crosspost from SD forum
Truck: 2006 F-250 FX4 Lariat, 6.0
Mods: bulletproofed, 6" lift, 35x12.5 aggressive MTs (really should get bigger tires...they look too small)

OK, I have not had much opportunity to use the 4wd on my truck since I got it 4 months ago, I would lock the front in when I get to the hunting lease, but that is it.

I have determined, I think, that the auto hubs are not working as intended.

We have a nice little cold snap, with ice and snow coming tomorrow, and I have to go into work, so I figured I would check out the 4wd today to make sure it worked.

I pulled into my very wet yard, at idle, rear tires slipping a bit, got stuck at about 50 ft. Put it into 4 low (light came on correctly), put it in drive, came off the brake, and rear tires where still slipping, no movement out of front tires. Got out, locked the front in manually, and she crawled out, albeit leaving behind a bit of a mess....7,000 lbs in a water logged yard and all...but did not slip tires while locked in.

So, conclusion, auto hubs not working, manual locking works as intended.

Now for the questions part:
as I was going down the driveway when I went to pull into the carport (with front hubs locked and in 4L) the front started binding really bad when near full lock to the left, same way my mud truck does that has spools in the axles.

I unlocked one hub, and she turned just fine still in 4wd, one hub locked.

I took it out of 4wd and re-locked both hubs, and she turned just fine. This was with the hubs still locked.

I'm a bit confused, as I have only had binding happen with spools, in which case, it should happen any time both hubs where locked, 4wd engaged or not, as the binding is across the tires, not the T-case.

from what I can gather, it means that it has to have a locker (or a limited slip where the clutches are stuck?), but for some reason, it is applying equal torque to the outside tire while not letting it spin faster than the inside.

does this make sense? Is this how they all work, at least when locked in?

Lastly, can I drive the truck safely, without compromising breaking something, with both hubs locked but the truck in 2wd, and put it in 4H only when crossing bridges/overpasses?

what about just driving it in 4wd with locked hubs the entire way? will the binding be enough to break something, hubs or diff most likely?

Would this happen with the hubs in auto provided that the auto hubs actually worked correctly? (or are they, and they just require more speed and/or engine or axle RPMs?)

TL;DR: getting binding on pavement with hubs locked in manually, but I need 4wd tomorrow on the roads due to essentially guaranteed icy roads and it seems that my autos are not working.

on edit, when purchased, I had been told that the previous owner had had some work done to the diffs, I do not know what exactly, and had had the tranny replaced

 

Hmm...

I think you are misunderstanding the system.

However, the issue you are having with the auto-locking hubs is not uncommon. In a lot of those cases it comes down to the vacuum system or the internals of the hubs. If they are not worked the internals can jam up. Or, there could be a leak in an air line causing the vacuum not to work. It is nice that the hubs are manual locking too - if you need to you still have that option, its just not possible to lock them in if you are going down the road...

My theory is to use 4x4 as little as possible - it isn't good for the driveline to run much. If you need it you need it, but having it in 4x4 "just in case" isn't the best for it - as you noted, when you do have traction you bind up the driveline and what gives first is generally tires slipping, which should not be happening normally and adds excessive stress/wear. If you have limited traction (are on a totally snow covered road) then the tires slipping won't bind up the driveline.

Your notes about the hubs and transfer case are spot on. If you had a locking differential and it was engaged then you would bind up the axle that has the locker in a turn, regardless of it being in 4x4 or 2wd. When you are in a turn the outside wheel spins faster than the inside - when your axle is locked both wheels spin at the same rate, therefore the tire with the least traction will slip/bind and turn at the same rate as the wheel with more traction.

A "differential", by nature, allows torque transfer to both sides provided they have traction, yet allows each wheel to turn at a different rate without binding. When you had the transfer case engaged and one wheel unlocked you were running the driveline at a constant speed - the front and rear driveshafts (from the transmission to the rear axle and the transfer case to the front axle) were turning at the same rate. When you turned, the outside rear wheel was turning faster than the inside rear wheel, the outside front wheel was turning faster than the inside rear wheel, but slower than the outside rear wheel, and the inside front wheel was spinning slower than all 3. The hub that you had unlocked was the loose end and took up the gearing change between the 3 other engaged wheels. There was no traction on it so the axle shaft on that side of the front differential was free to spin at whatever rate it needed to adjust for the engaged hub rotating different from the rest of the driveline (since the rear axle had traction on both tires it governed the speed that the rear axle shafts spun, the rear driveshaft, and front driveshaft - the front hub that was engaged didn't change the speed of the front driveshaft and the front driveshaft couldn't power the differential because there was no load on the loose hub).

I hope that made sense...

If you take a single differential axle and stop one wheel and turn the other the pinion gear/driveshaft connected to it will turn. If you stop the driveshaft and spin one wheel, the opposite wheel spins the opposite direction. Spin both wheels the same direction and the driveshaft spins the same direction.

I'm sure there's a youtube video showing what I'm trying to say...

I would not think that running the truck in 2wd with the hubs locked would cause as much wear and tear as if you ran it in 4x4 with the hubs locked - since the front axle in a turn will spin the front driveshaft at a different rate than the rear there is no connection between the two (through the transfer case) to cause any binding. It will, however, run the front driveline so there will be some parasitic load on the components.

 

Not true. In 4wd with open diffs in both axles you will get binding in tight turns. The issue is that you have a "spool" (no differential) in the transfer case and the front wheels need to travel father than the rear. It's possible that you have a locker or limited slip in one or both axles, but you'll get the binding in 4wd whether you do or not.

KC8 dealt with the rest of your post so I won't rehash it.

 

There is

 

Here we go. This guy did a pretty good job explaining what I was trying to say, but I think I had the axles backwards - front looks like it is outside the rear, not the other way around...

View this video first:


That brings up the question of why "part time" 4wd systems have usually been direct connect through the transfer case when engaged and haven't had the option of a third differential to lesson the stress on the drive train when engaged, probably a cost issue, but it would be a neat idea. Then if you wanted direct connection put a locker in there just like a front or rear diff.

View this video second:

 

These videos were my entertainment for the night... If you really want to be confused check out the video here on limited slip differentials:


and torque transfer through: