All wheel drive v, 4 wheel drive

Can anyone explain the difference, if any, between "all wheel drive" and 4 auto, like on a Ford Explorer? Thanks

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MB
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Most commonly, when the term "all wheel drive" is used it means a system that is always "turned on" with all 4 wheels connected together. To do that, there has to be some kind of differential mechanism or viscous clutch to allow some "slip" between the wheels since they are not always going the same distance/speed.

Most commonly 4 auto means there is a "between the axles" clutch that can be turned on and off very rapidly as needed. Whenever there is the start of wheelslip at one of the wheels the clutch will engage to partially or fully (depending on the amount of slipping) lock the front and rear axles together.

Theoretically, all wheel drive should be un-noticeable in operation since it's always on and simply "slips" as needed whereas auto 4x4 can be noticeable when it engages and disengages and there can be a lag between when you NEED it and when it engages.

The auto 4x4 has the advantage of being capable of 100% lock if needed whereas most of the "all wheel drive" are not capable of being fully locked and are not really intended as true off-road systems if you are looking for the best possible traction. Auto 4x4 often also includes a non-auto setting of 4x4-lo range; I don't know of any all-wheel drive that have lo range but perhaps there are some.

All-wheel drive is generally less complex and less expensive then any of the other variations of 4x4ing because generally it has the least "off road style" capability. However, for "on road" if may be the best way to go.

Each has it's advantages and disadvantages, it depends on what you want to do with the vehicle that would determine which would be best for you.

-- Elbridge Gerry, of Massachusetts:

"What, sir, is the use of militia? It is to prevent the establishment of a standing army, the bane of liberty. . . Whenever Government means to invade the rights and liberties of the people, they always attempt to destroy the militia, in order to raise a standing army upon its ruins." -- Debate, U.S. House of Representatives, August 17, 1789

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AZGuy

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