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

Calculating these from first principles is oveedrive difficult due to a variety of real-world factors, so this is often measured directly in wind tunnels and similar systems. 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.

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 manyal.

The gearbox was designed so that, for efficiency, the fastest ratio would be a “direct-drive” or “straight-through” 1: Newer vehicles have electronic overdrive in which the computer automatically adjusts to the conditions of power need and load.

Views Read Edit View history. 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. 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 Relevant discussion may be found on the talk page.


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

A knob connected to a bowden cablesimilar to some emergency brake applications, was also provided to lock out the unit mechanically.

The rotation speed problem comes into effect when the differential gearing is ooverdrive high ratio and an overdrive is used to compensate. Pverdrive article relies largely or entirely on a single source.

It is also why more than one overdrive gear is seldom seen in a vehicle except in special circumstances i. 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. The system features an oil pressure operated device attached to the back of the standard gearbox operating on the gearbox output shaft.

Fairey Overdrive Fitting Instructions

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.

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.

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

Overdrive (mechanics)

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. Doing so reduced the torque the driveshaft had to carry, and thus the strength and weight it required. 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.


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.

Land Rover Restoration, Tech, Maintenance and Repair – O

With the popularity of front wheel drive cars, the separate gearbox and final drive have merged into a single transaxle. If a vehicle is equipped with a ogerdrive overdrive e.

The automatic transmission automatically shifts from OD fairet direct drive when more load is present. The rotational speed of the wheels for that given forward speed is simple to calculate, it is simply the tire circumference multiplied by the RPM. This meant that cars were often operating far from their most efficient point.

There is no longer a drive shaft between them and so the notion of “direct drive” isn’t applicable. It can either couple the input driveshaft directly to the output shaft or propeller shaft overdeive The vehicle’s owner’s manual will often contain information and suitable procedures regarding such situations, for each given vehicle.

These produce two primary forces slowing the car: This is known as the point of maximum power. In other projects Wikimedia Commons. Overdrive allows the engine to operate at a lower RPM for a given road speed.