This morning I was driving my 2017 XLT FX4 and put it in 4 Hi for no great reason as I was slowing to a red turn signal. I made a U turn from the light and the inside rear tire skipped around the turn as if I had the rear differential locked (I did not have the e-locker engaged). This is not normal behavior when in 2WD. What am I missing? Putting it in 4 Hi without the e-locker shouldn’t have done anything to the back of the truck in this situation, right?

 

Since the front and back are locked together in 4 Hi/low, something has to skip to release the binding that will happen. That tire had the least traction so it is what skipped to release the binding.

 

Maybe I need to Wikipedia how a transfer case works. I understood putting it in 4WD would engage the front differential, but since both front and rear are open there is no binding.

 

Some more explanation (in simplified terms), in a differential, the drive shaft rotates at the average speed of the 2 wheels. When locked or going in a straight line, the tires are rotating at the same speed and so is the driveshaft. This is true for both the front and rear axles.

In 4 Hi or 4 Low, there is no differential between the front and rear, so they have to move at the same speed. In 4 A (Lariat or higher trim), there is some extra mechanism (a clutch I think) that allows the front and rear to slip a little and not bind.

When turning, the rear tires are making a smaller circle and therefore are trying to move at a slower relative speed. This is what causes the binding you probably felt/heard and the skipping of one or more tires.

 

You could try starting with this video:


And he has some more that get into 4WD and AWD. I haven’t watched them to confirm if they are good videos, but it is at least a start.

 

Engineering explained has a gift for explaining such things to noobs.

 

From page 193 of your owners manual (which you should read):

Do not use 4H or 4L mode on dry,
hard surfaced roads. Doing so can produce
excessive noise, increase tire wear and may
damage drive components. 4H or 4L mode
is only intended for consistently slippery or
loose surfaces.