Why Front Axle Disconnect (FAD) on some and not others?

[HPNQ420]

The front differential looks like it has a vacuum line to it, could that be it? I looked for one on the real differental but could not find one in the pics.

That could well be it. On my old XJ the disconnect was only on one side and it was at the differential, not the hub.

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[Lakelife36]

I'd like to revive this thread, even though I might be the only one interested

The real reason I want to know, is in both cases BD and OBX 4.27 w/o FAD they are available with stand alone Adv 4x4. The exception is BB 4.27. It shows no FAD, but also ADV 4x4 is not shown available as a stand alone w/o Sas. I'm just triple checking to see if there is a way to get Adv 4x4 on a BB without Sasquatch before I can't modify my order.

A month ago my dealer tried to add it in WEBDO and couldn't w/o Sas. I'm just checking with the experts to see if there is a work around.

That is correct, the only way to get advanced 4x4 on BB is with Sasquatch. It's not directly stated on the build sheets but if you connect three or four dots you can figure it out. There is a good chunk of a thread somewhere dedicated to this but I don't recall what it's named.

disco sway is to get you to upgrade.

Id order the base with the sasquatch if it was part of the package...but its not so I guess I am going BADLANDS

This is about the different mechanisms that lock in 4x4, not about the SBD.

 

[NCOBX]

I really hope we aren’t going back to the 1980s back to vacuum operated actuators.

Typically FAD have an electronic actuator in the diff.

 

[North7]

Front Axle Disconnect aka Integrated Wheel Ends (IWE) are in the front wheel hubs. It has nothing to do with the transfer case or differential.

That could well be it. On my old XJ the disconnect was only on one side and it was at the differential, not the hub.

@BearWithMe thank you for pointing out and explaining Integrated Wheel Ends (IWE) is where the locking occurs, new to me but glad to learn and understand them.

 

[grimmjeeper]

There are two ways to disconnect the tires from the rest of the drivetrain in a 4x4.

The first way is locking hubs. This disconnects the wheel hub from the axle shaft, letting them spin independent of each other. Old school manual hubs have been around forever. Ford (and others) have used a vacuum operated system to "auto lock" the hubs for you when you shift into 4WD. The Dana 60 from a 2002 F350 that I'm putting into my Jeep Comanche has this feature. Though I will be using a modified manual setup that stands up to off road abuse better.

The other way is to do an axle shaft disconnect. This uses a two piece driveshaft on one side with an engagement collar that either connects or disconnects the two pieces of the axle shaft together. The outer hubs are permanently engaged. This means that the outer axle shafts are still spinning but since the shafts are disengaged from each other, only the spider gears in the differential spin. The differential carrier and main axle gears don't move much if at all, nor does the driveshaft or the front output of the transfer case. Until you put it into 4wd. Then the shift collar engages on the two piece axle shaft and the system works like normal 4WD.

The early Jeep XJ Cherokee (84-early 90's) and the current JL Wrangler (2019+) both use an assembly integrated into the long side axle tube. You can see the cast piece around the axle tube where the mechanism lives. It has an access cover and wires or vacuum tubes connected to operate the shift collar. The mid 1980's full size Jeep Wagoneer, along with many GM vehicles, have a differential housing that has a space cast into the differential housing. The extra wires/vacuum tubes connect to the differential housing and operate the shift collar there.

Good detail on the Jeep axle:



I don't have any actual information on what exactly is in the Bronco but since they call it a "Front Axle Disconnect" and the axle comes from Dana, just like the Jeep, I suspect the system will be similar between the two. It could still be disconnect hubs but I suspect it's an axle shaft disconnect.

 

[North7]

Here is a good video of how the Ford FAD IWE works, for those of us learning.

 

[kencantrell]

@North7 I’m learning my way around 4WD systems, and am very interested in this thread. What is the difference between front axle disconnect and locking hubs (example: the G2 hubs on the 4WP build from Moab)? My bottom line question: when in 2WD can the front driveshaft, differential and axles remain stationary until 4WD is engaged, or do they always turn? Seems their constantly turning is a waste of energy. Thanks for the help.

 

[etmccaus86]

@North7 locking hubs (example: the G2 hubs on the 4WP build from Moab)?

Ah, yes; the lone piece of the 4WP build I have interest in, and the lone piece they've been (oddly) reticent to talk about...

 

[North7]

@North7 I’m learning my way around 4WD systems, and am very interested in this thread. What is the difference between front axle disconnect and locking hubs (example: the G2 hubs on the 4WP build from Moab)? My bottom line question: when in 2WD can the front driveshaft, differential and axles remain stationary until 4WD is engaged, or do they always turn? Seems their constantly turning is a waste of energy. Thanks for the help.

All axles are always turning, are they under power, that is the second question.

If the FAD is engaged then the front axles are under power. If the electronic lockers are engaged it allows traction in whatever uneven terrain your in.

 

[kencantrell]

All axles are always turning, are they under power, that is the second question.

If the FAD is engaged then the front axles are under power. If the electronic lockers are engaged it allows traction in whatever uneven terrain your in.

Thanks. No front lockers for my non Sas BD. Seems like a free spin kit from Dynatrac and others would be an answer but man, they are expensive.

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