A4WD vs. 4WH ?
- Thread starter hlygrail
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IAExpy
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I belive A4WD (automatic 4 wheel drive) is when your truck is in rear wheel drive mode, but will automatically flip into 4WD if the rear wheels start to slip (like on an icy road, or in my case going through mud deeper than i expected) whereas 4WH is just your regular 4WD with normal gearing, as opposed to lower gearing (less confident about that answer)
someone else may be able to provide a more detailed answer
someone else may be able to provide a more detailed answer
sgtowing
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That about sums it up.
panda24619
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4wd is a pain in the but to turn with on the street. front tires want to go the same speed as the rear tires. A4wd is what IAE has already said. it switches on when it senses rear wheel slip. ford designed it to be used during the rain.
DF5.4
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A4WD engages the transfer case and engages the front axles when slip is detected. 4WH is full 4WD. Don't use it on dry pavement. It will wear/break something in the drivetrain.
DF5.4
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You can run anytime with A4WD. The only thing is you are still turning the transfer case and front drive shaft all the time. 4WDHigh you should not use all the time.
mindgame
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Is this correct? (Assuming that you place the Expy on all 4 jack stands, for diagnostics)
2H - Hubs disengaged, BUT transfer case still spins. Another words, front wheels will not spin, when though the half-shafts are spinning.
4AWD - Hubs disengaged, but if ABS sensor detects speed difference, IWE solenoid is disengaged to prevent vacuum from going to the hub actuators. Thus all 4 wheels end up spinning.
4H - All wheels ar espinning.
4L - All wheels spinning...
Just asking.. When on the road, when I switch to 4AWD, it sounds and feel like 4H is on instead... Anyone experienced this? I have already repalced the IWE solenoid.. I am thinking I am having ABS/Speed sensor issues...
Thanks1
2H - Hubs disengaged, BUT transfer case still spins. Another words, front wheels will not spin, when though the half-shafts are spinning.
4AWD - Hubs disengaged, but if ABS sensor detects speed difference, IWE solenoid is disengaged to prevent vacuum from going to the hub actuators. Thus all 4 wheels end up spinning.
4H - All wheels ar espinning.
4L - All wheels spinning...
Just asking.. When on the road, when I switch to 4AWD, it sounds and feel like 4H is on instead... Anyone experienced this? I have already repalced the IWE solenoid.. I am thinking I am having ABS/Speed sensor issues...
Thanks1
Idahokid
Full Access Members
I was useing the 4awd last night since we got 6-8 inches of snow.I think it works slick.Sometimes on pavement,then slick ice.The 4awd doesn't jerk going around corners.The 4wd drive is like any other 4wd.4awd runs in 2wd untill the tires slip then goes into 4wd and back to 2wd when tires stop spinning.It was the first time I used it and worked good.
In Four High (4H) mode, the center multi-disc differential (inside the transfer case) is locked, locking the front and rear propeller shafts together for a permanently locked front:rear 50:50 torque spilt.
Due to this "locked-up" nature, Four High should NEVER be used on pavement, not even on wet pavement. Torque windup and drivetrain binding will occur, which will shorten the life of the four-wheel drive system. Under prolonged binding, drivetrain failure will occur.
Sometimes people will describe Auto mode as "its like a automatic Four High. Under slip it auto engages Four High", or some similar description.
This is rather incorrect as Auto mode is a bit more complex than that. The front axle, front differential, and front propeller shaft are always engaged in Auto mode, whether they receive torque or not.
Also, torque is sent to the front wheels in 10 percent increments (10, 20, 30, 40, up to 50 percent - 100 percent in newer versions) based on tractive conditions and wheel slip.
The front:rear torque split in Auto mode (for the BorgWarner 4406 transfer case) is variable from 0:100, 10:90, 20:80, 30:70, 40:60, up to 50:50 (lock). As the center multi-disc differential allocates the engine’s torque output, increasing the percentage of torque sent to the front wheels, the percentage of torque sent to the rear wheels is decreased. The torque split is also adjusted or "fine-tuned" if wheel slip lessens or worsens while torque is being transferred.
Auto mode will not keep the 50:50 torque split very long, to guard against torque windup and drivetrain binding while on pavement.
From 2003 to present (BorgWarner 4416 and 4417) the ControlTrac system can send 100 percent of the engine’s torque output to the front wheels – for "temporary front-wheel drive". This capability of putting 100 percent of torque to one axle or the other is called "torque biasing".
The front:rear torque split in Auto mode is variable from 0:100, 10:90, 20:80, 30:70, 40: 60, 50:50, 60:40, 70:40, 80:20, 90:10, up to 100:0.
ControlTrac four-wheel drive is not you’re grandfather’s 4x4 system. It has a computer control system with dedicated microprocessor, and advanced control software that is artificially intelligent.
In Auto mode, it thinks and learns. Its also monitors your driving input and from 2003 onward, it can also predict traction loss before it happens.
Even when you think its driving along sending torque to the rear wheels, it will periodically supply torque to all four wheels. In this respect, its very much a full-time system.
