Hello folks.

***update - After some more reading, I suspect the upper bushing on the struts may be worn. I see no record of their replacement in the records (which are extensive) and the car has 91K on the clock. It seems there are two different part numbers with some debate about which is the right one depending on the TSB (which I've not seen) so I ordered both types:

115-326-16-68-MBZ

114-326-00-68-MBZ

The 114 number may be thicker and correct, but Ill have both to test with.

My 1991 560SEL has a significant harsh clunk in the rear suspension when going over say a railway track, bridge expansion joint, or some other similar uneven surface. Its as though the rear tire bangs down after rolling over the edge of the raised surface, and back down onto the general road surface. In typical driving conditions the car seems to ride just fine, but whenever there is a significant road surface bump or pothole, you can expect this harsh bang - like a very stiff suspension. The car does not sag, nor bounce oddly - there are really no signs of an issue until you go over a large enough bump / hole in the road.



I have records on this car back to the dawn of time, and the nitrogen spheres were most recently replaced in 2013 - but only 6000 miles ago. The rear sway bar links were replaced at the same time. There is also a record of an accumulator replacement less than 1000 miles ago - but its unclear if they meant the nitrogen spheres. I also had the car inspected and there are no leaks anywhere from the SLS system, both struts are also leak free from a visual inspection.



If we assume the spheres are fine, and the struts are not leaking, and the rear sway bar links are also good - what might account for this clunk / bang in the rear - its quite ....noticeable when it occurs.



Thanks


Allan.