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1997 CL500
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1,210 Posts
Discussion Starter #1
The rear suspension makes a "thumping" noise when i drive over any uneven road. If feels very hard, not comfortable at all. What could it be ?
 

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1994 S600 Coupe, 1995 S600 Coupe
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1,876 Posts
Do searches on rear suspension clunks, upper shock mounts, lower shock bushings, lower rear supporting joint, rear sway bar bushings, rear sway bar links, sls or ads pressure spheres. It could be any or any combination of the above. Without knowing what you've checked and eliminated and exactly what suspension your car has (I'm assuming it has SLS or ADS if it's a US coupe unless a prior owner changed it), it's impossible to narrow it down. The DIY threads are full of good info on suspension issues. Start searching, reading, and checking things.
 

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1994 S600 Coupe, 1995 S600 Coupe
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1,876 Posts
Probably not just them. Until you inspect all aspects of the rear suspension, you won't know for sure. As a minimum, you need to change the accumulators, and flush the fluid. If they are bad and were ignored by the previous owner, there's probably other problems that they ignored. Bad accumulators will put unusual stresses into the rest of the suspension, especially the shocks, and their mounts. Bad accumulators essentially make the rear suspension solid.
Is your shock warning light lit on the dash?
 

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1997 CL500
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1,210 Posts
Discussion Starter #6
Probably not just them. Until you inspect all aspects of the rear suspension, you won't know for sure. As a minimum, you need to change the accumulators, and flush the fluid. If they are bad and were ignored by the previous owner, there's probably other problems that they ignored. Bad accumulators will put unusual stresses into the rest of the suspension, especially the shocks, and their mounts. Bad accumulators essentially make the rear suspension solid.
Is your shock warning light lit on the dash?
My S500 Coupe does not have a shock warning light.
 

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93 SL500, 95 SL320, 96 S320, 98 S500, 2002 E320 4Matic Wagon & A little 91 5.0 FORD Mustang
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7,955 Posts
yes...all CL's 97 onward have the SLS. So would the accumulators make also a thumping noise ?
The accumulator does the "shock function" . The "shocks" are like hydraulic rams on excavator.

You will need to flush out all the fluid-Do a fluid exchange.

Martin
 

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96 sl600,97 s420(gone) 96 CL600
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618 Posts
Do accumulators first. The "thump" could be just the stiffness, but most likely its also either the upper shock mounts or the lower bushings. The mounts are a poor design, but are replaceable-they're on with some super threadlocker and need lots of heat to remove or you'll snap the stud. The lower bushings require some ingenuity. There's a thread on here somewhere about how to do them with turned down bmw control arm bushings.
 

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1997 CL500
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1,210 Posts
Discussion Starter #9
The accumulator does the "shock function" . The "shocks" are like hydraulic rams on excavator.

You will need to flush out all the fluid-Do a fluid exchange.

Martin
This car has only 69750 miles, and has not been driven in 6 years. Where is the location to flush the old fluid and to put new fluid in ? What kind of fluid is recommended ?
 

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1997 CL500
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1,210 Posts
Discussion Starter #11
It seems that the "thumping" sound is coming from the rear passenger side wheel only. The car seems to maintain it's level when it's loaded, and the hydrolic fluid is at normal level. The accumulators upon inspection seem to be in good shape. Again the car has only about 69500 miles, but has not been driven for a few years.
Any other suggestions besides the accumulators, what else could be the issue ?
 

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96 sl600,97 s420(gone) 96 CL600
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618 Posts
There isn't anything to be learned from a visual inspection of the accumulators. Mileage isn't controlling, age plays a role. Fluid level? Often folks top it up. It might drop when the accumulator initially fails, but it will hold after that. Any bushing/mount in the rear suspension could clunk, check them all. If all ok visually, suspect upper mounts, which can fail due to age alone.
 

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'95 S600
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426 Posts
As jal1224 and others have said you need to get the car in the air and have it inspected by someone with knowledge. Too many possibilities to enable an accurate diagnosis over the internet when it comes to this sort of thing.
 

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95 S500
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158 Posts
There isn't anything to be learned from a visual inspection of the accumulators. Mileage isn't controlling, age plays a role. Fluid level? Often folks top it up. It might drop when the accumulator initially fails, but it will hold after that. Any bushing/mount in the rear suspension could clunk, check them all. If all ok visually, suspect upper mounts, which can fail due to age alone.
I can relate to this situation.
Mine just hit 70,000 miles. (95 S500)
I replaced accumulators and also top mount. (SLS shocks).
The ride is still quite harsh though. (I have 18" rims running about 30-32 PSI)
The fluid level is fine, color is fine, flushed twice.
Now the passenger side makes a weird creaking sound (intermittently.. )
the sound goes away if I park my car for a while.. it comes back after driving it for 20-30 min. (especially after some rough roads).

Maybe I got bad parts (accumulator). Or.. maybe the accumulators are not always the culprit.
I am thinking about replacing the shocks but it's just frustrating.
any thought?

JayK
 

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'97 CL600
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2,897 Posts
JayK, Take a close look at the rubber bushings in the SLS strut bottom. Mine were shot. Luckily we found a local who could replace them without having to buy a new strut.
Anziani
 

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95 S500
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158 Posts
anziani,

Last year when I replaced the top mounts, those looked ok.
Well, I can unbolt them again and check the bushings again after done dealing with "overheating" issues I have.
Thanks for your input!

JayK
 

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1997 CL500
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1,210 Posts
Discussion Starter #19
Here is an update. I checked the hydrolic oil level with the engine running, and noticed that the fluid level is at minimum. What could cause that ? If i want to renew the hydrolic oil, how many quarts do i need ? How often is it recommended to do this ? Shall i renew the hydrolic oil first and see if i still hear the "thumping" sound, before tackling the accumulators ?
 

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1994 S600 Coupe, 1995 S600 Coupe
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1,876 Posts
Low fluid is typical of accumulator failure. The space that used to be taken up by nitrogen, is now taken up by fluid. If there are no leaks, that is the only place fluid can go.

Just change the accumulators. You will need at least two liters, but I would get three. Use only the specified fluid. When you change them, suck the remaining fluid out of the reservoir. Between that, and all the oil in the accumulators, you will be changing the majority of the fluid.

I'm doing this job this weekend. I hope your car is rust free because it is a PITA even with one. I can't imagine doing it on a rusty car.

There is a DIY on v12uberalles.org.
 
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