Rear whinning noise. Rear differential or bearing Problem??

[jaesto]

I have a 2002 Montaineer AWD and the famous rear whinning noise started about a week ago. It starts at around 40 MPH and it gets better at 75 MPH; however, it does not go away. The noise stays if I accelerate or not and even when I change to Neutral while driving, no difference at all. No changes if I turn right or left.
I changed the front wheel bearings about a year ago and that noise was very obvious because it got worse when turning.
What are the symptoms for bad rear wheel bearings?. Do they make more noise when turning?.
I am trying to determine if the problem is coming from the rear differential (ring and pinion issue), the rear wheel bearings or perhaps something else I may be missing.

 

[Carguy3J]

Jack up the rear (wheel(s) off the ground) Grab the tire and try (hard) to move it in various directions it shouldn't go. A little in/out play is ok. That's the axle moving a little in the diff. Movement in any other direction is BAD, and a sign of wheel bearing going. My landlord has had two of them go on his. He didn't bring it to me until they were, literally, about to fall apart. Don't ignore a wobbling wheel.

 

[thepotroast]

The rear diff whine usually goes away when you let off the throttle....if it's a diff clutch pack or ring/pinion issue. In your case, you're saying the sound is there whether or not you're on the gas, which sounds more like a bearing issue.

My diff makes the humming sound from the 35-45MPH range, after that it quiets down, but if I let of the gas anywhere in that range, the sound also goes away. Ford already replaced the diff clutch pack and R+P in this X at 60k miles, the sound is back and I'm at 132k now....not going to have it serviced again for the same issue :thumbdwn:

As Carguy said above, jack up the rears, and check for any play. However I have to disagree with what he says about a little wobbly being ok. Explorer's don't have a solid axle, the wheels bearings aren't in an axle, they are a hub assembly that the axle shafts slide into. There should be no wobbling whatsoever. If there is play, they are going bad, if there is lots of play...replace them NOW.

 

[clarks2001]

I was told by "manny moe and jack" (pep boys) lol that there are axle bearings inside the diff where the axle meets at that could go. I was thinking that was a load of poo, so i went to ford and they said that it is the rear wheel bearing, having had the passenger one replaced not too long ago, would i be correct to assume its the driver side? What if there is no play in the wheel? My front passenger wheel had no play when i went to work on it, pulled the hub off and turned it in my hand and it felt and sounded rough, put the new one on and all was fine.

 

[Carguy3J]

The rear diff whine usually goes away when you let off the throttle....if it's a diff clutch pack or ring/pinion issue. In your case, you're saying the sound is there whether or not you're on the gas, which sounds more like a bearing issue.

My diff makes the humming sound from the 35-45MPH range, after that it quiets down, but if I let of the gas anywhere in that range, the sound also goes away. Ford already replaced the diff clutch pack and R+P in this X at 60k miles, the sound is back and I'm at 132k now....not going to have it serviced again for the same issue :thumbdwn:

As Carguy said above, jack up the rears, and check for any play. However I have to disagree with what he says about a little wobbly being ok. Explorer's don't have a solid axle, the wheels bearings aren't in an axle, they are a hub assembly that the axle shafts slide into. There should be no wobbling whatsoever. If there is play, they are going bad, if there is lots of play...replace them NOW.

I wasn't referring to a wobble, but rather straight in/out play. But yes, you are right, the 3rd gens (Not all explorers) have an IRS rear, so they should no play at all. However, 1st gen ('91-'94) and 2nd gen ('95-'01) do have solid axle rears, and in that case the in/out play would be a normal condition.

 

[Opera House]

I wouldn't just assume it is the other wheel bearing that is bad. If the wheel bearing was not torqued down enough, that bearing could be bad in a year.

 

[thepotroast]

I was told by "manny moe and jack" (pep boys) lol that there are axle bearings inside the diff where the axle meets at that could go. I was thinking that was a load of poo, so i went to ford and they said that it is the rear wheel bearing, having had the passenger one replaced not too long ago, would i be correct to assume its the driver side? What if there is no play in the wheel? My front passenger wheel had no play when i went to work on it, pulled the hub off and turned it in my hand and it felt and sounded rough, put the new one on and all was fine.

Well there are of course bearings inside the diff where the axle shafts slide into, but more than likely this is not the cause of the hum at all. It is pretty much always the diff clutch pack, pinion & ring, or bad rear hub/bearing assemblies. Easy to tell the difference, because if it's bearings...the hum doesn't go away when you let off the gas...if it does go away, then it's inside the diff, because bad bearings will make noise whether you're on the gas or not.

 

[jaesto]

Well. It looks like it may be the rear driver's side bearing going bad. I am not sure 100% yet but that was the only wheel with a little play (not much) when I lifted the car up.
Assuming that I have to change that wheel bearing.
Should I change both the hub and bearing or only the bearing itself and use the same hub. The bearing is about $70 and the hub/bearing set is around $130. I do not want to spend the higher amount if I do not have to. Any issues with changing only the bearing?
Do you guys know where I can have the bearing pressed in on out of the hub/knuckle (NAPA, Autozone, Advanced parts ?????)

 

[thepotroast]

Well. It looks like it may be the rear driver's side bearing going bad. I am not sure 100% yet but that was the only wheel with a little play (not much) when I lifted the car up.
Assuming that I have to change that wheel bearing.
Should I change both the hub and bearing or only the bearing itself and use the same hub. The bearing is about $70 and the hub/bearing set is around $130. I do not want to spend the higher amount if I do not have to. Any issues with changing only the bearing?
Do you guys know where I can have the bearing pressed in on out of the hub/knuckle (NAPA, Autozone, Advanced parts ?????)

It's a general rule of thumb on the rear bearing replacement to also replace the hub as well. As you know, that assembly has to be pressed in (unlike the fronts which are a complete pressed unit). You will have to take the bearing/hub to a machine shop or an auto repair shop that can press it in for you. The auto parts stores do not perform that service. You do not want to use the old hub, because the bearing/hub that are currently on it "groove" the mating surfaces, and if you have a worn bearing, that also means that the hub is likely worn in that grooved surface, and putting a new bearing into a worn part will lead to failure.

I wish there were complete units made for the rears, it's been discussed on here before that if someone with a press would perform this and sell the completed units, there would be a demand for it. So you'll have to buy that $130 set (which also comes with a snap ring) and have a shop press it in for you. The rest is pretty easy to do, much more so than the front on a 4x4

Glad you found the culprit...my rears need to be done soon as well, I did my fronts about 10k miles ago, and didn't much enjoy the work associated with it...due to stubborn hub bolts in the old assemblies. The PITA with the rear is just getting the bearings pressed into the new hub. If you have the time and dough, just get both done at the same time. If one is failing, the other is right behind it.