Nitro Budget Expedition Overland

[Martinjmpr]

The Expedition has a multi-plate centre differential:

https://en.wikipedia.org/wiki/ControlTrac

and

https://en.wikipedia.org/wiki/Electromagnetic_clutch#Multiple_disk_clutches

The jerkiness you sensed may be the energizing from 2WD to AWD mode with a worn centre diff (speculation). Once in AWD/fulltime mode the multi-plate center-diff does it's thing like a normal differential via software.

Part time is just 4HI with the centre multi-plate diff locked of course.

There is something called the "brown wire mod" that locks out the AWD on the later trucks - basically intercepts the current to the centre diff and allows you to put a toggle switch on it. It effectively re-enables the 2WD mode on the early UN93 platform.

It's a good system. I have no qualms about not having a lever in the cab of my truck.

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OK, thanks for the correction. I guess it all comes down to whether you consider the multi-plate unit in the T-case to be a 'differential' but I suppose if it does what a differential would do, then that's what it is, minor quibbling aside.
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I did some Google searching and apparently my Suburban has something similar, although it's not a Borg Warner, in the NVG246 T-case:

[The NVG 246 EAU provides 5 modes, Auto 4WD, 4HI, 4LO, 2HI and Neutral. The Auto 4WD position allows the capability of an active transfer case, which provides the benefits of on-demand torque biasing wet clutch and easy vehicle tuning through software calibrations. The software calibrations allow more features such as flexible adapt ready position and clutch preload torque levels. The technology allows for vehicle speed dependent clutch torque levels to enhance the performance of the system. For example, the system is calibrated to provide 0-5 ft lb of clutch torque during low speed, low engine torque operation, and predetermined higher torque for 40 km/h (25 mph) and greater. This prevents crow-hop and binding at low speeds and provides higher torque biases at higher vehicle speeds, in order to enhance stability.

The only thing I don't like about it is how quickly it (seemingly) switches back into 2wd once the front and rear driveshaft speeds are equal. On my 4runner with the multi-mode T-case I could just leave it in unlocked 4wd (i.e. AWD) as long as I wanted to.

The 4wd gas tanks are supposed to be 30 gallon. When I had my down to replace the fuel pump, it had "30 gal" molded into the plastic of the tank. However I've never pumped more than 27.5 gallons.

The 2wd tanks are 26 or 27 gallon. Not sure why those get smaller tanks.

As far as the jerkiness, try pulling fuse #104 from the underhood fuse box. That solved my issues. Then I did the brown wire mod.

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Assuming yours is a Ford, though, not a Chevy? Don't know if the "brown wire" mod would work on my 'Burb but in any case it wasn't really a "problem" as I was able to easily fix it by just switching to 4wd (not "Auto") mode. The road was covered with slushy snow so I didn't need to be worried about drivetrain binding. EDITED TO ADD: Am I right in understanding from the above that there is no 2wd position on the Ford Transfer cases? If so then that is quite different from the one on my Suburban which has the 5 modes mentioned above (2hi, 4hi, Neutral, 4lo and Auto 4wd.)
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As for the gas tank thing, I guess this isn't the first time I've seen Edmunds have less-than-accurate information, so I'll stand corrected on that as well. :ylsmoke:

 

[Root Moose]

Early (1997-1998) UN93 Ford Expedition's have 2WD selectable via the main switch. It's a software function and can be more or less retrofit to the the later UN93 trucks (1999-2002) via the brown wire mod.

As far as whether it is a differential or not - it differentiates the input/output shafts so... Viscous, electronic, gears; a diff is a diff.

 

[1stDeuce]

There is no center diff in either the ford or GM t-case that has "auto-4wd" and 2wd. (or even the later Expedition with 2wd missing) They both use clutch packs that are electrically controlled to engage the front in "auto" mode. (And in normal 4wd and 4-low, usually)

Both versions are always RWD, until rear slip exceeds a threashold, at which point the controller loads the clutches to transfer some torque to the front. While this is not "awd" in the standard sense, it is a 4wd system that can be driven on pavement with no need for constant shifting, and in a truck applilcation, it works pretty well.

The downside is that this layout is less stable than true center diff awd when you need to turn on a slick surface, because it can only let the front turn faster than the rear if it's freewheeling ahead. It can't send torque to the front at all if the front needs to turn faster than the rear, except for negative torque (aka binding) which is not helpful. But that's a conversation for another fire...

Nice to see a non-traditional build. I think many vehicles would make excellent rigs for normal overlanding. The notion that you need lockers and big lift, and solid axles is largely hype in my experience. Nothing so depressing as meeting a Subaru or AWD minivan on a "Jeep" trail and watching them move happily along with a smoother ride than my Jeep...

Hope the tranny gets fixed, and they get to do some more stories!

 

[drifterdan]

Root Moose, tell me more about the brown wire mod. I have a 2001 Expedition that I wish I could just put in 2wd at times.
Thanks, Dan.

 

[nitro-gear]

We're at an impasse with the Expedition at the moment. We had the rig fully loaded and headed to Moab as a support rig for Easter Jeep Safari when several disasters seemed to occur at the same time. Specifically it developed a misfire that turns out was not fuel or ignition related. Opting to continue down the highway with less than perfect performance we then lost the transmission just west of Ontario, Oregon. AAA towed it into town and the Expedition spent the week in Ontario, before being loaded onto a trailer in place of a Jeep (thanks Build It Offroad) for the trip back to Washington on the way home. We're still determining what the best course of action is on continuing this build, but it will live again.