How does the 4A work?

[Dubsesd]

From my understanding if the Bronco is in 4A, if a wheel is slipping it will engage the 4WD but if nothing is slipping it should remain in 2WD . In 2H it will only be in 2 wheel no matter what. Is that correct?

I lifted my Bronco and when in 2H everything is fine, but when I click 4A and under slight acceleration I have a drive line vibration. I can replicate it very easily. I'm just trying to diagnose the situation and trying to see how exactly the systems work.

Thanks in advanced for any help.

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[Ser Arthur Dayne]

This is a question I have asked multiple times on here and have not been given a good answer.

It's very important to me because it goes to 4A in Sport Mode. I have very little ACTUAL mechanical knowledge, but I do know you don't use 4WD on pavement ... but some people put it in Sport Mode all day every day.

I understand 4A is not Full-Time FWD but still.

Anyway good question.

 

[PWillette]

4A is basically AWD...when in 4A under normal conditions the drive train is in 2wd (RWD) as you state. Under slippery conditions power will automatically be distributed as needed to the front and/or rear wheels independently...it's an active system that changes with conditions vs. just 4WD (4H).

 

[drew707]

From how I’ve understood it, 4A primes the transfer case to be ready at a given moment to engage the front driveline. Essentially the transfer case is engaged vs being just passive in 2H.

This would explain what you might be feeling.

 

[VelocityBronco]

You are correct. In 2H, it will never engage anything but the rear wheels.
In 4A, 4 wheel drive is engaged when low traction condition is detected using clutches inside of the transfer case.
I am not sure how well the 4A system works in the Bronco yet, but when I monitor the power distribution screen when in 4A, it shows equal power to all 4 wheels all the time...
I also have a drive train noise when in 4A or 4H, noticeable when accelerating and goes away when you let of the gas/coasting. This is similar to my F-150, so I just assumed it was normal? Maybe its not?

 

[PWillette]

This is a question I have asked multiple times on here and have not been given a good answer.

It's very important to me because it goes to 4A in Sport Mode. I have very little ACTUAL mechanical knowledge, but I do know you don't use 4WD on pavement ... but some people put it in Sport Mode all day every day.

I understand 4A is not Full-Time FWD but still.

Anyway good question.

Correct, no 4WD (4H) on pavement. 4A can be run on dry pavement like any other AWD vehicle and lots of people do. Draw back is fuel mileage.
I thought that you could switch to 2H in Sport mode...no?

 

[zuke]

In 4A and accelerating (even slight) you will likely have some power going through the transfer case and driving the front axle.

The most likely cause for the vibration in this case is going to be the front driveshaft, when the lift was installed, was care taken to set the pinion angle properly for the new height?

 

[PWillette]

https://www.caranddriver.com/features/a27630736/awd-vs-4wd/

 

[PSUTE]

4A is convenient for me, my road is 1.1/2 miles unmaintained by government. Everything else can be dry, but mine remains covered in snow and ice in places. I like being able to set it and forget it...

 

[Bmadda]

From my understanding if the Bronco is in 4A, if a wheel is slipping it will engage the 4WD but if nothing is slipping it should remain in 2WD . In 2H it will only be in 2 wheel no matter what. Is that correct?

I lifted my Bronco and when in 2H everything is fine, but when I click 4A and under slight acceleration I have a drive line vibration. I can replicate it very easily. I'm just trying to diagnose the situation and trying to see how exactly the systems work.

Thanks in advanced for any help.

Did the lift include a diff drop?

 

[Laminar]

4A automatically engages partially when you accelerate from a stop. It disengages when decelerating and when turning the steering wheel.

https://jalopnik.com/how-all-wheel-drive-works-a-ridiculously-detailed-tech-1846233533

 

[Bradnewt]

I think that there is more to it than wheel slippage detection. I have noticed when in 4a, there is power going to the front wheels under hard acceleration on dry pavement with the traction control on. You can monitor this by selecting the % of power to the wheels screen. 2wd in Sport Mode is a yes.

 

[TX-Hans]

From my understanding if the Bronco is in 4A, if a wheel is slipping it will engage the 4WD but if nothing is slipping it should remain in 2WD . In 2H it will only be in 2 wheel no matter what. Is that correct?

I lifted my Bronco and when in 2H everything is fine, but when I click 4A and under slight acceleration I have a drive line vibration. I can replicate it very easily. I'm just trying to diagnose the situation and trying to see how exactly the systems work.

Thanks in advanced for any help.

If you put it in 4H and accelerate, do you get the same driveline vibration? (You can use 4H on drive pavement for testing this but just keep it generally in a straight line...meaning no sharp turns right or left or you'll feel the front binding)

 

[BR0NCO]

In New England I’d stick it in 4A at the beginning of winter and back in 2WD in the spring. 4WD off road only

 

[mjrcu]

I switch it back into 2H after putting it into sport. I know you technically leave it on, but on dry pavement sunny day, feels weird to have it even in 4A if its not even possibly needed. Kind of a pain though, I wish I could put it into Sport and stay in 2 with the option to turn on 4A if needed.

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