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68-635: The truck has a relatively simple manual gear-shift , or alternatively, the Electronic Power Shift (EPS), is available, as well as a fully automatic box. The truck is powered by a 12-litre straight 6 engine ( OM457LA ), or 6.4-litre straight 6 engine ( OM906 ) Originally the Axor was only available as a tractor but with the 2005 facelift , former Atego models over 18t were made part of the Axor Range. Tractor Rigid This truck-related article

136-515: A chess pawn when attached to the gear stick. The shift knob's principal function is the ergonomical interface between driver and the manu. The gear stick, as the name implies, is often just a machined or cast aluminium or steel rod with or without threading the shift knob is fitted on its end. In recent years, manufacturers have increased the variety of shifts knobs available to the consumer from inexpensive plastics to diamond-studded white gold. Overdrive (mechanics) Overdrive

204-522: A Volvo version. The Volvo version kept the same package size as the J-type but with the updated 18 element freewheel and stronger splines through the planet carrier. The Gear Vendors U.S. version uses a larger 1.375 outer diameter output shaft for higher capacity and a longer rear case. Over a period of 40 years, Laycock Engineering manufactured over three and a half million overdrive Units, and over one million of these were fitted to Volvo motorcars. In 2008

272-408: A car at any given set of conditions and speed is straightforward to calculate, based primarily on the total weight and the vehicle's speed. These produce two primary forces slowing the car: rolling resistance and air drag . The former varies roughly with the speed of the vehicle, while the latter varies with the square of the speed. Calculating these from first principles is generally difficult due to

340-419: A central "neutral" position. Some vehicles have a special button to prevent accidental engagement of reverse. Others require that the lever be lifted (e.g. Nissan ), pressed down (e.g. Volkswagen ), or moved with extra force (e.g. BMW ) to engage reverse. In transmissions with reverse directly below fifth, there may be a mechanical lock-out preventing selection of reverse other than from neutral, thus preventing

408-490: A certain speed is reached (usually 70+ km/h [40-45 mph or more] depending on the load). When it is off, the automatic transmission shifting is limited to the lower gears. Overdrive should usually be selected when the average speed is above 70 km/h (40-45 mph). The automatic transmission automatically shifts from OD to direct drive when more load is present. When less load is present, it shifts back to OD. Under certain conditions, for example driving uphill, or towing

476-471: A driver used to a six-speed transmission from engaging reverse while trying to select sixth. Some transmissions also have an electronically controlled error-prevention safeguard that blocks the first and sometimes the second gear from being selected if the vehicle is moving fast enough to exceed the engine's maximum RPM. This gear pattern can also be found on some heavy vehicles – such as lorries and tractors – in which first gear

544-796: A few. Another British company, the former aircraft builder Fairey , built a successful all-mechanical unit for the Land Rover , which is still in production in America today. The first production vehicle to feature the Laycock system was the 1948 Standard Vanguard Saloon. The first unit to be created was the A-type overdrive, which was fitted to many sports cars during the 1950s, and into the late 1960s. Several famous marques used A-type overdrives, including Jaguar, Aston Martin, Ferrari, Austin-Healey, Jensen, Bristol, AC, Armstrong Siddeley and Triumph's TR sports car range, from

612-409: A higher ratio first gear, which means more gears between the first and the last to keep the engine at its most efficient speed. This is part of the reason that modern automobiles tend to have larger numbers of gears in their transmissions. It is also why more than one overdrive gear is seldom seen in a vehicle except in special circumstances i.e. where high (numerical) differential gear is required to get

680-421: A lower gear, with the engine turning at higher RPM. The power produced by an engine increases with the engine's RPM to a maximum, then falls away. The point of maximum power is somewhat lower than the absolute maximum engine speed to which it is limited, the " redline ". A car's speed is limited by the power required to drive it against air resistance, which increases with speed. At the maximum possible speed,

748-440: A physical clutch pedal. Gear sticks are most commonly found between the front seats of the vehicle, either on the center console (sometimes even quite far up on the dashboard ), the transmission tunnel (erroneously called a console shifter when the floor shifter mechanism is bolted to the transmission tunnel with the center console to cover up the shifter assembly when used with a rear or front-wheel drive vehicle), or directly on

