Mercedes-Benz W123 rear control arm bushings and rattle
W123 rear control arm bushings: why does the car rattle over potholes?
Worn control arm bushings (rubber bushes) let the arm move, which is heard as rattling or creaking. The rubber bushings of the mounting are available as spare parts, so they are meant to be replaced. After replacement the rattling has stopped.
How do I replace the rear control arm bushing on a W123?
The old bush can be cut through with a hacksaw: remove the blade, thread it through the bush and attach it back. A bush that has been sawn through comes out easily. The new bushings are not a tight fit. The control arm mounting and the spring are under load, so be careful with the spring.
Do I have to lower the rear subframe or the rear axle to replace the bushing?
Not always. The outer bushing can be replaced by removing the bolt at the outer end of the arm and levering the arm down with a plank. Alternatively, the whole rear axle assembly can be lowered with a jack after first detaching the driveshaft and the anti-roll bar mounts. Seized bolts come loose more easily on the floor.
Do I need to deal with a rusted rear control arm cup?
If the control arm cup has rusted almost through, replacing the bushing alone is not enough. The rusted parts can be replaced with sandblasted and painted ones, and the bearings are renewed at the same time. Wheel suspension is safety-critical, so have a workshop check the result of the work.