The brief
The GLC200 had developed a clunking noise from the engine bay and vibrations coming up through the steering, the signs that the drivetrain mounts have had it. He brought it in. The engine and gearbox sit on rubber mounts that hold their weight and absorb the shake, keeping it out of the cabin. As the rubber ages it sags and cracks, and once it does the drivetrain moves around more than it's meant to: the vibration comes straight through to the steering and the body, and the slack lets it clunk against its stops. On a car this size and weight the mounts work hard and tend to go together, and left long enough the loose drivetrain stresses other parts, so they need changing as a set.
The diagnosis
On the lift each mount got a pry-test. The engine mount and the gearbox mount had sunk visibly with cracked rubber, the play obvious under load. All of the drivetrain mounts were tired at the same time. When they go together like that, you do them as a set, fitting one fresh mount next to a sagging one just loads the new one harder, so the call was the full set.
The work
The engine and gearbox were taken onto transmission jacks to take their weight, and each tired mount came off in turn. New genuine Mercedes-spec mounts went in across the set, every fastener torqued to the manual figures. With everything bolted up, the drivetrain was checked to be sitting square in the bay before the engine was let down to load onto the fresh mounts. A road test confirmed the clunk and the steering vibrations were gone.
The outcome
Smooth at idle, no clatter on shifts or over bumps, no vibration through the steering, and the engine note back to normal. The GLC200 went home with the drivetrain held properly again. Engine and gearbox mounts wear as a set and they take the rest of the drivetrain's refinement down with them, so doing the whole set together resets the lot rather than chasing the next sagging one a few months later.
