With 4A, what do I need 4H for?

[Scott R Nelson]

I've done quite a bit of off road driving, including the 100 mile White Rim Trail out of Moab, and the Tower Arch trail in Arches NP. I've also driven to the top of a number of mountain peaks in southwest Idaho.

I have yet to find a case where I felt that using 4H would be an improvement over using 4A. Yes, I've found many reasons to use 4L, but I don't understand when 4H is going to make my Bronco behave better than 4A.

It's a 2-door Base Sasquatch, if that makes a difference.

I have yet to find a good explanation of how exactly 4A works, everything I've read is kind of vague, except that I can still use it on pavement - and even forgot to switch back to 2H a few days ago coming back from going to the top of Scott Mountain north of here.

Gratuitous photo from the drive a couple of days ago at about 8000 feet:

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[BR0NCO]

4A is normally rear wheel drive and engages the front when it selects slipping, 4H engages the front at all times. Less wear and tear on the clutches and quicker reaction. At least that’s how I understand it in my head

 

[Kimberley]

I have had to many times "plow the road" with my vehicles when it snows and for those times I am in 4H and have total control. If a plow has gone by, I can use 4A and let it do its job. Not risking going through 6 inches of snow in 4A with hills and frost heaves.

 

[RagnarKon]

4A is basically an all-wheel drive mode. Very similar in nature to the systems you would find on Subarus, and many of the other countless crossovers/SUVs these days with AWD systems. The Bronco system is tuned a bit more for off-road use, but it's still an AWD system and it dynamically changes the power to the wheels based on the specific situation.

4H is a traditional 4x4 setup. Really intended for off-road only. If you want the computer to get out of your way so you can control your vehicle—which is needed in many off-road situations—then 4x4 High is the mode for you.

Fun fact... Broncos with the EMTC (Advanced 4x4) are actually classified as All-Wheel Drive vehicles rather than 4x4 vehicles.

 

[Bigmoose]

With 4H you are locking the transfer case which results in a near zero friction coefficient. This means minimal heat generation.

4A has some non zero friction coefficient. As you put higher torque through the transfer case, like driving in deep sand, you generate more heat. If the transfer case can't cool fast enough it will overheat. This was the case with bronco sports trying to drive in deep sand, they would over heat the system and shut down.

 

[MillerAndCheeto]

4A is basically the vehicle in 2 high, and the front wheels engage when necessary. Also you don't have to worry about wrecking your front wheels when turning. 4 high keeps the front wheels engaged at all times. You'll feel it wanting to tear up your tires when you turn on asphalt - intended for when the front tires can spin freely, ie. snow, dirt, off-road etc.

Here's a little video as well on AWD (4A in a sort) vs 4x4 (4H).

 

[Scott R Nelson]

4A has some non zero friction coefficient. As you put higher torque through the transfer case, like driving in deep sand, you generate more heat. If the transfer case can't cool fast enough it will overheat. This was the case with bronco sports trying to drive in deep sand, they would over heat the system and shut down.

I can see the need of 4H for deep sand, but I've only ever been in deep sand once for a rather short distance on the White Rim trail. And I guess a little bit in Arches NP too, but that was mostly downhill. I might have switched to 4H for those.

The idea of generating more heat in 4A helps me understand it a bit better. I'll keep that in mind in the future.

 

[Felix808]

4A is also operating off a clutch pack vice just the chain drive in the transfer case in 4H & 4L. So the driveline is not locked up in 4A.

 

[BR0NCO]

4H = off road
4A = street, snow/rain

 

[AZMikeL]

Lots of washboard here in AZ (which always seems worse when there is a big drop-off on either side). 4h is the way to go if you start to slip and lose it around a bend. Give it a little more gas and the front end digs in and goes where you point it. I'd rather not let the computer decide when I'm slipping in that case. Not sure what its reaction time is.

In my old F350 I would give new passengers the following disclaimer:

"There will be times on this trail where I will only be suggesting where the truck is going. Rest assured, I have YET to kill anyone"

It's much harder to break the Bronco loose, but not impossible. Just a touch on the gas in 4h corrects it every time.

I'm the opposite - still trying to find a use for 4a, but then again I have to drive a couple of hours to get to snow. When it starts to rain here in Phoenix, the pavement gets so slick form all the oil leaks, even 10-wheel drive won't be of much help, so I don't bother going into 4a in the rain.

 

[Silver-Bolt]

As a side note, in 4A if it gets too hot from slipping it will automatically switch to 4H. For my usage, if I am on road I tend to use 4A. Off-road, 4H.

 

[cashe3]

Here is the simplest explanation.

4H = off road
4A = street, snow/rain

 

[BroncoSarge]

Cannot use 4H on dry pavement, 4A would be better for dry pavement and intermittent puddles or loose gravel.

 

[MNBigfoot]

When driving on snow/ice, 4H will prevent slippage, were 4A will only attempt to help you out of a slide, I'd rather not have slippage in the first place on snow/ice.

 

[Rick Astley]

Did you try searching?

There is a great article on how 4A works and it's been posted on here at B6g.

Yes, you will have to read an entire article, but you did ask for an answer..... And it answers your question.
https://www.bronco6g.com/forum/threads/how-awd-works-includes-fords-4a-system.13882/

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