Due to this "locked-up" nature, Four High should NEVER be used on pavement, not even on wet pavement. Torque windup and drivetrain binding will occur, which will shorten the life of the four-wheel drive system. Under prolonged binding, drivetrain failure will occur.
Sometimes people will describe Auto mode as "its like a automatic Four High. Under slip it auto engages Four High", or some similar description.
This is rather incorrect as Auto mode is a bit more complex than that. The front axle, front differential, and front propeller shaft are always engaged in Auto mode, whether they receive torque or not.
Also, torque is sent to the front wheels in 10 percent increments (10, 20, 30, 40, up to 50 percent - 100 percent in newer versions) based on tractive conditions and wheel slip.
The front:rear torque split in Auto mode (for the BorgWarner 4406 transfer case) is variable from 0:100, 10:90, 20:80, 30:70, 40:60, up to 50:50 (lock). As the center multi-disc differential allocates the engine’s torque output, increasing the percentage of torque sent to the front wheels, the percentage of torque sent to the rear wheels is decreased. The torque split is also adjusted or "fine-tuned" if wheel slip lessens or worsens while torque is being transferred.
Auto mode will not keep the 50:50 torque split very long, to guard against torque windup and drivetrain binding while on pavement.
From 2003 to present (BorgWarner 4416 and 4417) the ControlTrac system can send 100 percent of the engine’s torque output to the front wheels – for "temporary front-wheel drive". This capability of putting 100 percent of torque to one axle or the other is called "torque biasing".
The front:rear torque split in Auto mode is variable from 0:100, 10:90, 20:80, 30:70, 40: 60, 50:50, 60:40, 70:40, 80:20, 90:10, up to 100:0.
ControlTrac four-wheel drive is not you’re grandfather’s 4x4 system. It has a computer control system with dedicated microprocessor, and advanced control software that is artificially intelligent.
In Auto mode, it thinks and learns. Its also monitors your driving input and from 2003 onward, it can also predict traction loss before it happens.
Even when you think its driving along sending torque to the rear wheels, it will periodically supply torque to all four wheels. In this respect, its very much a full-time system.
Last edited:
rexster314
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I know it just works and works great. When I have A4WD on in the rain I can tell it's more surefooted
hammerg26
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I have seen a lot of posts on the "Brown Wire Mod", and I don't really want to start messing with "stock"...
However, question is this: how much "drag" is caused by the transfer case / front diff when the A4WD is not "engaged" (i.e. computer not sensing the rear wheels spinning)? I ask for this reason - on a hill by my house which I travel everyday in either my truck (99 Expy 4x4 with 5.4 and 4r100) or a 2008 Suburban 4x4 (with 2wd, Auto, 4hi, 4 low) in "2wd only" and the Suburban picks up considerably more speed (i.e. crest of hill at 45 mph in both yields 48 - 50 mph in my truck, and over 50 mph consistently in the Suburban).
Any ideas?
However, question is this: how much "drag" is caused by the transfer case / front diff when the A4WD is not "engaged" (i.e. computer not sensing the rear wheels spinning)? I ask for this reason - on a hill by my house which I travel everyday in either my truck (99 Expy 4x4 with 5.4 and 4r100) or a 2008 Suburban 4x4 (with 2wd, Auto, 4hi, 4 low) in "2wd only" and the Suburban picks up considerably more speed (i.e. crest of hill at 45 mph in both yields 48 - 50 mph in my truck, and over 50 mph consistently in the Suburban).
Any ideas?
A 1999 Expedition will not be as efficient as a much-newer 2008 Suburban or even a 2008 Expedition for that matter. Your Suburban may be producing more torque, have different gearing, tire size, etc. I do know throttle response will be improved on the newer Suburban over a 1999 Expedition. All those things must be taken into account. There is never a "silver bullet answer".
The drivetrain/front axle for Auto mode, when in good working order, has little resistance – virtually none. This "back-driving resistance" of the front axle when torque is not supplied was reduced even further with the 2003 model Expedition redesign.
Axle resistance also translates into mpg. To give you an idea – as far as axle resistance – the Two High mode offers only a half-a-mile per gallon of gasoline improvement over Auto mode. That’s how little resistance there is, and shows there is almost no improvement in mpg concerning Two High vs. Auto.
This mpg improvement figure is solely based on axle resistance, not how much Auto mode calls the center multi-disc differential into action. Naturally when the center multi-disc differential is transferring torque front and rear, mpg will increase a little more.
The drivetrain/front axle for Auto mode, when in good working order, has little resistance – virtually none. This "back-driving resistance" of the front axle when torque is not supplied was reduced even further with the 2003 model Expedition redesign.
Axle resistance also translates into mpg. To give you an idea – as far as axle resistance – the Two High mode offers only a half-a-mile per gallon of gasoline improvement over Auto mode. That’s how little resistance there is, and shows there is almost no improvement in mpg concerning Two High vs. Auto.
This mpg improvement figure is solely based on axle resistance, not how much Auto mode calls the center multi-disc differential into action. Naturally when the center multi-disc differential is transferring torque front and rear, mpg will increase a little more.
hammerg26
Full Access Members
Excellent - thank you.