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816-404: A shifting linkage due to its shift-by-wire principle. It has the added benefit of allowing for a full width bench-type front seat (though some models with bucket seating as an option include it). It has since fallen out of favor, although it can still be found widely on North American-market pick-up trucks , vans, emergency vehicles (both law enforcement and EMS – the column shifter

884-500: A similar lever is known as a gear selector . A gear stick will normally be used to change gear whilst depressing the clutch pedal with the left foot to disengage the engine from the drivetrain and wheels . Automatic transmission vehicles, including hydraulic (torque converter) automatic transmissions , automated manual and older semi-automatic transmissions (specifically clutchless manuals), like VW Autostick , and those with continuously variable transmissions , do not require

952-478: A single "L" (for "low") position, which will hold the transmission in whatever lower ratio is required for climbing steep grades or for heavy acceleration: P-R-N-D-L . More modern automatic transmissions have employed a "J-gate" (pioneered by Jaguar ) where some gears are on the left-hand "arm", some on the right, and there is a sideways movement at the rear of the pattern. The second-generation Range Rover from 1995 used an "H-gate", with two parallel PRND gates on

1020-527: A trailer, the transmission may "hunt" between OD and the next highest gear, shifting back and forth. In this case, switching it off can help the transmission to "decide". It may also be advantageous to switch it off if engine braking is desired, for example when driving downhill. The vehicle's owner's manual will often contain information and suitable procedures regarding such situations, for each given vehicle. Virtually all vehicles (cars and trucks) have overdrive today whether manual transmission or automatic. In

1088-504: A variety of models, including 1968–1980 MGBs , the MGC , the Ford Zephyr , early Reliant Scimitars , TVRs, and Gilberns . The J-type overdrive was introduced in the late 1960s, and was adapted to fit Volvo, Triumph, Vauxhall/Opel, American Motors and Chrysler motorcars, and Ford Transit vans. The P-type overdrive marked the last updates and was manufactured in a Gear Vendors U.S. version and

1156-407: A variety of real-world factors, so this is often measured directly in wind tunnels and similar systems. The power produced by an engine increases with the engine's RPM to a maximum, then falls away. This is known as the point of maximum power . Given a curve describing the overall drag on the vehicle, it is simple to find the speed at which the total drag forces are the same as the maximum power of

1224-443: Is a stub . You can help Misplaced Pages by expanding it . Gear-shift A gear stick (rarely spelled gearstick ), gear lever (both UK English ), gearshift or shifter (both U.S. English ), more formally known as a transmission lever , is a metal lever attached to the transmission of an automobile . The term gear stick mostly refers to the shift lever of a manual transmission , while in an automatic transmission ,

1292-417: Is achieved through the gearbox ratios, or by an unusually high final drive. Generally speaking, overdrive is the highest gear in the transmission. Overdrive allows the engine to operate at a lower RPM for a given road speed. This allows the vehicle to achieve better fuel efficiency, and often quieter operation on the highway. When it is switched on, an automatic transmission can shift into overdrive mode after

1360-419: Is an extra-low ratio for use in extreme standing-start conditions, and would see little use in normal driving. Automatic transmissions traditionally have had a straight pattern, adopting the classic P-R-N-D gate , with "P" being to the front, topmost position (or "P" all the way to the left on a column-mounted shifter); the corresponding shift positions being: All automatics use some sort of manual override of

1428-611: Is another example. It is a revival of an approach used in the 1950s by the Chrysler push-button PowerFlite and the Packard Touchbutton Ultramatic . A shift knob also known as a gear knob , gear shift knob and stick shift knob is the physical interface between the gear stick and the driver's hand. Made of many materials from simple plastics through to platinum , it comes in many shapes sizes and weights. OEM shift knobs are generally spherical in shape, often resembling

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1496-404: Is instead in a "dog leg" position, to the left and rearwards. There is usually a spring-loading to return the stick to the central position. Reverse gear is commonly positioned in the best choice of location to avoid accidental engagement. A typical manual transmission vehicle, with (for example) five forward gears, will thus have seven possible positions: the five forwards gears, reverse gear, and

