W140 rear shocks...help!
 

I have an earlier post this week asking if $500 was a decent price to replace the rear shocks on a '92 500SEL. I am now told by the shop (an honest indy) that the car requires self-leveling shocks with a list price from MB of an astronomical $800 PER SHOCK! I have a query in the "Parts" portion of this wonderful forum looking for a decent used one and hopefully that will produce results. My question here though is this: Does this car absolutely NEED these self-leveling shocks, or can others such as Bilstin be fitted and not loose stability/performance? If so, which model numbers will work?
Help....I can't afford $1600 for two shocks!

I think you'll find its more complicated than just replacing the self leveling shocks with regular shocks.
The shocks you have are able to level the car because they actually support a percentage of the weight of the car... regular shocks do not...
So, I'd expect if you want to change out to regular shocks in the back, you'll also have to change the rear springs, etc to carry the additional load.
Hope this helps.

Why would you want to replace your shocks, they are about indestructable? Are they leaking?

I need to replace the passenger-side shock because the bushing is shot...causing the metal to metal thump that will probably escalate into a nightmare knowing these cars all too well!
But I love the car.

If the honest indy didn't know off the top of his head that a 92 500SEL is fitted with hydraulic struts for the self leveling suspension in place of conventional shock absorbers, I wonder what other critical information about the job he doesn't know.

Sixto
95 S420
87 300SDL

shocks
 

Go find a bushing, and replace. Your mechanic does not know MB very well either. The shocks are $400 ea at discount, and come with the mount, it is unique. Visit your MB parts guy, they might sell them they sell the locking nuts seperately.

Is the bottom bushing bad or the top. The top is what I see fail and cause noise. It is available separately: 140 320 09 44.

The real problem that takes out these parts and the shocks eventually are the accumulators. Long before you notice how bad they make the car ride they are doing damage. As their capacity drops they start "bottoming out". Once every bump is a "bottom out" the problem gets addressed.

Steve,
Then you'd be an advocate to replace the spheres based on time/mileage?
What's your recommendation based on past experience... ?
Thanks.

Yes, you could say that. I haven't actually thought to much about it but I would definitely say every 100K, but I might say every 5 years.

We have had MB station wagons for shop vehicles for about 20 years. I would say that we replaced the accumulators every 5 years, but I am very sensitive to the problem. Our first shop wagon was a euro 280TE we imported ourselves in 1985. We used it to tow our 19 foot Wellcraft bowrider for years which probably stressed them a bit. Our current wagon is a 91 300tE and we have replaced them once and will probably do it again in the next year.

Steve,
Good to know. I'm a huge believer in preventative repair... but, in order to be effective without throwing huge amounts of money at it, past history of the design is badly needed...
My data point is only one car... that's now 7 years old with about 95K on the clock... so, I'll put a pair of spheres on my list for when the weather warms up...
Many thanks.

Thanks for all of the replies....you all have been extremely helpful! So, the top bushing is replaceable....is that what I'm reading here?
To sixto....I said he was an honest indy, not a particularly great one when it comes to MBs...obviously....LOL! His forte is BMWs

Steve's forte is also BMWs.

Sixto
95 S420
87 300SDL

I am obviously not a mechanic....what is an accumulator? Is this something that could cause a thumping on this car (W140)? Is it a replaceable part seperate from the shock?

The accumulator is a sphere that kinda does the job of a spring and shock. It's external to and separate from the hydraulic strut. You can replace the accumulators without touching the strut. When the ride gets really stiff, usually a sphere has failed. It becomes like an overly stiff spring.

Sixto
95 S420
87 300SDL

In the rear you have hydraulic struts. These are hydraulic pistons. If one forces fluid in the piston gets longer. View them sort of like the pistons lifting the boom of a wrecker. Add fluid and they lift.

This is how the height is adjusted in the leveling system. More pressure and the struts get longer holding the car up. That is a simple concept. Now think about what happens when a bump is encountered. The normal concept is for the strut to shorten as the suspension compresses. The above concept would have none of such. Fluid being non-compressible a strut thus becomes a rod and there is no suspension.

