I've just bought an E34 525i and found that it's fitted with Bilstein B8 dampers and lowered springs. The dampers are the ~50mm diameter upside down jobs.
The offside front suspension crashes out over speed bumps and potholes - even when driven slowly. It goes solid as if hitting the bumpstops. The near side is fine which suggests it can't be the design. I've taken the strut off and the damper rod moves smoothly all the way into the damper case so it isn't bottoming out. I've changed the upper suspension arm, a/roll bar drop link and the strut top mount as I thought it was that. I can't find any wear in other suspension components.
I'm wondering if the valving could have failed in the damper - driving along normally is fine until hitting a pothole or ridge.
All thoughts appreciated.
Also, do you have the number for Bilstein in the UK?