The brief
Mr Lim's C180 had an unusual noise from the underside, the sort you hear when you turn and feel over bumps, and he wasn't sure what it was. He brought it in for us to find. A front-end noise like that means something in the suspension has worn and developed play, and play that's left alone wears its neighbours and starts to affect the steering and the way the car sits. The usual cause on these is the front control arm bushes. Each front control arm holds the wheel in place and seals to the body through rubber bushes, and those bushes take every bump and every bit of cornering load for years until the rubber cracks and tears away from its sleeve. Once that happens the arm shifts when it shouldn't, you get a clunk on turns and over bumps and a vague feel through the wheel, and a worn bush doesn't recover. Control arms come as a left and a right, so they get changed as a pair.
The diagnosis
On the lift the front got a thorough check. Both front control arm bushes were worn, the rubber cracked and the arms showing play under a pry bar, which is the clunk on turns and the loose steering feel. The drop links, the strut mounts and the rest of the front were fine. When the bushes are gone you do the control arms as a pair, putting one fresh arm against a worn one just leaves the noise and uneven wear, so the call was both sides.
The work
Both front control arms came off and new genuine Mercedes-spec arms went on, every fastener torqued to the manual figures and the suspension bolts done up at ride height so the new bushes aren't pre-loaded. With both arms in, the C180 went on the alignment rig and the front geometry was set back to Mercedes spec, since new arms shift the numbers. A road test confirmed the noise was gone, the steering tight, and the car tracking straight.
The outcome
No clunk on turns, no knock over bumps, tight and precise steering, even tyre contact, and the car tracking straight. The C180 went home with the front end solid again. Worn control arm bushes only get noisier and start eating tyres and dragging the alignment off, so doing both arms and resetting the geometry put the whole front right in one go.
