The brief
The CLA180 had had its front struts replaced at another workshop, but it was still knocking over bumps. The owner brought it in to find out why. The first question with a knock that survives a strut change is always whether the job was done as a set. The front strut sits in a top mounting that locates it to the body and lets it pivot with the steering, and that mounting wears with age just like the strut does. When only the strut gets changed and the worn mounting is left, the new strut works against a sloppy mount, which keeps the knock going and can throw the front geometry off. To fix it properly, the struts and the mountings go in together as a set.
The diagnosis
On the lift the new struts were sound, but the front top mountings were worn, with play in the bearing and the rubber tired. That play was the knock, and it was also why the new struts weren't sitting quite right. So the call was to do what should have been done first time, replace the front mountings to match the struts, as a set, with a check of the front geometry after.
The work
The front struts came down, and new genuine Mercedes-spec top mountings and bearings went on, the struts reseated, and everything torqued to the manual figures. With the front loaded properly again on fresh mountings, the geometry was checked. A road test confirmed the knock over bumps was gone and the front felt solid.
The outcome
Knock over bumps gone, the front solid and quiet, and the geometry checked and good. The CLA180 went home with the front suspension done properly. Struts and their mountings wear together, so doing the absorbers without the mountings leaves the job half done, and a fresh matched set is what stops the knock for good.