One note I neglected to clarify in my original post - when I said "...picks up considerably more speed...", I meant to convey those speeds were COASTING DOWN from the crest of a hill, not getting to the top of it...
That being said, I think your response still applies, and I greatly appreciate your thoughts.
Hammer
One note I neglected to clarify in my original post - when I said "...picks up considerably more speed...", I meant to convey those speeds were COASTING DOWN from the crest of a hill, not getting to the top of it...
That being said, I think your response still applies, and I greatly appreciate your thoughts.
Hammer
spncrgr
New Member
Thanks so much for this explanation. My Dad and I were just having a "heated" discussion about this, this morning, and this post clears it up for me!
What are your thoughts on this scenario:
When driving on snowy/icy roads in A4WD I notice the truck is harder to control through acceleration, coasting, and, especially, braking. However, when I switch to 4H, control is much better and everything feels more "stable". Is that an appropriate use of 4H? How much would tire type & condition affect the ControlTrac system's ability to appropriately compensate?
What about when the snow & ice is patchy? Based on the comments here, it sounds like it's just best to leave it in A4WD? For example, I was on a road yesterday, turned a corner, where there was a large patch of ice, and started to lose control. If I'm in an area where I know there's going to be a lot of patches of ice and snow, am I better off leaving it in A4WD, or should I temporarily switch it to 4H until I'm out of that area?
Thanks!
What are your thoughts on this scenario:
When driving on snowy/icy roads in A4WD I notice the truck is harder to control through acceleration, coasting, and, especially, braking. However, when I switch to 4H, control is much better and everything feels more "stable". Is that an appropriate use of 4H? How much would tire type & condition affect the ControlTrac system's ability to appropriately compensate?
What about when the snow & ice is patchy? Based on the comments here, it sounds like it's just best to leave it in A4WD? For example, I was on a road yesterday, turned a corner, where there was a large patch of ice, and started to lose control. If I'm in an area where I know there's going to be a lot of patches of ice and snow, am I better off leaving it in A4WD, or should I temporarily switch it to 4H until I'm out of that area?
Thanks!
hammerg26
Full Access Members
The issue with running 4WD "just in case" is that if the wheels cannot slip, you risk doing damage to the differential / transfer case. In your example, had you turned the corner in 4WD, and there had not been ice, you may have some binding occur, and thus damage.
Last week we had some ice here in ATL, and I was in A4WD almost all the time. When I got to places I knew were icy, then I moved it into 4WD and the truck was a champ.
Last week we had some ice here in ATL, and I was in A4WD almost all the time. When I got to places I knew were icy, then I moved it into 4WD and the truck was a champ.
ExpeditionAndy
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The first week of January we got about 12" of snow. The roads were unplowed and I ran in 4WD Low because 1. I wasn't going over 40 MPH 2. I have air suspension and I wanted the clearance (air suspension raises a couple of inches in 4WDL). After the roads were plowed and they couldn't get down to pavement, I ran in 4WD High to get better grip until the snow started to melt and we started to see pavement a couple of days later, then I switched back to AWD. Once we were back to dry pavement, (a couple of days after that) I switched back to 2WD and the truck worked like a champ. I'm totally happy with it.
Expedition907
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winter time I use A4WD, works fairly well. summer time 2wd unless im crossing a shallow river out in the country ill use 4wd
One of the things I've read is using 4x4 Low on ice and snow isn't a good thing because the extra torque to the wheels can cause them to lose traction. The possible exception being a deep snow where losing traction wouldn't be as big a deal. With my '11 EL, I usually drive around in 2H. I'll usually switch to AAWD during wet conditions (just to periodically use that mode) and patchy snow/ice conditions. I'll use 4H and 4L as conditions merit. Usually only going to 4L in deep sand where I didn't air down enough and get stuck. Or, if I haven't run it in a while and am on gravel/sand/grass surfaces.
Here's a site with rich information on 4x4 systems and using 4x4 in various conditions. Note that AWD systems he is referring to are not the same as Auto 4x4 mode for our pat time 4x4 vehicles:
all 4WD/AWD on one page - a simple, easy to understand overview - all available 4WD, all wheel drive and 4x4 systems and their differences - 4WD concepts, their function, their layout, their purpose, their advantages
As an added bonus, here's a great reference to the Ford IWE system that engages and disengages the front wheel hubs. This is important to know.
Everything You Wanted To Know About The IWE System....And Then Some! - F150online Forums
Enjoy!
Here's a site with rich information on 4x4 systems and using 4x4 in various conditions. Note that AWD systems he is referring to are not the same as Auto 4x4 mode for our pat time 4x4 vehicles:
all 4WD/AWD on one page - a simple, easy to understand overview - all available 4WD, all wheel drive and 4x4 systems and their differences - 4WD concepts, their function, their layout, their purpose, their advantages
As an added bonus, here's a great reference to the Ford IWE system that engages and disengages the front wheel hubs. This is important to know.
Everything You Wanted To Know About The IWE System....And Then Some! - F150online Forums
Enjoy!
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