So along comes accumulators. They are a sphere with say a 1000psi nitrogen gas pressure inside. The gas keeps a diaphram pasted against the wall of the cylinder. Now we have a compressor that desires to make 2000psi so that it can lift the rear end of the car. Instantly the fluid in the system goes to 1000psi as any compression of fluid brings instant pressure as it isn't compressible. The full system can not accept one drop as the preesure would go to infinity in the ideal system, BUT we now have the liquid line running to the accumulator which has a compressable gas inside so that extra drop goes into the accumulator and the pressure of the now further compressed gas goes up a little.

The compressor continues pumping and fluid continues to be forced into the accumulators with the continued compression of the gas. The diaphram now has moved off the wall of the chamber and as the gas pressure raises to say 2000psi the car starts to rise.

The system is now leveling the car. The accumulator is maybe half filled with 2000psi liquid and half filled with 2000psi compressed nitrogen gas. And we hit that bump. The strut wants to shorten which causes the fluid to need to go somewhere as it is non compressable. The fluid goes into the accumulator and the diaphram is pushed further and the pressure rises to say 3000psi and the event is equalized and the pressure now rebounds like a compressed spring.

This happens over ever bump. Some bumps are small and the pressure increase is thus small. Some bumps are bigger and the strut will push a lot of fluid to the accumulator. When new the accumulator can hold the car with sufficient space left in gas to accept full movement of the struts. Remember the struts will push a finite amount of liquid out when they are fully compressed. The only space for this to happen is the space where the compressed gas exists.

Over time some of the gas passes through the diaphram and the space available is smaller when the fluid hits the pressure necessary to lift the car. Slowly the large bumps bottom out. Eventually even the dullest of drivers figures something is wrong.

When totally exhausted the spheres are full of liquid only and the struts are rigid. In this condition the force applied to the system when a bump occurs is out of this world and tears up the rest of the system. This is when the struts fail. It is some really good stuff though as there are plenty of the dullest drivers owning these cars and even after months the struts usually live through it. Always amazes me.

One more "Q" steve.
 

I have 95 S500C,I replaced my accumaltors and the upper shock
mounts.Still have right side thump over bumps,not as violent as before bit still very annoying,at what point do you blam the shock?(no leaks!}
Thanks.
Hulio.

I too am having a similar problem with my 92 500SEL. Whenever I hit a bump the passengers in the rear experience lift off. After reading this thread I will look into the acumulator as the culprit. If an accumulator diagnostic thread has been posted in the past, would someone please direct me to this. Also a link to a good online parts store for ordering Mercedes replacement parts would be appreciated.

Thanks,

Jim

Top of the page!
 

I think the firmness of the ride you're describing is the diagnostic... if not convinced, go back a page and read Steve's description again.
As for internet parts, suggest you go to the top of this page and click on Fastlane... they are a sponsor of this site where you get all this neat information for zip.... least we can do is support them.
You'll find that Phil is the best!

There actually is very definite procedures for identifying a deficient accumulator. Unfortunately it requires a good high pressure gauge. It also requires enough labor that if you were paying for it it would be cheaper to buy a new accumulator (but not two)

A good accumulator will have the same pressure nitrogen charge as when new. That pressure is stamped on the sphere and read in bar or atmosperes (same thing sorta).

If the sphere was rated at 1000psi (take bars or atmosheres and multiply by 14.2) then it should have 1000psi pressure inside. Since the gas is captive it can't be directly measured but almost. The way to do it is to install the gauge and start the pump. The pressure will instantly go to the pressure of the gas and then slowly build as the sphere is injected with fluid.

On load leveling systems both spheres and both struts are hooked together so testing this way will only rate the worse sphere. To do the test on each sphere the other must be disconnected and the line plugged.

The question then becomes: at what pressure do you throw them away. Beats me!

Steve,

Thanks for the input and direction, time to put on my coveralls.

Jim

2000psi? Time to put on the kevlar :)

Seriously, is there any residual pressure to expect when the pump isn't running? Do the nitrogen bladders fill the accumulators and flush fluid back to the reservoir?

Sixto
95 S420
87 300SDL

The pressure on the spheres is checked by the level valve. If not the car would drop. If the bleeder is openned at the valve all the fluid pressure is dropped and the nitrogen returns to its natural state (1000psi if thats the spec, less if its defective)

Re: One more "Q" steve.
 

