Automotive Technical Terms: Backfire to Brake Fluid

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Automotive Technical Terms: Backfire to Brake Fluid


Throughout this site we use many technical terms, and given the breadth of readership our site enjoys, sometimes we are remiss and incorrectly assume everyone knows what we are referring to. For those that do not, here are some explanations of the technical terms use.
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BA Threads


A range of small nuts and bolts widely used on British cars, particularly for electrical equipment. The range from the largest, 0 BA, down to 10 BA is sufficient for most everyday uses.
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Back Flushing


Cleaning out the cooling system by feeding water into the system the reverse way. The radiator is treated by flushing through the bottom hose and the cylinder block by flushing from the cylinder head.
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Backfire


Detonation of unburned fuel from the engine which has collected in the exhaust system. It is usually caused by an ignition fault or a defective exhaust valve.
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Backlash


The tendency for a spring to travel past its at-rest position when released from tension. The shock absorbers (or dampers) prevent backlash in road springs.
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Back Pressure


Build-up of gas in the exhaust system arising from a blockage in the pipe. When back pressure reaches a certain stage, it will prevent efficient scavenging in the engine and may even stop it.
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Baffle


Metal plates fixed inside the silencer to break up the flow of the exhaust gas and reduce the noise output. Baffles are sometimes used in sumps to prevent oil surging from side to side on cornering, possibly causing intermittent oil-starvation.
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Balancing Carburettors


Ensuring that the carburettors in a multi-carburettor system operate in unison. The throttle linkage has to be synchronized in addition to tuning by instruments. The still-popular method of gauging synchronization by listening to the hiss of air induction is subject to human error, and a visual instrument is acknowledged to be a positive method of balancing. An alternative is electronic tuning or the use of a vacuum (manifold depression) gauge.
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Ball Bearing


A friction-reducing device for carrying a shaft in its housing when speeds are low and no continuous lubrication is available. It consists of an inner race fixed to the shaft and an outer race fixed to the housing. A number of balls, often fitted in a locating cage to prevent them touching one another, are introduced between the races.
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Ball-Check Valve


Often referred to as a pressure-relief valve, it consists of a spring-loaded ball resting in a seating to seal (usually) a lubrication system. When pressure rises beyond a pre-determined level the ball is forced off its spring until the pressure falls again.
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Ball Joint


Ball Joint Ball Joint
Common name for ball-and-socket joints used on steering arm ends and suspension components where two-directional movement is required between joined components. The ball joint consists of a shaft terminating in a ball which fits into a cup to give a wide area of movement. Once lubricated by grease or heavy oil, ball joints are now made with a mixture of plastic and metal, or with a plastic liner, eliminating the need for lubrication.
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Ball Race


Strictly speaking, the ring against which the balls of a ball bearing run; often used to describe the entire ball bearing.
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Ball Valve


See Ball-check valve.
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Ballast Resistor


A resistor which reduces the voltage from the battery to the ignition coil. Cars using this system have a coil which works on about 8 volts, so the resistor is needed to drop the 12 volts from the battery down to this value. During starting, however, when the load from the starter motor reduces the battery voltage, the ballast resistor is bypassed and the coil gets the full available voltage.
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Band


A brake band, externally contrasting, which is found in automatic and semi-automatic gearboxes to produce the desired ratios to the final drive.
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Banjo Connection


Banjo Connection
A fluid-line connection in which the pipe terminates in a circular connection. A hollow stud passes through the circular unit to connect the feed-pipe to another component to allow full flow of the fluid and offer a high mechanical strength. Sealing arrangements are usually through washers.
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Banjo Rear Axle


A design of rear-axle casing for a front-mounted-engine to-rear-wheel drive, in which the propeller shaft terminates in the casing containing the back-axle mechanism and from which the final drive shafts emerge. It is so-called because of its resemblance to the musical instrument.
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Barrel


Common term for the cylinder of a single-cylinder engine, usually air-cooled and incorporating cooling fins. Also an American term for choke, as in four-barrel (four-choke) carburettor.
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Base Circle


Base Circle
The lower part of the valve-driving cam, which is a segment of a true circle. The base circle is the 'idling' part of the cam operation and gives place to the ramp and flanks as the cam rotates.
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Bath-Tub Combustion Chamber


