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Odd noise- what is causing it? (technical question)

Long story short, bought an approved used Mercedes a couple of months ago.

I noticed a slight thumping noise, but put it down to road surface / expansion joints.
However it has got louder and is much more noticeable, particularly when cornering, especially on a left hand curve. Its always present, more when cornering, but doesn't get louder under braking.
Its rhythm speeds up and slows down with the speed of the car. Its loudest at 70mph on a curve e.g. the M6(s) M56 junction.
If you put a foot on the floor you can feel it through the floor of the car.

Sooooo, its been back to the dealer, first time they couldn't diagnose and wanted me to bring it back so they could strip it down.
Second time round they have diagnosed corroded front discs. This sounds odd to me as when you are driving normally the discs wouldn't be touching anything and if the discs where warped then they would get noisy and vibrate under braking surely?

Personally I would have thought it to be a wheel bearing or a CV joint.

Thoughts?

Apart from the issue of being sold a car with fucked discs (not a safety issue apparently, so not covered by warranty or the approved scheme checks) and then wanting £450 to put it right (they have offered a goodwill payment of £100); but this is a story for another thread.
 
Long story short, bought an approved used Mercedes a couple of months ago.

I noticed a slight thumping noise, but put it down to road surface / expansion joints.
However it has got louder and is much more noticeable, particularly when cornering, especially on a left hand curve. Its always present, more when cornering, but doesn't get louder under braking.
Its rhythm speeds up and slows down with the speed of the car. Its loudest at 70mph on a curve e.g. the M6(s) M56 junction.
If you put a foot on the floor you can feel it through the floor of the car.

Sooooo, its been back to the dealer, first time they couldn't diagnose and wanted me to bring it back so they could strip it down.
Second time round they have diagnosed corroded front discs. This sounds odd to me as when you are driving normally the discs wouldn't be touching anything and if the discs where warped then they would get noisy and vibrate under braking surely?

Personally I would have thought it to be a wheel bearing or a CV joint.

Thoughts?

Apart from the issue of being sold a car with fucked discs (not a safety issue apparently, so not covered by warranty or the approved scheme checks) and then wanting £450 to put it right (they have offered a goodwill payment of £100); but this is a story for another thread.
Shocks shagged? Broken spring?
 
Could be a cracked spring. The car will sit ok when parked but under load will thump.
 

OneTenner

LE
Book Reviewer
Tyres.
Merc's (and a few others) have a habit of putting load and therefore wear on the inner edge of the tyres, mainly rears. Run your hand over the inner edge, if it feels stepped or 'wavy', then they need replacing.
Distorted or corroded brake discs tend to behave unless under braking - usually by shaking the steering if it's front braske discs. Generally a wheel bearing would initially present as wandering or pulling steering and a worn CV joint would click during low speed / high steering angle events, such as parking.
Some tyres, such as Pirelli have a sound absorbing bitumen foam strip bonded to the inside, if the tyre overheats - for example, due to low pressure, then this can become detached and lead to odd noises and handling.
BTW, 'corroded' doesn't mean faulty, just 'enviromental factors' causing premature wear, hence not a warranty issue - if you purchased within the last six months, them push a bit harder, if you purchased on credit, let them push as bit harder... If you can show long journeys on fast roads as your typical weekly drive, then they should sort as this type of use should clear any surface corrosion, plodding around town or village once a week to collect pension won't clear any surface corrosion and is therefore not typical usage so not a dealer problem - the discs will be stamped with the minimum allowed thickness, if it's close or below, have a look at the MBI sheet which should give the brake pad thickness and disc thickness for each wheel - if it doesn't, ask why not as it's part of MB dealer standards for retailing used cars. Get the pads & discs measured & compare to the pre-sale measurements and mileage (typically 1mm = 1000 miles of mixed road use on pads, discs should last about 24k or two sets of brake pads.
 
