Question about 4WD Auto characteristics

[Lghtspeedz]

I have a 2020 Limited 4WD with the Heavy Duty Tow Package. It’s been cold and rainy here, so in some conditions traction is not as good. I don’t yet have winter tires on, so I’ve been utilizing 4A mode for extra grip I’m a few situations. Is it normal for the driveline to feel a little more coarse when accelerating in 4A mode? I’m not accelerating aggressively, but I can feel a little roughness through the engine and steering wheel. My previous vehicles were AWD, so it was pretty seemless. My one experience with 4WD is from an old ‘98 Explorer. I seem to recall a similar coarseness from that too but I guess I expected that to be refined out. Is this slight sensation a little normal?

Thanks all!

 

[BMW2FORD]

I do feel a difference in the return of the steering wheel on tight turns when accelerating (torque steer) and hear a little but more noise in 4wd. There are some discussions on this board that a slight ringing or metallic noise from the transfer case (around the center floor of the car) can also be heard in 4wd mode which all of these are pretty normal. I’ve driven a lot of 4wd cars and have to say this one has the most Jekyll and Hyde feel and sound between 2wd and 4wd. The one feel I don’t like that I’m still trying to figure out is that only in Sport 4wd in 3rd and 4th gears with about 1/3rd gas pedal load, there is a skipping feel from the driveline. It’s not there in normal 4wd or sport 2wd and no other transmission gears.

 

[99WhiteC5Coupe]

The 4A mode in my 2015 Expedtion sounds louder and coarser, than the 2H mode (dry or wet pavement).

 

[scottdm]

In 4A, the front hubs are locked and the front driveline is spinning, so it's normal in the Expy to feel the "coarse" feeling that is being described. This allows the transfer case to engage as needed to engage the front wheels. I almost always drive in 2H to avoid this issue unless the roads are snow covered.

 

[Lghtspeedz]

Thanks everyone. I suspected it’s normal. There are definitely some differences. Were it not for that coarse feeling, I’d probably prefer this mode. The front wheel engagement really makes the car feel more nimble to me. Ah well, it’s still a nice drive in 2WD.

Thanks again for putting my mind at ease.

 

[mr_dave]

In 4A, the front hubs are locked and the front driveline is spinning, so it's normal in the Expy to feel the "coarse" feeling that is being described. This allows the transfer case to engage as needed to engage the front wheels. I almost always drive in 2H to avoid this issue unless the roads are snow covered.

This is correct. We discussed this a little while ago and reached the same conclusion:

- 2H = rear wheels only (obviously) however front hubs will be engaged with engine off, or if there's a vacuum issue
- 4A = entire front drivetrain always engaged (hubs, diff, driveshaft) with the transfer case automatically applying power to the front as needed
- 4H = all 4 wheels driven all the time

Mechanic says not to use 4a all the time

I can spin the wheel in when off it just spins the shafts and driveshaft with it. I don’t think I’ve ever tried it running.

www.expeditionforum.com

 

[chuck s]

Not sure how the 2020 dash works but on my 2017 I can put one panel in the "off road" display mode and the dash will indicate where the power is going. Just a tiny goes to the front axle in normal driving with more as needed. There's also an inclinometer in that same display which is interesting in the mountains -- just don't get dashboard fixation.

I normally only engage 4A in the rain or other potentially slippery road conditions. (Or when my family borrows "the truck" for whatever reason they think they need it.) I can feel the added drag of the front axle immediately when I engage 4A.

-- Chuck

 

[mhExped]

I experienced a problem awhile back where my '18 Limited w/ HD Tow Pkg began making a grinding/rubbing sensation. Initially it was limited to 4A and when under load (driving uphill and/or towing), but got worse over time to the point where the symptoms could be felt/heard even in 2H and on level ground and w/o towing.

Turns out I had a bad front diff at that time. After that got replaced, the problem was "better" but I continue to feel a slight rubbing/grinding while in 4A under load. I do a decent amount of towing and drive on hills frequently and don't recall experiencing this when the car was new. The dealer tells me it's "normal" when in 4A due to the front hubs being locked.

Here's a repeatable scenario, I'm curious if anyone else wants to give it a try and report back...Find a hill in a quiet, less-trafficked area. Put the car in 4A and drive up the hill at a steady speed 10-15 mph to minimize road/wind/engine noise/vibrations - you can even drop into manual to take the trans out of the equation. Do you feel/hear the same regular/rhythmic rubbing/grinding? Do we all agree this is normal/expected?

@Lghtspeedz, I wonder if what I've described could at all be related to what you've described? Is the "roughness" you describe steady or rhythmic/pulsing? What if you repeat the test described above? Does the problem get worse or change in anyway?

 

[ROBERT BONNER]

Unexpected noises/vibrations are always something to be concerned about. That being said, with a vehicle equipped as yours (and mine) are, there is the eLSD in back and a viscous clutch transfer case amidships that are constantly varying torque transfer between the front and rear axles as well as between the two rear wheels while in any of the A4WD modes. As those clutches tighten/loosen and allow slip they make a lot of noise. The moaning and groaning coming out of those two clutch systems scared me half to death the first few times I took mine through mud holes off road with the windows down. Once you get used to it...you start to expect it. There is no doubt that any steering angle change in combination with any slip causes differences in clutch pressure and changes in the sounds. Additionally, if you are towing on anything other than perfectly dry, flat sand and gravel free pavement, you will experience enough slippage somewhere to change the pressure in the clutch(es).

 

[mhExped]

...constantly varying torque transfer between the front and rear axles as well as between the two rear wheels while in any of the A4WD modes. As those clutches tighten/loosen and allow slip they make a lot of noise...

That's the interesting thing about the uphill test I outline above...I hear/feel these vibrations/grinding even with constant speed, constant angle of ascent, steady steering (i.e., driving straight), dry smooth pavement, constant gear, etc. And, previously those symptoms (albeit more pronounced) indicated a trashed front diff.

Although these modern power delivery systems are capable of adjusting various aspects on-the-fly as conditions change, I wouldn't expect any changes to power delivery systems under constant conditions. Am I wrong here?