How 4A mode works?

[Buyer2021]

The regular 4A transfer case also has 4H and 4L, which at least in the first generation cases; locks the friction clutch pack together the best it can in both high and low range.

FYI review of the 2022 WSM confirms that strategy / mechanism is the still same for the latest "regular" TOD without IWE configuration ("Regular" being Lariats, etc without the Raptor / Tremor dog clutch).

For those "regular" configurations the 4H and 4L settings simply result in "... the TCCM outputs a constant 97% duty cycle to the clutch field coil."

The 2022 WSM has discussion of TOD TC overheat protection strategies for both 4H and 4L modes (similar to 4A mode), the extreme of that being temporary disable of all 4x4 modes until the TC cools off (with notification on the IPC display). That's obviously less than desirable in some situations but I suppose better than grenading the TC / clutch pack due to overheat. You might know (I do not) if the first / early generation TOD cases employed similar 4H/4L overheat-protection strategies or if that was a later refinement.

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[Tomatoboy]

The real limitation on the 4A mode on the TOD TC is slow off-road applications, especially sand. Where the transfer case will overheat.

Because of this limitation the Raptor and some Tremor trucks are equipped with the Hi-lock TC that has a dog clutch in addition to the friction clutch pack to turn the TOD TC into a conventional part-time TC for heavy off-road use.

The regular 4A transfer case also has 4H and 4L, which at least in the first generation cases; locks the friction clutch pack together the best it can in both high and low range. This works fine if you are carrying enough momentum off-road but if you are rock crawling or driving like you want to get stuck in deep gravel or sand, then the clutch pack can still slip.

Ford saw fit to have the first generation Navigator only in 4A for all highway and city driving for the entire life of the vehicle and there’s still some available used with over a quarter million miles.

As from my earlier post, if you have 4A, just do as Ron Popeil says.

Indeed.

The “weakness” of the 4A is that under three fairly limited use cases it can run into issues.

As you noted, when rock crawling or in certain sand environments at low speed when maximum torque demand is placed on the case, the clutch pack *can* overheat. This isn't very common, I haven’t read many accounts of folks actually managing to overheat this model of TOD case the 4A vehicles use since A) it requires a fairly specific set of demands and B) few high-trim vehicles are used for rock crawling, which is the bigger concern, as in sand you really have to get hard into the stupid before you’d run into an overload issue. I personally wouldn’t hesitate to drive a 4A on sand. Heck, folks drive 2011-2019 FWD-biased Explorers on sand with their far less robust PTU and rear clutch pack AWD system without thermal overload. Knowing the limitations of the system, I would avoid placing undue stress on it by keeping up momentum, but I wouldn’t be worried about it. I *already* wouldn’t take my Lariat rock crawling because the bumpers, air dam, and whatnot were not designed to give the appropriate approach and departure angles, but I wouldn’t take the 4A true crawling absent that issue because it’s precisely the sort of low-speed, high-torque, long-duty cycle the Hi-Lock was designed to compensate for in the Raptor, and knowing the limitations of the 4A system, I would worry about thermal overload. Plus, losing your front axle in sand means at worst you get stuck, again unless you’re being really stupid. The consequences rock crawling can be more severe. The one takeaway I see is that, despite the auto lock feature that shoves it into 4H from 4A if more demand is noted by the system, it would seem wise to disregard that and act as though it doesn’t exist, putting the system in 4H on your own the minute you hit sand, to minimize clutch heating.

The other use case the 4A can run into is high-power engine mods. Like all clutch pack systems, the 4A TOD case has a maximum torque spec, and you can overpower the clutch pack with enough engine output. You can see this was probably a known issue because when Ford offered the Limited with the Raptor‘s HO 3.5 EcoBoost several years back they included the Hi-Lock. The Raptor’s duty cycle combined with HO engine necessitated the Hi-Lock on it, and when Ford applied that engine to another trim, they stuck with the case. (Ford no longer offers that engine on anything but the Raptor).

