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

Under certain conditions, for example driving uphill, or towing a trailer, the transmission mannual “hunt” between OD and the next highest gear, shifting back and forth. Borg Warner provided the box that was factory-installed between the transmission and a foreshortened driveshaft. The most 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.

The reason manuzl 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. Generally speaking, overdrive is the highest gear in the transmission.

Overdrive (mechanics) – Wikipedia

In these cases, there is no separately identifiable “overdrive” unit. There is no longer a propeller shaft and so one meaning of overdgive can no longer be applied.

Achieving an overdriven ratio for cruising thus required a gearbox ratio even higher than this, i. In the U. The purpose of such a gear may not be immediately obvious. With the early development of cars and the almost universal rear-wheel drive layout, the final drive i.


A car’s speed is limited by the power required to drive it against air resistance, which increases with speed. The vehicle’s owner’s manual will often contain information and suitable procedures fajrey such situations, for each given vehicle. The power produced by an engine increases with the engine’s RPM to a maximum, then falls away. The point of maximum power is somewhat lower than the absolute maximum RPM to which the engine is limited, the ” redline ” RPM.


Although adding the cruising gear to the main gearbox was possible, it faire generally simpler to add a separate two-gear overdrive system to the existing gearbox. A knob connected to a bowden cablesimilar to some emergency brake applications, was also provided to ovetdrive out the unit mechanically.

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

This is known as the point of maximum power. 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 former varies roughly with the speed of the vehicle, while the latter varies with the square of the speed. Another British company, the former aircraft manhal Faireybuilt a successful all-mechanical unit for the Land Roverwhich is still in production in America today.

The higher speeds on the driveshaft and related parts can cause heat and wear problems if an overdrive and high differential gearing or even very small tires are combined, and create unnecessary friction.

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. Overdrive allows the engine to maanual at a lower RPM for a given road speed. Such add-on overdrive boxes were available from the s to the s for cars and light trucks.

The system features an oil pressure operated device attached to the back of the standard gearbox operating on manhal gearbox output shaft. If one is not supplied, the engine is forced to run at a higher RPM than optimal. The obvious solution to this problem would be to add more gears to the transmission. However the fundamental meaning, that of an overall ratio higher than the ratio for maximum speed, still applies. This defines the maximum speed the vehicle is able to reach.

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.

As the fzirey for better fuel economy grew, especially after the oil crisisthe need for a “cruising gear” became more pressing. When engaged, the overdrive would drop the revs from by RPM, or from the drop would be RPM to net.


Overdrive (mechanics)

Therefore, a car needs one gearing to reach maximum speed but another to reach maximum fuel efficiency at a lower speed. 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 mmanual of most gearboxes was 1: Given a curve describing the overall drag on the vehicle, it is simple to find the speed at which the total drag manua are the same as the maximum power of the engine.

Newer vehicles have electronic overdrive in which the computer automatically adjusts to the conditions of power need and load.

It is also why more than one overdrive gear is seldom seen in a vehicle except in special circumstances i. Views Read Edit View history. As power is the product of RPM and torquerunning the shaft at higher RPM allowed more power to be transferred at lower torque. overdeive

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. An overdrive consists of an electrically or hydraulically operated epicyclic gear train bolted behind the transmission unit. Doing so reduced the torque the driveshaft had to overdrivd, and thus the strength and weight it required. This allows the vehicle to achieve better fuel efficiency, and often quieter operation on the highway.

Indeed, in modern vehicles this is common. When using overdrive gearing, the car’s engine speed drops, reducing wear and normally saving fuel. A transmission with a gear ratio of 4: Overdrive simply adds effective ranges to the gears, thus overdrive third and fourth become in effect “third-and-a-half” and a fifth gear.