If you could reprogram the 4A system to "lock" into 50/50 split between front and rear wheels, would it perform exactly like 4H while letting you drive on dry surfaces? If yes, is there a reason why they don't do that and abolish traditional 4H? If it would somehow be different in function/performance, what would that difference be?

 

The point of 4A IS that it isn't "locked" 50/50, which is what allows you to drive on dry paved surfaces. The binding caused by the axles turning at different speeds in turns is what causes damage when you drive in 4H on dry paved surfaces.

 

It's not true AWD, but torque on demand. System detects slippage and engages the clutch locking in the TC. AWD provides power to all wheels at the same time, but in a split distribution, 60/40. The Ford Flex/Taurus/Fusion AWD provide 60% front and 40% rear, and can provide more power rear if needed.

Would be nice if it had the system like the Explorer did. Had a 97 with the 5.0 and AWD. It just didn't have 4Low.

 

In the 70's & 80's, trucks were available with Full Time 4wd - exactly as you described. But as fuel economy became more important they were phased out. I remember there being "Kits" for sale that converted Full Time 4wd transfer cases to 4H...
Makes me feel old - bought my 1st F150 in 1978
http://www.f150hub.com/drivetrain/np203.html

 

No, the old all wheel drivetrain are not fuel efficient and are obsolete now.

4A or all wheel drive uses nothing more than an electronic clutch to drive both front and rear axles at the same time. There's clutch slippage so that the front axle turns at a different rate than the back and therefore, doesn't allow binding when turning. The system engages only AFTER wheel slip is detected. After a determined amount of time and no wheel slip is detected, the system will default back to 2WD.

I found it useless in my previous 4A 2008 Sport Trac. The idea of true 4WD is to prevent wheel slip because once wheel slip happens it's much harder to regain control and traction. The Sport Trac was always in 4A as it offered no 2Hi. It only offered 4A, 4Hi, and 4 Low.

There's no reason to offer 2HI as 4A runs in 2WD most of the time until slippage is sensed. However the front axles are always turning even though the front axles are disengaged from the transfer case, and use more fuel so with the F150, 2HI is offered to get that last amount of fuel economy as it disengages the front axles from turning.

 

If power is only delivered to the front axle when slippage is detected, why does the power distribution display show otherwise? It shows power to the front when starting from every stop, even on dry pavement with no slippage. It does drop to 2WD when cruising however.

 

Our 2015 Explorer was like that and it was AWD all the time, no 2Hi, 4Hi, or 4Lo, just AWD all the time.

Off starts to gain better traction, it engages and as you should notice all the power after that, diverted to the rear axle only. With the All the time, AWD vehicles, the front axles stay engaged all the time.

 

Here is how the service manual describes it...