Here at engines and gearboxes we are able to assist you in finding the right used gearbox or reconditioned gearboxes. By using us, you are able to put your request for a gearbox forward to multiple breakers throughout the UK. This saves you the hassle of having to contact scrap yards or breaker yards to find the right gearbox for your car. All our gearboxes are supplied with a 100% money back guarantee.
What are Gearboxes?
Using the principle of mechanical advantage, a transmission or gearbox provides a speed-torque conversion (commonly known as “gear reduction” or “speed reduction”) from a higher speed motor to a slower but more forceful output or vice-versa. Early gearboxes included the right-angle drives and other gearing in windmills, horse-powered devices, and steam engines, in support of pumping, milling, and hoisting.
Most modern gearboxes are used to increase torque while reducing the speed of a prime mover output shaft (e.g. a motor drive shaft). This means that the output shaft of a gearbox will rotate at slower rate than the input shaft. This reduction in speed will produce a mechanical advantage, causing an increase in torque. A gearbox can be setup to do the opposite and provide an increase in shaft speed with a reduction of torque.
Some of the simplest gearboxes merely change the physical direction in which power is transmitted. Many typical automobile gearboxes include the ability to select one of several different gear ratios. In this case, most of the gear ratios (simply called “gears”) are used to slow down the output speed of the engine and increase torque. However, the highest gears may be “overdrive” types that increase the output speed.
Uses Gearboxes have found use in a wide variety of different—often stationary—applications, such as wind turbines. Gearboxes are also used in agricultural, industrial, construction, mining and automotive equipment. In addition to ordinary transmission equipped with gears, such equipment makes extensive use of the hydrostatic drive and electrical adjustable-speed drives.
Automotive basics
The need for a transmission in an automobile is a consequence of the characteristics of the internal combustion engine. Engines typically operate over a range of 600 to about 7000 revolutions per minute (though this varies, and is typically less for diesel engines), while the car’s wheels rotate between 0 rpm and around 1800 rpm. Furthermore, the engine provides its highest torque outputs approximately in the middle of its range, while often the greatest torque is required when the vehicle is moving from rest or travelling slowly.
Therefore, a system that transforms the engine’s output so that it can supply high torque at low speeds, but also operate at highway speeds with the motor still operating within its limits, is required. Gearboxes perform this transformation. Most gearboxes and gears used in automotive and truck applications are contained in a cast iron case, though sometimes aluminium is used for lower weight.
There are three shafts: a main shaft, a countershaft, and an idler shaft. The main shaft extends outside the case in both directions: the input shaft towards the engine, and the output shaft towards the rear axle (on rear wheel drive cars- front wheel drives generally have the engine and transmission mounted transversely, the differential being part of the transmission assembly.) The shaft is suspended by the main bearings, and is split towards the input end.
At the point of the split, a pilot bearing holds the shafts together. The gears and clutches ride on the main shaft, the gears being free to turn relative to the main shaft except when engaged by the clutches. Types of automobile gearboxes include manual, automatic or semi-automatic transmission.
Manual transmission come in two basic types:
A simple but rugged sliding-mesh or unsynchronized / non-synchronous system, where straight-cut spur gear sets are spinning freely, and must be synchronized by the operator matching engine revs to road speed, to avoid noisy and damaging “gear clash”
And the now common constant-mesh gearboxes which can include non-synchronised, or synchronized / synchromesh systems, where diagonal cut helical (and sometimes double-helical) gear sets are constantly “meshed” together, and a dog clutch is used for changing gears. On synchromesh boxes, friction cones or “synchro-rings” are used in addition to the dog clutch.
The former type is commonly found in many forms of racing cars, older heavy-duty trucks, and some agricultural equipment. Manual gearboxes dominate the car market outside of North America. They are cheaper, lighter, usually give better performance, and fuel efficiency (although the latest sophisticated automatic gearboxes may yield results slightly better than the ones yielded by manual gearboxes). It is customary for new drivers to learn, and be tested, on a car with a manual gear change.
In Malaysia, Denmark and Poland all cars used for testing (and because of that, virtually all those used for instruction as well) have a manual transmission. In Japan, the Philippines, Germany, Italy, Israel, the Netherlands, Belgium, New Zealand, Austria, the UK, Ireland, Sweden, France, Spain, Switzerland, Australia, Finland and Lithuania , a test pass using an automatic car does not entitle the driver to use a manual car on the public road; a test with a manual car is required.
Manual gearboxes are much more common than automatic gearboxes in Asia, Africa, South America and Europe.Non-synchronousThere are commercial applications engineered with designs taking into account that the gear shifting will be done by an experienced operator. They are a manual transmission, but are known as non-synchronized gearboxes. Dependent on country of operation, many local, regional, and national laws govern the operation of these types of vehicles.
This class may include commercial, military, agricultural, or engineering vehicles. Some of these may use combinations of types for multi-purpose functions. An example would be a PTO, or power-take-off gear. The non-synchronous transmission type requires an understanding of gear range, torque, engine power, and multi-functional clutch and shifter functions. Also see Double-clutching, and Clutch-brake sections of the main article at non-synchronous gearboxes.
Automatic
Most modern North American, and many larger, high specification German cars have an automatic transmission that will select an appropriate gear ratio without any operator intervention. They primarily use hydraulics to select gears, depending on pressure exerted by fluid within the transmission assembly. Rather than using a clutch to engage the transmission, a fluid flywheel, or torque converter is placed in between the engine and transmission.
It is possible for the driver to control the number of gears in use or select reverse, though precise control of which gear is in use may or may not be possible. Automatic gearboxes are easy to use. In the past, automatic gearboxes of this type have had a number of problems; they were complex and expensive, sometimes had reliability problems (which sometimes caused more expenses in repair), have often been less fuel-efficient than their manual counterparts (due to “slippage” in the torque converter), and their shift time was slower than a manual making them uncompetitive for racing.
With the advancement of modern automatic gearboxes this has changed. Attempts to improve the fuel efficiency of automatic gearboxes include the use of torque converters which lock up beyond a certain speed, or in the higher gear ratios, eliminating power loss, and overdrive gears which automatically actuate above certain speeds; in older gearboxes both technologies could sometimes become intrusive, when conditions are such that they repeatedly cut in and out as speed and such load factors as grade or wind vary slightly.
Current computerized gearboxes possess very complex programming to both maximize fuel efficiency and eliminate any intrusiveness. For certain applications, the slippage inherent in automatic gearboxes can be advantageous; for instance, in drag racing, the automatic transmission allows the car to be stopped with the engine at a high rpm (the “stall speed”) to allow for a very quick launch when the brakes are released; in fact, a common modification is to increase the stall speed of the transmission. This is even more advantageous for turbocharged engines, where the turbocharger needs to be kept spinning at high rpm by a large flow of exhaust in order to keep the boost pressure up and eliminate the turbo lag that occurs when the engine is idling and the throttle is suddenly opened.
Semi-automatic
The creation of computer control also allowed for a sort of cross-breed transmission where the car handles manipulation of the clutch automatically, but the driver can still select the gear manually if desired. This is sometimes called a “clutchless manual,” “dual-clutch,” or “automated manual” transmission. Many of these gearboxes allow the driver to give full control to the computer. They are generally designed using manual transmission “internals”, and when used in passenger cars, have synchromesh operated helical constant mesh gear sets. Specific type of this transmission includes: Easy tronic, Gear tronic, and Direct-Shift Gearbox. There are also sequential gearboxes which use the rotation of a drum to switch gears
