Mercedes-Benz W211 front-end knocking: causes and diagnosis
Mercedes-Benz W211 front end clunks: where does the knock usually come from?
The most common sources are the lower control arm ball joint, the anti-roll bar joints and bushings, the thrust rod mounting, the upper ball joint and the top of the shock absorber. Sometimes the cause is simply a loose bolt or the loose mountings of the level control compressor, which rattle in potholes.
What is the "dog bone" and does the knock come from its joints?
The dog bone is the rod that runs from the anti-roll bar to the lower control arm's ball joint. The knock often comes from its ball joint or its rubber bushings, and the joint can be replaced separately. Play in the anti-roll bar joint cannot be properly seen until the rod is removed.
How is the source of the W211 front-end knock located?
Lift the car and test for play: ball joints, control arms and bushings. If the ball joints, control arms and dog bones are fine, the fault is usually in the shock absorber or its top. Also check the wheel bearing's vertical play, and the brake pad plates and caliper mountings. The brakes are a safety-critical part, so have a workshop check the result.