1564-467: Is no need to package either remote mechanisms or complex interlocking arrangements. This has allowed designers to replace the gear stick completely with either button, rotary knobs (current Jaguar , Land Rover and Ford models are good examples of this), or a miniaturized gear stick on the center console. This can be seen in some Audis , BMWs and the Lincoln Continental . Japanese finger shift

1632-687: Is retained where a floor shifter is unfeasible due to mounting the mobile data terminal and 2-way radio), and "full-size" US sedans such as the Ford Crown Victoria . A dashboard mounted shift was common on certain French models such as the Citroën 2CV and Renault 4 . Both the Bentley Mark VI and the Riley Pathfinder had their gear lever to the right of the right-hand drive driver's seat, alongside

1700-406: Is the operation of an automobile cruising at sustained speed with reduced engine speed (rpm), leading to better fuel consumption, lower noise, and lower wear. The term is ambiguous. The most fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is over-geared , and cannot reach its potential top speed, i.e. the car could travel faster if it were in

1768-481: Is used simply to keep the engine running at this speed. Every cycle of the engine leads to wear, so keeping the engine at higher RPM is also unfavorable for engine life. Additionally, the sound of an engine is strongly related to the RPM, so running at lower RPM is generally quieter. If one runs the same RPM transmission exercise outlined above for maximum speed, but instead sets the "maximum speed" to that of highway cruising,

1836-545: The English company Laycock Engineering (later GKN Laycock), at its Little London Road site in Sheffield . The system devised by de Normanville was adopted and manufactured by Laycock after his chance meeting with a Laycock Products Engineer. De Normanville overdrives were found in vehicles manufactured by Standard-Triumph , who were first, followed by Ford , BMC and British Leyland , Jaguar , Rootes Group and Volvo to name only

1904-440: The transmission unit. It can either couple the input driveshaft directly to the output shaft (or propeller shaft ) (1:1), or increase the output speed so that it turns faster than the input shaft (1:1 +  n ). Thus the output shaft may be "overdriven" relative to the input shaft. In newer transmissions, the overdrive speed(s) are typically as a result of combinations of planetary/epicyclic gearsets which are integrated in

1972-434: The "gearbox" or "transmission" mounted behind the engine, and the "final drive" mounted in the rear axle at the rear of the car. The reason for this separation of duties between the front and back of the car was to allow the drive shaft to run at lower torque, by using higher RPM. As power is the product of RPM and torque , running the shaft at higher RPM allowed more power to be transferred at lower torque. Doing so reduced

2040-666: The TR2 through to the end of the 1972 model year of the TR6. In 1959, the Laycock Engineering Company introduced the D-type overdrive, which was fitted to a variety of motor cars including Volvo 120 and 1800s , Sunbeam Alpines and Rapiers , Triumph Spitfires , and also 1962–1967 MGBs (those with 3-synchro transmissions). From 1967 the LH-type overdrive was introduced, and this featured in

2108-411: The U.S. company Gear Vendors, Inc. of El Cajon, California purchased all the overdrive assets of GKN to continue production of the U.S. version and all spares for J and P types worldwide. The system features an oil pressure operated device attached to the back of the standard gearbox operating on the gearbox output shaft. Through a system of oil pressure, solenoids and pistons, the overdrive would drop

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2176-437: The additional advantage that it could be offered as an easily installed option. With the use of front-wheel drive layouts, the gearbox and final drive are combined into a single transaxle. There is no longer a drive shaft between them and so the notion of "direct drive" is inapplicable. Although "overdrive" is still referred to, this is now mostly a marketing term to refer to any extra-high ratio for efficient cruising, whether it

2244-529: The automotive aftermarket you can also retrofit overdrive to existing early transmissions. Overdrive was widely used in European automobiles with manual transmission in the 60s and 70s to improve mileage and sport driving as a bolt-on option but it became increasingly more common for later transmissions to have this gear built in. If a vehicle is equipped with a bolt-on overdrive (e.g.: GKN or Gear Vendors) as opposed to having an overdrive built in one will typically have

2312-450: The axle), and tire size. The rotation speed problem comes into effect when the differential gearing is a high ratio and an overdrive is used to compensate. This may create unpleasant vibrations at high speeds and possible destruction of the driveshaft due to the centripetal forces or uneven balance. The driveshaft is usually a hollow metal tube that requires balancing to reduce vibration and contains no internal bracing. The higher speeds on

