Torsen front diff, 4HI on dry now okay?

[Tomatoboy]

Considering a 400a tremor with the Torsen front diff. Will this allow me to drive on dry or mixed surfaces in 4HI without windup on turns? The jump to 402a just for 4A is a lot.

Thank you

No. The Torsen front diff will not let you operate the system in 4H/4L on dry pavement. You’ll still have front to back windup. You need the unit with 4A -operating in 4A- to operate on dry pavement. For that matter, even the 4A units should not be used on dry pavement in the 4H/4L settings.

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[Tall Tail]

adding it to my XLT, I agree

Any advice on how to add 4A to XLT?

 

[DBL R]

Torsens are great diffs, but diffs nonetheless. There's no center diff available in the F150, just simply a locking center(XL / XLT), a slipping center (4a), and a slipping center that can lock (raptor / tremor) -- and the latter is only needed for some heavy 4WD action (I personally don't see the reasoning of using the F150 as a HD 4WD machine as there's better options available for such purpose). The 4a should be standard while the 4H only TC should be left in the parts bin.

Torsens just make for a better front diff so a vehicle is closer to 4WD than 3WD when a front tire is loose. They don't affect the TC at all. Typically 3WD is plenty (when the rear diff is locked).

I've not explored if ford has a competent electronic traction system or not that would help by braking the 'loose' front wheel. It's not a replacement for a good diff, but it's a whole hell of a lot better than an open diff peg-leg.

Regardless your diffs, running in 4H is a bad idea. 4A is fine as it's really just 2H until slipping occurs.

That’s actually misinformation about 4a. It is not 2WD until 4WD is needed. It’s an actual AWD system using pressure and clutches providing continuously variable torque split front to rear that the computer controls based on throttle, steering, wheel spin, drive mode, and other factors.

 

[Tomatoboy]

That’s actually misinformation about 4a. It is not 2WD until 4WD is needed. It’s an actual AWD system using pressure and clutches providing continuously variable torque split front to rear that the computer controls based on throttle, steering, wheel spin, drive mode, and other factors.

Correct.

In 4A, the transfer case operates in a manner functionally identical to an electromagnetically clutched AWD system…since it is one, just one with additional functionality. The system uses an electromagnetically actuated clutch pack to vary torque provided to the front axle. It transmits anywhere from 0% to 50% of power continuously to the front wheels depending on a litany of factors and from a functional standpoint, it’s identical to an AWD system, it just also has a high-low range (for 4L) and the ability to force fully open (2H) or force fully closed (4H) the clutch pack as added features.

It isn’t like older 4A systems that needed to detect slip and had significant engagement/disengagement delays and clunks, as such systems are always active below any disengagement speed they might have and can very quickly vary torque. You can verify this while driving by watching the power distribution, below highway speeds you will see power going to the front wheels in varying amounts regularly, such as during acceleration, while in 4A. That display merely spits out what the ECU is commanding the system to do, so you can easily see when it is commanding more power to the front wheels, and at least in my driving conditions it rarely doesn’t show at least -some- power to the front below highway speeds.

I mention highway speeds for a reason, many electromagnetically clutched systems have a designated cutoff speed above which the clutch pack opens unless called for (on my Explorer, it’s 55mph). I have noticed my F-150 opens the clutch more often at highway speeds unless I honk on the accelerator, but I’ve yet to establish a firm cutoff speed or find one in literature. If anybody knows if there is one and what it is, chime in.

On the non hi-lock transfer cases (Raptor, available option Tremor), 2H is just the clutch fully open, and 4H is just the clutch fully closed (4L is clutch fully closed -and- a ratio shift). The hi-lock units add mechanical lock for 4 modes other than 4A* but otherwise work the same as the Lariat+ non hi-lock ones. Because your clutch pack is jammed shut, even on the non hi-lock 4A transfer cases you wouldn’t want to run it on drive payment regardless of the Torsen OP brought up when set to the 4H setting, because you can still have front to rear driveline binding since the clutch doesn’t provide slack for slipping when fully closed. While it should be obvious, I’ll note you also wouldn't want to do it on the locking ESOF or hi-lock units since they’re mechanically locked.

*this solves the rare situation where you might overcome clutch torque by not relying solely on clutch pressure to lock front and rear power while still allowing 4A when the lock is disengaged.

 

[hotrodmex]

Any advice on how to add 4A to XLT?

Buy the T-case, TCCM, and Switch, then slap them in. Not a lot to it. There's a whole thread at f150forum on it, but that's really it.

The only thing that might be an issue now, if you get a post '22 setup, is that you might have to get IWE eliminator sleeves, as the current 4A setups have front axles locked and no eIWE signal.

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