Wheel bearings? Rear diff?

[AZShawn]

A little info on the truck: it's a '99 A4WD 3.73 w/ LS

I've had a mysterious howling/roaring sound for years that I honestly have a tough time hearing if it's coming from the front or rear. It's also accompanied by a vibration at highway speeds, which I always assumed was from crappy tires/worn out suspension. Over the last couple years I've refreshed the front suspension, got an alignment, and put some new tires on. I definitely noticed an improvement BUT I still have the noise, and very slight vibration.

The noise coincides with throttle, the second I let off the pedal it quiets down quite a bit. I barely feel the vibration, but I can see my passenger seat, and my kids carseat in the middle row, shake while i'm driving.

I removed the front driveshaft a couple weeks ago and it has made no difference. I'm leaning towards rear wheel bearing, I just jacked it up and tried to test for play on the wheel but no noticeable play. I spun the tires and there is a little noise but it just sounds like it's probably the brake pads.

Should I be at all concerned about the differential or its bearings? Or do you think it is likely wheel bearings even though I didn't notice much play with the wheels in the air?

 

[coupe11]

I've had a couple bearing issues over the years (not in a Ford).

One one it was the inboard bearing on the driver's side. I'd hear the rear end howl when I pushed the pedal down. The worn bearing allowed the pinion gear to push the ring gear further to the left which changed the spacing between the gear teeth. Let up and the noise changed/went away. Press the pedal down and it would come back.

On the other one it was an outboard wheel bearing on the passenger side. I could barely hear that one and only when accelerating and turning to the right.

Sometimes you just have to pull the cover and take a good look at the gear oil for metal particles or jack it up, grab the wheels and see how much you can move it around (up, down, left/right).

 

[Trainmaster]

It's more likely a front bearing than a rear, though it's very hard to differentiate. Sometimes they show no play, and only make noise under load. Try taking some turns and see if the noise changes between right leaning and left leaning turns. That will nearly assure it's a wheel bearing, but it's still difficult to tell which side.

You can run the car up on a lift or jacks and see if the vibration is still present. That should eliminate wheel bearings and possible point to a driveline problem. Have you checked your rear driveshaft universal joints and that slip joint? They wear also, and I've replaced them in my 2000.

The truck's 23 years old, and it could be any bearing, but normally the fronts and "u" joints are the ones that fail soonest.

 

[AZShawn]

Thanks all! My gut is telling me it is rear end (though I could be wrong). I just need to decide if I want to save some money and just do the rear wheel bearings/seals and hope that takes care of it, or if I want to get crazy and put a TrueTrac back there while I have the diff open...

Another question though; IF it is for sure one of the rear wheel bearings and it's been howling like that for a few years now, is it likely that the axle shaft itself would be damaged and need replacing? Or not likely? I know that I won't know for sure until I look at it, but just curious what the odds are...

 

[tekrsq]

I don't see how a wheel bearing could be bad for several years and not just TOTALLY fail.

Having said that, about 2 months ago, I noticed a slight growl from my rear, and what felt like "slipping" when turning right from a dead stop, under acceleration. Like everybody else, I assumed it was a wheel bearing, but couldn't find any wheel play, or other indication of the problem.

After some research, I found multiple articles claiming it was the clutches in the limited slip diff, and I should change the diff fluid. I've got 185,000 miles on it, and no idea if it had ever been changed. I changed the fluid, along with 4 oz of Motorcraft friction modifier. It solved the issue...for about 300 miles. Last week, I noticed what felt like the "slipping" was returning when I was making right turns. I was given the recommendation to drain out a few oz's of fluid, and replace it with another 4 oz's of friction modifier. So, over the weekend, I added 4 oz more friction modifier. The 60 mile round trip to/from work today was quiet, and no slippage. So I'm waiting to see how it does after a few hundred miles, however the rear end issue is apparently a very common problem in the 1st gen Expy's and F150's of the same years with the 9.75" LS rears.

 

[mnachreiner86]

How many miles on it? Sounds like a howling rear diff.


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[AZShawn]

I do think it was a bit of a case of howling rear diff. However the vibration is what I am really hoping to solve with wheel bearings. That and the fact that i'm not sure if they've ever been changed on the truck and it's got about 210k miles on it now.

I just got done replacing wheel bearings/seals, passenger side axle shaft, parking brake shoes, rotors and brake pads. Haven't had a chance to drive it yet. The passenger axle had some wear on it where it sat in the bearing. It didn't cut a groove into it, but the stock shaft had little factory grooves around it (will try to include a pic below) and they had been worn down to smooth metal on part of it. It may have had something to do with the the large dent someone had somehow put in the axle tube housing right in front of the bearing. It made getting the bearing out an absolute nightmare.

Anyway I got all the parts replaced, now i'm just hoping no leaks develop. I really did a number to the inside of the axle tubes, but we'll see what happens *fingers crossed*

 

[AZShawn]

Here you can see the wear on the axle shaft.



And here you can see the dent that somehow got put into the axle tube housing. I heated it with a torch and tried to hammer it out a little bit and also hit it with a die grinder. This whole job on both sides was quite a chore. Almost wish I would’ve just bought a whole new/used rear end. And who knows, if the seals don’t hold I might still have to!