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  • Layshaft

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    Sectioned 3-speed manual 'crash' gearbox, for a car c. 1935 A layshaft is an intermediate shaft within a gearbox that carries gears, but does not transfer the primary drive of the gearbox either in or out of the gearbox. Layshafts are best known through their use in car gearboxes, where they were a ubiquitous part of the rear-wheel drive layout. With the shift to front-wheel drive, the use of layshafts is now rarer. The driving shaft carries the input power into the gearbox. The driven shaft is the output shaft from the gearbox. In car gearboxes with layshafts, these two shafts emerge from opposite ends of the gearbox, which is convenient for RWD cars but may be a disadvantage for other layouts. For gearboxes in general, gear clusters mounted on a layshaft may either turn freely on a fixed shaft, or may be part of a shaft that then rotates in bearings. There may be multiple separate clusters on a shared shaft and these are allowed to turn freely relative to each other.

  • Shift time

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    Shift time refers to the time interval between gear changes in a transmission. This interval is the time in which power delivery is interrupted and engine speed is reduced or increased to synchronize speed for the next selected gear. Shift time is usually in reference to motor vehicles but can apply to any gearbox. Reducing shift time is important in performance vehicles or race cars because the shifting process generally interrupts power delivery to the wheels. Shift time in a manual gearbox is dependent on the driver, but in automatic or semi-automatic cars the electronic or hydraulic control mechanism must be calibrated and tuned to deliver a fast gear change. Generally, a dual-clutch transmission (DCT) shifts faster than a standard automatic or semi-automatic transmission. This is possible because the DCT can pre-select the next gear change and switch between two separate clutches to the next pre-determined gear, thus reducing shift times. Using a freewheel may reduce shift time as it may not be necessary to use the clutch. A shift kit is also intended to reduce the shift time of a manual vehicle.

  • Close-ratio transmission

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    A close-ratio transmission is a vehicle transmission in which the difference between the gear ratios of the gears is minimized relative to other transmissions used in similar vehicles. The use of "close" describes nearness rather than open-ness (i.e. open vs close). There is no industry standardization between manufacturers as to what constitutes a close-ratio transmission. Therefore, a transmission that one manufacturer terms close-ratio may not necessarily be considered close-ratioed by another manufacturer.

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