2015 Ecoboost - Humming from Front Driver Side Wheel in 4A

[Aaron407]

I noticed on the weekend that our 2015 Navigator (same engine/drivetrain as an Expedition but a heftier price tag) had a subtle but more noticeable humming noise specifically from the front driver side wheel area when driving at highway speeds in 4A. The sound goes away completely after switching to 2WD, sounds almost like light engine braking, and is not really noticeable under about 55 MPH. I've noticed other people mentioning noise related to IWE still partially locked when switching to 2A, but I haven't found info on noise only when in 4A. Would it be worth changing out the 4WD solenoid and check valve to rule them out since they're reasonably cheap? Any ideas of what else it could be? It sounds like it's coming specifically from the one corner, so I'm leaning away from transfer case issues, but I'm not sure.

 

[99WhiteC5Coupe]

I noticed on the weekend that our 2015 Navigator (same engine/drivetrain as an Expedition but a heftier price tag) had a subtle but more noticeable humming noise specifically from the front driver side wheel area when driving at highway speeds in 4A. The sound goes away completely after switching to 2WD, sounds almost like light engine braking, and is not really noticeable under about 55 MPH. I've noticed other people mentioning noise related to IWE still partially locked when switching to 2A, but I haven't found info on noise only when in 4A. Would it be worth changing out the 4WD solenoid and check valve to rule them out since they're reasonably cheap? Any ideas of what else it could be? It sounds like it's coming specifically from the one corner, so I'm leaning away from transfer case issues, but I'm not sure.

Often a humming sound indicates a wheel bearing issue.

The solenoid and check-valve would not cause a humming noise. If one or both were defective, it could cause an issue with the IWE hub engagement, which sounds like a clicking noise (such as taking an empty 12-oz. aluminum soda pop can and trying to bend it).

 

[Aaron407]

Normally I would think wheel bearing when there's humming, except that it goes away in 2WD and it doesn't really vary in tone depending on speed. It's a bit more 'rough' of a sound than a consistent hum as well. When I was thinking about the IWE, I was wondering about the possibility of it not having fully engaged and having something rubbing. I'll probably jack it up and check for play in the wheel bearing just to rule it out, though, and maybe manually toggle the 4WD to see if things are locking and unlocking properly. We have had issues with the IWE system on that wheel before, but it seemed to be remedied a couple of times by replacing the check valve.

 

[Aaron407]

Update:

Now the humming is still there in both modes, but the tone drops slightly when I switch from 4A to 4x2. When I switch from 4x2 to 4A at speed, the humming sound briefly goes away completely, then comes back. I discovered that if I stop and turn the steering wheel full left (haven't tried full right), I can drive for about a quarter mile with no humming sound before it abruptly comes back. I also found that if I play with the throttle a bit at about 65 MPH, I can get it to briefly stop humming for about a second, but downshifting to 5th or 4th doesn't change it. Maybe vacuum related, but I'm not sure.

I jacked up the corner and toggled the AWD mode and it seemed to operate as expected in terms of locking to the axle. However, starting in 4A, I then cranked the wheel all the way to the left and noticed that it wouldn't switch - the IWE was locked in in both modes and there was no vacuum on the line. However, I straightened out the wheels and switched to 4x2, which it did just fine, then turned the wheel full left again. This time it had vacuum on the line as expected.

So, I'm trying to figure out a couple of things:

-Will the system not allow unlocking the IWE when at full steering lock?
-Is this maybe just intermittent/weak vacuum being applied to the IWE? I replaced the actuator, which made no difference. I had replaced the check valve a few years ago, but maybe it's the issue again? Blowing into it from each side suggested it was working, but maybe not well enough.

Anyway, I'm hoping for some thoughts. If I need to replace the IWE, no big deal, but I don't want to go through all of that if the issue is elsewhere.

 

[Aaron407]

New check valve made no difference, unfortunately.

 

[07mustangman]

Had a problem in my 2011 with the four-wheel drive doing the same thing in the front. It turned out to be the airline was broke almost completely in two going from one wheel to the further in the front. Had already replaced the solenoid and check valve and that didn't help. Might want to check your line that goes from one side in the front to the other and also at the wheels.

 

[Aaron407]

Thanks, I'll take a look. Considering that it can be in a spot where it's "happy", or at least not making the humming noise, it really seems like a vacuum issue.

 

[07mustangman]

Glad I could help. I tested my hubs with vacuum pump to make sure they operate ok. Found some videos on YouTube about how to test them. Good luck.

 

[Aaron407]

Yeah, I plan on jacking it back up and putting my hand vacuum pump on, then rotating the hub to see if it still holds vacuum properly in case the seal is bad. The lack of vacuum switching from 4wd to 2wd at full left lock is a weird thing, though. I haven't found anything online that says it would be blocked from switching, which makes me wonder if maybe there's a vacuum line problem, maybe at the other wheel, that fully loses vacuum when turned to the left. Lots of troubleshooting to do at any rate.

 

[Utah Driver]

My 16' basically does the same thing for years. I think it's normal. The cabin is very quiet so you are hearing the transfer case and power transfer. I've put mine on jack stands and checked it out. 4A drops my fuel mileage by 2 mpg so I only use when roads are wet or snowy.

 

[Aaron407]

I wouldn't be as concerned if it had always done this, but it was fine for the previous 155,000 miles and just started making the louder noise.

 

[Aaron407]

Latest update: I just tested both front IWEs under vacuum. They both held 16" with no issues, including when rotating the wheels.

I also tested vacuum level from the system at each IWE, which came in at 26". There was no variation when cranking the wheel either.

Since everything seems to be locking and unlocking as expected, but it will still go without a hum for a short distance after going full left lock, I can't help but wonder if it's the wheel bearing getting shifted a bit and re-seating to the noisy position after that distance (which is weirdly consistent, by the way). There was no discernible play in the bearing, though.

One thing I hadn't mentioned is that this vehicle spends a large amount of time on the gravel. I didn't see anything, but maybe there's a stone lodged somewhere? Kind of grasping at straws...

 

[Aaron407]

New updates in my hopes of figuring this out:

I replaced the hub/bearing and IWE. Everything's back together and functioning, but the sound is still there. I also noticed that abruptly pulling off the throttle when at highway speed will usually see the sound briefly go away completely. I'm making an appointment to take it into a shop, but the working theory now is a bad pinion bearing in the front differential. I guess we'll see. I'd be open to any other thoughts as well!

 

[tacoduck]

Just curious, why are you running in 4a at highway speeds? I was told growing up to never run 4wd above 45-55 mph.

 

[Aaron407]

4A is fine to use basically all the time since it just adds spinning weight of the axles with the IWEs locked but nothing is actually being powered unless there's a loss of traction since the clutch isn't normally being applied in the transfer case.

Per the manual regarding 4A: "This mode is appropriate for all on-road driving conditions, such as dry road surfaces, wet pavement, snow, or gravel."

We live on a gravel road up in Saskatchewan and like the extra assurance versus just 2WD mode. We don't run in 4x4 mode unless we're really stuck, though, as that would be continuously applying the clutch in the transfer case and would be brutal on the driveline on dry ground.

 

[Aaron407]

Final follow-up: we took it into a shop and they found the CV-type joint on the front driveshaft was broken. They replaced the driveshaft and the noise is gone.

 

[Machete]

Service your transfer case. Also, I don't recommend only doing one axle. Its like doing ball joints or shocks on one side.