Bearing/Different Issue - Bearing Noise at 30-50mph...

[medmo54]

I'm having issues with my 2002 Explorer 4WD 4.0L -- it started with a slight "humming" noise from the front end...can start to hear it at about 20 mph and gets really loud at 30-40 mph -- then seems to go away after about 50 mph. Here's what I have checked/replaced:

1. First, really thought it was a wheel bearing as they seem to be pretty common and really sounded like it was coming from the left front -- also, ABS light is on. Replaced left front wheel bearing -- no change in noise.

2. Wondered - maybe both wheel bearings were bad or I replaced the wrong side? ABS light still comes on as well. Put ohmeter on hub (ABS speed sensor) I removed, no resistance --- checked new one I put in and shows .856. Checked the right front and that one doesn't have any resistance either. Went and got another bearing and replaced right front -- noise and ABS light both still there.

3. After researching I am wondering if I have a front diff problem. I haven't pulled the cover off yet to look but am willing to -- just wanted to get some feedback. I thought about CV axles but doesn't seem to be similar to ones I've dealt with in the past....

4. Full symptoms -- humming/bearing type noise now heard pretty much all the time but worst at 30-40 mph. Lock into 4wd and gets louder yet. Turning left or right doesn't seem to effect the noise much. Noise can almost be "felt" under feet on drivers side floorboard. No popping/clicking noises while turning regardless of speed. Noise goes away periodically if I let off gas (ex....if I take off from a stoplight noise starts to get bad about 30 mphs -- if I get to my cruising speed and lightly let off the gas it seems to go away as quickly as I take my foot off the throttle -- but as soon as I apply any pressure to gas pedal again it comes right back.) Noise pitch changes with actual speed and not RPM's.

Any help would be great...maybe others have had this same issue? I've researched on here alot and find alot of similar stuff but almost every single one of them seems to end with a bad wheel bearing -- wish that was the case for me! (I've come to the conclusion also that maybe the ABS issue is something more wiring related or possibly in one of the sensors in the rear end....I will diagnose that further to make sure it's not a wiring issue or whatever -- this noise just really worries me)

Thanks in advance!

 

[jav1]

Not an expert but I've gone through most of this. Wheel bearings are a fairly common weakness. Constant hum from the front is usually the wheel bearings but replacing them fixes the noise instantly.

Having said that, wheel bearing usually do not respond to lifting off the throttle...the bad news is that differential gear whine does (another weakness in our cars). I just redid the rear differential in mine (as well as the rear wheel bearings) and all is quiet again. I've not heard of any front diff failures... and I'd be surprised if it was the problem sinsce it's not seeing load under normal circumstances so it shouldn't repsond to accel/decel noises.

The ABS sensor on top of the rear diff is yet another weak link- I've replaced mine twice- both times curing the ABS light.

BTW- everything I've read (and in speaking with a few top notch guru's), all suggest the noise is annoying and nothing more. It shouldn't have any effect on reliability or longevity. I can confirm that when I redid my diff, the bearings and gears looked perfect... almost a shame to change them and I started to question if that was the source of the noise. I did it anyway and the noise is gone which I'm told is quite common.

 

[medmo54]

Thanks jav1 -- yeah, I kind of thought that might be the case...unfortunately. My question - did you end up pulling the whole thing out to fix it? I was a auto tech for 6 years but have been in the boat business for the last 5 years and am kind of out of loop on this stuff all the sudden. I was thinking to myself that you could tear all the way down to removing the CV shafts and be able to replace the seals/bearings where those go into the differential? Maybe I'm wrong on this...just trying to figure out the best way to go about repairing this. It doesn't look too horribly hard to get the whole unit out of I needed to -- maybe remove all that stuff and drive it as a 2WD while I go thru the diff if that's the case.

Also - you were right on with that rear speed/ABS sensor. I had a feeling that was what it was -- will pick one up today and get that taken care of. Thanks again!

 

[jav1]

I did pull the whole diff (rear one). Servicing it in the truck is not possible in the rear. Not sure on the front but again- I tend to doubt the front one is the noise source since it's not seeing loads normally.

 

[medmo54]

Oh - ok, I was really leaning towards the front one being the issue because I can "feel" the noise right under my feet while driving and that's where the front is. Also - seems to get worse when putting in 4wd and driving it. Wondering if maybe it's be worth pulling the shaft off going to the front and driving it to see if the noise goes away?

 

[jav1]

Am I correct that you only replaced 1 front wheel bearing? If it were me, I'd have replaced both sides I just bought new hubs- they weren't too expnesive- an my front end noise disappeared.

I'm not sure pulling the front shaft is going to do much but it may be worth a shot if your convinced the noise IS coming from the front. I'm not sure if you can run without the front shaft and I'm not sure if the front diff won't still be backdriven by the wheels.

I'd be more inclined to have someone drive the car while you climb arund the back to better isolate the noise source. Vibrations/noise tend to carry and their source can sometimes be easier to pin point by listening from different locations.

 

[medmo54]

Good point - maybe that's a good next step. I did replace both front wheel bearings. You very likely might be right about the noise traveling...it's just stuck in my mind it's the front because of hearing and feeling the noise right under the drivers front floorboard. I'll have to do a little more digging and I'll let you know what I find. Thanks for the ideas!

 

[jrford]

do you have access to a hoist. One trick is lift it on a hoist and get all the weight of the wheels. using a stethoscope listen to each bearing as you rotate each wheel.

Try and find someone who can pull ABS codes, that will pinpoint it. Most common reasons for the ABS light are: Brake Master Cyl switch ($20 part), Rear ABS sensor on the diff ($50), then front bearings.

 

[medmo54]

Thanks for the info - I think that might be my best option right now. I hadn't really paid attention as I thought for sure this was a wheel bearing issue -- but after looking under the truck this morning I see the rear end is pretty wet with fluid leaking. Again - it sure sounds like it's in the front end but maybe it's just traveling through the transfer case/front drive shaft? I think I will try the stethoscope thing and probably just pull both front and rear diff covers off to take a look. Front one doesn't seem to be leaking (at least not "wet" like the rear is) but does have some build up on it.

Any other ideas are welcome - thanks for all the help and I'll hopefully be able to check all this over the weekend and report back!

 

[jav1]

You can't pull the back cover on the rear diff without taking the diff out. The rear diff cover actually has the 2 main mount points to the frame. The whole diff must come out to get the cover off.

Also- seeing whats the causing the noise is unlikely even taking everything apart... just removing the cover won't allow acces to see anything but catastrophic defects which would likely produce much more horrendous noises than you described.