Download file Free Book PDF Land Rover Overdrive Manual at Complete Installation Manual Series Land Rovers Options Fairey Overdrive. OVERDRIVE UNIT AND SELECTOR MECHANISM. -. Ye |. 17 Gasket, overdrive to transfer box. Dipstick FITTING INSTRUCTIONS. (in). Fairey Overdrive Fitting Instructions. Page history last edited by Stephen Jarman 10 years ago. Download: Fairey Overdrive Fitting

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Fairey Overdrive Fitting Instructions

The overdriv fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is over-gearedand cannot reach its potential top speed, i.

As noted earlier, however, this would cause the engine to operate at too high an RPM for efficient cruising.

Anatomy of the Motor Car. When engaged, the overdrive would drop the revs from by RPM, or from the drop would be RPM to net.

With the early development of cars and the almost universal rear-wheel drive layout, the final drive i. For other uses, see Overdrive. A car’s speed is fzirey by the power required to drive ovwrdrive against air resistance, which increases with speed. Doing so reduced the torque the driveshaft had to carry, and thus the strength and weight it required.

Borg Warner provided the box that was factory-installed between the transmission and a foreshortened driveshaft. Wikimedia Commons has media related to Overdrives. This article relies largely or entirely on a single source.

GKN or Gear Vendors as opposed to having an overdrive built in one will typically have the option to use the overdrive in more gears than just the top gear.

How Do I? – Fairey Overdrive manual PDF | Land Rover UK Forums

However the fundamental meaning, that of an overall ratio higher than the ratio for maximum speed, still applies. The P-type overdrive marked the last updates and included both a Gear Vendors U. In this case gear changing is still possible in all gears, even with overdrive disconnected. The former varies roughly with the speed of the vehicle, while the latter varies with the square of the speed.

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. This is part of the reason that modern automobiles tend to have larger numbers of gears in their transmissions. Overdrive is a term used to describe the operation of an automobile cruising at sustained speed with reduced engine revolutions per minute RPMleading to better fuel consumption, lower noise, and lower wear.


This was particularly important in the early days of cars, as their straight-cut gears were poorly finished, noisy and inefficient. Calculating these from first principles is generally difficult due to a variety of real-world factors, so this is often measured directly in wind tunnels and similar systems. Virtually all vehicles cars and trucks have overdrive today whether manual transmission or automatic.

This is known as the point of maximum power. Often the final drive ratio varied between models within a range, a “sports” model having a lower ratio.

When using overdrive gearing, the car’s engine speed drops, reducing wear and normally saving fuel. At mph, or inches per second, the wheel will be turning For instance, the overdrive system applied to a Triumph TR5 operates on 2nd, 3rd and top gear.

Overdrive (mechanics)

Relevant discussion may be found on the talk page. Using overdrive with the main 3-speed transmission in 2nd gear was similar in ratio to 3rd gear, and with the main transmission in 3rd, the overall ratio was fractional i. As the desire for better fuel economy grew, especially after the oil crisisthe need for a “cruising gear” became more pressing. In the automotive aftermarket you can also retrofit overdrive to existing early transmissions. Inthe Laycock Engineering Company introduced the D-type overdrive, which was fitted to a variety of motor cars including Volvo and sSunbeam Alpines and RapiersTriumph Spitfiresand also MGBs those with 3-synchro transmissions.

With the use of front-wheel drive layouts, the gearbox and final drive are combined into a ooverdrive transaxle. Generally speaking, overdrive is the highest gear in the transmission. As popular cars became faster relative to legal limits and fuel costs overdrivw more important, particularly after the oil crisisthe use of 5-speed gearboxes became more common in mass-market cars.

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Overfrive 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. The propeller shaft linking gearbox and rear axle is thus overdriven, and a transmission capable of doing this became termed an “overdrive” transmission.


The vast majority of overdrives in European cars were invented and developed by a man called de Normanville and manufactured by an English company called Laycock Engineering later GKN Laycockat its Little London Road site in Sheffield.

In the U.

As power is the product of RPM and torquerunning the shaft at higher RPM allowed more power to be transferred at mnaual torque. This allows the vehicle to achieve better fuel efficiency, and often quieter operation on the highway. This is chosen for efficiency, as it does not require any gears to transmit power and so reduces the power lost by them.

When it is off, the automatic transmission shifting is limited to the lower gears. Faiirey as more powerful cars appeared, especially during the s, this disparity between the maximum power point and desired speed grew considerably. The power needed to propel 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.

The higher speeds on the driveshaft and related parts can afirey heat and wear problems if an overdrive and high differential gearing or even very small tires are combined, and create unnecessary friction. However, due to historical particularities, this was not always practical.

Thus the output shaft may be “overdriven” relative to the input shaft. Although the designer was theoretically overvrive 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: This defines the oberdrive speed the vehicle is able to reach. All engines have a range of peak efficiency and it is possible for the use of overdrive to keep the engine out ,anual 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.