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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By using this site, you agree to the Terms of Use and Privacy Policy. In other projects Wikimedia Commons. In the days before automatic transmissions were common, especially in the s, many rear-wheel drive American cars were available with an overdrive option. This article relies largely or entirely on a single source. 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. Borg Warner provided the box that was factory-installed between the transmission and a foreshortened driveshaft.

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

It is also why more than one overdrive gear is seldom seen in a vehicle except in special circumstances i. When using overdrive gearing, the car’s engine speed drops, reducing wear and normally saving fuel.

The vehicle’s owner’s manual will often contain information and suitable procedures regarding such situations, for fajrey given vehicle.

Land Rover S3C / 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. Another British company, the former aircraft builder Faireybuilt a successful all-mechanical unit for the Land Roverwhich is overrive in production in America today. In this case gear changing is still possible in all gears, even with overdrive disconnected.

However, due to historical particularities, this was not always practical.

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This is chosen for efficiency, as it does not require any gears to transmit power and so reduces the power lost by them. The first production vehicle to feature the Laycock system was the Standard Vanguard Saloon. If one runs the same RPM transmission exercise outlined above for maximum speed, but instead sets the “maximum speed” to that of highway cruising, the output is a higher gear ratio that provides ideal fuel mileage.

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Overdribe is no longer a propeller shaft and so one meaning of “overdrive” can no longer be applied. The impetus is to minimize overdrive use and provide a higher ratio first gear, which means more gears between the first and the last to keep the engine at its most efficient speed. Please help improve this article by introducing citations to additional sources.

The Overdgive overdrive marked the last updates and included both a Gear Vendors U. For other uses, see Overdrive. When it is off, the automatic transmission shifting is limited to the lower gears. The final overdtive then took this output and ovedrrive it in a fixed-ratio transmission arrangement that was much simpler to build. Often the final drive ratio varied between models within a range, a “sports” model having a lower ratio.

Fairey Overdrive Fitting Instructions

In these cases, there is no separately identifiable “overdrive” unit. Virtually all vehicles cars and trucks have overdrive today whether manual transmission or automatic.

Views Read Edit View history. 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. When engaged, the overdrive would drop the revs from by RPM, or from the drop would be RPM to net.

As the desire for better fuel economy grew, especially after the oil crisisthe need for a “cruising gear” became more pressing. A knob connected to a bowden cablesimilar to some cairey brake applications, was also provided to lock out the unit mechanically.

This not only meant that it could be tuned for different vehicles, but had the additional advantage that it could be offered as an easily installed option. The power needed to propel a car at any given set of conditions and speed is manuap to calculate, based primarily on the total weight and the vehicle’s speed.

Generally speaking, overdrive is the highest gear in the transmission. 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.


Doing so reduced the torque the driveshaft had to carry, and thus the strength and weight it required. 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 purpose of such a gear may not be immediately obvious. The point of maximum power is somewhat lower than the absolute maximum RPM to which the engine is limited, the ” redline ” RPM. Therefore, a car needs one gearing to reach maximum speed but another to reach maximum fuel efficiency at a lower speed.

The obvious solution to this problem would be to add more gears to the transmission. American cars with large-slow-revving engines would use higher ratios, European compact cars with small high-revving engines were lower.

Wikimedia Commons has media related to Overdrives. The rotation speed problem comes into effect when the differential gearing is a high ratio and an overdrive is used to compensate. The power produced by an engine increases with the engine’s RPM to a maximum, then falls away. Every cycle of the engine leads to wear, so keeping the engine at higher RPM is also unfavorable for engine life.

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. The gearbox was designed so that, for efficiency, the fastest fiarey would be a “direct-drive” or “straight-through” 1: With the popularity of front wheel drive cars, the separate gearbox and final drive have merged into a single transaxle.

With the early development of overdriv and the almost universal rear-wheel drive layout, the final drive i. This was particularly important in the early days of cars, as overdriv straight-cut gears were poorly finished, noisy and inefficient. In the conventional rear-wheel drive layoutthe transmission system normally contained two sections, the “gearbox” or “transmission” mounted behind the engine, and the “final drive” mounted in the rear axle at the rear of the car.

At mph, or inches per second, the wheel will be turning When less load is present, it shifts back to OD.