My 93 940T has been a source of angst. I want to like it, but it follows a tough act I guess. Anyway, I have been complaining about rough ride since I swapped the Bilstein HD's that I had in my 90 740, and which I was happy with. So how did the Same shocks come to annoy and irritate me so much, you ask?
Heh, well, I changed the conical bushings also. I had never done those before, myself. And therein hangs the tale.
The conical bushings are installed by removing the diagonal arm, or sometimes called the control arm stay. There is a big bolt and nut that holds the back of it to the body. Inside the end is a big rubber bushing, one that takes most of the braking load, and it swings up and down slightly with the control arm.
Here's what happened. I knew that the bolt should only be tightened when the suspension is sitting at loaded position, that is as though it was on more or less level ground. And we, my friend and I, did that. But we did not have a torque wrench. And the bolt needs to be hella (trans. purty dang, also Way, also gol-darn) tight. Which we did.
But I had developed a sort of groaning noise in the front, which was determined to be in the area of that attachment point.
The bolt had come loose. And here is what I believe happened. 'Purty dang' tight is somewhat less than 90 ft.lbs, which is what is required. So the action of the arm slowly worked the bolt/nut loose, but before it became actually Loose, it was taking the suspension movement and moving the steel spacer through which the bolt passes, in the rubber bushing. So the movement of the arm was always somewhat jerky or 'nervous', which translated to an apparent roughness to the riders.
Now that the bolt is properly tight, the arm movement is all taken up by the rubber bushing, thus restoring a supple ride. Especially also because I put the wheels on, put the car on ramps, and we bounced it up and down a lot so the rest or neutral position was achieved while the bolt/nut was in place but not at all tight, and only then was it fully secured, so the rubber bushing had a true neutral starting point with no preload.
Understand, the car is still very firm. It just is not 'rattle your teeth out' firm, but actual supple movement is apparent.
So, I am again a Bilstein HD fan.