Vibration under seat at most speed

[arrrxivvv]

On my 201k miles 2004 XC70, feeling vibration under the driver seat at all speed, frequency of vibration proportional to speed, a bit more pronounced downhill.

The vibration is persistent, acceleration/deceleration/coasting doesn't matter) but irregular (frequency not exactly constant, sort of like driving on a rough road, but felt through the driver seat).

No hearing any noise.

No vibration at steering wheel, very faint vibration through gas pedal. Car drives and handles fine otherwise, no pulling left or right of steering wheel, mpg decrease or side hopping.

Have had tire balanced, alignment done, most suspension and engine mounts replaced in the last three years, front and rear shock and springs, front end links, control arms, ball joints, rear trailing arm bushings.

Both front axles replaced with GKN, propshaft with Colorado driveshaft.

Wheel bearings probably original.


What could be possible causes? Could the wheel still be out of balance/shape after balancing at a tire shop? The rebuilt Colorado driveshaft not good? Or something else like wheel bearings?

Appreciate any suggestions.

[jonesg]

can you hear it or just feel it.?
bad wheel bearings hum, easy to detect.

check the usual suspect, engine mounts, tranny mount.
put it in drive, step on the brake and raise the rpm, look for undue engine shifting..(2 people test)

lift all 4 wheels and run it in drive, use a stethoscope w/ extension to locate the source.

https://www.amazon.com/Buorsa-Stethosco ... 165&sr=8-3

[arrrxivvv]

Thanks.

Engine mounts are fairly new, about three years old.

can you hear it or just feel it.?
bad wheel bearings hum, easy to detect.

check the usual suspect, engine mounts, tranny mount.
put it in drive, step on the brake and raise the rpm, look for undue engine shifting..(2 people test)

lift all 4 wheels and run it in drive, use a stethoscope w/ extension to locate the source.

https://www.amazon.com/Buorsa-Stethosco ... 165&sr=8-3

[Blacklab467]

Have a real good look at the propshaft, this was a post I did last year that you may find helpful. New propshaft are extremely expensive but I think you could reorient the bracket with a grinder and reweld the bracket 180 degrees opposite to utilize the rubber support that isn’t sagged out and get another 20 years out of it. I might try this with the old shaft. Also the support bearing out be bad although I haven’t heard of this happening much
viewtopic.php?p=634499#p634499

[arrrxivvv]

Thanks. I've replaced the propshaft with a Colorado Driveshaft rebuild. Hopefully that can rule it out?

Have a real good look at the propshaft, this was a post I did last year that you may find helpful. New propshaft are extremely expensive but I think you could reorient the bracket with a grinder and reweld the bracket 180 degrees opposite to utilize the rubber support that isn’t sagged out and get another 20 years out of it. I might try this with the old shaft. Also the support bearing out be bad although I haven’t heard of this happening much
viewtopic.php?p=634499#p634499

[Blacklab467]

Sorry, didn’t see that you had replaced the propshaft, certainly wheel bearings could be the issue with that mileage although usually they have an associated “groaning” noise proportional to the speed but not always. Wheel bearings will be notable in that they would have gotten progressively worse over maybe six months, is this the case?
Why was the propshaft replaced and when? When did this vibration start and has it been consistent or getting worse with time?

[arrrxivvv]

Can the noise be heard with windows closed? With windows closed I don't think I'm hearing any noise, with windows open all I could hear is the wind noise.

I've always had some random intermittent vibration, but two weeks ago was the first time persistent vibration is felt, at highway speed.

Propshaft didn't really show symptom, but I heard it's probably on its way out at this mileage so decided to change it when I had the time to not use the car in a few days. I think the car drove exactly the same before and after the replacement.

Sorry, didn’t see that you had replaced the propshaft, certainly wheel bearings could be the issue with that mileage although usually they have an associated “groaning” noise proportional to the speed but not always. Wheel bearings will be notable in that they would have gotten progressively worse over maybe six months, is this the case?
Why was the propshaft replaced and when? When did this vibration start and has it been consistent or getting worse with time?

[arrrxivvv]

Managed to get the wheels off the ground to spin them.

Left rear wheel feels grittier and has some noise, compared to the others that are very smooth. No play in any of them, expected as the vibration is not bad to begin with, and no noise either.

Left rear when spinning feels a kind of friction, though I'm not completely sure it's not just coming from the brake pad contact.

Perhaps the left rear wheel bearing?

If so is it common practice to change both rear ones?

[jonesg]

wheel bearings drone or hum.
friction noise, more likely to be the dust shield or brake shoe/pad clearance but you wouldn't feel it in the driver seat.
pain in the neck but you could reinstall the prop shaft to eliminate. or disconnect it to eliminate anything in the rear end.
or turn the radio up and wait til it becomes more obvious.

[scot850]

Check your parking brake shoes have not delaminated and come loose. They will cause a vibration and dragging.

Have you tried a tire rotation to eliminate a bad tire or bent rim?

Neil.