Mercedes CLS... not good vibrations

[Robertb]

I've got an issue with my 2014 CLS 350CDI Shooting Brake and I wonder if the PH collective can help... The car is a well-maintained 1 previous owner car, with 79k miles now, running on airmatic suspension.

At above 70 mph its developed an odd resonance/vibration in the car... its like a low frequency hum, I don't think I can feel it through the steering wheel or anywhere specific, but its there. Its not bad, but its enough to detract from what is otherwise a very refined car on the motorway. At below 70 its absolutely fine.

I've had the wheels checked (one had a small crack and was buckled, but repaired successfully) and all four tyres recently replaced. I've had a Hunter 4 wheel alignment done, with corrections made to front and rear toe settings.

The front discs were replaced a year ago, but have developed a very slight judder under braking from higher speeds. There is no evidence of a sticky calliper or binding brakes.

My next steps in the absence of anything else is to find a place with a Hunter Road Force balancer, and also have the front discs skimmed.

Any other things to check or any ideas gratefully received!

[MustangGT]

Could be a wheel bearing.

[Robertb]

Thanks... I'll add it to the list. Would a faulty bearing like this manifest in a way that could be identified in a workshop as there are no rumbles or squeaks otherwise?

My money is still on the wheels/tyres, if only because when I test drove it before purchase it made the same or similar noise, and it went away when the dealer fitted new tyres. What's foxing me is that this time the noise has remained the same despite two separate rebalances and a new set of tyres.

I'm hoping that a proper wheel balance should at least confirm whether or not the wheels are at fault then I can move on... otherwise I'll have to drive everywhere at 69mph max!

[E-bmw]

Robertb said:

Would a faulty bearing like this manifest in a way that could be identified in a workshop as there are no rumbles or squeaks otherwise?

It is difficult to diagnose in a workshop as quite often the wheel needs to have weight on it to replicate the same conditions.

Having said that they may need to come out for a drive with you & should be able to diagnose it then.

[Robertb]

Thanks... I'll ask my indy what he thinks.

[Demelitia]

When you say resonance, is it possible it could actually be something resonating due to air flow?
A loose trim panel, under body cover, air intake ducting/box?
Did it develop anytime after any work was done on the car like a service that might have left loose or worn fasteners?

[MustangGT]

Brake judder is usually caused by build up of pad deposits and can often be fixed by a series of high brake force applications, e.g. heavy braking from motorway speeds in a repetitive pattern. Need an empty motorway for that

[Robertb]

Demelitia said:

When you say resonance, is it possible it could actually be something resonating due to air flow?
A loose trim panel, under body cover, air intake ducting/box?
Did it develop anytime after any work was done on the car like a service that might have left loose or worn fasteners?

It does sound like it could be that...Id have thought something mechanical would make an actual vibration rather than the resonance. I've wondered if for example the alignment of the sunroof is slightly out or something but I'm clutching at straws. I don't recall a particular moment when it started, but the car has had both a full service and a gearbox service in the last 12 months. I've a friend who has a four-post ramp so I will get it on that and have a good poke around underneath as you suggest to check for loose panels.

[Robertb]

MustangGT said:

Brake judder is usually caused by build up of pad deposits and can often be fixed by a series of high brake force applications, e.g. heavy braking from motorway speeds in a repetitive pattern. Need an empty motorway for that

Funnily enough I did try something similar the other night on the way to picking my daughter up, but I've not driven it since. I suspect some cheapo brake pads fitted by the supplying dealer may be to blame... if no joy from the repeated bedding-in I will buy some good pads and fit them at the same time as the skimming.

Its all a bit frustrating as the car is like a swiss watch otherwise, so refined and relaxing, but I feel like I'm going down a rabbit-hole with this noise!

[TwinKam]

MustangGT said:

Brake judder is usually caused by build up of pad deposits and can often be fixed by a series of high brake force applications, e.g. heavy braking from motorway speeds in a repetitive pattern. Need an empty motorway for that

Just find a section of m-way (or dual-c'way) with two junctions close together and do it on the slip-offs, repeat back and forth as required... it gives them some recovery time that way too.

