98 expedition 4x4 intemittent grinding noise

[Fitz98]

I have a 98 4WD expedition with approx 150K miles.
I have recently noticed an intermittent grinding noise (it almost sounds like a fan blade grinding against a piece of plastic. It seems to be coming from somewhere on the front end, but since it only happens while in motion it's hard to pinpoint. It presents usually after a mile or 2 of driving and is most audible on deceleration from about 35 mph all the way to stop. It is intermittent, comes and goes, louder at some times, and sometimes not at all. It is audible in sync with the speed of the vehicle, slower at slower speeds, faster at faster speeds, so it seems most likely to be a suspension drivetrain issue. Does not change with motor RPM's. Almost sounded like a rapping rod at times. Brakes and rotors are new, balljoints feel tight upon inspection. At first I thought it was a bad water pump, since the first time I heard it was when I flushed the cooling system. It sounds like a dry pump type sound, but water flows well and the noise does not change with RPM's. Any ideas?

 

[Trav]

Did you check the fan clutch?

 

[bmwtechguy]

Sister's 98 4WD Expedition had a U-joint going out on the front driveshaft when she showed up in town for a visit recently. Had 149k miles on the odo when she got here. Check it out. Bad one was easy to spot with all the rust around it. When I dropped out the front driveshaft, that U-joint was nearly seized. I'm sure she would not have made it up to Cleveland OH another 600 miles. Yours may just be starting to go bad.

 

[MNgopher]

Since it seems to be in sync to vehicle speed and not the engine rpms, focus on the driveline. Wheel bearings / CV joints / driveshaft u joints, etc...

 

[Warstud]

Sounds like a wheel bearing.

 

[Fitz98]

I am leaning in this direction too. Visual inspection seems fine, boots are clean, no clunking noise that might be associated with a u-joint. No play in bearings or ball joints. and the hubs feel just slightly warm to touch.
I am thinking that because it starts when things get heated up that it is related to one of these components just starting to go bad...unfortunately, I cannot hear the noise by manually turning the wheels when jacked up (yet)
Question- is there supposed to be any vertical or horizontal play where the drive plates enter the front differential (not sure if this is the right term)..the plate that the half shafts bolt to where it enters into the diff. I have some small amount of vertical movement (slop) there on the left side and some horizontal movement on the right side. Is that normal, or possibly worn differential bearings?

 

[bmwtechguy]

Worn differential carrier bearings could be a possiblilty with the type of play you noted. On my sister's truck, we rebuilt the REAR diff at the same time we replaced the u-joints on the front driveshaft, due to the racket the carrier bearings were making. All new bearings and clutches. The gears were still fine.

 

[Fitz98]

Anybody have any advice for inspecting and troubleshooting bearings for wheels and front differential and cv joints. Again, this is an intermittent noise and not really bad enough yet to present an obvious problem, but there is a problem somewhere otherwise there would not be this noise.

 

[Fitz98]

A new piece of information for troubleshooting.
It seems like the grinding noise presents on every 1/2 rotation of the wheel and as I have said it is intermittent when it happens, but presents almost always when I decelerate with heavy force applied to the brakes. Gradual deceleration or light braking is random, but almost always when heavier force applied to brakes at low speed.

 

[Fitz98]

Thanks to everyone for their help.
So in the end, I took the cv axle out, the stabilizer link and the front hub. The brakes were already in known good condition.
The cv axle boots were still great, and the movement of them was easy, felt well lubricated in all directions.
The wheel hub bearing, when disconnected from everything else, did have that dry grind sound to it and for whatever reason, a very slight rubber type squeek on every 1/2 turn. Maybe a bad seal or something?
No play in the bearing and no major binding. I guess I caught it early to where it would only make noise when it got somewhat hot.
So I replaced the bearing hub, which felt obviously more lubricated than the one I took out and after re-assembly and a quick test drive, all seems to be back to normal.
So intermittent grinding noise upon braking or deceleration on every 1/2 rotation of the tire = bad bearing.
Thanks to everyone for the help along the way.
I should also mention that the stabilizer link was not installed proerly. It was in the larger triangle hole of the lower control arm, which caused the bushing to wear unevenly. It was still in tact, but not properly alighed or installed. Replaced that as well, but I don't think it was a contributing factor to the noise.