sphell

Please help me find the cause of this noise, it's driving me nuts!

I've done numerous searches but can't seem to find what I'm looking for!

Here are the facts:

• 2007 Mercedes E350 Avantgarde (104,000km)
• Knocking sound (sometimes a fast rattle/knock sound) from the REAR LEFT over bumps.
• The sound is more pronounced when I have passengers in the back seat or I have a full tank of fuel (Eg - more weight in the back of the car).
• The sound is more pronounced at low speed.
• The sound is synchronous with the up and down movement of the left rear wheel/suspension travel.
• Car does NOT have Airmatic suspension - it's an Avantgarde with Sport package (bigger brakes, coil springs w/shocks, 18" wheels etc).

What I have checked so far:

• Not headrests rattling on parcel shelf.
• Not rear parking brake drum assembly rattling.
• Not rear disc brake protection plate rattling.
• Not exhaust assembly or heat shield rattling.
• All rear suspension bushes seem to be in good condition (upon visual inspection).

What I did find was that if you push up on the fuel tank (left hand side) underneath the fuel pump, it makes a very loud squeaking noise. I removed the fuel pump and found that it has a sliding spring loaded mechanism as part of the fuel pump. When you push on this spring loaded mechanism it makes the squeaking noise which is amplified when it is installed in the tank. HOWEVER, this noise is different and I don't see how it could even move inside the tank because the fuel tank would have to flex substantially for it to make noise.

I am yet to check the shock absorber, but I can't replicate the sound when the car is parked and I jump up and down on the back of the car to make it bounce, which leads me to believe the shock absorber on the left side is fine.

Can anyone shed any light on this?

Thank-you!!

EvoTechnik

Sounds like a wheel bearing. Jack up the car and see if there is any play in wheels.

F1Fan

Rear shocks have been known to make a noise when they are worn out. Although the sound is usually more of a thump instead of a rattle.

3rdmbwagon

My thought as well, wheel bearing.

sphell

Thanks for the suggestions guys - tonight I jacked up the car to check the wheel bearing and there was no play in the wheel. The shock absorber looked pretty simple to remove so I took it out and when you press down on the shock it makes the noise!!! The noise is being amplified by the vibrating through the rear strut tower/sheet metal it seems. I took a video which I'll post up tomorrow. So now I'm on the look out for a replacement shock, the OEM number is A2113260200 but it is made by SACHS. I believe the correct replacement is a SACHS 317 382, I just need to track down who sells them in Australia.

3rdmbwagon

Good find. Good luck finding the shock.

sphell

Just an update with some pics & video of the faulty shock absorber. I searched and searched and everything was related to W211's with rear air shocks. This might be able to help someone diagnose their own car running standard/sport suspension. I ordered the Monroe OE shocks in the pic below from Rockauto. They should arrive in a few days so I'll post another update.


Rear left shock absorber 2008 E350 Avantgarde w/ Sport Pack (no air ride)

sphell

Update - Monroe shocks arrived and I installed them last night. I'm a bit concerned that they are bigger than the factory shocks by about 50mm (see pics). However they both compress down to the same level as indicated by the purple tape in the other picture. I've sent a email to Monroe to see what they have to say. Does anyone know any possible implications of this? My thought is that the shocks now installed are already 'pre-loaded' as such, which might contribute to the firmer ride???

Well the good news is that the knocking noise over bumps is gone! My initial feeling was these shock absorbers are fairly firm. Roads seemed bumpier than before and the ride just didn't seem as 'luxury' as it should be for an E-class. I did a bit of Googling tonight and it seems the general consensus for these shocks is that they are firmer than the factory ones across all models of European cars. I'm not really a fan but I can't be too picky as I got two of these for $170 delivered when a single Mercedes OEM shock was $403+GST.


Monroe bottom, OEM top.

Bottom of both dustshields meet the top of the purple tape when each shock is compressed fully.