Ohsix

Post #5 is a good answer
The link is just more questions

Ssls6

How about the manual? There are two pieces of information:

Using the 2-Speed Automatic 4WD System (If Equipped)
This system includes an electronically controlled transfer case with a high capacity clutch. The system is interactive with the road, continually monitoring and adjusting torque delivery to the front and rear wheels to optimize traction.

4A (4X4 AUTO) - provides electronic control four-wheel drive with power delivered to the front and rear wheels, as required, for increased traction. This is appropriate for all on-road driving conditions, including as dry road surfaces, but is especially useful on wet pavement, snow, dirt, or gravel.

The key here is the high capacity clutch and the truck electronics which varies the pressure of the clutch. You DO NOT go into and out of 4x4 mode. You are in 4x4 mode but the clutch allows slip between the front and rear driveshaft. How much slip is varied. The cool thing is the slip removes any driveshaft bind that occurs when you turn. Turning causes the front tires to move faster than the rear tires which will bind a normal 4x4. On a slippery surface like snow or gravel (and ford states this in the manual) this isn't a problem for 4H as the fronts/rears will slip as needed.

RLK

rogerswt

In daily driving, I use 4a on paved roads in wet or slick conditions. A good example of its usefulness is a steep, sweeping uphill curve near my house. In wet conditions on this stretch, the rear wheels spin out frequently in 2WD as I accelerate up the hill. In 4a, the front wheels are engaged as needed and I climb the wet hill without any wheel spin. Its a great feature for city and highway driving in wet or slippery conditions.

I use 4WD when I'm off-road ... rutted dirt roads, gravel, sand etc. where the surface is rough enough or loose enough that no driveshaft bind occurs.

Chad Walker

The definition of all wheel drive is the capability to provide power to all wheels. Ford's 4A is an on demand AWD system like most other manufacturers. Some cars like the Highlander are full time AWD. 4X4 systems are technically AWD.

Ohsix

4x4 4A has a switch with 2H 4A 4H 4L
4A transfer case uses clutch’s and Advance Trac to power wheels
4H transfer clutches are Electronic Locked Don’t use this position on Dry Pavement
4L Transfer clutches are Electronic Locked Used for heavy towing in sand snow etc will not engage above 3 mph

seadragon

In 4A, you are in 4wd every time you leave from a stopped position with power going to the front wheels. It will stop sending power to the front once at cruising speed with little load on the drivetrain. The power distribution display shows this and I can hear it also. It’s a very useful feature in wet and slippery conditions as it prevents the rear from breaking loose. I use it a lot in non-dry conditions.

Mike Up

That's not entirely true. All new AWD system use an on-demand system as Fords 4A. Only Subaru does not. Fords AWD crossovers use on demand 4A as does Honda, Toyota, Nissan, and GM.

I've had the on demand system in my 2008 Sport Trac 4.6L 3 Valve. No 2WD option, 4A all the time, or Part-Time 4WD.

Our 2012 Escape and 2015 Explorers had on demand AWD all the time as well. It does not even compare to "LOCKED" part-time 4WD. If you have 4WD Part-Time and KNOW HOW TO USE IT, you'll never waste your time on an AWD mode that's severely inferior. Add in the locking rear differential with some good tires, and not much will stop you from moving.

rdg04578

This biggest difference between true AWD and 4WD with auto function is the use of a transfer case. If your vehicle has a transfer case it is a part time system where the system shifts the transfer case into 4wd when it senses the need due to wheel slippage.

An all wheel drive system uses a central differential that usually does not contain a low range feature. The system is always in 4 wd no matter what--what changes is the amount of torque applied to the front or rear wheels--(subaru system differs in the fact it can adjust wheel to wheel) --usually bias one way or the other but there is always power applied to all 4 wheels. Bottom line it is never 100% to just front or rear.

4A function on our trucks uses an auto shift function that shifts in and out of 4 wd as needed. If it is needed all power goes only to the rear wheels. Because there is no central differential torque applied to to front and rear can never exceed 50:50 unless it is in 2wd. All wheel drive systems can adjust for any combination that adds to 100% and do not have a transfer case--it is not needed.

Mike Up

Once again this information is incorrect. ALL AWD now do not use a center differential except for Subaru, and all vector 100% of the torque to either front or rear axles when the demand for the other axle is not needed by the detection of slip.

No offense, but you are singing the praises of yesteryears technology which doesn't hold true today unless it's Subaru.

rdg04578

My mistake concerning the "on demand systems" however they do not use a transfer case but do use a center differential to accomplish that. They normally deliver power to the front only for fuel economy and in this case the center differential is only capable of delivering 50 percent of the torque to each drive axle. This type of system is used primarily in front wheel drive cars and suv's and is not a truck type system

The one system not mentioned would be the torque vectoring system which is used by Acura.

In either case neither of these AWD systems are used in the F-150 or any other full size truck that I am aware of. Point being our trucks are part time 4wd as opposed to AWD.

Sorry for the "technical" mistake on my part