2380-426: The benefit to fuel economy. Overdrive is included in both automatic and manual transmissions as an extra gear (or two in some cases). When using overdrive gearing, the car's engine speed drops, reducing wear and normally saving fuel. Since 1981 U.S. corporate average fuel economy (CAFE) legislation, virtually all domestic vehicles have included overdrive to save fuel. One should refer to the car's owner's manual for

2448-417: The clutch engaged causes it to lurch forwards or backward since the starter motor by itself produces sufficient torque to move the whole vehicle; this can be highly dangerous, especially if the parking brake is not firmly applied and can be injurious to the starter and drivetrain. Therefore, novice drivers are taught to rock the knob of a manual gearbox from side to side before starting the engine to confirm that

2516-403: The console or on steering column stalks instead. Manual shifters on the steering column, if having only three forward speeds, are typically called a three on the tree , and floor shifters having four forward speeds, are called four-on-the-floor . The lowest of these gears, if set at a much lower ratio than a typical 1st-gear ratio, is often called a granny gear . Starting the car in gear with

2584-451: The days before automatic transmissions were common, especially in the 1950s, many rear-wheel drive American cars were available with an overdrive option. With substantial improvements developed in Muncie, Indiana , by William B. Barnes for production by its Warner Gear Division, BorgWarner provided the box that was factory-installed between the transmission and a foreshortened driveshaft. Since

2652-447: The desire for better fuel economy grew, especially after the 1973 oil crisis , the need for a "cruising gear" became more pressing. The obvious solution to this problem would be to add more gears to the transmission. Indeed, in modern vehicles this is common. However, due to historical particularities, this was not always practical. In the conventional rear-wheel drive layout , the transmission system normally contained two sections,

2720-420: The driver's door, where it was not unknown for British cars to also have their handbrake . ( Left-hand drive models received a column shift.) In some modern sports cars , the gear lever has been replaced entirely by "paddles", which are a pair of levers, usually operating electrical switches (rather than a mechanical connection to the gearbox), mounted on either side of the steering column, where one increments

2788-399: The driveshaft and related parts can cause heat and wear problems if an overdrive and high differential gearing (or even very small tires) are combined, and create unnecessary friction. This is especially important because the differential gears are bathed in heavy oil and seldom provided with any cooling besides air blowing over the housing. The impetus is to minimize overdrive use and provide

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2856-430: The engine is running at its point of maximum power, or power peak , and the car is traveling at the speed where air resistance equals that maximum power. There is therefore one specific gear ratio at which the car can achieve its maximum speed: the one that matches that engine speed with that travel speed. At travel speeds below this maximum, there is a range of gear ratios that can match engine power to air resistance, and

2924-414: The engine. This defines the maximum speed the vehicle is able to reach. The rotational speed of the wheels for that given forward speed is simple to calculate, being the tire circumference multiplied by the RPM. As the tire RPM at maximum speed is not the same as the engine RPM at that power, a transmission is used with a gear ratio to convert one to the other. At even slightly lower speeds than maximum,

2992-445: The final drive ratio, it made sense for all transmissions to use direct drive as the highest gear. As noted earlier, however, this would cause the engine to operate at too high an RPM for efficient cruising. Although adding the cruising gear to the main gearbox was possible, it was generally simpler to add a separate two-gear overdrive system to the existing gearbox. This not only meant that it could be tuned for different vehicles, but had

3060-437: The floor. Some vehicles have a column shift where the lever is mounted on the steering column  – in vehicles with a manual four-speed gearbox such as 1950s Mercedes-Benz cars and all two-stroke Trabants , this is actually a manual gear lever connected to the gearbox with a linkage. In automatic transmission cars, the lever functions more like a gear selector, and, in modern cars, does not necessarily need to have

3128-412: The gear selection system, i.e. the positions to which the gear stick should be moved when selecting a gear. In some older manual transmission vehicles, the knob may incorporate a switch to engage an overdrive ; in some automatic transmission vehicles it may incorporate a switch to engage a special mode such as a sports mode or to disengage overdrive. Both of the above-mentioned switches may also be found on