[MustangGT]

TwinKam said:

MustangGT said:

Brake judder is usually caused by build up of pad deposits and can often be fixed by a series of high brake force applications, e.g. heavy braking from motorway speeds in a repetitive pattern. Need an empty motorway for that

Just find a section of m-way (or dual-c'way) with two junctions close together and do it on the slip-offs, repeat back and forth as required... it gives them some recovery time that way too.

Great suggestion.

[Robertb]

TwinKam said:

MustangGT said:

Brake judder is usually caused by build up of pad deposits and can often be fixed by a series of high brake force applications, e.g. heavy braking from motorway speeds in a repetitive pattern. Need an empty motorway for that

Just find a section of m-way (or dual-c'way) with two junctions close together and do it on the slip-offs, repeat back and forth as required... it gives them some recovery time that way too.

Handily there is a section of the A34 not to far away which is ideal.

Is the idea that repeated hard use of the brakes creates additional friction over normal use which removes the deposit, or that you build some heat up which helps?

[Summit_Detailing]

I had what sounds like a similar thing on an S-class a few years ago - I too went down the wheels/tyres/alignment route first but after taking it to my mechanic for a service it was pointed out to me that one of the undertrays was missing a couple of its fixings, I didn't think this would solve it - but I was proven wrong!

Given how many VAG products you see on the road with the undertray flapping around I can't help but think how noisy it must be inside!

Good luck with your problem solving.

Cheers,

Chris

[Kawasicki]

Get them checked for force variation on a hunter. Aim for under 60N Radial Force Variation (RFV) at the first harmonic. 80N max.

Try your best to warm the tyres up for at least 10 miles before the measurement and not leave the car parked for anything more than a few minutes before the wheels are removed. I like to drive straight onto a hoist. This is to avoid short term flatspots corrupting the measurement.

[Robertb]

Summit_Detailing said:

I had what sounds like a similar thing on an S-class a few years ago - I too went down the wheels/tyres/alignment route first but after taking it to my mechanic for a service it was pointed out to me that one of the undertrays was missing a couple of its fixings, I didn't think this would solve it - but I was proven wrong!

Given how many VAG products you see on the road with the undertray flapping around I can't help but think how noisy it must be inside!

Good luck with your problem solving.

Cheers,

Chris

Thanks- it would be great if it was something like that!

[Robertb]

Kawasicki said:

Get them checked for force variation on a hunter. Aim for under 60N Radial Force Variation (RFV) at the first harmonic. 80N max.

Try your best to warm the tyres up for at least 10 miles before the measurement and not leave the car parked for anything more than a few minutes before the wheels are removed. I like to drive straight onto a hoist. This is to avoid short term flatspots corrupting the measurement.

Thats my plan... the nearest place I've found to me in South Oxon is nearly an hr away, so plenty of time for a warm up. Cheers for the tip on the measurements.

I see Litchfield do it too, quite tempted to go there as I imagine they know what they are doing even if a diesel Merc isn't their usual fare!

[trevalvole]

There's a section on page 54 of the latest issue of the MB Club Gazette about front end vibrations on W221 and W222 S-Classes - the issue being that the front discs were no longer running true; requiring new discs and pads. The view of the likely cause was not following the correct procedure when tightening the wheel bolts, which, in the reporter's B-Class, is to initially torque to 80Nm and then to 130Nm.

[Robertb]

trevalvole said:

There's a section on page 54 of the latest issue of the MB Club Gazette about front end vibrations on W221 and W222 S-Classes - the issue being that the front discs were no longer running true; requiring new discs and pads. The view of the likely cause was not following the correct procedure when tightening the wheel bolts, which, in the reporter's B-Class, is to initially torque to 80Nm and then to 130Nm.

Thank you… they will hopefully rectify any run out with the disc skimming. I will get them to tighten the wheels as you set out.

[300sl-24]

Prop shaft rubber coupling/centre bearing could be the issue.

[Robertb]

300sl-24 said:

Prop shaft rubber coupling/centre bearing could be the issue.

Thanks… I’ll add it to the list.