The brief
Mr Koh brought his E250 in with an irritating squeak, an abnormal squeaking sound while turning. He had it looked at, which is the right call, that kind of noise points at a worn suspension joint, and a proper diagnosis catches it before it leads to more damage. The culprit was the front lower control arm. The lower control arm locates the bottom of the front suspension, with a rubber bushing at its inner pivot and a ball joint at the outer end. As the bushing ages it cracks and dries out, and a dry, perished bushing squeaks as the arm moves under steering load. Worn control arm bushings don't recover, and the play affects handling and tyre wear, so the arm needs replacing.
The diagnosis
On the lift the front suspension got the once-over. The lower control arm on the affected side had a cracked, perished bushing and a trace of play, exactly what makes that squeak when turning. The arm on the other side and the rest of the front suspension checked out, still good. That's a control arm replacement on the affected side, a complete new arm rather than just a bushing, then a four-wheel alignment.
The work
The worn front lower control arm was unbolted and removed, and a new genuine Mercedes-spec arm with a fresh bushing and ball joint fitted, every fastener torqued to the manual figures. The car went on the alignment rig and the front geometry set to specification so the steering tracks true and the tyres wear evenly. A road test confirmed the squeak was gone, the steering tight and steady through turns.
The outcome
No more squeak when turning, tight, steady steering, the car tracking straight, and the alignment set so the front tyres wear evenly. The E250 went home with the noise sorted. A perished control arm bushing only squeaks louder and the play grows, so replacing the arm and resetting the alignment put it right before it became a bigger job.