'Service Manual For The Land Rover Overdrive'
The Fairey 'Superwinch' Overdrive..
This detailed Illustrated manual is for the Land Rover Overdrive Unit For The Land Rover Series I, II and III standard Gearbox..
DON'T GET CAUGHT OUT!
KNOW EXACTLY WHAT GOES WHERE!
This is a fully illustrated Manual covering the Land Rover Overdrive Unit showing you how to remove and refit the unit, it also includes an overdrive parts numbers list for reference.
Publication Part No. 811/RTC8020 ENG
Published by Rover Technical Communication
Rover Group Limited..
What Is An Overdrive?
An over drive is like fitting a 5th gear to a 4 speed Land Rover gear box.
It does this by reducing the final drive ratio by 0.7821 : 1. As a result you can theoretically gain 27.88% speed, that is from 55mph to 70 mph.
Of course the drive ratio will not result in this linear extension of speed as other factors come into play such as tyre drag and wind resistance.
The major benefit is one of fuel economy again up to 27.88% in theory.
Best of all an overdrive reduces wear and tear on the engine and drive train components of your vehicle and reduces the rpm’s so reduces noise level. I think you end up with eight forward gears, and two reverse gears, in each ratio that’s at least 26 gears to play with..
History..
Early manual automotive transmissions were limited to three or sometimes four speeds, with only the most sophisticated being five speeds.
This left an unfulfilled need for a higher gear ratio for highway cruising, which was filled by the addition of separate overdrive units.
However, automotive manual transmissions manufactured since the 1980s tend to include a larger selection of gear ratios than before, the highest of which is usually greater than 1:1.
This trend has rendered overdrives a complex and obsolete solution to economy gearing in automobiles, and very few cars are fitted with them today, although they still appear on large trucks, where more gear ratios are always in demand..
Usage..
Generally speaking, overdrive (OD) is the highest gear in the transmission. Most automatic transmissions have three speeds and overdrive (fourth speed). Overdrive allows the engine to operate at a lower rpm for a given road speed. This allows the vehicle to realize better fuel efficiency, and often quieter operation on the highway.
When you switch it on, you allow the transmission to shift into overdrive mode after the certain speed is reached (usually 70+ km/h [45+ mph] depending on the load).
When it is off, the transmission shifting is limited to the lower gears. For normal driving conditions, operation of the overdrive should be enabled only if the average speed is above 70 km/h (approx. 43 MPH).
It may be necessary to switch it off if the vehicle is being operated in a mountainous area.
The automatic transmission automatically shifts from OD to third gear when more load is present. When less load is present, it shifts back to OD.
Under certain conditions, e.g.: driving uphill or towing a trailer, the transmission may "hunt" between OD and the third gear, shifting back and forth. In this case, switching it off can help the transmission to 'decide'. It may also be advantageous to switch it off if engine braking is desired, for example, driving downhill. The vehicle's owner's manual has information and procedures regarding such situations..
How An Overdrive Works?
The overdrive consists of an electrically or hydraulically operated epicyclic gear train bolted behind the transmission unit.
It can either couple the input driveshaft directly to the output shaft (or propeller shaft) (1:1), or increase the output speed so that it turns faster than the input shaft (1:1 + n).
Thus the output shaft may be "overdriven" relative to the input shaft. In newer transmissions, the overdrive speed(s) are typically as a result of combinations of planetary/epicyclic gearsets which are integrated in the transmission.
In these cases, there is no separately identifiable "overdrive" unit. A number of such transmissions and transaxles are manufactured by Aisin, for use in vehicles produced by many different manufacturers.
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. Newer vehicles have electronic overdrive in which the computer automatically adjusts to the conditions of power need and load..
Specification..
This is for a digital manual, number 811/RTC8020. It is a new reproduction in digital form hence no oily fingerprints, rips or tears.
If you lose or damage it just print off another or select the page you need as and when.
With essential fitting and maintenance instructions, including parts list / numbers, many good informative illustrations, technical data and operating instructions.
Commonly seeno on many Land Rover models including the Land Rover series I, II, and III.
Also Includes: Land Rover Gear Ratios..
This Manual eBook Fully Covers the Land Rover
Fairey 'Superwinch' Overdrive.
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