W140 Suspension
 

1997 S-500. 46,000 miles.
Couple of questions here....car rides great - but hit a bump, it sounds like the back seat is loose. I have checked the seat, spare tire, muffler and anything else I can think of - nothing is loose. Is there something else that would cause this clunk sound?
Question #2 - does th PSE have anything to do with suspension?

Thanks!

Don't know about the rattle - but in answer to #2 - PSE has nothing to do with suspension.

PSE duties:
Lock / Unlock doors & fuel flap (not related to the self-close feature of the doors and trunk lid)
Release rear headrests in cars without reclining rear seats
Provide additional vaccuum reserve for HVAC under conditions of low engine vaccuum, or when HVAC used in REST mode
Provide pressure for lumbar supports in front seats
In early 140's - retract/extend the parking masts on the rear fenders of the car adjacent to the trunk lid.
Extend/retract the trunk lid handle
Extend the trunk lid latching pawl when the trunk lid is opened.

If the car has self-leveling suspension (I think most of the S500's did), it could be a rattling strut, but I've read that those are really durable and last a long time.

Get someone to ride in the backseat and duplicate the problem if you can - maybe you can further isolate the location of the rattle.

Have your "spheres" (accumulators) checked . . probably leaking and thus the thud when you go over a bump.

Pete's site has a good article here: http://v12uberalles.com/Accumulators.htm

Recently replaced mine b/c of the same problem. Now it's just like new.

Good advice on the accumulators + a couple of more things:

Check your battery hold down clamps. (Don't ask me how I know :))

Also check your lower shock mount bushings. They can appear tight but will rattle when the car goes over bumps. It sounds like the whole back end of the car is coming loose.

If the spheres are bad you will have more than a clunk, you will have a rock hard ride because the spheres have lost the ability to compress the nitrogen and absorb the shock.

On my coupe, the problem was the rubber bumpers on top of the legs, aka (incorrectly) shocks or struts. I did a post on replacing them about a year ago.

accumulators are new....so shouldn't be those.
battery is tied down.....
I will check on the lower shock mount bushings....thanks!

Any other ideas?

Top bump stops could also be bad. I had a creaking / rattling noise coming from what I thought was the top of the rear seat back...turned out to be a creaky strut. Acoustics fooled me.

http://v12uberalles.com/Rear_Struts.htm

everything appears to be in order......but clunk still exists.
Anything else you guys can think of? Is there anything else under the seat or anything that could be making this noise?

The car is riding very well, car level is good (back end is not high or low), hydraulic fluid level is good, battery is tied down, spare tire is tied down, muffler is not loose.....making me crazy!

Check the bolts that hold the shocks to the lower control arms. You said the the accumulators are new so that means you recently had the shocks out, right? When I replaced my rear shocks, I torqued the bolts to the spec in the WIS and the shocks still rattled when going over bumps. I finally got under there and tightened them 'till they felt "tight +- 10 ft/lb" and the clunking went away.

Did you ever figure out what the problem was? I have the same problem on a s-500, left rear clunk sound. Just replaced a broke sway bar link. Now it sounds like a board on an old ship, at low speeds,,,5mph... no sagging, normal ride height, just the annoying 'wood about to break' kind of sound.