S320 - hissing sound

[ScoobyDooLondon]

My car is giving a harsh and firm ride. Took it to Waynes Gates and he can't find any problems but did advise on changing all four tyres and they're finished. Tyres are on order so will have to wait a few days and see if that resolves the problem.

One thing I have noticed, when I park the car and lock it, I hear this "hissing" sound, like air being escaped. This seems to happen more often than not.
Is this normal?

FYI, my car is S320 2008 and its usually parked on the road outside, which is level and flat. I'll have to check tomorrow, but the car body seems level compared to the wheels, so it hasn't dropped overnight.

Never paid much attention to the hissing sound but could it be related to the harsh ride?

 

[m2287]

The noise is normal, it's the air suspension.

 

[ScoobyDooLondon]

Thanks mate, sooo relieved.

Was reading another thread and suddenly remembered the hissing sound.

Can sleep easy, thought it might be a big bill looming.

 

[mirras]

If the ride is harsh there are a few things could cause that. Tyres rated XL ( extra load ) can cause the car to feel a bit bumpier than you would expect. Additionally, if you've selected 'S' (Sport) or 'M' (Manual) mode this stiffens up the shocks and gives a firmer ride than 'C' (comfort).

I had a few issues with my Airmatic a couple of years ago which turned out to be a faulty valve block. A full test on STAR at the dealer didn't show any errors but I could feel it. Once the valve block was replaced all was well.

The hissing is normal.

 

[Major774]

If the ride is harsh there are a few things could cause that. Tyres rated XL ( extra load ) can cause the car to feel a bit bumpier than you would expect. Additionally, if you've selected 'S' (Sport) or 'M' (Manual) mode this stiffens up the shocks and gives a firmer ride than 'C' (comfort).

I had a few issues with my Airmatic a couple of years ago which turned out to be a faulty valve block. A full test on STAR at the dealer didn't show any errors but I could feel it. Once the valve block was replaced all was well.

The hissing is normal.

Question, how did you know it was the valve block?

I keep getting 'visit workshop' on my W211. I have no air leaks, none of the corners sink down... Even after 2 weeks sitting on my drive. Star showed nothing as well.

 

[ItalianTuneUp]

Yes, hissing is normal upon locking the car after a journey if you have airmatic suspension. I guess it's just releasing compressed air from the air chamber used to feed the air struts via the valve distribution block?

I had knackered front struts (cracks on epoxy tops) and a leaking valve distribution block which was diagnosed by using the good old soapy water bubble test at an MB workshop.

 

[ItalianTuneUp]

If the harsh ride is being caused by the airmatic system, I suppose it's definitely set to 'convenience' mode, and not sports 1 or sports 2 modes? At least they're called that on the W220.

Other things apart from tyres, as already mentioned, could be things like engine/gearbox mounts or other damping components like bushes. Just a thought.

Is the car relatively vibration-free parked in neutral?

 

[ItalianTuneUp]

Which tyres did you order?

 

[ScoobyDooLondon]

Yes, the mode is set to Comfort.

I ordered the Michelin Primacy HP's - fronts 255/45/18 99Y MO and 275/45/18 103Y MO on the rear.

Only had the car around 10 months or so - my first 'decent car' so absolutely thrilled with it.

Once the tyres are on, hopefully will see how much of a difference it makes.

Is it wrong to feel so excited about a new set of four tyres!!

 

[ItalianTuneUp]

Has the harsh ride been consistent over the last 10 months, or has it recently worsened?

Enjoy the new tyres, hopefully they will improve things. Let us know.

Once I got a new set of Conti 5 contact sports, the ride quality was greatly improved, so cross fingers.

 

[ScoobyDooLondon]

That's a very good question. I don't recall it being harsh, so think its developed over the past few months. On the motorway, its a dream!

On local roads, you can feel every uneven surface and the whole car moves.

Having had a major service at Waynes Gates, Terry drove the vehicle and agreed it was a hard ride but couldn't find anything wrong with it. So its comforting in that sense, its now just a waiting game for the tyres to arrive so I can get them fitted.

Seriously, I'm loving these forums. Too often I've had to make do with crap cars and finally got a fabulous Merc. Even now, when I go to get into the car, it still feels incredible!! So solid, built like a tank, I'm seriously loving it!

