Low frequency 'thrumming' at speed

[Parrot of Doom]

Just picked this up lately, at about 60mph theres this quiet low frequency 'thrrruuuummm.........thrrruuuumm.........thrrrruuummm', as I speed up it gets a bit faster. Its pretty quiet, turn the radio on slightly and you can't hear it. I can feel a bit of vibration through the steering wheel, its obvious when you turn the sunvisor down, you can see it shaking slightly.

The car doesn't knock, creak, make any noises from forward to reverse, and behaves well, changes gear normally, etc. No odd noises, bangs, whistles, anything really. Below 50mph you'd never even know about it.

So the first suspect is the rear tyres (fronts are brand new), which admittedly are down to the markers now, and will be changed very shortly. Is it worth inspecting anything else in the drivetrain? Is there anything on the rear suspension I should look at? The car very obviously tramlines in the grooves on the motorway lane 1.

 

[malcolm E53 AMG]

Has the noise appeared since you fitted the new front tyres. It may be the first place to look. Changing the rears to the front would provide a quick check.

 

[Parrot of Doom]

Yes it has - I might check that. The tyres are Continentals, never had a noise issue with Conti's before though.

 

[tom7035]

I'd suspect the propshaft centre u/joint particularly, but the rubber 'doughnuts' are a starting point to check. Just been discussing those on the transmission thread.

 

[cossiedude]

Sounds like the rubber donuts to me, the front one on mine did the same, the center bearing rubber coupling went before that but that was knocking at low speed and pull away.

 

[Parrot of Doom]

Additional info:

On the way home the other night, everything seemed fine apart from this noise. Anyhow, driving out of a services up the M6, and accelerating up the sliproad, there was a significant amount of wobbling from the back end - it felt like a wheel very badly out of balance.

At 60mph it was terrible, so I pulled over thinking maybe I had a flat - the tyres were fine. Got back in the car, accelerated away, and it was fine again.

Its booked in to be checked tomorrow.

 

[Ian Brown]

Additional info:

On the way home the other night, everything seemed fine apart from this noise. Anyhow, driving out of a services up the M6, and accelerating up the sliproad, there was a significant amount of wobbling from the back end - it felt like a wheel very badly out of balance.

At 60mph it was terrible, so I pulled over thinking maybe I had a flat - the tyres were fine. Got back in the car, accelerated away, and it was fine again.

Its booked in to be checked tomorrow.

Sounds like you may have a distorted tyre on the rear jack up the rear of the car and turn the rear wheels and see if there is any distortion in them

 

[Parrot of Doom]

The noise has been diagnosed as a faulty wheel bearing, nearside front, so along with the brakes I'm going to replace both fronts. They're only cheap little things. Propshaft is fine.

 

[Ian Brown]

The noise has been diagnosed as a faulty wheel bearing, nearside front, so along with the brakes I'm going to replace both fronts. They're only cheap little things. Propshaft is fine.

I doubt very much if the front wheel bearings would give the symptoms you say it was coming from the rear of the car a wheel bearing normally gives a whining noise and gets louder or quieter when going round bends once a wheel bearing is noisy its always noisy it not intermittent as you say your problem is.

 

[tom7035]

Just picked this up lately, at about 60mph theres this quiet low frequency 'thrrruuuummm.........thrrruuuumm.........thrrrruuummm', as I speed up it gets a bit faster. Its pretty quiet, turn the radio on slightly and you can't hear it. I can feel a bit of vibration through the steering wheel, its obvious when you turn the sunvisor down, you can see it shaking slightly.

The car doesn't knock, creak, make any noises from forward to reverse, and behaves well, changes gear normally, etc. No odd noises, bangs, whistles, anything really. Below 50mph you'd never even know about it.

So the first suspect is the rear tyres (fronts are brand new), which admittedly are down to the markers now, and will be changed very shortly. Is it worth inspecting anything else in the drivetrain? Is there anything on the rear suspension I should look at? The car very obviously tramlines in the grooves on the motorway lane 1.

From your original post (above), faulty front wheel bearing/s is quite a feasible diagnosis though it/they must be very badly worn and 'corrugated' to cause your sunvisors to vibrate, but your later one regarding a rear-end wobble confuses the issue a bit! Sounds an unrelated symptom.

 

[Parrot of Doom]

Well they're only cheap, so I'll do them anyway 165000 miles is probably about right for a wheel bearing.

The wobble could be anything really, but its only done it the once. Might even be a dodgy bit of tarmac on that section, but the rear tyres will want doing soonish so I reckon the problems will vanish once its all been done.

 

[Parrot of Doom]

Right. We've replaced the nearside front bearing, and the 'thrumming' noise has pretty much gone away.

The wobblyness remains though, and I've figured out how to induce it.

If I enter a motorway (say, J17 of M60), and accelerate up a long slope (anti--clockwise, the slope here is over a mile long), the wobblyness comes on. Starts very very weak, and over a speed of 50mph builds up slowly, until it feels like a badly balanced wheel. If I back off the accelerator once on a flat bit of motorway, it gradually goes away.

It only seems to appear when I'm accelerating to motorway speeds for a minute or so, and going uphill at the same time.

It seems to me to be centered around the nearside rear wheel.

The tyres are about 1mm off the markers.

The propshaft has been checked and passed (by Greenvale in Whitefield)

The diff is totally silent at all speeds, the gearbox seems nice and quiet.

So, any more ideas? Are there any suspension linkages that I should be checking there? Perhaps a worn CV joint?

 

[tom7035]

A worn driveshaft c/v joint would certainly set up a vibration, and there are lots of bushings in the rear suspension set-up, for camber, track (yes, even on the rear), torque and thrust control. It would be so easy to say replace the lot to be sure! Investigation in this area is certainly called for.

 

[mercmonkey]

something ive learned from bitter experience (a near death one at that) whatever you do to one side of the suspension (ie a new bush) do the same on the other even if it *appears* OK. Keeps everying nicely balanced

 

[Silverado]

I,ve just had the same symptoms on my c280, I tried swapping tyres around, checking driveshafts etc. It turned out to be a broken r.o.s. spring, two new ones at £21 each and £30 to fit them sorted the job.

 

[amwebby]

Any update on this Parrot? I've just experienced something very similar on my W215 so anxious how much the cost is going to be and how long it is going to take tracking it down.

 

[Ger Donohue]

We purchased our first Merc over a year ago, E220 CDI Year 2001 and love it, what a treat to drive. However over the past three months its gotten very wobbly on the road, like a loose wheel etc. Got four new shocks (approx €400.00), but no improvement, swapped wheels made it worse, we are now going to get four new tyres on it and hopefully it will improve driveability, because I love this car and so does my husband. Irish Country roads don't help, lots of potholes that one has to avoid. Any tips or suggestions if any of you has experienced anything like this, its going to be a process of elimination I think.

 

[Parrot of Doom]

Yes, I've isolated the problem to:

1) Poor alignment (had a laser alignment done and improved matters greatly)

2) Cheap tyres on the back


When I replace the tyres, I'm having the new tyres balanced while still on the car (the old fashioned and superior way), or with a wheel balancing machine that does road force balancing.

 

[amwebby]

Thanks for the update. I've just had the rear wheels balanced and it does look as though they had shed a weight. They also advised that there were slight flat spots on the wheels, which the weights should compensate for but which will obviously make the wheels more sensitive to balancing. So, it looks as though the geometry on Mercedes-Benzs is extremely sensitive.