A design of combustion chamber which, viewed upside down, looks like a hip bath, the deeper portion containing the valves and plug orifice and the rest tapering off to nothing across the remainder of the piston area. Thus, as combustion spreads, the flame front of the unburnt gas gets narrower, helping to keep the 'end gas' cool and to lessen the likelihood of detonation or pinking.
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Battery


Device for storing electrical energy by a chemical process. In the normal car, this is a lead-acid battery, in which the chemical process is reversible so that the battery can be re-charged - impossible with dry batteries. Such batteries have a potential of 2 volts per cell when charged, so that most cars have batteries of six cells connected in series to produce 12 volts. A common battery rating is 56 ampere-hours, which means it should deliver 56 amps over a period of one hour or 1 amp over 56 hours.
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Battery Charger


A device for restoring the charge of a battery. It consists, essentially, of a mains transformer to reduce household mains current (in Britain, 240 volts AC) to 12 volts DC. A built-in rectifier changes the alternating current to direct current. As a rule, a domestic battery charger has an output of about 2 amps although they can be obtained to charge as high as 6 amps. The more sophisticated models have an ammeter built in to check the charging rate and an automatic limiter which reduces the output as the battery charge rises (6-volt chargers are also available).

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Battery Coil Ignition


Generally-used means of ignition in motor vehicles in which the 12-volt output from the battery is transformed into approximately 30,000 volts to energize the ignition system. The coil is, in effect, a direct-current transformer operated by the make-and-break effect of the contact-breaker points in the distributor. The 12-volt supply flowing in the primary winding of the coil is interrupted by the opening of the points, which excites a flow of electricity at approximately 30,000 volts in the secondary winding.
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Battery Condition Meter


Essentially a voltmeter which records the voltage output of the battery, from which can be gauged the battery's overall condition and any problems in the electrical system. The theoretical voltage of a cell is 2v but this can rise to as high as 2.7v during charging. When taken off charge, the cell will register 2.1 volts for a while and this will gradually fall to 1.8v when the battery is fully discharged. Voltage scales on a battery condition meter show the extremes of voltage readings and a centre band indicates when the battery is functioning properly. If the register needle falls consistently outside this permitted band, it indicates a fault in the battery itself or possibly in the charging system.
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Battery Polarity


Negative (-) and positive (+), the plus and minus symbols being marked on the battery posts. The majority of cars are of the negative earthed type, which means the negative (�) terminal is connected to an earthing-point on the car, usually through an uninsulated braided cable.
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Baulk Pin Synchromesh


The principles of synchromesh are relatively simple. The actual mechanical details of the various systems, however, are a good deal more complex but, basically, synchromesh is really an improvement on the dog clutch. Dog clutches were the next stage in the development of the gearbox, once the problems of sliding pinion engagement had become apparent. Instead of sliding the gears in and out of mesh, the dog clutches locked each gear to the mainshaft when the gear lever was moved in the appropriate direction. Although an improvement, dog clutches also suffered from the need for accurate synchronization and synchromesh systems were designed to automatically adjust the speed of the dogs to permit easy engagement.
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Baulk Ring Synchromesh


The baulk ring synchromesh system is only one of several ways of obtaining "unbeatable" synchromesh, though it is among the most widely used. It has been employed, with minor variations, on cars manufactured by Ford, Vauxhall (General Motors) and British Leyland. Its name derives from the fact that it has rings that "baulk" or refuse to allow the dog clutch to engage until the speeds of the dog clutch and the relevant gear wheel are synchronized. Like most synchromesh systems, the baulk ring design is double-ended.
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BDC


See bottom dead centre.
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Beads


Beads
The two edges of a tyre, composed of hoops of steel wire round which the casing is wrapped and moulded into shape to hold the tyre securely on to the wheel rim.
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Beam Axle


Beam Axle
A one-piece forging across the width of the car to carry the front wheels. It is now obsolete with the universal use of independent front suspension. Used widely before the advent of independent front suspension, beam axles became more prevalent as part of the rear suspension set-up of front wheel drive cars through the 1970’s and 1980’s. They are a one-piece solid transverse members usually suspended on coil springs, but in the case of heavy commercial vehicles they are used as a front suspension component in conjunction with leaf springs.
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Beam Setting / Beam Alignment


