Limited AWD vs Platinum 4WD Drivetrain

[Smitdog]

Electronic locking is ideal to have both rear wheels locked to go in a straight line like pulling. Boat out of the water or in deep snow= mud

Thanks for the description Henryrlee.

Helps my understanding somewhat, but raises the same questions related to how the mutually-exclusive options of "Non-Limited Slip" vs "Electonic Locking" functionality works in the various 2H, 4A, 4H, 4L modes.

My current understanding based on the thread replies and other info on the web:

1. So with the "Non-Limited Slip" standard axle option on a 4x4 configuration, when in 2H mode, the rear axle is not locked, and torque is applied to the specific wheel(s) with the best traction (could be one or both wheels).​

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In 4A mode, neither axle is locked, and torque is applied to the "axle" with the best traction. My understanding is that the rear axle will have at the very least 50% of the torque, and the front axle at most will have 50% of the torque. Said a different way, in 4A mode the rear axle will have anywhere from 100% to 50% of the torque distribution, and the front axle will have anywhere from 0% to 50% of the torque distribution. My assumption is that in 4A mode, both wheels on their respective axles have equal torque applied, i.e.; it is not "wheel-specific" torque.​

In 4H mode, both axles are locked, and torque is applied equally to the front and rear axles (50%/50%).​

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In 4L mode, essentially the same as 4H, just in a much lower gear.​

2. With the "Electronic Locking" axle option on a 4x4 configuration, when in 2H, the rear axle is not locked, and torque is applied to the wheel(s) with the best traction (same functionality as with the "non-limited slip" option above).​

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With the "Electronic Locking" option, does this mean that 4A mode goes away, and only 4H / 4L is available (as 4H / 4L are described above)?​

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Not sure if I'm overthinking this or just dense, but I still don't feel I'm understanding the functionality of 2H, 4A, 4H, 4L as it relates to the "Non-Limited Slip" and "Electronic Locking" axle options (and pro/cons of each).​

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[Bryan Simon]

Not locking axles (open differential) supply power to both wheels providing both wheels have equal traction.
With limited traction, the wheel that has less traction will spin (and will at twice the speed of the speedometer.
The open differential will allow the wheels to turn at constant varying speeds for inside and outside turn radius.
Old time lockers will only allow different speeds for an extremely short distance before “lockup” is achieved.
Then there are the differentials with clutch packs that allow slipping of an independent axle while still providing traction to both wheels.
The front differential on my truck is dead locked when in 4x4 with no slipping at all.
In 2hi, when making a hard turn with some power applied, the inside rear will chirp on pavement as soon as it locks. Does not happen when easing into a right turn from stop sign, but if I’m in a bit of a rush it chirps—does not squeal.

 

[Roger350]

Thanks for the description Henryrlee.

Helps my understanding somewhat, but raises the same questions related to how the mutually-exclusive options of "Non-Limited Slip" vs "Electonic Locking" functionality works in the various 2H, 4A, 4H, 4L modes.

My current understanding based on the thread replies and other info on the web:

1. So with the "Non-Limited Slip" standard axle option on a 4x4 configuration, when in 2H mode, the rear axle is not locked, and torque is applied to the specific wheel(s) with the best traction (could be one or both wheels).​

​

In 4H mode, both axles are locked, and torque is applied equally to the front and rear axles (50%/50%).​

​

In 4L mode, essentially the same as 4H, just in a much lower gear.​

2. With the "Electronic Locking" axle option on a 4x4 configuration, when in 2H, the rear axle is not locked, and torque is applied to the wheel(s) with the best traction (same functionality as with the "non-limited slip" option above).​

​

With the "Electronic Locking" option, does this mean that 4A mode goes away, and only 4H / 4L is available (as 4H / 4L are described above)?​

​

Not sure if I'm overthinking this or just dense, but I still don't feel I'm understanding the functionality of 2H, 4A, 4H, 4L as it relates to the "Non-Limited Slip" and "Electronic Locking" axle options (and pro/cons of each).​

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So the electronic locking differential has nothing to do with 2H, 4A, 4H, or 4L. It is locking the two rear tires together, so they both get 50% of the torque that is applied to rear axle, regardless of whether the vehicle is in 2H, 4A, 4H, or 4L.

