Rear axle behavior in different 4wd modes

[lsupcar]

I have a '23 rebel with 4wd auto option. In exploring the functions of my new truck, I drove it in a slow maximum steering lock turn on a dirt road in the various axle options. I noticed inside rear wheel binding/scrubbing in rear diff lock and also in 4wd low and 4wd high. I was surprised to have the rear seeming locked, or binding, when in 4wd high or 4wd low when the rear locker was not engaged.
Is this appropriate? It would seem to preclude driving in 4wd high on a paved road without very slippery conditions. Is the rear axle actually locked when in 4wd low or high, even without pushing the rear locker button?
Thanks.

 

[John Galt]

as far as I know 4WD auto sends power to the front drive shaft. Nothing else.

do you have the LSD option? That can cause power to be sent to both rear wheels if you’re on loose surface.

normally, you would be correct, you shouldn’t drive in 4WD on dry pavement. 4WD auto is presumably different because it can “turn off” the front axle when it‘s not needed and allow the front drive shaft to spin free, thus protecting the center diff from blowing up but 4WD is not AWD, even 4WD auto….but that has nothing to do with the rear axle locking up.

 

[Rick3478]

In auto, the transfer case de-clutches the front axle when it is not needed. But in 4 wheel low or high the front and rear axles are locked together, and when you turn the wheels sharply the front must move much farther for the same wheel rotation as the rear. Or conversely the rear must slip so that it can cover less distance. This is a common artifact of 4WD systems, sometimes just called "bind". In extreme cases, you can actually break things like axles and U-joints, but usually just get binding/scrubbing. And occasionally, squirrelley behavior like going straight on ice even though the steering wheel is turned.

 

[Rlaf75]

Yes that's normal

 

[Jmac509]

I just came here to say the same thing. Any 4wd system that locks the front and the rear axles together will bind when going around a corner. I believe there is a warning to use the 4wd system on loose terrain only. Any vehicle that can drive in tight circles that is 4wd is either disconnecting the front and rear axles or it has a center differential.

 

[WXman]

Also note that if you have the 4Auto setting your truck will not lock the front and rear together regardless of mode. ALL modes use the clutch system. It simply applies more pressure when in 4High or Low....but it will still slip and/or overheat if you really push the truck in off-road scenarios. That is why the Rebel used to never have the 4Auto t-case as an option.

Apparently the GM trucks are the same way, as I recently saw a video where a 2023 ZR2 Silverado overheated on a very simple off-road trail.

Ford from what I'm told still locks their front and rear via chain, the way it should be done, when in 4Low.

 

[Bt10]

The Tradesman does not have the 4auto tcase either. Chevy has 2 tcases as well, don't know if either doesn't have clutches.

Bind is normal as said above.

 

[John Galt]

Also note that if you have the 4Auto setting your truck will not lock the front and rear together regardless of mode. ALL modes use the clutch system. It simply applies more pressure when in 4High or Low....but it will still slip and/or overheat if you really push the truck in off-road scenarios. That is why the Rebel used to never have the 4Auto t-case as an option.

Apparently the GM trucks are the same way, as I recently saw a video where a 2023 ZR2 Silverado overheated on a very simple off-road trail.

Ford from what I'm told still locks their front and rear via chain, the way it should be done, when in 4Low.

On Rams the locking mechanism/clutch is actually on or near the front differential. 4WD locks the front and rear drive shafts and they always spin and have power. In Auto the front differential can unlock somehow, not sure of it’s a clutch or something else….haven’t had a chance to look into it yet.

this is why 4WD auto is “safe” to drive on dry pavement- you just give up some fuel economy because you’re spinning another drive shaft, but 4WD Hi and Low locks the front differential to the front drive shaft……somehow.

 

[WXman]

On Rams the locking mechanism/clutch is actually on or near the front differential. 4WD locks the front and rear drive shafts and they always spin and have power. In Auto the front differential can unlock somehow, not sure of it’s a clutch or something else….haven’t had a chance to look into it yet.

this is why 4WD auto is “safe” to drive on dry pavement- you just give up some fuel economy because you’re spinning another drive shaft, but 4WD Hi and Low locks the front differential to the front drive shaft……somehow.

What you speak of is called the "FAD" for Front Axle Disconnect. Yes, it locks the front differential when ANY 4x4 range is selected and it stays locked the entire time the truck is in any 4x4 mode.

The center differential inside the transfer case is a totally separate item. It has a clutch that slips in 4 Auto, and this is why it's safe to drive in all conditions. In 4 High or Low it applies more force and attempts to lock the front and rear driveshafts, but since it's a clutch it cannot ever achieve full 100% lock up the way a transfer case with a chain or gears can.

That's why guys who want to use their trucks off road, or to pull other vehicles free that are stuck are better off with the trucks that do not have 4 Auto.

 

[theblet]

It could be BLD also

 

[Ramroo]

Whenever I’m in any mode of 4WD, I personally never go full turn on my steering, even at very low speeds. Too much popping and bad noises from bad angles. Can‘t be good.

 

[lsupcar]

Thanks. I understand what is happening now with the different turn radii front and rear.