Beam Setting / Alignment
The alignment of the headlamp beams. The main beams should point horizontally ahead of the car when it is normally leaded; the dipped beams should point at a prescribed angle towards the nearside kerb.
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Bearing


Bearing
An arrangement whereby a rotating component can be carried on either a matching stationary component, or one moving at a different speed, with the minimum of friction. Bearings may be of the ball, roller or plain type, the former being used when there is no constant, positive lubrication. On a plain bearing, the facing surfaces are normally of different metals separated by a film of oil.
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Bearing Adjustment


A means of taking up slack caused by wear, usually limited to ball/roller type bearings and effected through a nut or other means of absorbing excess space.
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Bearing Caps


The lower half of a split bearing, such as a big-end or main bearing. It allows the bearing unit to be readily dismantled for replacement purposes.
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Bearing Crush (bearing nip)


A means of ensuring that a plain bearing is a secure interference-fit in its housing. The term is applied particularly to big-end and main bearings. The shells in both types stand slightly proud of their housings under light connecting pressure, but when the cap is fully tightened the proud portion is nipped back into the caps to become a tight fit.
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Belt-Drive


A method of transmitting power. Belts are made from fabric-based, rubber-based or plastic materials. The fan-belt is the most common example of power transmission in the car, followed by belt-drive to the camshaft in many popular cars. Belts are also used to transmit engine power in one type of automatic transmission. Driving belts may have a 'V' configuration to give maximum grip in grooved, smooth pulleys, or they may be toothed or cogged-faced to engage on metal sprockets.
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Belted-Bias Tyre


A tyre with 'criss-cross' fabric as in a cross-ply tyre, but with extra belts of material laid over it below the rubber tread. Used particularly on American cars in place of radial tyres. Also see Bias Belted.

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Bendix (or inertia) Drive


Bendix Drive
A system for self-engaging (and self-disengaging) the starter motor drive with the teeth on the engine flywheel. The inertia of a revolving pinion gained by the initial twist of the starter shaft throws the pinion into mesh with the flywheel and turns the engine. The shaft is fitted with a coil spring return to 'park' the pinion when the starter is switched off or when the engine is running.
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Bevel Gears


Conical-shaped gear wheels which mesh at an angle to each other, usually at an angle of 90� and used to transmit power from a driving shaft to a secondary shaft set at an angle to it.
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Belted-Radial Tyre


Belted-Radial Tyre
A tyre in which the material plies run parallel to each.
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Belted-Textile Cord


Multi-textile belt beneath tread and vertical to the tyre edge bead. Over this radial section ply belts running parallel to, and under, the tyre tread are applied.
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Bias Belted


Bias Belted
A tyre construction technique developed in the US that consists of a mixture of cross-ply and radial-ply construction. It is aimed at producing a superior ride comfort level than that found with a radial ply tyre without sacrificing any road-holding capabilities. The bias-belted tyre fell from favor during the late 1970’s.
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Bias-Ply Tyre


An alternative name for the conventional cross ply tyre in which the plies are laid 'on the bias', criss-crossing each other at an angle of 30�-40� to form the carcase under the rubber.
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Bi-Metal Strip


A 'sandwich' of two metals with different heat expansion rates. When heat is applied to the strip - such as when an electrical current is passed through it - it bends to make or break a circuit. Common usage is in the direction flasher unit where the audible clicks indicate the making and breaking of the circuit to flash the indicators.
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Big End


The connecting point of the connecting rod to the crankshaft.
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Bleeding


Removing all the air bubbles from a system using fluids by pumping out the contaminated fluid and adding new. Commonly applied to hydraulic brake and clutch systems, but it also applies to cooling and heater systems which have become air-locked.
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Block


An abbreviated term for the engine block�the main casting which contains the cylinders.
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Blooming


A paintwork defect usually caused by spraying in too low a temperature with a consequent chilling of the paint. The paint takes on a dull appearance but this can sometimes be polished out by the careful use of a mild cutting paste.
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Blow-Back


The ejection of a gas or liquid from a filling orifice when its direction is suddenly reversed, such as when an engine 'kicks back' to eject petrol from the carburettor. Also encountered when over-rapid filling of the fuel tank causes air to be trapped inside until the pressure rises and ejects petrol from the filler.