Without some form of locking or limited slip differential in the rear diff, a 4x4 truck becomes 2 wheel drive in the slippery mud, but it will be one wheel in the rear, and one in the front, because open diffs let the wheel with the least traction spin and no torque goes to the wheel that actually has better traction.

With a locking or limited slip diff in the rear, the above scenario becomes a 3 wheel drive truck, with both rear wheels getting some of the torque sent to the rear axle, and the front tire with the least traction getting all the torque to the front axle.

It used to be 3 wheel drive was the best you could get from the factory, because no OEM put a locker or limited slip in the front diff because they are not good in high traction settings, because you have to fight the locker to get the truck to turn. Now, trucks and jeeps with maximum off-road packages have been adding either limited slip or electronic locking diffs to the front so you can have true 4 wheel drive.

Bryan, what kind of locker did you put in your front diff?

 

[Bryan Simon]

Bryan, what kind of locker did you put in your front diff?

All factory unmodified
Will allow just a bit of differential action before locking—the front just locks

I think he is trying to understand how the 4A is working.
This goes back to the 70s (although with some refinements) and the GM, Jeep & Dodge full time 4x4.
Those transfer cases had a differential in them that distributed the power to all four and allowed speed differences between front and rear.
4Hi and the transfer case was not locked between front and rear and was used for hard dry ground.
4Hi LOCK, locked the differential within the transfer case and both axles did the same thing—-all 4 wheels if it had limited slip
4Lo LOCK, same as above but in low range
Neutral, completely disengaged the TC
No 2hi on these.
If these trucks had open differentials (non locking), removing a driveshaft, or jacking up a single wheel, this thing is rolling away as all 4 needed to be on the ground in 4hi. Whether it is in park or not.
In 4hi (or low) LOCK, you can remove one shaft and still drive the truck, or jack it up and it would stay put.

So, those square body Chevys with 4x4 and automatic transmissions that so many people decided to put locking hubs on, it was pointless for a fuel mileage gain as one had to always drive in 4hi LOCK for the truck to move and the front shaft and the differential were still under power. They only succeeded in disconnecting the front wheels from the front axles that were still “working”, only now, they had to get out and lock hubs.
Part time transfer cases did not have a differential, so now you have 2hi.
My 76 manual trans—October, lock the hubs (yea, front end chirps and hops a bit) and only engage 4hi when needed for snow or slush and I did not have to get out and lock the front wheels.——- Turn the knob to “free” come April when weather smoothed out.


I should note that on icy roads, that full time 4x4 78 Chevy behaved much better on ice in 4hi mode than it did in 4hi Lock. Real squirrelly in 4hi lock.
The 76 k30 part time 4x4 I avoided at all costs in icy conditions. HD hard tires, HD rear springs. Next to zero traction on icy roads. But in any other condition was great.

 

[Smitdog]

So the electronic locking differential has nothing to do with 2H, 4A, 4H, or 4L. It is locking the two rear tires together, so they both get 50% of the torque that is applied to rear axle, regardless of whether the vehicle is in 2H, 4A, 4H, or 4L.

Without some form of locking or limited slip differential in the rear diff, a 4x4 truck becomes 2 wheel drive in the slippery mud, but it will be one wheel in the rear, and one in the front, because open diffs let the wheel with the least traction spin and no torque goes to the wheel that actually has better traction.

With a locking or limited slip diff in the rear, the above scenario becomes a 3 wheel drive truck, with both rear wheels getting some of the torque sent to the rear axle, and the front tire with the least traction getting all the torque to the front axle.

