The brief
Desmond's 640i came in for a regular service, and he mentioned a loud knocking sound every time he passed through a road hump. Two things in one visit: the service, and tracking down that knock. A service runs through the whole car, and the inspection that comes with it found the cause of the noise: the front anti-roll bar drop links, the short rods with ball joints connecting the anti-roll bar to the front suspension. The ball joints wear, go loose, and knock over every hump, and a worn link makes the handling feel vaguer too. So it was the service plus a drop link pair.
The diagnosis
The service check went through everything, and the front suspension investigation pinned the knock. The engine oil and filter were due, the air and cabin filters near the end, a couple of fluids wanting topping, and the front anti-roll bar drop links had worn ball joints with play you could feel, the cause of the knock over humps. The rest of the suspension and the underbody checked out. So it was a service plus a front drop link pair: the wear items refreshed, the fluids freshened, new links.
The work
The engine oil and filter were changed, the air and cabin filters replaced, the fluids topped, and a full diagnostic scan run. Both front anti-roll bar drop links were unbolted and removed, and a new pair of genuine BMW-spec links fitted, the ball joints torqued to the manual figures and seated properly. A road test confirmed a clean start, steady running, nothing leaking, the knock over humps gone, and the front end quiet and tight.
The outcome
A clean bill of health on the 640i, fresh oil and filters, fluids topped, a clean scan, no more knock over humps, and the front end quiet on new anti-roll bar links. The car went home serviced and quiet. Catching the worn drop links during the service caught the noise while the car was in, so it left better in one visit.
