W123 Front End Clunk?

[Cummmins]

I have a clunking sound coming from the right front area of my 1985 300D when I go over speed bumps. It doesnt seem to be making the sound right when I hit the speed bump under compression, but when the tire is starting to roll down the other side of the speed bump. This only happens at normal speeds. Going slow over the bump or a little fast will not produce the noise. It has been doing this since I bought the car about a year ago. Since then I have replaced many of the front-end parts: wheel bearings, sway bar bushings, upper control arms, shocks, guide rods, lower ball joints, lower control arm bushings, outer tie rods, steering idler bushings, tightened up the steering box, alignment, wheels and tires. I have gone over all of the parts and everything is tight. Any ideas?

[mespe]

Define "Normal speed" if normal speed is 25MPH, it's going to clunk. Could be that at the particular speed you are travelling, coupled with the resonant frequency of the damping effect of the shock causes the control arm to hit the travel limiting stop piece of metal welded to the frame. Going slower the wheel doesn't bounce up, going faster the shock dampens it to where no contact is made.

[Cummmins]

For myself, and most others I would assume, a "normal" speed for traveling over a speed bump would be in the ballpark of 2-8mph for the average parking lot "bump." I would never go over a speed bump at 25mph in anything that I own.

[Stretch]

Well if you are sure that all the parts you mention are OK I'd go for engine mounts. There's a thread on the forum somewhere with a great in wheel arch video that showed the movement of the front suspension - I think in that thread after lots of head scratching it turned out to be engine mounts...

[Cummmins]

That sounds reasonable, Stretch. Supposedly the motor mounts were replaced about a month before I bought the car, which would make them just over a year old. I have not yet replaced the engine shock bushings, or tested them to see if they are still good. I wonder if the passenger side shock/bushings are so worn that the motor is bouncing up a little then slamming down going over a speed bump at just the right speed. I do have a go pro camera that I could mount on the car and watch what is happening. But, I am moving soon so that it is packed right now.

[Stretch]

I don't think the mounting of a wheel arch camera is necessary - apparently shoving the engine to one side produced a large movement and a replication of the noise (well I think that's what was reported!)

[Cummmins]

Oh, mine doesn't move that much!