| Topic group | Topic | Summary |
| Basic layouts | Front-wheel drive layout | In front-wheel drive vehicle layouts, the engine can be mounted transversely or longitudinally. Drive is transmitted to the front wheels through a transaxle. |
| Rear-wheel drive layout | In a conventional rear-wheel drive layout, the engine and transmission are mounted longitudinally at the front of the vehicle and drive is transmitted to a rear axle assembly by a propeller shaft. |
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| Four-wheel drive layout | In a conventional four-wheel drive vehicle, propeller shafts connect a transfer case at the rear of the transmission to final drive units on both front and rear axles. |
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| All-wheel drive layout | In a conventional full-time four-wheel drive vehicle, a third differential is located in the transfer case. |
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| 4WD vs AWD | All-wheel drive systems continuously power all four wheels and provide maximum traction in all driving conditions. In a part-time system the driver manually shifts between two- and four-wheel drive, and a part-time 4WD vehicle should not be driven on dry roads when in 4WD mode. | |
| Front-wheel drive | Front-wheel drive shafts | In front-wheel drive vehicles, the drive shafts transfer the drive directly from the differential to the front wheels. |
| Front-wheel final drives | In front-wheel drive vehicles, the final drive gears are incorporated in the transaxle assembly. |
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| Front-wheel differentials | When a vehicle is turning, a standard differential allows the two drive shafts and the driving road wheels to rotate at different speeds while still applying an equal turning effort to both. | |
| Rear-wheel drive | Rear-wheel drive shafts | The propeller shaft transfers the drive from the transmission to the final drive. It is normally of a hollow, tubular construction. |
| Universal joints | The most common type of universal joint fitted to propeller shafts is known as a Hookes joint or a cross and roller joint. |
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| Rear-wheel final drives | In a conventional rear-wheel drive vehicle, a crownwheel and pinion transfers the drive through ninety degrees and provides a final gear reduction to the driving road wheels. |
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| Salisbury axles | In Salisbury axles the carrier is integral with the axle housing and a removable cover gives access to the final drive components. |
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| Rear-wheel drive differentials | The differential gears are bevel gears which are mounted at right angles to each other inside the differential case. |
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| Limited slip differentials | Limited slip differentials allow differential action under normal driving conditions but reduce or prevent differential action when conditions are not normal so that a wheel cannot spin. | |
| Four-wheel drive (part-time) | Four-wheel drive shafts | In a conventional four-wheel drive vehicle, drive is transferred from the transfer case to the front and rear axle assemblies by propeller shafts. Drive shafts enclosed within the axle housings transmit the drive to the wheels. |
| Four-wheel final drive | In part-time four-wheel drive vehicles, drive is transmitted through the rear final drive to the rear wheels, in all drive ranges. Drive is only transmitted through the front axle final drive, when a four-wheel drive range is selected. |
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| Four-wheel drive transfer case | In a conventional part-time four-wheel drive vehicle, the transfer case allows the vehicle to be operated in high range in 2-wheel drive and/or 4-wheel drive, in low range in 4-wheel drive only and in a neutral condition for a power take-off. |
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| Free wheeling hubs | On part time- four-wheel drive vehicles, free wheeling hubs can be installed on the front hubs, to disconnect the hubs from the axle shafts, and prevent rotation of the front axle components. |
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| Four-wheel drive differentials | In part-time four-wheel drive vehicles, differentials are fitted to both front and rear axle assemblies. | |
| All-wheel drive | Full-time four-wheel final drives | On all-wheel, or full-time four-wheel drive vehicles, drive is transmitted to the front and rear wheels at the same time. |
| All-wheel drive transfer case | In a conventional full-time four-wheel drive vehicle, the transfer case allows the vehicle to be operated in high range or low range, or in a neutral condition for a power take-off. |
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| Transfer case differential action | When operating in high range in a conventional full-time four-wheel drive vehicle, a third differential in the transfer case caters for the speed difference between front and rear propeller shafts. | |
| Final drives procedures | Checking free play |
The objective of this procedure is to show you how to check a final drive unit for wear and free play. While final drive components must be held firmly in position by bearings and thrust washers, there must be operational clearance between meshing components. This check determines the amount of free movement between the crown wheel and pinion. |
| Checking drive shaft joints |
Drive shafts require joints at either end to allow for angular change. Drive shafts turn at high speed. The Universal and Constant Velocity Joints allow drive to be transmitted through an angular change. This requires the shafts to be well balanced with minimal free movement. The objective of this procedure is to show you how to check drive shaft joints for wear. |
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| Checking manual transaxle/differential oil | The objective of this procedure is to show you how to check gearbox/differential oil for manual transmissions. You will need to refer to the owner's manual for exactly where to check the oil level. |
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