Slight bumping in the rear - Benzworld.org

pcmaher · 05-25-2005, 09:04 PM

OK, I've read every thread I can find concerning thumping from the rear of a W140. I haven't found a posting with exactly my situation, but some are close. Here goes. My son heard a very slight thumping in the back while the car was moving a couple weeks ago. I hadn't noticed the thumping before because it was so quiet. Now that I'm aware of it, I hear it while driving along smooth sections of road. I don't hear it going over bumps. I hear it better at slow speeds, as low as 5 mph. It almost sounds like something is loose back there in the trunk. I pulled the trunk lining out and looked around. I found a rats-nest of wiring for some Godzilla sound / video system that a previous owner had installed . Some of the wires were heavy gage, and looked like they might be knocking around. So I pulled all that wiring out. I also found a module housing that had broken away from it's mounting tabs, and it was hanging loose against the quarter panel. That could easily have made a thumping noise, so I re-mounted it using some good tape. I took it out for a drive, and within 20 feet I could tell the thumping was still there. I turned the steering wheel rapidly to the left, then right, and repeated this to get the car to bank back and forth to see if the thumping got worse. It didn't, and in fact I couldn't hear it at all while doing this. If it was the top shock bushing, wouldn't I hear the thumping while doing this? I jacked the car up, pulled off the wheel, and looked at every bushing down there (except the top shock bushing...can't see that one). They all look good and there is no play in any of them. I tried yanking on and moving the shock, and felt no play. I jacked under the rear control arm to compress the spring and shock somewhat, and still felt no play. I suspect that the shock is still pressurized though, and that may eliminate any play that may be present. I put the wheel back on, lowered the car, and pushed down on the rear corner. I sometimes hear a creak. Not always. I wonder if this could be what I'm hearing. What could be creaking back there? Is it a bushing? What do you all think this could be?

p.s. I changed the nitrogen spheres (accumulators) last year.

Brett San Diego · 05-25-2005, 10:28 PM

Mine weren't worn to the point of making noise, but I would definitely check all 4 of your CV joints. Also there's the flex disc on the driveshaft.

Brett

Merc600sec · 05-27-2005, 01:25 PM

OK I have just had some experience with this.. it is an ongoing LOUD problem at the moment.. not constant..I changed the top mounting on the LH rear..and the bottom bearing but... still got the noise.. I am starting to think its the strut..

Brett San Diego · 05-27-2005, 04:03 PM

Or is it irregular. I would expect driveline thumping to be a regular and speed-dependent sound. Otherwise maybe it's in the suspension, as you're thinking.

Brett

pcmaher · 05-29-2005, 12:47 PM

It's completely irregular Brett. From the inside of the car, it sounds exactly like something loose bumping against the right rear quarter panel. There were some loose things back there that are now secured. When pushing down on that corner, I sometimes hear a creak from somewhere. I can't locate the source though. So yesterday I sprayed lithium grease on all the linkge bushings. It didn't help. I'm thinking it's that top strut bushing starting to go. I really don't feel like taking that apart. I'm a little burned-out.

pcmaher · 05-31-2005, 10:29 AM

I pulled all the trunk liners out, and had my son push down on the right rear corner while I listened by placing my ear on a long screwdriver on the top strut mouting area. The sound is a creaking / scrunching noise, and it's definately coming from the top of the strut. To make a LONG story short, I pulled the strut out. I was expecting to see the infamous rubber bushing on top, but there isn't one. There is an eclosed, spherical metal shell at the top of the strut. I imagine there are bushings inside this sphere? It does not look like it can be opened. Anybody familiar with these struts? Is this a sealed thing, or can it be opened?

bass1175 · 05-31-2005, 01:47 PM

I had the same problem I believe, it was a squeeqing sound every time i hit bumps. I lubed up every bushing back there and the problem was still there.
I had someone bounce the rear while i went under trying to pinpoint the bushing doing this. I was cupping each bushing with my hands trying to hear for a noise change and finally I found it, for me it was the lower bushing, first one on the bottom. I removed the bolt and lubricated them with oil and the problem went away. I did learn that spraying them on the outside alone does not help. I believe you must get that oil inside them alone with its shaft , or simply change them once you find the right bushing. It was very time consuming trying to confirm which one was at fault.

pcmaher · 05-31-2005, 08:15 PM

Good info bass1175. I'll make sure I lube that bolt up when I put it back together. Here's the scoop on that top metal sphere. It is a replaceable item on this strut. It's called a Strut Bump Stop, and the part number is 140 320 09 44. I'm picking one up from the dealer tomorrow, along with the steel line that ripped while trying to remove the fitting feeding the strut's oil line. Dealer's prices are higher than online shops, but I'll be able to pick them up tomorrow. Sometimes it's worth the extra money to get the parts fast. I'll be very happy if this is really the fix. I thought I would need a $650 strut, instead it's an $80 bushing. I do have one more question. The steel line between the strut and the ADS damping valve is secured against the body with a bolt. My problem is that the bolt head must be on the trunk side somewhere. I can't find the damn thing! Anybody know where the head of this bolt is?

Merc600sec · 06-01-2005, 12:13 AM

How do you manage to do ALL of these things..
Whilst the strut is out and runnig free you might check for free movement up and down.. see if it is Hydralics making the noise.. the UPPER bush rarly fails.. if the suspension is doing its job.. its constructed to act as the upper bump stop..and only realy has any efect when the strut is fully compressed...

pcmaher · 06-01-2005, 06:39 AM

Good question T[:)]. I try to tell myself I'd rather not do this stuff. But the truth is I'm happiest when I'm in my garage working on my toy. I hope you're wrong about the bump stop! I'd rather spend 80 bucks as opposed to 650. The strut moves freely, and I did not feel any binding in it. I'll be messing with it tonight, and I'll look more closely at it. The noise certainly sounded like it was coming from the top mounting area. It sounds like creaking/crunching rubber. I imagine there has to be rubber bushings in that bump stop. This stop also supports the weight of the car, so it is possible for it to wear out. What surprises me is that this bump stop contacts the car body directly. It's metal on metal. There are no signs of wear on either of the mating surfaces though, so I suppose it works as designed.