prevents gear engagement until gear speeds are synchronised. It works with the synchro cone to ensure smooth gear changes.
Ball bearing
A type of rolling-element bearing where hardened steel balls separate the inner and outer races. Ball bearings reduce friction in rotating assemblies such as wheel hubs and gearbox outputs.
Ball check valve
A one-way fluid valve where a ball seals the passage to allow flow in one direction only, often used in hydraulic or pneumatic circuits.
Ball Joint
A flexible joint using a ball and socket type of construction, used in steering and suspension setups, commonly track and tie rods. Their flexibility helps to compensate for the changes in the suspension and steering when turning or hitting a bump on the road. There are usually upper and lower ball joints attached to the upper and lower A-arms. Some ball joints have a grease nipple to allow periodic lubrication.
Band Brake
A braking mechanism where a flexible band wraps around the inside of a drum; tension in the band applies braking force. Typically found in older or specialised applications.
Banjo Axle
A tubular rear-axle design where the differential casing resembles a banjo, with two “necks” to either side carrying the axle shafts.
Banjo Union
A tubular rear-axle design where the differential casing resembles a banjo, with two “necks” to either side carrying the axle shafts.
Battery
An electrochemical device that stores and supplies direct current (DC) electrical energy. Automotive batteries are typically lead-acid types used to start the engine and supply electrical power when the engine is not running.
Bead
The portion of a tyre designed to sit tightly against the wheel rim, forming a seal that retains internal air in tubeless tyres.
Beam Axle
A rigid axle that supports wheels at both ends; movement of one wheel directly affects the other. Common in heavy vehicles and some rear suspension layouts.
Bearing
A mechanical device that supports relative motion between parts while minimising friction. Includes anti-friction types (ball, roller) and plain bearings in powertrain and wheel applications.
Bearing Cap
A component that encloses and secures a bearing shell in its housing, maintaining alignment and preload.
Bearing Preload
The controlled static load applied to a bearing to ensure minimal play and consistent rolling contact in assemblies such as wheel hubs.
Bearing Race
One of the rings in a rolling element bearing (inner or outer) that provides a smooth surface for balls or rollers to roll upon.
Bevel Gear
A conical gear used to transmit rotation and torque between shafts at an angle, commonly found in differential final drives and steering gearboxes.
Before Bottom Dead Centre (B.B.D.C.)
The crankshaft position where the piston is just before reaching the lowest point of its stroke.
Before Top Dead Centre (B.T.D.C.)
The crankshaft position where the piston is just before reaching the highest point of its stroke.
Bell Housing
The housing on a transmission that encloses and protects the clutch (manual) or torque converter (automatic) and connects the gearbox to the engine flywheel.
Bellows
Sealed, accordion-like chambers that protect moving components (e.g., steering racks) from contamination while accommodating motion.
Belly pan
Sealed, accordion-like chambers that protect moving components (e.g., steering racks) from contamination while accommodating motion.
Belt
A continuous flexible band used to drive auxiliary components (e.g., alternator, pump) or, in toothed form, to drive camshafts in an engine timing system.
Belt tensioner
A device that maintains correct tension on an accessory or timing belt, often spring-loaded in automatic systems.
Big End
The larger end of a connecting rod that attaches to the crankshaft journal.
Big End Bearing
A journal bearing at the large end of the connecting rod that supports rotational motion at the crankshaft.
Bihexagon
A 12-sided profile used for fasteners and tools, offering multiple contact points for torque application.
Bimetal
Two bonded metals with differing thermal expansion rates; used in thermostats and temperature-responsive mechanical devices.
Binding
Contact or friction between brake shoes/pads and braking surfaces (drums/discs) that impedes free rotation.
Black Smoke
Dark exhaust emissions indicating incomplete combustion and excessive fuel in the combustion chamber.
Blade Impeller
The rotating vane assembly in a centrifugal pump that imparts motion to the fluid.
Blanking Plate / Blanking Piece
A flat metal plate used to close off or seal an opening or fluid passage.
Bleed / Bleeding
The process of removing air entrainment from fluid systems (braking, cooling, or fuel) to ensure consistent hydraulic behaviour.
Bleed Nipple
A hollow screw fitting that allows controlled release of fluid and air from hydraulic systems, such as brake circuits.
