I recently had the rear subframe on my wife’s 2010 C300w4 fail and literally start to fall apart after a service visit to an authorized MB dealer. It started to exhibit some serious handling issues and when I jacked up the right rear and removed the tire, I found a crack next to one of the aluminum suspension struts mounting flange. Being out of warranty and with 94k I realized there was little MB would do. I’d worked for 2 Mercedes Benz dealers over 40 years and sold millions of dollars worth of cars, but I knew what the answer would probably be. I just didn’t realize how bad the problem was. The dealer had the factory rep look at problem who said that MB would not cover it. I elected to have a friend’s MB Certified body shop do the work at a cost of $4000.; the dealer wouldn't give me an exact cost but was suggesting somewhere around $5500-$6000.
From just looking at the subframe it was difficult to see the extent of the damage but upon removal of the old unit, it was surprising how much rust had taken place from the inside. The entire flange holding one of the links completely fell out!
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The above photo shows the extent of the rust on the underside of the flange and how serious the damage was. This could not be seen without removing the subframe. I’ve since written the NHTSA.gov and registered a report of my finding. It appears that a number of W204 sedans have suffered this problem with very few getting any factory help. The car was bought new in February 2010, garaged kept, serviced regularly at MB dealers and every suggested repair done. A year ago we had a $6,000.00 sunroof water leak repair bill. Luckily insurance covered most of that amount.
I placed a call and spoke to two different MB customer service representative- I was offered $1000.00 towards the price of a new C class.
What’s even more interesting is the fact that 3 weeks prior to my finding the crack, I had the car in for a service and was told it needed: new idler pulley and serpentine belt, a transfer case reseal, a transmission service, new springs, (btw, no mention of the subframe deterioratio) at a cost of close to $7000.00! Hell, the car’s only worth $7-9000.00!
if anyone has had a similar problem, and I would suggest anyone with an W204 C Class, to look carefully at the rear subframe with a good tech who doesn’t just look! You need to pry on all the suspension links and look for movement. You should also go on the NHTSA.gov site and register a complaint. don’t wait until it’s too late.