3196-496: The gear stick. The Land Rover Freelander introduced a button for that company's Hill Descent Control system feature, which uses the brakes to simulate the function of a low-ratio gearbox in steep descents. Traditional four-wheel drive vehicles have one or more additional "shift levers" to engage a low-ratio gearbox (used on tough terrain ), a transfer case (which switches between two- and four-wheel drive), or differential locks. Some more modern traditional vehicles combine

3264-411: The gearbox is in neutral. For the same reason, modern cars require the clutch pedal to be depressed before the starter will engage (though some modern vehicles have a button that disables the clutch start requirement if held down when starting, for rare situations when starting the car in gear is necessary). The latter practice is also useful in extremely cold conditions or with a weak battery, as it avoids

3332-416: The gears up, and the other down. Formula 1 cars used to hide the gear stick behind the steering wheel within the nose bodywork before the modern practice of mounting the "paddles" on the (removable) steering wheel itself. A knob, variously called gear knob, shift knob, gear shift knob or stick shift knob, forms the handle for the gear stick. Typically the gear knob includes a diagram of the shift pattern of

3400-425: The low-ratio gearbox and transfer case into one lever, with 3 positions: 2H (for 2-wheel drive in the standard high-ratio gearbox); 4H (for 4-wheel drive in the standard high-ratio gearbox); and 4L (for 4-wheel drive in the low-ratio gearbox). The shift pattern refers to the layout of the gears. In a typical manual transmission car, first gear is located to the left, and forwards. In many trucks and some sports cars it

3468-406: The most fuel efficient is the one that results in the lowest engine speed. Therefore, a car needs one gearing to reach maximum speed but another to reach maximum fuel efficiency at a lower speed. With the early development of cars and the almost universal rear-wheel drive layout, the final drive (i.e. rear axle ) ratio for fast cars was chosen to give the ratio for maximum speed. The gearbox

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3536-493: The need for the separate overdrive gearbox. With the popularity of front wheel drive cars, the separate gearbox and final drive have merged into a single transaxle . There is no longer a propeller shaft and so one meaning of "overdrive" can no longer be applied. However the fundamental meaning, that of an overall ratio higher than the ratio for maximum speed, still applies: higher gears, with greater ratios than 1:1, are described as "overdrive gears". The power needed to propel

3604-408: The opposing legs of the "H" for both high range and low range ratios, for normal and off-road driving, respectively. Most modern manumatics , such as Alfa Romeo 's Sportronic and Porsche 's Tiptronic , have a traditional automatic shift pattern on the left or right side of the gear selector, along with a connected longitudinal gate with "+" and "-" positions on the other side in which movement of

3672-543: The option to use the overdrive in more gears than just the top gear. In this case gear changing is still possible in all gears, even with overdrive disconnected. Overdrive simply adds effective ranges to the gears, thus overdrive third and fourth become in effect "third-and-a-half" and a fifth gear. In practice this gives the driver more ratios which are closer together providing greater flexibility particularly in performance cars. An overdrive consists of an electrically or hydraulically operated epicyclic gear train bolted behind

3740-458: The output is a higher gear ratio that provides ideal fuel mileage. In an era when cars were not able to travel very fast, the maximum power point might be near enough to the desired speed that additional gears were not needed. But as more powerful cars appeared, especially during the 1960s, this disparity between the maximum power point and desired speed grew considerably. This meant that cars were often operating far from their most efficient point. As

3808-425: The overdrive function, if enabled, could be shifted by simply easing up on the accelerator without depressing the clutch pedal , the action was much like a semi-automatic. Also, an electrically operated solenoid would deactivate the unit via a switch under the accelerator pedal providing the equivalent of the kickdown of the automatic. A knob connected to a bowden cable , similar to some emergency brake applications,

3876-433: The proper speed to run at overdrive. All engines have a range of peak efficiency and it is possible for the use of overdrive to keep the engine out of this range for all or part of the time of its use if used at inappropriate speeds, thus cutting into any fuel savings from the lower engine speed. Overall drivetrain reduction comes down to three basic factors: transmission gearing (including overdrive), differential gearing (in