It used to be 3 wheel drive was the best you could get from the factory, because no OEM put a locker or limited slip in the front diff because they are not good in high traction settings, because you have to fight the locker to get the truck to turn. Now, trucks and jeeps with maximum off-road packages have been adding either limited slip or electronic locking diffs to the front so you can have true 4 wheel drive.

Thanks Roger350... I think I'm beginning to understand, but have a few more questions.

1. Given a 4x4 configuration, does the Electronic Locking / Non-Limited Slip option pertain to the front differential, rear differential, or both?

If the front differential does come into play with the Electronic Locking / Non-Limited Slip option, then I would think 4A/4H/4L modes would have something to do with it (which is contrary to your first sentence). If the front differential does not come into play, then I get it.

2. If I'm never going to use the truck for off-road use (mud/sand), and am only getting the 4x4 for driving in snow conditions, would the standard Non-Limited Slip option be the best bet? On my current 2010 4x4 Lariat, when I do engage 4H in the winter, I do notice a "stutter chop" effect on the tires when making tight turns in parking lots that are a patchy mix of snow and dry pavement.

 

[Roger350]

Thanks Roger350... I think I'm beginning to understand, but have a few more questions.

1. Given a 4x4 configuration, does the Electronic Locking / Non-Limited Slip option pertain to the front differential, rear differential, or both?

If the front differential does come into play with the Electronic Locking / Non-Limited Slip option, then I would think 4A/4H/4L modes would have something to do with it (which is contrary to your first sentence). If the front differential does not come into play, then I get it.

2. If I'm never going to use the truck for off-road use (mud/sand), and am only getting the 4x4 for driving in snow conditions, would the standard Non-Limited Slip option be the best bet? On my current 2010 4x4 Lariat, when I do engage 4H in the winter, I do notice a "stutter chop" effect on the tires when making tight turns in parking lots that are a patchy mix of snow and dry pavement.

Short answer, it is an electronic locking REAR differential, it does nothing for the fronts regardless of 4H, 4L, or 4A setting.

On regular F-150s (meaning not a Raptor or Tremor) the front differential is an open diff, (non-locking and non-limited slip). The Raptor and even the Tremor may come with some sort of traction aid like a torsen limited slip in the front or even an electronic locker, but I've never shopped those trucks, so I cannot say what they have or do not have.

The beauty of the Electronic Locking Rear Diff is that when not activated I believe it operates like an open diff, which is the smoothest diff for everyday driving on paved roads. So it essentially is the best of both worlds, open when you want smooth operation, fully locked when you need maximum traction.

For snow and ice I believe open diffs will give you less chance of a random drivetrain induced spin, when you are already moving and you apply power because they will be the smoothest operating. This is where the older style Automatic-Locking diffs that were not driver controlled can be clumsy and cause you to fishtail.

However, open diffs will be the hardest to get the truck rolling from a stop in snow/ice, because the open diffs send all the power to the wheels with the least traction. Technically with open diffs, if the right side tires are on the shoulder where the gravel and grass give you something to bite into, and your left side tires were on sheet ice, with open diffs the left side tires would spin, and your right side tires would do nothing.

If I were ordering a truck only for winter conditions, I'd do a little research to confirm my belief up top that the electronic locking rear diff acts like it is a completely open diff when not engaged, and if that is confirmed, I'd order the Electronic Locker. The reason I say that is there will be no downside to the electronic locker, and plenty of upside, including resale. Personally I would never buy a 4x4 without the electronic locker, and I'd never buy a 2wd truck without the electronic locker, but then again I'd never buy a 2wd truck period, and I live in Texas. (Don't worry, I grew up in Chicago and have driven enough in snow to know about those driving conditions). If you have any hills in your area where the stop sign is at the bottom of the hill, and you have to get up that hill when it's covered in snow/ice, the electronic locker will be important to get you going from a stop - but good luck going down the other side, we all know 4wd does no good when you are trying to stop...