Folks tend to view these minor ”weaknesses“ of the 4A units as a bigger deal than they are. They exist, but they’re really not something 99.95% of F-150 owners realistically need to worry about, because the situations where it can be an issue are very limited...while the benefit of having an always-available AWD system are HUGE for the average F-150 owner. Personally, I wish Ford would offer buyers the option of cases when ordering regardless of trim, because I would have preferred to be able to get a 4A on lower trims.

 

[Buyer2021]

Folks tend to view these minor ”weaknesses“ of the 4A units as a bigger deal than they are. They exist, but they’re really not something 99.95% of F-150 owners realistically need to worry about, because the situations where it can be an issue are very limited...while the benefit of having an always-available AWD system are HUGE for the average F-150 owner.

 

[Tomatoboy]

FYI review of the 2022 WSM confirms that strategy / mechanism is the still same for the latest "regular" TOD without IWE configuration ("Regular" being Lariats, etc without the Raptor / Tremor dog clutch).

For those "regular" configurations the 4H and 4L settings simply result in "... the TCCM outputs a constant 97% duty cycle to the clutch field coil."

The 2022 WSM has discussion of TOD TC overheat protection strategies for both 4H and 4L modes (similar to 4A mode), the extreme of that being temporary disable of all 4x4 modes until the TC cools off (with notification on the IPC display). That's obviously less than desirable in some situations but I suppose better than grenading the TC / clutch pack due to overheat. You might know (I do not) if the first / early generation TOD cases employed similar 4H/4L overheat-protection strategies or if that was a later refinement.

Technical aside: I would love to have been a fly on the wall when they selected 97%. I’ll now wonder for years if that’s because A) it’s to allow some slop in the system front to rear, B) it’s because it modestly reduces load on the field coil (under the assumption the field coil maybe doesn’t like being fully engaged?), C) it’s because 97% is sufficient to lock the clutch pack, or D) it is due to some arcane change in duty cycle calculation. I would have expected 100% to avoid any slop in the clutch allowing unnecessary heat production, so I have to assume there’s some engineering consideration placed on selecting 97% percent.

 

[Buyer2021]

Technical aside: I would love to have been a fly on the wall when they selected 97%. I’ll now wonder for years if that’s because A) it’s to allow some slop in the system front to rear, B) it’s because it modestly reduces load on the field coil (under the assumption the field coil maybe doesn’t like being fully engaged?), C) it’s because 97% is sufficient to lock the clutch pack, or D) it is due to some arcane change in duty cycle calculation. I would have expected 100% to avoid any slop in the clutch allowing unnecessary heat production, so I have to assume there’s some engineering consideration placed on selecting 97% percent.

? All fair enuf, IMO

I think I'm gonna run with the notion that a truly 100% "locked" clutch pack could result in some traumatic consequence in some rare but extreme situation they wanted to avoid.

But whatever, I have confidence that the 2022 system does reflect the latest best-effort refinements of some talented and considered engineering. As you and others have suggested I have no reason for regret in choosing a trim with the 2022 iteration of the TOD TC.

 

[Pedaldude]

One of the things that I noticed is that the videos that I have seen when people got stuck with 4A, they would have gotten stuck with spools front and rear on a part-time TC.

Doddering around or stopping to take pictures only gets you stuck in certain situations. Then once they’re stuck, they spin the wheels and dig themselves up to their axles.

All I know for sure is it doesn't behave like 4A in my previous truck, a GMC...

If the TC was the BW4485, it looks like that’s a true AWD with a permanent 40/60 front/rear split and a planetary differential.

When did Ford ditch the IWE? They just ditched the vacuum system and went electronic in the 21’s.

Sometime around 2022 MY if I remember correctly, they stopped including IWEs on the regular 4A TCs.