 

[ItalianTuneUp]

Question, how did you know it was the valve block?

I keep getting 'visit workshop' on my W211. I have no air leaks, none of the corners sink down... Even after 2 weeks sitting on my drive. Star showed nothing as well.

Someone here mentioned that changing tyre size caused this message to appear iirc...I'll try and find it for you...

 

[ItalianTuneUp]

That's a very good question. I don't recall it being harsh, so think its developed over the past few months. On the motorway, its a dream!

On local roads, you can feel every uneven surface and the whole car moves.

Having had a major service at Waynes Gates, Terry drove the vehicle and agreed it was a hard ride but couldn't find anything wrong with it. So its comforting in that sense, its now just a waiting game for the tyres to arrive so I can get them fitted.

Seriously, I'm loving these forums. Too often I've had to make do with crap cars and finally got a fabulous Merc. Even now, when I go to get into the car, it still feels incredible!! So solid, built like a tank, I'm seriously loving it!

Your description of it feeling like a dream on motorways (higher speed driving) versus rough ride at lower speeds on local roads rings a bell with me, for sure, as my car had very similar sounding symptoms.

The cause in my car's case was knackered front struts. I had those replaced with new ones, and a leaky valve distribution block replaced. Lovely again at slower speeds after that...the bumpy, gritty feeling disappeared completely.

In my car's case there was a clunking sound when travelling over bumps at slow speeds. The S class is so quiet you might have to strain your ears to hear it though. And this is the strange part...I didn't hear the clunking sound from the front airmatic struts until after a new valve distribution block had been fitted. The strut top epoxy seals had been repaired using the MB strut repair kit originally, but after the valve block was replaced the internal strut problems (bottoming out + clunking) appeared. Thus new struts were fitted and since then, no further issues.

Has your car done about 80k to 120k miles?

If you're interested in the gory details, try searching for my airmatic threads.

 

[ScoobyDooLondon]

I also get a sound when going over bumps, its hard to describe, but the slower I go over the bumps, it becomes more obvious. Then again, I didn't notice these sounds before.

I really hope the tyres fix the problem, really can't afford to shell out too much on expensive fixes.

The car has covered 72k.

 

[ItalianTuneUp]

I also get a sound when going over bumps, its hard to describe, but the slower I go over the bumps, it becomes more obvious. Then again, I didn't notice these sounds before.

I really hope the tyres fix the problem, really can't afford to shell out too much on expensive fixes.

The car has covered 72k.

Again, this sounds similar to the problems my car experienced. The slower, the worse the ride and the noisier the clunking (once the strut top seals had been repaired, which then showed the internal strut problems).

72k miles...not far off 80k. Iirc they are rated at about 80k to 100k miles...at least the drop-in replacements made by Arnott Industries are. Depending on the kind of driving the car has done, maybe 72k miles has been enough to wear them out?

 

[ScoobyDooLondon]

I don't even want to think about such expensive fixes. But you're right, the symptoms are very similiar to yours.

If you don't mind me asking, what did it cost to fix yours?

 

[ItalianTuneUp]

£1500 for two new MB front airmatic struts, think valve block was an additional £300

Still, looking on the bright side, they should last a long time now.

Those prices include labour and VAT.

The rear airmatic struts rarely break apparently.

Thanks, your thread has reminded me I need to buy a pair of rear tyres...continental contact 5 sport.

I'd be interested to know what you think of your new tyres once you try them.

 

[mirras]

Question, how did you know it was the valve block?

It was a guess based on some extensive Googling.

 

[ScoobyDooLondon]

Just to keep everyone in the loop, the tyres arrived today.

But only the front two tyres!! ;-(

Rear tyres are in transit, so will have to wait another day or two.

Since I'll be putting on new tyres, going to have the existing wheels refurbed at the same time. Didn't plan on doing so, but just want to make sure there are no problems with the wheels when the new tyres are fitted.

I don't have any spare wheels, so going to have to give in the car with the new tyres. Anyone care to recommend a suitable place for tyre refurbishment and fitting of new tyres, where I can leave the car with them? Willing to travel, based in Maidenhead.