Blocker ring
A synonym for baulk ring in synchromesh gearsets that prevents gear engagement until synchronisation is achieved.
Blow back
The unwanted flow of mixture or exhaust gases backward through a carburettor due to valve timing or sticking valves.
Blowby
Combustion gases that escape past the piston rings into the crankcase, leading to pressure rise and the engine “breathing” through vents.
Blower
A mechanical compressor (e.g., Roots or twin-screw) that forces additional air into the engine intake to increase charge density and power.
See: Roots Supercharger
Blow-off valve
A one-way pressure-relief valve that vents excess boost pressure in turbocharged systems to prevent compressor surge.
Blue smoke
Exhaust coloration indicating oil burning inside the combustion chamber, often from worn rings or valve seals.
Boot
Positive intake air pressure above atmospheric provided by forced induction systems (turbochargers or superchargers) that increases engine volumetric efficiency.
Boost (Pressure)
Positive intake air pressure above atmospheric provided by forced induction systems (turbochargers or superchargers) that increases engine volumetric efficiency.
Body roll
Exhaust coloration indicating oil burning inside the combustion chamber, often from worn rings or valve seals.
Bottom Dead Centre (BDC)
The piston position at the lowest point of its stroke in the engine cylinder.
Bottle Jack
A compact hydraulic lifting tool shaped like a bottle used to raise vehicles or heavy assemblies.
Bore
The internal diameter of an engine cylinder in which the piston travels.
Bowden cable
A flexible control cable operating a mechanism (clutch, throttle) through a sliding inner wire and outer sheath.
Bottoming out
A condition where a suspension component reaches the end of its travel, often felt as a harsh impact over a bump.
Bottom end
The piston position at the lowest point of its stroke in the engine cylinder.
Boxer Engine
A flat, horizontally opposed engine configuration with pistons moving in opposite directions.
Bra (Vehicle Protection)
A protective cover fitted to the front of a vehicle to shield finish and components from debris.
Bracing
A protective cover fitted to the front of a vehicle to shield finish and components from debris.
Braided Hose
A flexible hose reinforced with woven wire, commonly used in high-pressure brake and clutch systems.
Brake Booster / Vacuum Servo
A device that reduces the physical effort required by the driver to apply the brakes. It uses engine vacuum (or an auxiliary vacuum source) to multiply the force applied to the brake pedal before it acts on the master cylinder. Brake boosters assist braking but do not apply brakes independently.
Brake Fade
A reduction in braking effectiveness caused by excessive heat in braking components. Heat can reduce friction between pads and discs or cause brake fluid to vaporise, leading to increased pedal travel and reduced braking force.
Brake Line
A rigid or flexible hydraulic conduit that transmits pressurised brake fluid from the master cylinder to wheel braking components. Brake lines must withstand high pressure and resist expansion to ensure consistent braking response.
Brake Pad
A replaceable friction component used in disc brake systems. Brake pads press against a rotating brake disc to convert kinetic energy into heat, slowing the vehicle.
Brake Shoe
A curved friction component used in drum brake systems. Brake shoes expand outward against the inner surface of a brake drum to create braking force.
Brake Rotor / Brake Disc
A flat, circular metal disc mounted to the wheel hub in a disc brake system. The rotor rotates with the wheel and is clamped by brake pads to produce braking force through friction.
Brake Torque
The rotational force generated by a braking system to resist wheel rotation. Brake torque depends on hydraulic pressure, friction coefficient, and effective brake radius.
Brake Wear Sensor
A device that monitors the wear state of brake pads. When the pad material reaches a minimum thickness, the sensor triggers a warning to indicate that service will soon be required.
Bridge Rectifier
An electrical circuit using four diodes arranged to convert alternating current (AC) into direct current (DC). In vehicles, bridge rectifiers are used in alternators to supply DC power to the electrical system and charge the battery.
Bucket Seat
An individual contoured seat designed to support the occupant during cornering and braking. Bucket seats improve lateral support compared to bench seating but do not affect vehicle control systems directly.
Bypass Valve (Suspension / Damping)
A valve within a hydraulic damper that allows fluid to bypass the main damping circuit under specific conditions. Bypass valves influence damping characteristics, particularly during low-speed suspension movement or high-frequency inputs.