So 4A is not what I had thought...

[John Bronco_ I am here]

Let me just add fuel to the fire here. There have been several posts already that are 100% correct, that is all I have to say about that. What I would like to point out is there is only 2 quarts of fluid in the transfer case and if one uses 4A a lot I would suggest changing out the fluid often. Not only from heat build up but the materials from the clutch wear. There is no filter in the transfer case like in trans or engine.

I would say at least every 25-30K and/or at the end of winter conditions.

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[ErectionGreen]

I guess I don’t understand what the mystery is and have seen concerns about this in numerous posts. Since 2000, I’ve had several German cars with permanent AWD systems that drove all 4 wheels all the time and distributed power to any of the wheels as needed (merc e320/e500/e350) all 4matic. And now have a cayenne with AWD (that incidentally also can lock the transfer case and rear diff). These cars are always AWD, are shifting power as needed, where needed through the use of unlocked transfer case and differentials. The bronco does the same in 4A, except that it appears to have 100% bias to the rear when coasting (not accelerating or otherwise experiencing slippage). In 4A you can accelerate through a Uturn on dry pavement and not bind up your tranny (unlike 4H or 4L). When it is rainy out, I stick mine in 4A and go about my business and drive like I normally would with no worries about what it is doing to tranny.

I believe most these systems were visco-lock not clutch pack systems. So it would be different. I know all the BMW era Range Rovers we're visco-lock transfer cases that you could lock.

 

[66Fan]

I guess I don’t understand what the mystery is and have seen concerns about this in numerous posts. Since 2000, I’ve had several German cars with permanent AWD systems that drove all 4 wheels all the time and distributed power to any of the wheels as needed (merc e320/e500/e350) all 4matic. And now have a cayenne with AWD (that incidentally also can lock the transfer case and rear diff). These cars are always AWD, are shifting power as needed, where needed through the use of unlocked transfer case and differentials. The bronco does the same in 4A, except that it appears to have 100% bias to the rear when coasting (not accelerating or otherwise experiencing slippage). In 4A you can accelerate through a Uturn on dry pavement and not bind up your tranny (unlike 4H or 4L). When it is rainy out, I stick mine in 4A and go about my business and drive like I normally would with no worries about what it is doing to tranny.

^^ This.
4A is no different from AWD.
I drove my last AWD vehicle (Honda Pilot) over 70k miles in AWD and nothing ever exploded/broke. It's what it does.

 

[Rebel Bronc]

I’ve had my 4door Badlands manual for a month, and have had wet, snowy and icy conditions. I’ve used 4A in ECO, Normal or Slippery modes, and it’s been awesome and I’ve never lost control. I love driving this thing!

 

[HeliPilot]

My Raptor stayed in 4a for over two years without issue. My bronco is getting the same.

 

[KABQ]

I'll just leave this here. It's up to you take the time for some learnin'
https://jalopnik.com/how-all-wheel-drive-works-a-ridiculously-detailed-tech-1846233533

 

[uncledoodoo]

So 4A is the same as it's been since the 80s (at least). Got it.

 

[Cygnusx1]

I believe most these systems were visco-lock not clutch pack systems. So it would be different. I know all the BMW era Range Rovers we're visco-lock transfer cases that you could lock.

the newest versions of 4matic, Quattro, and whatever Porsche calls its system are clutch pack. They allow the transfer case to free up from front at highway and drive only rear wheels. Also, the locking diff function on the newer Porsche's is actually a simulated lock and not a truly locking diff (pin or air locker)

 

[BigMeatsBronco]

So 4A is the same as it's been since the 80s (at least). Got it.

Not really....in the 80s most used an actual differential in the transfer case ....with no computers controlling anything. These days there is a electromagnetic wet clutch pack, it is activated by an electromagnet which has various degrees of pressure available. This system uses a set of ball bearings in a truncated slots. The slots the balls roll in are tapered, so the further they roll up the ramp the more pressure is applied to the clutch pack. I've posted pictures of the internals already on other threads. This is controlled and activated by the computers. Also the system uses pulse width modulation at 12v input, NOT a solid 12v on/off type switch. This allows the system to apply pressure to the clutches in various degrees seamlessly. It can make hundreds of adjustments per SECOND...One of the best systems available.

