W140 rear suspension clunk.. driving me NUTS! - PeachParts Mercedes-Benz Forum

bhatt · #1 02-10-2008, 04:26 PM

Hello all,

I have a '92 500SEL with approximately 145,000 miles on it. It had about 115,000 miles when I bought it 2 years ago.

The rear suspension clunks over big bumps. The ride is PERFECT and has never been hard/bouncy/etc. It's just that this annoying clunk comes from the rear.

When I bought the car, the tech (who has worked at MB for years and knows his stuff) said replacing hydraulic shocks was rare but he really thought mine were gone. He had a set that had only 5000 miles on them (long story, but another customer had MB replace shocks when that was not the problem, so my mechanic bought them cheap from the customer).

So we replaced both rear springs (one had broken), both rear hydraulic shocks, there was no lever connecting the hydraulic fill/dump valve so he replaced that part and adjusted the rear suspension. He also replaced a rear "control arm bushing" as he called it.

He thought one of the "bushings" (metal ball at the top of the shock) was a bit loose on the old shock. So he was sure that was the problem. I don't remember exactly, but I'm 99% sure the new shocks had bushings already on them so he in fact did install new bushings with the shocks.

Still clunked....

Took it to another top MB tech in the area for a 2nd opinion. He looked at everything quickly in the rear and said he didn't see any obvious problems. Everything "looked tight" according to him. When I test drove the car with him, he certainly heard it. His only idea was to replace the accumulators because they were old and rusty (original to the car) and he said everything else looked in great shape.

A few months later I finally replaced both rear accumulators and flushed/refilled the hydraulic system.

NO change in the clunk at all. The ride was perfect, same as before. Didn't change at all. But the clunk was still there.. ARGH!

The only way I can reduce the clunk is to lower the rear tire pressure. But it only improves the problem a bit, doesn't fix it.

Any ideas? I don't know what's left and this car is driving me crazy. I am actually considering getting rid of it just because I can't maintain my sanity while driving it (clunk clunk clunk.. I have actually started to swerve a bit when I drive, avoiding cracks and potholes in the road, just because the noise is driving me nuts!)

Yes, the Bose audio system helps a lot but I can still hear the clunk

ILUVMILS · #2 02-10-2008, 04:38 PM

Check the rear sway bar links for free-play. If you're not sure, disconnect them and see if the noise goes away.

bobs · #3 02-10-2008, 07:08 PM

I 2nd the sway bar links diagnosis. I have the same clunk and I'm waiting for mine to come in right now. If you search around, you can get a full set (fronts & rears) for less than $40 on ebay.

syljua · #4 02-11-2008, 04:01 AM

Quote:

Originally Posted by bhatt

Any ideas?

bhatt, do not give it up!

I also had one of these and know the feeling...

Be sure that it actually is at the rear.
I thought mine was, but it was the front.

Also try to strain the suspension on only one side, or both
sides at same time, and see if there is a difference. The sway
bar system will only be put under strain in the non-symetrical
case.

Try to bounce the rear (or front) of the car, to reproduce the clunk.
For the rear, you can stand on top of the trunk loading entrance and
hold on to the inside of the trunk lib and sway up and down to get
the car to really bounce a lot. If you hear the clunk, have a friend to
do the bouncing, and with the protective cover of the lower suspension
arm, feel the parts of the suspension to find out where the loose mount
is. (you may have to put the rear wheels on a ramp or something to get
under to feel). With the sensitivity of one of our most precious instruments,
your fingers, you should be able to feel any play, even when it is not
large enough to make a sound.

Mine was the lower mount of the front shock. The bolt was really tight,
but there was enough play for the metal insert in the shock bushing
to rattle against the bolt.

br,
syljua

dpetryk · #5 02-11-2008, 03:16 PM

Check the ball joint at the bottom of the hydraulic cylinder rod where it connects to the trailing arm. These joints sometimes wear out before any other part in the system and can cause the exact problem you are experiencing. Unfortunately that ball joint it not available as a separate item. At least I was not able to find any. If you do find a source please post the information here for everyone to see.

Try this to confirm that the ball joint is the problem.

Load the car up with as much weight as possible. Get 3 football players in the back seat and fill the trunk with luggage. If the clunking goes away, its is the ball joints.

The added weight causes the ball joint to stay seated because a majority the additional weight is now handled by the shock. When there is no weight in the car the shock is lightly loaded and can cause a worn joint to rattle.

John1 · #6 02-11-2008, 04:07 PM

I know this sounds stupid, but after owning a trans shop for 15 yrs I have seen a lot soooooooo-

"Are you sure there is nothing in your trunk loose"?

I had a customer with a loose tire iron under the spare that "clunked" when hitting a bump.

John1

Fred Berry · #7 02-28-2008, 12:19 PM

I had the clunk also on my 92 500SEL but new rear shocks, new accumulators and flush fixed everything. Is battery strapped down? Do you have anything in the compartment right between the battery compartment and rear bumper?

dpetryk · #8 02-28-2008, 12:25 PM

I wonder if he ever found the problem.

bhatt · #9 02-28-2008, 07:41 PM

I did.. by accident...

Turns out (of all things!) none of the mechanics that have seen the car ever checked the muffler!

I was underneath the car trying to shake/move all kinds of suspension parts, when I raised my leg or knee and must have pushed against the muffler. It went CLANG as it hit the bottom of the trunk. The muffler mounts look fine but I can push it up about 1/2" and it will hit the car.

A 1/2" piece of wood wedged between the muffler and body seems to have TOTALLY fixed the problem!

Lesson learned... before people start assuming things and diagnosing other problems, check the simple stuff. I can't believe nobody ever grabbed the tailpipe and tried to move it. I was able to stand behind the car and reproduce the banging noise with my hand on the tailpipe just by lifting it. Didn't even have to get under the car!

The car is like new now. Of course I can hear small rattles and squeaks that I could never hear over the banging, and now THEY are driving me crazy. I need to look at the rear interior light and the sunshade for sure, because I know they're rattling.