First, there is nothing different between the pushbutton 4WD and the stick-driven 4WD except the transfer case. The entire front end, diffs, driveshafts, and all are the same. No additional sensors or motors.

The way the automatic locking hubs work is when the front driveshaft turns and applies force to the hubs at the wheels, the hubs will lock and drive the wheels. When the wheel is turned in the reverse direction without force from the axle-shaft, the hubs disengage. The axles are not turning all the time with the newer systems as I have verified this with my pushbutton Bronco. Want to see your automatic locking hubs work? Climb under your Bronco and turn the front driveshaft either direction. You will only be able to get about half a turn from it before the hubs lock. Then you won't be able to move it either direction.

It appears the difference would be in the transfer case. There must be a clutch type of setup for the front axle controlled by the electronic motors on the transfer case.

 

[updated:LAST EDITED ON 29-Nov-01 AT 12:08 PM (EST)]>There's one other way to prove this. Start out in 2hi and
>pull the lever back very lightly. You will hear this nasty
>scraping sound.

I will? No, seriously, I pull it into 4hi at 60mph+ all the time. All it does is allow the t-case to start *powering* the front d/s which will already be spinning if the hubs are locked. If the hubs are not locked then it will start spinning the front d/s which will in turn spin: yoke to pinion to ring gear to carrier to axleshafts. The spinning shafts will, of course, engage the locking hubs, but it appears Ford does not want them to be forced to engage at speed.

>I am not sure, but I think this "shift on
>the fly" pushbutton stuff, is totally different. Isn't that
>servo motor engaging and disengaging something in the front
>differential? And on the newer system, the axles turn all
>the time.

The t-cases are gonna be the same internally. It's just the exterior to fit the shift motor for push-button.
Clearly (IMO) Ford says to not shift into 4hi unless the auto hubs are already locked because they are concerned the hubs could blow if forced to lock at speed.

 

That's what I get for talking about something I know nothing about. I was guessing about the pushbutton system, and adelyser's explanation could be possible if the transfer case had clutches that slipped to get the frontend moving. I don't know, but I am curious as to how if you are going down the highway, and the front drivetrain is sitting still, how you suddenly get all that stuff moving so everything can be engaged.

 

Yo Franklin and guys; here is a possible explanation of the system:

http://www.findarticles.com/cf_0/m3102/n8_v117/21019130/p2/article.jhtml?term=

 

Thanks AIM. Looks like they do have mechanisms to get the front end parts moving before it engages the transfer case. I am glad though, I have the old manual hub system. Too much expensive stuff to break, looks like to me, on those newer systems. :-X23

 

I just got my '91 with the transfer lever on the floor and had fun reading the "back and forth" on this subject. My owner's manual is pretty clear on the difference in 4WD engagement procedures for the push button and the lever actuated. My '96 had the push button and it could be put in 4Hi at speed but the lever version states to be stopped when first going to 4WD. Once you're in, you can go back and forth at speed until you decide to disengage the hubs. The "touch drive" version makes a nasty noise when popped in at speed and I always engaged at very slow speeds if not stopped and never had an auto hub problem, even on a '93 Explorer(terrible vehicle). Putting that much stress on system can't be healthy even if it says it's ok in the manual. The previous owner of my '91 obviously followed the "book" as at 118,000 miles the auto hubs still work perfectly. I'm going to change them out anyway..Merry Xmas everyone!!

 

That's odd about your manual. My '86 Bronco w/ auto hubs and be changed between 2Hi and 4Hi on the fly. Only have to stop and put it in neutral to go to 4Lo. It has the lever transfer case shifter.