Noises are about impossible without being there. The possibilities include bad parts and all the other components. A loose piston inside the shock is a possibility. Check the subframe mounts also.

Great response
 

Steve you are remarkable with all your answers! MY dealer even says if they don't leak don't replace the struts. On my 92 I noticed the level drop in the reservor, never put much thought into it, they topped it off at a service. Then it got bouncy in the rear, replaced the "spheres", as good as new with 75k miles. "Duh" no leaks where did the fluid go now I know!

Filled them buggers right up.....

steve...
 

i've been on the fence to change out my spheres for about two yrs(i puschased my spheres in 2002-haven't used them yet).i also have the rub noise some are talking about.i traced it down to the bushings and tried and tried to locate someone to redo the bushings but to no avail.now you've given me hope.thanks a ton!
my question is pertaining to the valve near the diff.is it too dangerous to go under the car while runnig and adjust the valve?if im looking at the car from the rear,do i push the valve to the right or left to raise the rear?

I have found that small adjustments can not be immediately seen when adjusting under the car. I can do that on my alignment lift with skid pads (skid pads allow the wheels to move in and out as height changes). Even with skid pads I find that If I make an adjustment that actually moves the car it will be much higher after a ride around the block. The arm is fairly flexible and you should be able to move it one way or the other to see which is up and down. Once you know make a small, matter of fact, adjustment and drive the car. If you went the wrong way go back and adjust it the other way. If you need more or less do it in steps.

looked at that part#
 

steve :went to partslane and looked up your part #.not at all what i thought i would see.i thought we we're talking about the shock rubber bushing that mounts the shock/strut to the subframe?am i confused as to the layout of the assembly or have you posted the wrong #?
i assume the noise was coming from the lower bushing,after thinking about it i guess your saying it is the upper mounting where the noise comes from.correct??is this what your experience has told you?is it ever the lower mount?:confused:

Item #14 - 140 320 09 44

Accumulators recharging?
 

Is there any interest in recharging the nitrogen in the accumulators?

I do this for accumulators in the Infiniti active suspension system, have the equipment and methods, and own a sl-600, had 2- 560sel's

I would charge what the market will bear, up to 50% of alternative new parts.

It is my impression that the reason the chambers lose their gas is due to leaks in the diaphram. I wouldn't think that recharging would be practical if thats the case. I have not heard or anyone recharging a german type hydraulic pressure accumulator. I have bought reconditioned chambers for Rolls, but only the early cars as their late cars have cheaper accumulators than MBs and just as inaccessible to recharging.

Interesting thread and some interesting comments. I recently changed the accumulators and the struts on my 500E and it made all the difference in the world, like driving a new car and worth the expense. When disposing of the old acumulators it is important to drill a small hole in the cell to make sure it is completely deflated. Ifit is shot, you will get hydrauil oil all over your drill bit ! They are exactly the same as aircraft accumulators and I see no mileage in trying the recharge them as, as Steve rightly suggests, the diaphram is usuall shot. Good reading !

Sphere replacement
 

Just changed out the Spheres on my 500 SEL. Rides like a dream. Thanks Guys.

How much was it to replace the spheres? (My '95 S500 has a 'thud' noise in the back right when I go over bumps.)

$300 and up depending who does it, $90 or so for the spheres, labor and oil.

Sphere replacement
 

$120 ea for the Spheres...$15 ea for two quarts of Hyd oil. Labor...DIY or Approx $250 Mechanic labor

Has anyone ever come up a solution for that thumping noise that you hear in the back of a 140? I've been trying to track mine down, I've replaced both upper strut mounts and both lower control arm ball joints and it is still there. I can only hear it on the left hand side, sounds almost like a muffler is bouncing up and down against a mount over choppy bumps.

Its a 92 500SEL and the car rides other then the noise.

Thanks

http://v12uberalles.com/pressure_spheres.htm

http://v12uberalles.com/Rear_Struts.htm

http://v12uberalles.com/ADS.htm

Solution to your problem found.
 

Those are kind of lame, they cost as much as fixing it the right way.