The "stutter chop" effect you notice is totally normal when you drive a 4x4 in 4H on paved roads with mixes of ice, snow, and clear patches where you have good traction. 4x4 is happiest going straight, when you turn, and especially sharp turns like in a parking lot there are a lot of moving parts that bind up. If the tires are on a low traction surface, most of that bind is eliminated because the tires slip a little and free things up. If the tires are on a high traction surface they won't slip, and that's when you get some pops and bangs and feel that stutter you are talking about.

In my opinion, the electronic locker should come standard on all 4x4 trucks, it is silly that it does not. Luckily it's a cheap upgrade. If you ever launch a boat off a boat ramp the electronic locker is more important than 4x4, because almost all the weight is shifted to the back tires, so even when you put it in 4H the fronts aren't going to give you that much pull, but the electronic locker will keep both rears turning.

Sorry for the long winded post, I hope it helps.

 

[Bryan Simon]

I have done some reading in the owners manual about the electronic locking rear axle.
It appears to me this is offering the best of both worlds when engaged.
Owners manual claims the the ELRA automatically disengages at speeds over 25mph and will re-engage at about 20mph.
This seems to be a plus to me.
Only place I would see this could cause concern are turns coming from a stop signal on wet pavement in 2wd mode.

I won’t have 4A on my truck, but over 40yrs of old timey manual 4x4, this new stuff is gonna be interesting for me. Mechanical behavior wise.

 

[Smitdog]

Thank you Roger350!!!

Your last post is the best explanation I've received on the topic, and I now "get it". ?

Bottom line, I was looking for a valid reason and pros/cons of getting the Electronic Locking differential, based on my intended usage.

And while winter driving is the majority of my interest, I do use a boat ramp about 4x per year (launch in the Spring, take out in the Fall), and there have been times where the cement ramp is slick with algae, and the 4x4 comes in handy there too.

To get more specific on the 2021 F-150, is the electronic locking automatic, or is it something you manually engage when needed?

Now just need to decide on the axle ratio... 3.31, 3.55, or 3.73 (I know the pros/cons on this topic). Seems odd that the various gear ratio options would have a different price points, as I would think there would not be much (if any) difference in material or labor costs going from a 3.31 to a 3.73.

 

[Roger350]

To get more specific on the 2021 F-150, is the electronic locking automatic, or is it something you manually engage when needed?

It has a driver engaged on/off switch that is on the drive mode dial. Once you turn it on, it is like Brian stated, where it disengages itself above a certain speed, and reengages when you drop back below that speed. I believe in 4L it is just constant on, because it knows that wheel speed and ground speed are not likely the same thing when you are stuck in the mud and engage 4L to try and get out.

I intend to use the on/off switch to control the diff. I know when I want it on (specifically when I am trying to get moving in slick mud, a boat ramp, or that snow covered hill. I also know when I want it off, when I'm turning and in general when I'm on high traction surfaces, or once I get going in the snow/ice from a stop.

I wouldn't turn it on as a "set it and forget it" type thing and let the speed sensors engage it and disengage it unless I was going to be in low traction mud/sand conditions for a prolonged period, like out at the deer lease or something.

For snow/ice I'd say only turn it on when you are stopped and need to get going, and then turn it off.

 

[Roger350]

Thinking about it more, some of the Drive Modes may also turn on the Electronic Locker, like specifically the "Deep Mud/Sand" mode probably turn it on. Hopefully the "Slippery" or Snow/Ice" modes don't default to the Locker being on, or at least let you control it, but those vehicle dynamics engineers are pretty smart, and their "electronic nannies" do a dang good job of keeping driver error at bay when the conditions are bad, so I trust they thought of all the pros/cons when they programmed the system. I'm sure the 700 page owners manual covers this somewhere...

 

[Smitdog]

Thinking about it more, some of the Drive Modes may also turn on the Electronic Locker, like specifically the "Deep Mud/Sand" mode probably turn it on. Hopefully the "Slippery" or Snow/Ice" modes don't default to the Locker being on, or at least let you control it, but those vehicle dynamics engineers are pretty smart, and their "electronic nannies" do a dang good job of keeping driver error at bay when the conditions are bad, so I trust they thought of all the pros/cons when they programmed the system. I'm sure the 700 page owners manual covers this somewhere...

