The brief
Mr Loy's Mercedes had a recurring knocking from the front that had already had various parts replaced elsewhere without curing it, so he brought it to us to find the real cause. A persistent knock that survives a round of parts swaps usually means the actual worn component was missed, so the job here was a careful diagnosis rather than another guess. The front cross shaft is a linkage component that ties the front end together and takes load as the suspension and steering work. Like any pivoting part it wears, the joints and bushings on it developing play over the years, and once it has play it knocks over bumps and on turns. It's not the first thing people check, which is how a knock like this gets chased through a string of other parts. A worn cross shaft doesn't tighten back up, so it gets replaced.
The diagnosis
A thorough check of the front end, taking its time because the obvious parts had already been done, pinned it: the front cross shaft (left side) had play in it, which is the knocking that wouldn't go away. The parts that had been replaced elsewhere were fine, they just weren't the cause. That's a front cross shaft replacement, the actual worn part, rather than another part swap that wasn't going to fix it.
The work
The worn front cross shaft was removed and a new genuine Mercedes-spec cross shaft fitted, every fastener torqued to the manual figures and the suspension bolts done up at ride height so nothing is pre-loaded. With it in, the front geometry was checked and set back to Mercedes spec, since changing a front linkage part shifts the numbers. A road test confirmed the knock was gone, the front end tight, and the car tracking straight.
The outcome
No knock over bumps or on turns, the front end tight, even tyre contact, and the car tracking straight. Mr Loy got his Mercedes back whisper-quiet and a pleasure to drive again. The fix here was finding the part that was actually worn rather than swapping more parts that weren't, which is the difference between a knock that comes back and one that's gone for good.