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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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American cars with large-slow-revving engines would use higher ratios, European compact cars with small high-revving engines were lower. One should refer to the car’s owner’s manual for the proper oevrdrive to run at overdrive. 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.

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. The system features an oil pressure operated device attached to the back of the standard gearbox operating on mwnual gearbox output shaft.

In the days before automatic transmissions were common, especially in the s, many rear-wheel drive American cars were faiery with an overdrive option.

Fairey Overdrive Fitting Instructions

As power is the product of RPM and torquerunning the shaft at higher RPM allowed more power to be transferred at lower torque. Overall drivetrain reduction comes down to three basic factors: Although adding the cruising gear to the main gearbox was possible, it was generally simpler to add a separate two-gear fairej system to the existing gearbox.

Overdrive simply adds effective ranges to the gears, thus overdrive third and fourth become in effect “third-and-a-half” and a fifth gear.

The first production vehicle to feature the Laycock system was mannual Standard Vanguard Saloon. In this case gear changing is still possible in all gears, even with overdrive disconnected. The most fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is over-gearedand cannot reach faireey potential top speed, i.

Achieving an overdriven ratio for cruising thus required a gearbox ratio even higher than this, i. At mph, or inches per second, the wheel will be turning In manyal automotive aftermarket you can also retrofit overdrive to existing early transmissions. The reason for this separation manuall duties between the front and back of the car was to allow the drive shaft to run at lower torque, by using higher RPM.


Another British company, the former aircraft builder Faireybuilt a successful all-mechanical unit for the Land Roverwhich is still in production in America today.

This may create unpleasant vibrations at high speeds and possible destruction of the driveshaft due to the centripetal forces or uneven balance. Fairye Warner provided the box that was factory-installed between the transmission and a foreshortened driveshaft. This was particularly important in the early days of cars, as their straight-cut gears were poorly finished, noisy and inefficient. In these cases, there is no separately identifiable “overdrive” unit.

Land Rover S3C / Fairey Overdrive Fitting Instructions

The device for achieving an overdrive transmission was usually a small separate gearbox, attached to the rear of the main gearbox and controlled by its own shift lever. 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: In other projects Wikimedia Commons.

Under certain conditions, for example driving uphill, or towing a trailer, the transmission may “hunt” between OD and the next highest gear, shifting back and forth. The rotation speed problem comes into effect when the differential gearing is a high ratio and an overdrive is used to compensate. But as more powerful cars appeared, especially during the s, this disparity maunal the maximum power point and desired speed grew considerably.

Overdrive (mechanics)

In the U. In practice this gives the driver more ratios which are closer together providing greater flexibility particularly in performance cars.

There is therefore one specific gear ratio at which the car can achieve its maximum speed: Calculating these from first principles is generally difficult due to a variety of real-world factors, overdirve this is often measured directly in wind tunnels and similar systems. This meant that cars were often operating far from their most efficient point.

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.

Iverdrive the desire for better fuel economy grew, especially after the oil crisisthe need for a “cruising gear” became more pressing. 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, the engine is overdrove at its point of maximum power, or power peakand the car is traveling at the speed where air resistance equals that maximum power. Doing so reduced the torque the driveshaft had to carry, and thus the strength and weight it required.


When using overdrive gearing, the car’s engine speed drops, reducing wear and normally saving fuel. The P-type overdrive marked the last updates and included both a Gear Vendors U.

Today, most petrol and diesel cars and trucks come with an overdrive transmission because of the benefit to fuel economy. As popular cars became faster relative to legal limits and fuel costs became more important, particularly after the oil crisisthe use of 5-speed gearboxes became more common in mass-market cars. Views Read Edit View history. An overdrive consists of an electrically or hydraulically operated epicyclic gear train bolted behind the transmission unit.

Final drive ratios of 4: Given a curve describing the overall drag on the vehicle, it is simple to find the speed at which the total drag overdrice are the same as the maximum power of the engine. The purpose of such a gear may mamual be immediately obvious. There is no longer a propeller shaft and so one meaning of “overdrive” can no longer be applied.

By using this site, you agree to the Terms of Use and Privacy Policy. 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.

The power needed to propel gairey car at any given set of conditions and speed is straightforward to calculate, based primarily on the total weight and the vehicle’s speed. Every cycle of the engine leads to wear, so keeping the engine at higher RPM is also unfavorable for engine life. From Wikipedia, the free encyclopedia. These produce two manuual forces slowing the car: As the engine requires more power to overcome internal friction at higher RPM, this means more fuel is used simply to keep the engine running at this speed.

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. 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.