FWIW, I don't plan on getting the "Offroad" package, which I believe includes a few additional user-selectable modes for specific driving conditions.

 

[Roger350]

FWIW, I don't plan on getting the "Offroad" package, which I believe includes a few additional user-selectable modes for specific driving conditions.

I didn't order FX4 either, as it is too expensive for aftermarket shocks, floor mats, skid plates, and a few extra drive modes. I'd like the skid plates to protect the plastic oil pan, but I can add those after purchase for a lot less than $1k. I do think the rock crawl drive mode uses the front brakes to act like a limited slip in the front diff, which would be nice in the mud, but again, a lot of money for very little usage. And something like a drive mode might be easy for a computer hacker / tuner to add after the fact anyway.

 

[GABAR]

Why does one need the 4X4 features of a pickup truck when one doesn’t live in an area that doesn’t get real or harsh winters?

The ELD should be plenty for the vast majority of people without the complexities and possible failure points of the full 4X4 system.

Just curious.

 

[Roger350]

Why does one need the 4X4 features of a pickup truck when one doesn’t live in an area that doesn’t get real or harsh winters?

The ELD should be plenty for the vast majority of people without the complexities and possible failure points of the full 4X4 system.

Just curious.

Those of us who enjoy the outdoors, and travel the country in our trucks need 4x4 just as much as people that have traditional winters. I cannot get from the paved road to the bunk house on our hunting lease in 2wd. We have pulled many who have tried out of the muck. Texas clay gets pretty slick when wet. We also like to vacation in the mountains of CO and UT, and enjoy the snow there.

There is also some truth to the philosophy that what is another $3500 when you are looking at a $70k MSRP.

I'm not usually a resale person, as I keep my trucks forever, hence the 2007 Tahoe we bought in Nov 2006 that we are finally replacing, but some will say resale is better too.

Bottom line for me, I grew up in Chicago, still visit there in the winter every few years, and enjoy hunting from Texas, to Tennessee, to Missouri, to Wisconsin, and I'm of the opinion that every truck should be 4x4.

 

[daemonic3]

Why does one need the 4X4 features of a pickup truck when one doesn’t live in an area that doesn’t get real or harsh winters?

The ELD should be plenty for the vast majority of people without the complexities and possible failure points of the full 4X4 system.

Just curious.

I was in this boat. I wanted 4x2 only for the extra 200# of payload and the extra 1mpg. We don't get snow and I do not do any offroading. When we've gone to the snow we won't go if it is actually snowing or chains required on the pass. So no need.

Well one campground we fell in love with had an awesome state park nearby, and the shortest path had an unpaved (we didnt know by looking on google maps) road for the final 15 miles AND it was grades up to 10 degrees! (I was watching the offroad setting the whole time) I used the e-locker on the rear tires but the wife was freaking out the entire time every time the wheels slipped a little. Off to the passenger side was steep cliffs which didn't help the situation On the way back I took the LONG way around on paved roads, as I did NOT want to go downhill on that path and slide off a cliff!

Then at this same campground, the one-way exit loop was entirely unpaved dirt/gravel. Near the exit was a final short grade and I was pulling my 8000# GVWR trailer. My tires slipped a little but we made it out without getting stuck. She panicked and said we are getting a new truck with 4WD!

Anyway, we went back and took the kids this time, went again to the state park and it was SO FUN this time knowing what to expect and I cannot wait to try it again with the FX4 package and different settings. Hell, I may even try it going downhill with the hill descent and different settings!

I don't like losing 200# payload but I'm making up the MPG loss with the hybrid. And we never know when an unexpected situation may occur. Other campers have warned about sites with gravel/mud and trying to leave while towing and horror stories. Having FX4 will give more peace of mind.

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