Good plan to get it checked out properly, bearings as you say, Rhythm may be a clue.
Check for a body in the boot - just in case.
Its an estate, they always manage to get round the load cover.
 
Always remember listening to the American NPR radio program on the AFN network in Europe. Driving one day and loved the Car Talk program with the Tappet brothers, old fashioned auto mechanics. Knew everything about every car and The calls were live.

One time, a woman called in.

Tappet brothers , “So what’s the problem ?”

Woman... “well , it sounds like there is a bowling ball in the trunk of my car”

One of the Magliozzi brothers ( their real name) asks , what car are you driving?

Woman says . OH it’s a 2004 Chevy gas drinker.

Tom says , pull over and look in the trunk.

woman comes back and said.

” My husband left his bowling ball in the trunk , thank you “
 

OneTenner

LE
Book Reviewer
Tyres.
Merc's (and a few others) have a habit of putting load and therefore wear on the inner edge of the tyres, mainly rears. Run your hand over the inner edge, if it feels stepped or 'wavy', then they need replacing.
Distorted or corroded brake discs tend to behave unless under braking - usually by shaking the steering if it's front braske discs. Generally a wheel bearing would initially present as wandering or pulling steering and a worn CV joint would click during low speed / high steering angle events, such as parking.
Some tyres, such as Pirelli have a sound absorbing bitumen foam strip bonded to the inside, if the tyre overheats - for example, due to low pressure, then this can become detached and lead to odd noises and handling.
BTW, 'corroded' doesn't mean faulty, just 'enviromental factors' causing premature wear, hence not a warranty issue - if you purchased within the last six months, them push a bit harder, if you purchased on credit, let them push as bit harder... If you can show long journeys on fast roads as your typical weekly drive, then they should sort as this type of use should clear any surface corrosion, plodding around town or village once a week to collect pension won't clear any surface corrosion and is therefore not typical usage so not a dealer problem - the discs will be stamped with the minimum allowed thickness, if it's close or below, have a look at the MBI sheet which should give the brake pad thickness and disc thickness for each wheel - if it doesn't, ask why not as it's part of MB dealer standards for retailing used cars. Get the pads & discs measured & compare to the pre-sale measurements and mileage (typically 1mm = 1000 miles of mixed road use on pads, discs should last about 24k or two sets of brake pads.

thank you this is really interesting. I picked it up end of Oct, so I've had it 72 days now and have covered just about 2200 miles of mostly motorway driving. My commute is motoway / A road and I would describe my driving style as "enthusiastic". So this corrosion has not occurred in the last 70 days, so it was sold with this problem.

I think it has sat on the forecourt for about 4- 6 mths, looking at the MOTs its only covered about 500 miles between Jun 19 and me buying it.
The brakes were a bit grindy to start with , so I put them through some heat cycles and they quietened down.
Its on Conti Sport Contact 3s and I think they are noisy as ****..

eta:

its a CLA 250. The CLA 220 courtesy car was on the same tyres and a bit quieter.

I think it has to be something tyre / hub related because of the rhythmic nature of the sound and it is speed dependant.
 
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Before buying a car, any car, new, used, or certified, I always inspect it myself. If they don't want to put it on a lift so that I can personally check condition, then they really don't want to have my money.

Have the tires shaved/trued/balanced or replacements shaved/trued/balanced, and then start replacing suspension components that have experienced excessive wear because of the tires' uneven condition, like end link bushings.

It's a used econoshitbox, on discount tires, that just happens to wear a 3 point star... definitely on the bottom and no where near an S Class or AMG.
Not a lot of leeway for "enthusiastic driving" if you aren't going to upgrade lots of components.
 
Before buying a car, any car, new, used, or certified, I always inspect it myself. If they don't want to put it on a lift so that I can personally check condition, then they really don't want to have my money.

Have the tires shaved/trued/balanced or replacements shaved/trued/balanced, and then start replacing suspension components that have experienced excessive wear because of the tires' uneven condition, like end link bushings.

