How can you tell if wheel bearings are going bad?
 

This is kind of a general question about wheel bearings on my newly-purchased '97 S420 with 85k miles on it. The car rides just fine, although it needs shocks. What had me puzzled though is a slight rumble I feel through the steering wheel at highway speed. The only thing I can think of would be the wheel bearings going bad. Can anyone confirm/debunk this?

So far I have replaced the steering damper (it was leaking anyway), and had the (almost new) tires re-balanced. These two thing cleaned-up the front end's behavior quite a bit but I'm still trying to pinpoint the source of the rumble. My '97 S320 is smooth as glass in comparison. I'd appreciate any thoughts.

Jack up the front end.
Spin each front tire slowly ( listening for grinding/scraping sounds ).
Grab the wheel & wiggle it up/down, sideways, in & out.
That should tell you something.;)

Good point! So if it wiggles or makes grindy noises, that's not good, right? :eek:

That's right.
And I wouldn't drive it too far. ;)

Just to possibly save time.... After a bit of a drive, feel the area closest to the hub. If one wheel feels warmer than the other, check the warmer one first. (friction causes heat)

inspect the tread of the tires.
Tears and cuts on the tread an cause vibrations.

I handle the technical end of warranty claims for wheel bearings in our company. I've seen hundreds of customer and dealer narratives relating to bad bearings. The common complaints customers have when a bearing goes bad is that they hear a noise that is described as grinding, roaring, whining at 30 mph to highway speeds. I've never heard a customer describe a valid complaint as noise coming through the steering wheel. So I say look elsewhere for your noise, perhaps in the tires as oceanview suggested.

I've personally only experienced a bad bearing once while diagnosing a colleague's car. The noise was unmistakable and could easily give someone a migraine. The cause was a 2 mm spall on the race and the wheel was tight. If you find looseness when manhandling the wheel during your check, then the damage is far advanced and you should have heard noise long time ago.

Thanks for the info! From what you say then its probably not bearing-related. On the way in to work this morning I did a little experimentation and found that it goes from a slight rumble at 60mph to a definite shake (almost like an un-balanced tire) at 75-80. Like I said earlier, I just replaced the steering damper, had the tires re-balanced, and adjusted pressure to 27psi both front and rear. I guess its time to start looking at steering linkage and maybe have an alignment done.

Out of balance tires usually are the worst @ 60 - 70 mph.
It's not uncommon to have a tire vibration " go away " at higher speeds. ;)

I have had similar experiences on different vehicles. Almost always it has been the tires. Tires can have defects that cause out of roundness and density differences that feel exactly like and unbalanced wheel. I usually buy cheap tires and I have the problem often. The only solution is to swap out the tire that is rough. Shaving, balancing, rebalancing, nothing will fix a tire that is not uniform in density or composition. Never had a rough tire with Michelin.

Mark

Funny, because that's what is on the car. Michelin MXV4's

I had these same sort of symptoms on my 85 300D.
I had just replaced the engine, and soon after I started to feel more than
hear, something rough in the steering wheel and fuel peddle.
this was over the course of 3000 miles.
at first I thought, what`s wrong with the new eng? as time went on felt like gear noise, or roughness. the towards the end like snow tire type noise, but now loud.
changed the L/F tire, no change. finally pulled the hub and the inner bearing cage was starting to deform. replaced the bearings and races and
smooth as butter now. both hubs never felt hot.

Charlie

Were both hubs bad? Did you replace the grounding strap after replacing the engine? If the grounding strap is omitted, the engine will try to ground itself through the wheel bearings, and the bearings will destroy themselves in short order. So will the next pair.

I just replaced both bearings, what I can tell you is my bad bearing sounded like subway train on railway track at high speed! No words can explain!:confused:

Engine mounts? Flex joints?