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Just pulled one of the original rear dampers on my 2008 Z4M Roadster with 46K miles. Completely shot. It collapses with relative ease, and, once collapsed, stays there without a hint of any effort to expand again.

Data point 2:

Mine was on the originals all the way to about 120,000 miles (obviously past their best, but not 'broken' per se). Then I replaced the lot with Bilstein PSS10.

wyshyvanuk wrote: ↑Sun Sep 23, 2018 12:49 am Just pulled one of the original rear dampers on my 2008 Z4M Roadster with 46K miles. Completely shot. It collapses with relative ease, and, once collapsed, stays there without a hint of any effort to expand again.

Thanks for posting this, but what do you mean “expand again”? It’s a damper so should resist force in both directions when unsprung.

Quite true, but they are also gas pressurized. When mounted, the barrel spring supporting the weight of the car will partially collapse the damper against that gas pressure. When a dip or pothole is encountered, that gas pressure will assist the spring in pushing the wheel down to maintain contact with the road surface.

mmm-5, I now have a serious case of suspension envy.