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Automatic 4WD - How Does It Work?

I am thinking of buying a V8 Explorer some time this year and am curious about how the full time 4WD works. I know that it engages automatically when a rear wheel spins and that there is no way to lock the system in 4WD. What I am curious about is how the 4WD releases and returns to 2WD. In other words, when a wheel spins and the front wheels begin to drive, how long do they continue to drive and what event triggers them to stop driving?

My reason for asking about this is that I often use my '99 V6 Explorer to carry stuff into my back yard. I then lock it in 4WD to come up the hill out of the yard. If wheel spin happens, it will tear up the hill, so don't want that.

Reply to
John Shoemaker
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There are two different 4 wheel drive systems available on an Explorer. The Full Time 4WD system (also called AWD) uses a center differential and splits the torque front/rear by some fixed amount. The Control Trac 4WD system has an Automatic 4WD mode. It does not have a center differential. It does have a 4WD Hi mode and a 4WD Lo mode. It is more like a conventional 4WD system in that it has 2 speed transfer case that feeds power to the front and rear axles without a center differential. Since there is no center differential, you should not operate the vehicle in 4WD (Hi or Lo) on high traction surfaces. The Automatic 4WD Mode (A4WD) electronically controls the clutch to the front differential. When the system detects rear wheel slip (relative to the front), the transfer case clutch is cycled on and off at an increasing frequency until the slip is reduced. Even when there is no slip, the transfer case clutch is cycled at a very low rate, but I doubt if you could tell it. When you shift to 4WD (Hi or Low), the clutch is engaged 100% of the time.

Ed

John Shoemaker wrote:

Reply to
C. E. White

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