3944-399: The revs on whatever gears it was used on by 22% (.778). For instance, the overdrive system applied to a Triumph TR5 operates on 2nd, 3rd and top gear. When engaged, the overdrive would drop the revs from 3000 by 666 RPM, or from 3500 the drop would be 777 RPM to 2723 net. The advantages this reduced rpm had on fuel consumption was most often quite near 22% decrease during highway driving. In

4012-475: The shifter forward and backward increments the gears up and down, respectively. This can be useful in snow or dirt conditions, where it may be necessary to start from second gear. With the advent of drive by wire (or more properly, shift by wire ) computer-controlled transmissions (particularly in the case of automatics), the gear stick no longer needs to be mechanically connected to the transmission unit itself, and can, therefore, be made much smaller since there

4080-489: The starter motor also having to turn over a gearbox full of cold and highly viscous oil. Many automatic transmission vehicles have extra controls on the gear stick, or very close by, which modify the choices made by the transmission system depending on engine and road speed, e.g. "sports" or "economy" modes which will broadly speaking allow, respectively, for higher and lower revolutions per minute, before shifting up. Some specialist vehicles have controls for other functions on

4148-421: The torque the driveshaft had to carry, and thus the strength and weight required. Although the designer was theoretically free to choose any ratio for the gearbox and final drive, there is one additional consideration which meant that the top gear of most gearboxes was 1:1 or "direct drive". This is chosen for efficiency, as it does not require any gears to transmit power and so reduces the power lost by them. This

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4216-474: The total drag on the vehicle is considerably less, and the engine needs to deliver this greatly reduced amount of power. In this case the RPM of the engine has changed significantly while the RPM of the wheels has changed very little. Clearly this condition calls for a different gear ratio. If one is not supplied, the engine is forced to run at a higher RPM than optimal. As the engine requires more power to overcome internal friction at higher RPM, this means more fuel

4284-432: The transmission, with numbered positions in descending order marked below (or to the right) of "drive", which will prevent the transmission shifting to a gear higher than the selected, but maintaining automatic operation between all lesser numbered gears. Such gates will appear as P-R-N-D-3-2-1 for example. On some vehicles (mainly Japanese makes such as Honda , Toyota and Lexus ) these numbered positions are replaced by

4352-635: The transmission. For example, the ZF 8HP transmission has 8 forward gears, two of which are overdrive (< 1:1) gear ratios. In older vehicles, it is sometimes actuated by a knob or button, often incorporated into the gearshift knob, and does not require operation of the clutch . Newer vehicles have electronic overdrive in which the computer automatically adjusts to the conditions of power need and load. The vast majority of overdrives in European cars were invented and developed by Edgar de Normanville , and manufactured by

4420-521: Was also provided to lock out the unit mechanically. Using overdrive with the main 3-speed transmission in 2nd gear was similar in ratio to 3rd gear, and with the main transmission in third, the overall ratio was fractional (i.e., "true overdrive"). This was important in reducing wear, tear, noise, and difficulty in control. Such add-on overdrive boxes were available from the 1930s to the 1970s for cars and light trucks. Today, most petrol and diesel cars and trucks come with an overdrive transmission because of

4488-526: Was designed so that, for efficiency, the fastest ratio would be a "direct-drive" or "straight-through" 1:1 ratio, avoiding frictional losses in the gears. Achieving an overdriven ratio for cruising thus required a gearbox ratio even higher than this, i.e. the gearbox output shaft rotating faster than the engine. The propeller shaft linking gearbox and rear axle is thus overdriven, and a transmission capable of doing this became termed an "overdrive" transmission. The device for achieving an overdrive transmission

4556-509: Was particularly important in the early days of cars, as their straight-cut gears were poorly finished, noisy and inefficient. The final drive then took this output and adjusted it in a fixed-ratio transmission arrangement that was much simpler to build. Final drive ratios of 4:1 were common, meaning that the wheels would turn at one fourth the rate they would if directly connected to the engine. In an era when different models of car with different wheel sizes could be accommodated by simply changing

4624-462: Was usually a small separate gearbox, attached to the rear of the main gearbox and controlled by its own shift lever. These were often optional on some models of the same car. As popular cars became faster relative to legal limits and fuel costs became more important, particularly after the 1973 oil crisis , the use of five-speed gearboxes became more common in mass-market cars. These had a direct (1:1) fourth gear with an overdrive fifth gear, replacing

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