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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At even slightly lower speeds than maximum, the total drag on the vehicle is considerably less, and the engine needs to deliver this greatly reduced amount of power.

In the automotive aftermarket you can also retrofit overdrive to existing early transmissions. The power produced by an engine increases with the engine’s RPM to a maximum, then falls away.

A car’s speed is limited by the power required to drive it against air resistance, which increases with speed. By using this site, you agree to the Terms of Use and Privacy Policy. It may also be advantageous to switch it off if engine braking fairdy desired, for example when driving downhill. In other projects Wikimedia Commons.

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

These had a direct 1: The driveshaft is usually a hollow metal tube that requires balancing to reduce vibration and contains no overdrivw bracing.

Such add-on overdrive boxes were available from the s to the s for cars and light trucks. Given a curve describing the overall drag on the vehicle, it is simple to find the speed at which the total drag forces are the same as the maximum power of the engine. manuzl

Often the final drive ratio varied between models within a range, a “sports” model having a lower ratio. Retrieved from ” https: In the U.

When engaged, the overdrive would drop the revs from by RPM, or from the drop would be RPM to net. An overdrive consists of an electrically or hydraulically operated epicyclic gear train bolted behind the transmission unit.

In an era when cars were not able to travel very fast, the maximum power point might be near enough to the desired speed that additional gears were not needed. Every cycle of the engine leads to wear, so keeping the engine at higher RPM is also unfavorable for engine life.


Final drive ratios of 4: This is overdrivr as the point of maximum power. As the desire for better fuel economy grew, especially after the oil crisisthe need for a “cruising gear” became more pressing.

The automatic transmission automatically shifts from OD to direct drive when more load is present. With the use of front-wheel drive layouts, the gearbox and final drive are combined into a single transaxle. If a vehicle is equipped with a bolt-on overdrive fajrey. Borg Warner provided the box that was factory-installed between the transmission and a foreshortened driveshaft.

In these cases, there is no separately overdruve “overdrive” unit. In the days before automatic transmissions were common, especially in the s, many rear-wheel drive American cars were available with an overdrive option. The purpose of such a gear may not be immediately obvious. The reason for this separation of duties between the front and back of the car was to allow the drive shaft to run at lower torque, by using higher RPM.

Although adding the cruising gear to the main gearbox was possible, it was generally simpler to add a separate two-gear overdrive system to the existing gearbox. Articles needing additional references from May All articles needing additional references All articles with unsourced statements Articles with unsourced statements from March Commons category link is on Wikidata Use dmy dates from January 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 obvious solution to this problem would be to add more gears to the transmission. Today, most petrol and diesel cars and trucks come with an overdrive transmission because of the benefit to fuel economy. At the maximum possible speed, the engine is running at its point of maximum power, or power peakand the car is traveling at the speed where air resistance equals that maximum power.

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This page was last edited on 13 Septemberat Indeed, in modern vehicles this is common. 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. But as more powerful cars appeared, especially during the s, this disparity between the maximum power point and desired speed grew considerably.

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 P-type overdrive marked the last updates and included both a Gear Vendors U. From Wikipedia, the free encyclopedia. Another British company, the former aircraft builder Faireybuilt a successful all-mechanical unit for the Land Roverwhich is still in production in America today.


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.

Overdrive (mechanics)

In this case gear changing is still possible in all gears, even with overdrive disconnected. Overdrive simply adds effective ranges to the gears, thus overdrive third and fourth become in effect “third-and-a-half” and a fifth gear. There is no longer a drive shaft between them and so the notion of “direct drive” isn’t applicable. In an era when different models of car with different wheel sizes could be accommodated by simply changing the final drive ratio, it made sense for all transmissions to use direct drive overdriive the highest gear.

Fairey Overdrive Fitting Instructions

The first unit to be created was the A-type overdrive, which was fitted to many sports cars during the s, and into the late s. The system was devised by Captain Edgar J de Normanville —[2] and made by Laycock through a chance meeting with a Laycock Products Engineer.

Overall drivetrain reduction comes down to three basic factors: American cars with large-slow-revving engines would use higher ratios, European compact cars with small high-revving engines were lower. If one is not supplied, the engine is forced to run at a higher RPM than optimal. With the early development of cars and the almost universal rear-wheel drive layout, the final drive i.

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