It's a used econoshitbox, on discount tires, that just happens to wear a 3 point star... definitely on the bottom and no where near an S Class or AMG.
Not a lot of leeway for "enthusiastic driving" if you aren't going to upgrade lots of components.

A somewhat harsh assessment and I would not personally use the term shitbox. Its a CLA250 4Matic Engineered by AMG, so whilst not the full fat AMG, it is a step up from the run of the mill CLA.

Its hardly a Dacia.

If you regard Continental tyres as budget tyres, what are you using? Pirelli F1 C5s?
Granted the SP Contact 3 is marketed for performance road use, I'll be changing them for P Zero pz4 or Eagle Asy 5s when the time comes.

You now you can drive quite average cars enthusiastically, 9 tenths in a golf GTi can be more entertaining than Porsche at 5 tenths.
 
There's a thread from somewhere in the mists of time that suggested the noise could be due to flattening of the tyres if left unused for a lengthy period, especially if underinflated. As I recall, some posters said that the tyres would right themselves over time while others said it was a terminal fault.
 
A somewhat harsh assessment and I would not personally use the term shitbox. Its a CLA250 4Matic Engineered by AMG, so whilst not the full fat AMG, it is a step up from the run of the mill CLA.

Its hardly a Dacia.

If you regard Continental tyres as budget tyres, what are you using? Pirelli F1 C5s?
Granted the SP Contact 3 is marketed for performance road use, I'll be changing them for P Zero pz4 or Eagle Asy 5s when the time comes.

You now you can drive quite average cars enthusiastically, 9 tenths in a golf GTi can be more entertaining than Porsche at 5 tenths.

Oh... so you spent some extra for the special dual clutch "sports" trans, special "sports" front axle, the special tuned "sports" suspension, and the special speed-sensitive "sports" steering. Why didn't you say so in the first place?


By the way, how's that working out for you?
 
thank you this is really interesting. I picked it up end of Oct, so I've had it 72 days now and have covered just about 2200 miles of mostly motorway driving. My commute is motoway / A road and I would describe my driving style as "enthusiastic". So this corrosion has not occurred in the last 70 days, so it was sold with this problem.

I think it has sat on the forecourt for about 4- 6 mths, looking at the MOTs its only covered about 500 miles between Jun 19 and me buying it.
The brakes were a bit grindy to start with , so I put them through some heat cycles and they quietened down.
Its on Conti Sport Contact 3s and I think they are noisy as ****..

eta:

its a CLA 250. The CLA 220 courtesy car was on the same tyres and a bit quieter.

I think it has to be something tyre / hub related because of the rhythmic nature of the sound and it is speed dependant.

Flat spot on a tyre?
 
Perhaps it's as simple as a buckled rim. I bought a focus which seemed fine on a test drive but then in hindsite I did not go over around 55mph. I soon found out that above 65 mph it felt like the wheel was trying to throw itself off. Upon removal it had some serious hammer marks where someone had attempted to beat it back into shape. It looked fine from the outside and there was no way of knowing.

Either way I would be insisting that Mb do what it takes as there responsibility to get it sorted I.e full road test , check all suspension , driveshafts , cvs and bearings, even engine or gearbox mounts.
 

OneTenner

LE
Book Reviewer
...The brakes were a bit grindy to start with , so I put them through some heat cycles and they quietened down.
Its on Conti Sport Contact 3s and I think they are noisy as ****..

eta:

its a CLA 250. The CLA 220 courtesy car was on the same tyres and a bit quieter....
Get them to swap the wheels & tyres from another vehicle then road test with you in the vehicle. If the concern changes, for better or worse, this confirms wheels and/or tyres as the cause, the Conti's get to about 4mm tread depth and then they start distorting and getting noisy - also check they are at least MO grade on the sidewall.
The brakes are a red herring in my opinion.
 

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