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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Overdrive (mechanics)

One should refer to the car’s owner’s manual for the proper speed to run at overdrive. 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. When engaged, the overdrive would drop the fairry from by RPM, or from the drop would be RPM to net.

This allows the vehicle to achieve better fuel efficiency, and often quieter operation on the highway. Final drive ratios of faairey 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.

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

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. All engines have a range of peak efficiency and it is possible for the use of overdrive to keep the engine out of 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.

The final drive then took this output and adjusted it in a fixed-ratio transmission arrangement that was much simpler to build.

As noted earlier, however, this would cause the engine to operate at too high an RPM for efficient cruising. 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. When it is off, the automatic transmission shifting is limited to the lower gears. 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.


This defines the maximum speed the vehicle is able to reach.

Fairey Overdrive Fitting Instructions

The system features an oil pressure operated device attached to the back of the standard gearbox operating on the gearbox output shaft. GKN or Gear Vendors as opposed to having an overdrive built in overdfive will typically have the option to use the overdrive in more gears than just the top gear. The vehicle’s owner’s manual will often contain information and suitable procedures regarding such situations, for each given vehicle. This was particularly important in the early days of cars, as their straight-cut gears were poorly finished, noisy and inefficient.

Often the final drive ratio varied between models within a range, a “sports” model having a lower ratio. Since the overdrive function, if enabled, could be shifted by simply easing up on the accelerator without depressing the clutch pedalthe action was much like a semi-automatic.

An overdrive consists of an electrically or hydraulically operated epicyclic gear train bolted behind the transmission unit. 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.

There is no longer a drive shaft between them and so the notion of “direct drive” isn’t applicable. 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. This not only meant that it could be tuned for different vehicles, but had the faigey advantage that it could be offered as an easily installed mabual.

The vast majority of overdrives in European cars were invented and developed by oerdrive man called de Normanville and manufactured by an English company called Laycock Engineering later GKN Laycockat its Little London Road site in Sheffield. The purpose of such a gear may not be immediately obvious.

In this case gear changing is still possible in all gears, even with overdrive disconnected. This may create unpleasant vibrations at high speeds and possible destruction of the driveshaft due to the centripetal forces or uneven balance.

The automatic transmission automatically shifts from OD to direct drive when more load is present. In the conventional mankal drive layoutthe transmission system normally contained two sections, the “gearbox” or “transmission” fakrey behind the engine, and the “final drive” mounted in the rear axle at the rear of the car.


There is no longer nanual propeller shaft and so one meaning of “overdrive” can no longer be applied.

With the popularity of front wheel drive cars, the separate gearbox and final drive have merged into a single transaxle. The gearbox was designed so that, for efficiency, the fastest ratio would be a “direct-drive” or “straight-through” 1: The Volvo version oveedrive the same package size as the J-type but with the updated 18 element freewheel and stronger splines through the planet carrier.

This is known as the point of maximum power. The system was devised by Captain Edgar J de Normanville —[2] and made by Laycock through a chance meeting with a Laycock Products Engineer. In other projects Wikimedia Commons.

Overdrive (mechanics) – Wikipedia

Wikimedia Commons has media related to Overdrives. In the days before automatic transmissions were common, especially in the s, many rear-wheel drive American cars were available with an overdrive option.

In the automotive aftermarket you can also retrofit overdrive to existing early transmissions.

As power is the product of RPM and torquerunning the shaft at higher RPM allowed more power to be transferred at lower torque. The power needed to propel a car at any given set of conditions and speed is straightforward to calculate, based tairey on the total weight and the vehicle’s speed. The former varies roughly with the speed of the vehicle, while the latter varies with the square of the speed.

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

A car’s speed is limited by the power required to drive it against air resistance, which faire with speed.