The brief
The A4 came in complaining of a slew of noises from the undercarriage while driving, a knock over bumps the most disturbing of them. Undercarriage noises are easy to chase up the wrong tree, so the team put it on the lift and tracked it down. The knock was the front anti-roll bar drop links. The anti-roll bar runs across the front and ties the two sides of the suspension together so the car leans less in corners, and the links are the short rods with ball joints connecting that bar to the suspension. The ball joints wear out, the joint goes loose and rattly, and you get a knock every time the suspension moves over a bump. They're a small, common wear item, and a worn link only knocks louder, so they need changing.
The diagnosis
On the lift the front suspension got the once-over. The drop links were the culprit, the ball joints worn with play you could feel by hand, which is exactly what makes that knock over bumps. The rest of the front, the arms, the bushes, the shocks, checked out solid. When the links on an axle have gone, you do the pair, they wear at much the same rate, and a fresh one next to a worn one just means you're back under there soon for the other side.
The work
Both front anti-roll bar drop links were unbolted and removed, and a new pair of genuine Audi-spec links fitted, the ball joints torqued to the manual figures and seated properly. The rest of the front suspension was given a final check while everything was accessible. A road test confirmed the knock and the other noises were gone, the front end quiet and tight over bumps and through corners.
The outcome
No more undercarriage noise, the anti-roll bar working properly again, and the car flat and composed through corners. The A4 went home with the noise sorted. Worn drop links only knock louder and let the anti-roll bar work loose, so doing the pair put the front end back to quiet, the small job that makes a big difference to how the car feels.
