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2nd Gen - 2003 - 2006

A4WD vs. 4WH ?


This is a discussion on A4WD vs. 4WH ? within the 2nd Gen - 2003 - 2006 forums, part of the Ford Expedition Forum category!
Can anyone tell me the difference between A4WD and 4WH? When to use one over the other? Thanks, Chris...



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Old 12-06-2011, 08:03 PM   #1 (permalink)
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Default A4WD vs. 4WH ?

Can anyone tell me the difference between A4WD and 4WH? When to use one over the other?


Thanks,
Chris
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Old 12-06-2011, 08:14 PM   #2 (permalink)
 
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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
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Old 12-06-2011, 08:16 PM   #3 (permalink)
 
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That about sums it up.
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Old 12-06-2011, 08:18 PM   #4 (permalink)
 
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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.
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Old 12-06-2011, 08:25 PM   #5 (permalink)
 
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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.
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Old 12-06-2011, 09:23 PM   #6 (permalink)
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You guys are great!

It sounds like A4WD is pretty smart, but I understand I shouldn't keep it engaged unless driving during poor weather conditions, right?
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Old 12-06-2011, 09:37 PM   #7 (permalink)
 
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Originally Posted by hlygrail View Post
You guys are great!

It sounds like A4WD is pretty smart, but I understand I shouldn't keep it engaged unless driving during poor weather conditions, right?
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.
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Old 12-07-2011, 02:34 AM   #8 (permalink)
 
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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
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Old 11-10-2012, 10:57 AM   #9 (permalink)
 
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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.
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Old 01-30-2013, 10:18 PM   #10 (permalink)
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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.

Last edited by LocDoc; 02-16-2014 at 12:25 AM.
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