 

[ROBB1]

All I know for sure is it doesn't behave like 4A in my previous truck, a GMC. If I punched it on icy roads in my GMC all tires would 100% spin and pull me straight. Picture I go to turn and start sliding, punch it to correct the slide. With this truck they seem to alternate and do weird things and slide me side to side.

It also only has 1300 km on it so I don't know, but it definitely behaves differently. Slower to engage or something. Traction control is also quite different between the brands though. I usually turn it off in the winter unless im on the highway.

4A was a deciding factor for me choosing a Lariat because I pretty much always ran it when i need more traction, be it on the highway or offroad. Only in really demanding situations would I use 4H.

Now it seems I have less control on say snowy roads at low speed with this ford 4A, so I use 4H instead. Still 4A on highway though. This is all winter driving as I just got the truck a couple weeks ago.


Im not a set it and forget it guy though. I run 2wd most of the time unless it's icy or I'm off-roading.

What I can say for sure is the application of power to the front in 4A is different between drive modes. Normal and sport only seem to send power to the front at certain times and revert to rwd fairly quickly. Slippery mode seems to maintain more of a balanced front to rear distribution regardless of speed or condition.

 

[3Ranger11]

Sometime around 2022 MY if I remember correctly, they stopped including IWEs on the regular 4A TCs.

That makes sense. It probably has to do with the chip shortage since they switched to electronic IWEs.

 

[Chili]

Since Ford is so meh about touting the importance of 4a, I wish they'd put it on the XLT trucks or at least an option. It's the one thing I wish I had.

 

[Pedaldude]

There’s supposedly some folks who have installed the 4A case. Including at least one Hi-lock torque on demand TC.

It’s not the easiest job but it’s not super hard either and as I said earlier; the 4A pays for itself if it gets you out of a pickle!

 

[Buyer2021]

There’s supposedly some folks who have installed the 4A case.

@Jesse-Infotainment is one, as mentioned in this thread / post (ESOF swap to "regular" / non-HiLock TOD TC):

The swap to 4A is pretty simple. the transfer case isnt that big a deal. I did the whole swap in a few hours.

You do need the new ATCM(Switch in dash) TCCM, and the transfer case.

It is stupid for Ford to not offer it in lower trims. I do wish if I could go back in time I would get a powerboost. I wasnt very educated on the trucks when I bought it. We jsut needed one and the one I got met all the demands I had at the time. 4WD and sport appearance. Im not a chrome guy for my trucks.

The transfer case new could be had for about the price of used. You do want to confirm you get the correct one for the truck. I cant say for certain but there may be variations based on engine. I dont know.

The TCCM is a plug and go module. No programming required. THe ATCM is also.

The As Build changes are not that many.

It was a well worth it upgrade.

 

[daemonic3]

According to the most up to date information, that’s the old 4A. The new ones do it the other way around, more like an AWD and switch to RWD when it makes more sense; like in parking lots.

So my understanding all along has been the "old 4A" description you just gave. Now I'm interested in what you are calling old vs new? Is it Gen13 vs Gen14? Or is it model year '21 vs '22?

I have a '21 Powerboost and understood it to be the "old 4A" all along, but the "new" sounds more interesting.

I've used 4A extensively in the last 3 F150's I've had.
2018, 2021, 2022

The only real difference that I know of is that this 2022 doesn't have IWE's so it seems to show less difference in fuel economy between 2Hi and 4A. Driven as closely the same as possible, on a daily commute that hasn't changed in 22 years, I get a variance of less than 1mpg.

I do get a drop in mpg in heavy rain, but I suspect that is rolling resistance? It can cost as much as 1mpg on the same 46 mile round trip.

My figures aren't based on a single day result because it wouldn't factor in variations in traffic or the luck of the red lights. Instead it's just me repeating over and over the same commute that I could do in my sleep.

I've wondered why my 2022 Powerboost dropped its EPA rating of 24mpg (2021 Powerboost) to 23mpg. I can vouch that there literally is about a 1mpg difference. Is it the IWE removal? (or at least some portion of the 1 mpg is the IWE removal?)