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Blower


Anti-Roll Bar
Colloquial term to describe a super-charger or turbocharger.
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Blow-By


This refers to gas escaping past its sealing system in particular passing piston rings in worn engines.
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Blueprinting


Hand preparation and assembly of an engine or other mechanical components to ensure correct tolerances are achieved and thus optimum performance obtained. Can include x-ray type techniques used to determine minor imperfections not detectable to the human eye. Commonly includes; Block - Align hone main saddles, parallel boring and honing with deck plates, equal-distance decking; Pistons - Checked for size and dome height and then pin fitted; pistons are notched where necessary for valve clearances, indexed, machined; oil holes radiused, journals micropolished. The compression ratio is calculated for maximum performance; Balancing - The entire rotary assembly is precision electronically balanced.
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Body Filler


A compound used to fill small indentations which cannot be dealt with by orthodox panel beating.
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Body Panels


Various parts of the car body, most often used to describe replaceable items such as doors, bonnet and boot, but can also refer to wing assemblies and even the roof.
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Body Shell


The main structure of the car before the doors, boot and bonnet have been fitted.
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Borderline Lubrication


A condition where the amount of oil has reached its lowest acceptable point. The term also refers to a condition where the lubricant has become contaminated or heat has built up to a point where the lubricant is on the point of shearing or break-down.
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Bore


The diameter of an engine's cylinders, usually specified in millimetres in Europe but in inches in America. The term is often applied to, or in place of, 'cylinder'. The diameter of an engine's cylinders, usually specified in millimetres in Europe and Australia but in inches in America.
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Boring Bar


Boring Bar
A cutting tool used to bore out and increase the diameter of a cylinder, or to restore it to a true circular section.
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Bottle Jack


A lifting device which operates by the action of a threaded rod working through the boss of a squat cylinder. The broad base of the cylinder offers a steady platform and its similarity in appearance to a bottle gives the jack its name.
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Bottom Dead Centre


The greatest extension of a piston or crank when it exerts no effective power. Exactly opposite to top dead centre (TDC).
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Box Spanner


A form of socket spanner with deep flats on one end to give the maximum grip on a nut or stud. The other end incorporates two holes to accept a bar for leverage.
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Brake


Device for stopping a car through the application of a friction material to a disc or drum iron attached to the wheels. Also used in automatic or semi-automatic gearboxes to stop the rotation of a gear unit.
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Brake Back Plate


Part of a drum brake unit which carries the brake shoes and operating gear. It is bolted to a web or flange on the stub axle, and the brake drum with its wheel-bearing arrangements mate up with it.

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Brake Caliper


Part of a disc brake system which locates the brake pads on either side of a steel or cast iron brake disc in the same way as the rim-brakes on a bicycle.
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Brake Cam


Eccentric lobe in a drum brake system which forces the brake shoes apart to bear against che inside of the brake drum.
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Brake Disc


Steel or cast iron disc forming part of the disc brake system. Pads of friction material bear against it under hydraulic pressure.
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Brake Dive


The dipping of the front of the car under heavy braking application. The tendency is limited by the suspension system and has the positive advantage of helping to prevent the front wheels locking.
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Brake Drag


Retarding effect of incorrectly-adjusted brakes where the friction material is touching the brake drums. The term is sometimes used when a faulty brake does not fully clear the drum when the brake pedal pressure has been taken off.
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Brake Drum


Brake Drum
Cast-iron drum which is part of the braking system. The inside of the drum is machined to an accurate finish and the brake shoes, bearing against this surface, retard the speed of the car. The brake drum may also carry the road wheel. Drum brakes are nearly always confined to the rear wheels, disc brakes being used at the front on most cars manufactured today.
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Brake Drum Glaze


The result of friction between the brake lining and drum which causes a rise in temperature. Brakes which are consistently lightly applied keep temperatures down to a comparatively low level and a resulting chemical reaction places a hard layer on the surface of the linings. This layer has a much lower friction effect than desirable, resulting in relatively inefficient brakes. The glaze can be removed by the use of a coarse file or by heavy and repeated application of the brakes.
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Brake Fluid


The fluid used in hydraulic brake systems. It has no corrosive effect on rubber and has a high boiling point. Brake fluid has an affinity for water which, after a period usually reckoned to be 18 months, results in its becoming contaminated and needing replacement.
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