 

[BigMeatsBronco]

Let me just add fuel to the fire here. There have been several posts already that are 100% correct, that is all I have to say about that. What I would like to point out is there is only 2 quarts of fluid in the transfer case and if one uses 4A a lot I would suggest changing out the fluid often. Not only from heat build up but the materials from the clutch wear. There is no filter in the transfer case like in trans or engine.

I would say at least every 25-30K and/or at the end of winter conditions.

I disagree here wholeheartedly, the amount of slippage your referring to is so minimal it would not create ANY heat or wear UNLESS you go in tight circles endlessly or run tires that have big differences in air pressure or size. Most instances the difference front to rear is less than 2%. Not enough to wear anything out. Wet clutch are extremely durable and outlast dry clutches by far. They made their name in motorcycles most of which have NEVER needed the clutches replaced even with off-road abuse by less than perfect riders.

 

[bradcd]

I'll just leave this here...

 

[BigMeatsBronco]

If you input a steering angle that can cause the driveline to bind, it drops to 2wd. Cruising at highway speed with minimal throttle percentage, it’s rolling in 2wd.

If I understand the literature correctly, the t-case’s clutch setup allows the systems to vary power being distributed to the front axle (even if the PDM shows 50%) in the event of slippage - but in reality it’s almost always feeding some amount to the front the moment it sees you tip in the throttle.

Other than very low speed cornering, you are in 4A (a slippable version of 4H) this system is very proactive and not reactive like other OEM’s methodologies.

This is also related to keeping traction especially in off throttle turning conditions. ....in icey conditions by reverting to 2wd in certain situations can increase traction available, and prevent the wind up and bind from causing any of the tires to slip. For example in slippery conditions , while in a turn with the throttle.lifted (deceleration) by un hooking the front tires briefly, the system allows the fronts to keep traction and steering by eliminating the bind that could cause a loss of traction.

 

[mtclimb3r]

I'll just leave this here. It's up to you take the time for some learnin'
https://jalopnik.com/how-all-wheel-drive-works-a-ridiculously-detailed-tech-1846233533

Everyone should read this. This is one of the best car articles ever written imho. The Bronco AWD mode is very robust and was designed by one of the best companies. Like others have mentioned, F150s have had it and the new ranger will have it. It’s clutch based as mentioned that can vary how much the rear axle is engaged. Don’t use it off-road because the clutch can overheat and temporarily not be available. Varying power side to side is driven by the brakes still I believe. The Bronco sport has 2 clutch’s on the rear wheels in addition to the center clutch that allows torque vectoring side to side. Imho the bronco sport has one of the most capable AWD systems around. Honda might have it beat, not sure though.

Many of the other vehicles already mentioned use completely different setups and their effectiveness varies. Subarus are full time 4wd with a center differential. Prius AWD has a tiny 7hp electric motor in the back to give a little push. AWD is deceptive marketing and enthusiasts should make sure they understand the system. Many subaru owners don’t and get into tricky situations a lot from my experience.

Having 4A was a requirement for me because of mixed highway snow conditions, not being able to see the road surface at night, and having a partner who doesn’t want to think about switching in and out of 4H.

 

[uncledoodoo]

Not really....in the 80s most used an actual differential in the transfer case ....with no computers controlling anything. These days there is a electromagnetic wet clutch pack, it is activated by an electromagnet which has various degrees of pressure available. This system uses a set of ball bearings in a truncated slots. The slots the balls roll in are tapered, so the further they roll up the ramp the more pressure is applied to the clutch pack. I've posted pictures of the internals already on other threads. This is controlled and activated by the computers. Also the system uses pulse width modulation at 12v input, NOT a solid 12v on/off type switch. This allows the system to apply pressure to the clutches in various degrees seamlessly. It can make hundreds of adjustments per SECOND...One of the best systems available.

4A . Full time 4wd, as opposed to part time. i.e. can be driven on the street and actually engaged as opposed to the OP original assumption that it stays in 2H until slippage.

 

[John Bronco_ I am here]

I disagree here wholeheartedly, the amount of slippage your referring to is so minimal it would not create ANY heat or wear UNLESS you go in tight circles endlessly or run tires that have big differences in air pressure or size. Most instances the difference front to rear is less than 2%. Not enough to wear anything out. Wet clutch are extremely durable and outlast dry clutches by far. They made their name in motorcycles most of which have NEVER needed the clutches replaced even with off-road abuse by less than perfect riders.

We will have to disagree padawan.

Note: It is because of people like you that I never buy used.

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