I have become so accustomed to 4A in tropical wet driving conditions that I would retrofit it to an XLT if I was to acquire one. I prefer the additional weighted feel to the steering, as well as the truck being well planted overall.

In my '21 I have also tried benchmarking 4A vs 2H and no noticeable difference, but I also cannot perform an apples-apples test. So I suspect <1 MPG delta.

Anyway, after you guys confirm when the "old" vs "new" cutoff was, then I can start googling wtf an IWE is and why it would cost any efficiency on highway EPA ratings.

 

[Oxford_Powerboost]

So my understanding all along has been the "old 4A" description you just gave. Now I'm interested in what you are calling old vs new? Is it Gen13 vs Gen14? Or is it model year '21 vs '22?

I have a '21 Powerboost and understood it to be the "old 4A" all along, but the "new" sounds more interesting.



In my '21 I have also tried benchmarking 4A vs 2H and no noticeable difference, but I also cannot perform an apples-apples test. So I suspect <1 MPG delta.

Anyway, after you guys confirm when the "old" vs "new" cutoff was, then I can start googling wtf an IWE is and why it would cost any efficiency on highway EPA ratings.

The old way was probably before 13th Gen. But all 14th Gen with 4A operate in the “new” way in which you’re driving all 4 wheels with some amount of torque (the amount sent to the front is variable based on duty cycle commanded to the transfer case clutch) by default. Basically - you almost always have power going to the front save for certain scenarios like steady state cruising and parking lot maneuvers under light throttle (I should add though that thanks to the clutch which allows slip if needed, you can have all 4 wheels driven in tight turns without binding)

 

[daemonic3]

The old way was probably before 13th Gen. But all 14th Gen with 4A operate in the “new” way in which you’re driving all 4 wheels with some amount of torque (the amount sent to the front is variable based on duty cycle commanded to the transfer case clutch) by default. Basically - you almost always have power going to the front save for certain scenarios like steady state cruising and parking lot maneuvers under light throttle (I should add though that thanks to the clutch which allows slip if needed, you can have all 4 wheels driven in tight turns without binding)

I hope you're right! I would def use it more, knowing it engages all the time and not in "when needed" mode. I have only been turning it on when it is rainy or sandy/gravelly. Would love to use it more knowing that I paid for it and it works as AWD.

 

[Snakebitten]

So my understanding all along has been the "old 4A" description you just gave. Now I'm interested in what you are calling old vs new? Is it Gen13 vs Gen14? Or is it model year '21 vs '22?

I have a '21 Powerboost and understood it to be the "old 4A" all along, but the "new" sounds more interesting.



In my '21 I have also tried benchmarking 4A vs 2H and no noticeable difference, but I also cannot perform an apples-apples test. So I suspect <1 MPG delta.

Anyway, after you guys confirm when the "old" vs "new" cutoff was, then I can start googling wtf an IWE is and why it would cost any efficiency on highway EPA ratings.

IWE = Integrated Wheel End
A fancy acronym for an automatic locking hub rather than the old school manually locking hub on your dad's truck.

Manual hub: (remember seeing them in the center of the wheel?)

So Ford design a method to use vacuum to lock/unlock the hub so you didn't have to get out of the truck.

Google IWE problems and you will be overwhelmed with both how common the issue is AND how many years the issue has gone unresolved.

Then suddenly, in 2021 Ford introduced an electric IWE, instead of the legendary vacuum based IWE. But as amazing as that was to some of us old timers, one year later Ford dropped the IWE altogether for many trucks!

Me personally, I welcome it, although I was actually celebrating having the E-IWE on my 2021 Platinum Powerboost when I traded it for my special order 2022 KingRanch Powerboost with no IWE of any kind.

So yes, my 2022 front hubs are permanently locked, so to speak, and my front axles are always spinning.

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