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Muffled knocking from underneath C Class S205

Animal

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Joined
Oct 8, 2014
Messages
46
Car
S205 C250d Bluetec Sport Premium Plus, Est
I have just had both the front lower rear suspension arms replaced, now my indie says that all is in order underneath.
Despite this there is a muffled knocking coming from underneath giving the feeling that something is worn out, particularly noticeable when driving slowly on rough road (plenty of those in the UK).
Is there a common problem with this model that could be the culprit?

I've not had the best of luck with this car, bought it with 48k on the clock 5 years ago, it has now done 66k, in that time I've had replaced 2 nox sensors, the airbag module, torque convertor, 7G+ gearbox and this year the starter motor.
Might go Japanese next time!

All sensible ideas gratefully received.
 
No ideas then!
No solution yet.
Had 2 new tyres today in National tyres along with tracking. They gave the car a free inspection underneath and found no issues with suspension or exhaust.
The rattle/knocking continues!!
 
This might sound extremely silly. Not long after taking delivery of my C-Class W205 back in 2016 I noticed a muffled thump from somewhere underneath at the back. It went back to the Dealer a couple of times but the noise persisted.
I began to realise it occurred a short while after hitting a bump, or similar.
So, when I hit the next bump, I pulled over and had a look underneath.
There is a black plastic cover with a hinged lid covering something to do with the back axle (back nearside but I can’t be sure exactly where now) and sure enough the lid was hanging down.
My guess is it would open on a bump and then slam shut under wind pressure. Even when it went to the dealer they would probably close it and not think anything of it.
I closed it and secured it with a single cable tie.
Never had the problem since, but I did learn later that it’s not an uncommon problem.
might be a red herring but hope it helps.

edit. Cover might be protecting rear suspension arm, really can’t remember now and I don’t get under cars these days
 
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Thanks for your reply and idea Fourwheels.
I cant see anything obviously loose under that area.
I'm beginning to think it may be the anti roll bar bushes as it's clonking away constantly while driving slowly over uneven roads but I'm really surprised that no garage is picking this up!
 
Just found out that you can't replace the bushes on the anti roll bar on this model, you have to replace entire anti roll bar assembly. Omg this car's maintenance bills are eye watering. Gonna take it back to the indie to check over again.
 
Get your indy to use a chassis ear. You will find it then.
 
Whilst the anti roll bar bushes are not available separately anymore, you can use aftermarket poly ones. They may need to be pressed out using a machine press, and the new ones pushed in.
I know many people who have done this in G wagens over the years..
 
Went to see indie today, took him for a brief drive, he reckoned knocking was coming from left front, so have booked it in for inspection/repair. He said he'd never had to change an anti roll bar on these before and said how solid they were!! So maybe it's sumfink else!! As for a chassis ear, I'm in Cornwall, so they might not have one!!
I'll update in a few weeks.
Thanks guys
 
How about engine or gearbox mounts?
 
How about engine or gearbox mounts?
Hopefully not, I had a new 7G+ gearbox and torque convertor last year, as it was worn out at 64k, I'm thinking a suspension component, will find out in a few weeks.
 
How about engine or gearbox mounts?
Hopefully not, I had a new 7G+ gearbox and torque convertor last year, as it was worn out at 64k, I'm thinking a suspension component, will find out in a few weeks
 
Check the disc brake dust back plates - they are prone to corroding around the rivets and then they rattle around over uneven surfaces
 
Thanks Smiley, will do. I'm hoping for something cheaper than the usual this time round, fingers crossed :)
 
Thanks for your reply and idea Fourwheels.
I cant see anything obviously loose under that area.
I'm beginning to think it may be the anti roll bar bushes as it's clonking away constantly while driving slowly over uneven roads but I'm really surprised that no garage is picking this up!
I have a w211 which has a what I would call a soft knock as it doesn't sound metallic when driving slowly over uneven roads. My indie guy says he couldn't find it so, called into another indie for a second opinion. He also says he couldn't find it although, he could hear it. It's driving me crazy.
 
Thanks rosie5golf, that sounds very similar.
Mines just been back to indie and they checked all the bushes, all was good and they can hear the knocking but don't know what it is.
I am now thinking it could be the shocks possibly. Any thoughts!!
 
Have you tried replacing anti roll bar bushes? Had similar on my S320 a few moons ago and that was the problem, difficult to spot as nothing moves under the car.
 
On one of my cars I had a soft sounding not metallic knock that I chased for months........Then had a shock start to leak to decided to replace them all. Then I found the cause of the knock. One of the shock had a dead spot.....by that I mean that as the shock changed direction of travel there was about an inch of so of travel with no damping at all. The knock was the undamped travel followed by the sudden start of damping.
 
I have just had both the front lower rear suspension arms replaced, now my indie says that all is in order underneath.
Despite this there is a muffled knocking coming from underneath giving the feeling that something is worn out, particularly noticeable when driving slowly on rough road (plenty of those in the UK).
Is there a common problem with this model that could be the culprit?

I've not had the best of luck with this car, bought it with 48k on the clock 5 years ago, it has now done 66k, in that time I've had replaced 2 nox sensors, the airbag module, torque convertor, 7G+ gearbox and this year the starter motor.
Might go Japanese next time!

All sensible ideas gratefully received.
Went back to my Indie garage
Thanks rosie5golf, that sounds very similar.
Mines just been back to indie and they checked all the bushes, all was good and they can hear the knocking but don't know what it is.
I am now thinking it could be the shocks possibly. Any thoughts!!
Went back to my Indie garage who could also hear the knocking from the front left. After an inspection they can find nothing worn underneath and so the knocking continues.
 

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