W205 Clonking for first 10 minutes of journeys

[RonFleet]

Hi,

My 15 month old W205 has developed a clonking/knocking noise from the nearside rear of the car. It only occurs for the first 10-15 minutes of a journey and then disappears completely until the car has cooled down. I had a local garage inspect the rear suspension, suspecting it was a failed shock absorber, broken spring, faulty bush or something of that sort. They reported that there are no faults in that area and had checked the exhaust system and heat shields but found no problems there, either.

I'm flummoxed. If any members have useful ideas, I'd appreciate some help. The thought that's going through what passes for a brain is that it might be something inside the exhaust system that is loose but after a few minutes is expanding and seating properly.

 

[grober]

Does it vary with road speed. If so it may be related the transmission-propshaft-differential- drive shafts- rear hubs rear brakes- most likely I would guess would some some sort of malfunctioning handbrake mechanism- I believe its electrical on the W205? After 10 minutes you could try feeling the temperature of the rear brakes by touching the rear wheels[ careful - could be very hot!] this might give an indication of some sort of partial seizure.

 

[RonFleet]

Hi Graeme,

Thanks for the advice. It isn't road speed dependent, so I think the transmission, etc. are OK. I hadn't thought of the handbrake (it is electrical as you thought). I'll give that a try when I have the chance.

 

[RonFleet]

Hi Graeme,

I've checked the hubs after 10 minutes' drive as you suggested, but they are quite cool so I don't think it's the electric handbrake. Thanks for the thoughts, though. I'll keep on driving it and monitor the situation.

 

[Deleted member 113659]

Surely this can be investigated under warranty Ron?

Ant.

 

[RonFleet]

Good point. I'll get in touch with my nearest M-B dealership.

 

[RonFleet]

It's booked in at M-B for next Tuesday.

 

[RonFleet]

In case anyone is interested in the continuing saga... The dealer couldn't reproduce the problem so asked me to book it in for a couple of days so that they could check it from cold. This was done and they could hear it this time. It turns out that it is a known problem in the M-B "TOPIC" (I think that's what he called it) database. It also includes a metallic scraping sound that mine had developed over the last few days and there is a fix for it which involves partially dismantling the front suspension and applying "special" oil and grease to the shock absorber and the cup for the spring. It only affects some cars. I should have mine back on Tuesday (they have to order the "special" oil and grease). In the meantime, I have been lent a 4 door Smart car...in bright orange and silver - not my usual taste but it's transport, so I'm not complaining.

 

[RonFleet]

Update...the metallic scraping sound is cured, but the clonking is still there. Going back in to the workshop later in March.

 

[markjay]

Sorry to hear it wasn't fixed... and Good Luck.

 

[RonFleet]

The dealership has now replaced the rear nearside shock absorber, although they weren't convinced that that was the problem. The knocking has now ceased. My initial suspicion has been vindicated - experience won!

 

[rorf]

Well done - thumbs down for the dealership.

 

[ioweddie]

Shock absorbers should be replaced in pairs, to keep the wear rate even, as it might make the car unstable if one side is stiffer than the other.

 

[Aki]

Wow. I've had the exact same issue with mine. I've taken it to MB, Halfords and 2 local garages and they have said the offside rear shock is fine as they cant seen any fluid leaking from it. I think i will now buy a new rear shock and have it replaced. Thanks for your post its very helpful

 

[zenman63]

Sounds more like tyre skip and now its warmed up it disappears.
Shocks will rattle all the time and hard to spot as its inside the shock.
Spring cups should not move but the strut bearing should be nice and free or the spring will bang on turns.