The brief
The A4 had developed heavy vibration through the cabin, worst at idle and under acceleration, a clunk or bang from the engine bay when shifting between drive and reverse, and you could see the engine rock more than it should, with a thump felt through the body. He brought it in. That's the worn-engine-mount picture. The engine and gearbox sit on rubber mounts that take their weight and absorb the shake, and one of them is hydraulic, fluid-filled to damp it harder. As the rubber ages it sags and cracks, and a hydraulic mount can split and lose its fluid, and once they're tired the drivetrain moves around more than it's meant to: the vibration comes straight through, and the slack lets it knock against its stops on a gear change. Mounts that have gone together produce exactly that, so they need changing.
The diagnosis
On the lift each mount got a pry-test. The engine mount and the gearbox mount had sunk visibly with cracked rubber, and the hydraulic mount had lost its damping. 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 Audi-spec mounts went in across the set, the hydraulic one included, 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 heavy vibration was gone and the clunk on shifting between drive and reverse with it.
The outcome
Smooth at idle, no clunk between drive and reverse, no thump through the body, and no heavy vibration in the cabin. The A4 went home with the drivetrain held properly again. Engine 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.
